Zoogeography of the coral reef fishes of the north-eastern Gulf of Aden, with eight new records of reef fishes from Arabia

Abstract

A survey of the fish assemblages of Hadramaut and Shabwa provinces of the Republic of Yemen, in the north-eastern Gulf of Aden, reveals regionally high levels of diversity in some families of coral reef fishes, and striking local and regional species distribution patterns. The following species of fish are recorded for the first time from the coast of Arabia: Chaetodon trifasciatus, Chaetodon zanzibarensis, Halichoeres cosmetus, Thalassoma quinquevittatum, Ecsenius lineatus, Acanthurus leucocheilus and Acanthurus triostegus. A preliminary checklist of shallow coastal fishes of the north-eastern Gulf of Aden is provided, and a discussion of zoogeographic affinities of the species assemblage presented. A 'zoogeographically displaced' component of the northern Gulf of Aden fish community is almost entirely limited to a single small island, and may occur here because of complex oceanographic conditions arising from the seasonal monsoons of the Arabian Sea. This unusual assemblage raises the possibility that settlement strategies of larval reef fishes may in some cases affect species distributions at zoogeographic scales.

Full text

FAUNA
OF
ARABIA
18:
293-321
Date
of
publication:
30.11.2000
Zoogeography
of
the
coral
reef
fishes
of
the
north-eastern
Gulf
of
Aden,
with
eight
new
records
of
coral
reef
fishes
from
Arabia
Jeremy
M.
Kemp
Abstract:
A
survey
of
the
fish
assemblages
of
Hadramaut
and
Shabwa
provinces
of
the
Republic
of
Yemen,
in
the
north-east-
ern
Gulf
of
Aden,
reveals
regionally
high
levels
of
diversity
in
some
families
of
coral
reef
fishes,
and
striking
local
and
regional
species
distribution
patterns.
The
following
species
of
fish
are
recorded
for
the
first
time
from
the
coast
of
Arabia:
Chaetodon
trifasciatus,
Chaetodon
zanzibarensis,
Halichoeres
cosmetus,
Thalassoma
quinquevittatum,
Ecsenius
lineatus,
Acanthurus
leucocheilus
and
Acanthurus
triostegus.
A
preliminary
checklist
of
shallow
coastal
fishes
of
the
north-eastern
Gulf
of
Aden
is
provided,
and
a
discussion
of
zoogeographic
affinities
of
the
species
assemblage
presented.
A
'zoogeographically
displaced'
component
of
the
northern
Gulf
of
Aden
fish
community
is
almost
entirely
limited
to
a
single
small
island,
and
may
occur
here
because
of
complex
oceanographic
conditions
arising
from
the
seasonal
monsoons
of
the
Arabian
Sea.
This
unusual
assemblage
raises
the
possibility
that
settlement
strategies
of
larval
reef
fishes
may
in
some
cases
affect
species
distributions
at
zoogeographic
scales.
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INTRODUCTION
Considerable
work
has
been
carried
out
on
the
coastal
fishes
of
the
seas
around
Arabia
over
the
past
twenty
years
(see
RANDALL
1983,
1994,
1996;
SMITH
et
al.
1987;
ROBERTS
et
al.
1992;

294
J.M.
KEMP
SHEPPARD
et
al.
1992;
RANDALL
e t
al.
1994;
RANDALL
&
HOOVER
1 995),
but
the
ichthyofauna
of
large
areas
of
Arabian
coast
remains
poorly
known.
The
most
conspicuous
geographical
gaps,
where
very
little
is
known
of
shallow
marine
habitats
and
fish
species
distributions,
are
the
entire
Gulf
of
Aden
(with
the
possible
exception
of
Djibouti),
the
Arabian
Sea
coast
of
the
Republic
of
Yemen
between
the
Gulf
of
Aden
and
southern
Oman,
and
both
sides
of
the
Red
Sea
to
the
south
of
the
Farasan
and
Dahlak
archipelagos
(RANDALL
19 94,
KEMP
1 998
b).
Research
on
shallow
marine
communities
and
species
in
the
Gulf
of
Aden
has
been
extremely
sparse,
and
much
of
the
published
work
is
several
decades
old.
Studies
have
concentrated
on
the
southern
shores
of
the
Gulf
of
Aden,
in
the
area
of
Djibouti
and
western
Somalia
in
the
west
(PELLEGRIN
1904;
GRAVIER
1 910
a,
1910
b,
1911;
RANDALL
&
MAUGE
1 978;
BARRATT
&
MEDLEY
1990;
RANDALL
1994;
MCCLANAHAN
&
OBURA
1997;
OBURA
1997)
and
the
Socotra
Archipelago
in
the
east
(SCHEER
1 964,
1971;
KEMP
1997,
1998
a,
1998
b;
KEMP
&
OBURA
i n
press). Even
so,
none
of
these
areas
is
yet
very
well
characterised,
either
in
terms
of
habitats
or
of
detailed
species
distributions.
Prior
to
studies
by
FRASER-BRUNNER
(1950)
virtually
no
work
had
been
carried
out
on
the
northern
(Republic
of
Yemen)
shore
of
the
Gulf
of
Aden,
and
little
has
been
done
since.
With
the
exception
of
a
study
of
seagrasses
of
Khor
Umeirah,
to
the
west
of
Aden
(HIRTH
et
al.
1973),
no
information
about
this
coast
was
published
after
FRASER-BRUNNER'S
(1950)
work
until
ORMOND
&
BANAIMOON
(1994)
reported
on
macroalgae of
the
Hadramaut
coast
of
the
eastern
Gulf
of
Aden.
Subsequently,
in
1995,
a
rapid
survey
of
shallow
coastal
habitats
of
the
northern
shore
of
the
Gulf
of
Aden,
carried
out
for
a
fisheries
development
programme,
revealed
the
pres-
ence
of
well
developed
but
scattered
coral
communities
(HUNTINGTON
&
WILSON
1995,
SHEPPARD
e t
al.
in
press),
however,
no
significant
studies
of
fishes
were
carried
out.
In
1996
a
rapid
survey
of
several
sites
from
the
Bab
al-Mandab
to
Shasar,
east
of
al-Mukalla,
was
carried
out
(WATT
1996).
This
survey
revisited
many
of
the
sites
identified
in
the
1995
survey
and
added
some
detail
to
knowledge
of
distribution
of
coral
habitats,
but
again
no
studies
of
fishes
were
carried
out.
AL-SAKAFF
&
ESSEEN
(1 999)
provided
a
checklist of
195
fish
species in
75
fami-
lies
from
the
northern
Gulf
of
Aden,
on
the
basis
of
commercial
trawl
catch.
A
number
of
fami-
lies
on
their
checklist,
such
as
emperors
(Lethrinidae),
snappers
(Lutjanidae)
and
triggerfishes
(Balistidae),
are
frequently
found
in
association
with
coral
communities,
but
the
authors
pro-
vided
no
discussion
of
the
checklist.
Recent
studies
immediately
to
the
east
and
south
of
the
Gulf
of
Aden,
in
Oman
(RANDALL
&
HOOVER
1995;
RANDALL
1996)
and
at
the
Socotra
Archipelago
(KEMP
1997,
1998
b),
have
revealed
that
the
fish
fauna
of
southern
Oman
and
the
south-eastern
Gulf
of
Aden
is
distinctively
'South
Arabian'
(KEMP
1998
b),
and that
it
includes
a
minor
but
important
East
African
element.
This
assemblage
type may
serve
to
define
the
south
Arabian section
of
the
Arabian zoogeographic
sub-
province
proposed
by
KLAUSEWITZ
(1989).
The
East
African
influence
is
more
marked
at
Socotra
than
in
Oman,
and
at
the
Socotra
Archipelago
results
in
sympatry
of
sister
taxa
previously
believed
to
have
entirely
allopatric
distributions
(KEMP
1998
b).
An
expedition
to
the
Gulf
of
Aden
in
early
1998
enabled
studies
of
reef
fishes
to
be
carried
out
along
the
northern
coast,
in
Hadramaut
and
Shabwa
provinces
in
the
east
and
at
Ras
Imran
in
the
west.
Prior
to
the
1998
expedition,
the
ichthyofauna
of
the
north-eastern
Gulf
of
Aden
re-
mained
almost
entirely
undescribed,
and
the
distributions
of
characteristic
fish
species
from
the
Red
Sea,
Oman,
northern
Arabia,
and
the
Indian
Ocean
in
this
area
were
unknown.
The
purpose
of
this
paper
is
to
present
the
new
records
and
species
list
produced
as
a
result
of
the
1998
survey
in
Hadramaut
and
Shabwa
provinces,
and
to
provide
a
discussion
of
the
zoogeographic
affinities
of
the
assemblage.

Zoogeography
of coral
reef
fishes
of
the
Gulf
of Aden
295
Fig.
1:
Locations
of
the
survey
areas
in
eastern
Yemen.
Inset:
Hadramaut
and
Shabwa
provinces,
Yemen.
METHODS
AND
STUDY
AREA
The
author
accompanied
the
Arabian
Seas
Expedition
to
the
Arabian
Sea,
Gulf
of
Aden
and
south-
ern
Red
Sea
coasts
of
Arabia,
from
January
to
April
1998.
Surveys
of
coastal
fish
communities
and
habitats
were
carried
out
in
four
areas
of
Hadramaut
and
Shabwa
provinces,
of
the
Republic
of
Yemen,
in
the
eastern
Gulf
of
Aden,
in
February
and
March
of
1998
(Fig.
1).
These
areas
were
al-
Mukalla
in
Hadramaut
Province
(14°31'N
49°9'E)
and
Bir
Ali
(14°01'N
48°20E),
Belhaf
(13°59'N
48°
10'E)
and
Sikha
Island
(13°56'N
48°23E),
all
in
Shabwa
Province.
Sikha
is
l ocated
in
relatively
deep
water
approximately
8
km
offshore,
and
all
other
survey
areas
were
on
the
mainland
or
very
near-shore
islands.
Similar
surveys
were
carried
out
in
southern
Oman,
the
western
Gulf
of
Aden
and
the
southern
Red
Sea
during
the
expedition,
and
they
enable
comparisons
to
be
made
between
these
regions
and
the
north-eastern
Gulf
of
Aden.
The
benthic
habitats
of
the
northern
Gulf
of
Aden
are
dominated
by
unconsolidated
sandy
and
gravel
substrates,
but
rocky
habitats
and
extensive
high-cover
coral
communities
occur
in
a
number
of
locations,
including
the
survey
areas
of
al-Mukalla,
Bir
Ali,
Belhaf
and
Sikha
Island
(HUNTINGTON
&
WILSON
1995,
WATT
1996,
KEMP
&
BENZONI
2000,
SHEPPARD
et
al.
in
press).
The
coast
between
Belhaf
and
al-Mukalla
consists
of
igneous
rocky
headlands,
many
of
which
are
several
kilometres
in
length,
interspersed
with
sandy
bays.
The
sublittoral
morphology
at
rocky
shore
sites
was
typically
a

296
J.M.
KEMP
Table
1:
Quantitative
survey
sites
in
southern
Oman,
the
northern
Gulf
of
Aden
and
the
southern
Red
Sea.
Site
latitudes
and
longitudes
calculated
from
British
Admiralty
Charts
#
6,
3784
and
141.
Survey
area
Site
Location
Transect
depth
[m]
Southern
Oman
Hallaniyat
Islands
Shallow
1
17°30'N
56°20'E
3
Shallow
2
17°30'N
56°19'E
3
Shallow
3
17°29'N
56°20'E
3
Shallow
4
17°30'N
56°20'E
3
Deep
1
17°29'N
56°20'E
14
Deep
2
17°30'N
56°19'E
10
Deep
3
17°29'N
56°20'E
10
Deep
4
17°30'N
56°20'E
10
Rahah
Bay
(mainland)
Shallow
1
16°56'N
54°48'E
3
Shallow
2
16°56'N
54°48'E
3
Deep
1
16°56'N
54°48'E
12
Deep
2
16°56'N
54°48'E
12
Gulf
of
Aden
Hadramaut
Province
al-Mukalla
Shallow
1
14°30'N
49°09'E
3
al-Mukalla
Shallow
2
14°30'N
49°09'E
3
al-Mukalla
Shallow
3
14°30'N
49°10'E
2
al-Mukalla
Shallow
4
14°30'N
49°10'E
3
al-Mukalla
Shallow
5
14°30'N
49°10'E
3
al-Mukalla
Deep
1
14°30'N
49°09'E
10
al-Mukalla
Deep
2
14°31'N
49°09'E
13
al-Mukalla
Deep
3
14°31'N
49°09'E
10
al-Mukalla
Deep
4
14°30'N
49°10'E
11
al-Mukalla
Deep
5
14°30'N
49°10'E
11
Shabwa
Province
Bir
Ali
Shallow
1
14°01'N
48°21'E
3
Bir
Ali
Shallow
2
14°01'N
48°21'E
3
Bir
Ali
Shallow
3
14°01'N
48°21'E
3
Bir
Ali
Shallow
4
14°00'N
48°20'E
2
Bir
Ali
Shallow
5
14°00'N
48°21'E
3
Bir
Ali
Shallow
6
14°00'N
48°20'E
3
Bir
Ali
Deep
1
14°00'N
48°20'E
8
Bir
Ali
Deep
2
14°00'N
48°20'E
8
Bir
Ali
Deep
3
(Belhaf)
13°59'N
48°10'E
8
Bir
Ali
Deep
4
(Belhaf)
13°59'N
48°10'E
8
Sikha
Island
Shallow
1
13°56'N
48°23'E
2
Sikha
Island
Shallow
2
13°56'N
48°23'E
3
Sikha
Island
Shallow
3
13°56'N
48°23'E
3
Sikha
Island
Shallow
4
13°54'N
48°23'E
3
Sikha
Island
Shallow
5
13°54'N
48°23'E
3
Sikha
Island
Shallow
6
13°54'N
48°23'E
3
Sikha
Island
Deep
1
13°56'N
48°23'E
12
Sikha
Island
Deep
2
13°56'N
48°23'E
14
Sikha
Island
Deep
3
13°56'N
48°23'E
12
Sikha
Island
Deep
4
13°54'N
48°23'E
11
Sikha
Island
Deep
5
13°54'N
48°23'E
12
Sikha
Island
Deep
6
13°54'N
48°23'E
12
Ras
Imran
Shallow
1
12°45'N
44°45'E
3
Deep
1
12°48'N
44°38'E
8
Southern
Red
Sea
Kamaran
Islands
Uqban
Shallow
1
15°29'N
42°24'E
2
Uqban
Shallow
2
15°28'N
42°25'E
2
Uqban
Shallow
3
15°28'N
42°25'E
3
Uqban
Shallow
4
15°29'N
42°24'E
3
Uqban
Deep
1
15°27'N
42°23'E
14
Uqban
Deep
2
15°28'N
42°25'E
12
Uqban
Deep
3
15°28'N
42°25'E
10
Uqban
Deep
4
15°29'N
42°24'E
10

Zoogeography
of
coral
reef
fishes
of
the
Gulf
of
Aden
297
coral-covered
or
rocky
slope
of
between
10
and
50°,
extending
to
a
depth
of
between
8
and
14
m
where
it
meets
a
level
or
gently
sloping
sandy
sea
floor
(KEMP
&
BENZONI
2000).
In
places,
high-
cover
healthy
coral
communities
also
extended
several
hundred
metres
offshore,
sometimes
appar-
ently
developed
on
an
unconsolidated
sand/gravel
substrate.
Rocky
and
coral
habitats
at
depths
greater
than
14
m
were
only
encountered
at
Sikha
Island
where,
due
to
its
location
offshore
in
ap-
proximately
60
m
of
water,
the
sublittoral
slopes
steeply
to
between
15
and
60
m.
A
diverse
range
of
coral
community
types
is
present
throughout
the
north-eastern
Gulf
of
Aden
(KEMP
&
BENZONI
2000)
and
extensive,
well-developed
and
varied
shallow
coral
communities
are
present
at
many
loca-
tions
(Plates
1
and
2).
The
majority
of
studies
throughout
Hadramaut/Shabwa
were
carried
out
at
sites
with
a
hard
substrate
(rocks
and/or
coral),
although
extensive
qualitative
observations
were
also
made
at
two
sandy
bay sites
on
the
mainland
coast.
Detailed
studies
of
the
fish
communities
were
carried
out
at
34
sites
in
the
northern
Gulf
of
Aden,
12
sites
in
southern
Oman
and
8
sites
in
the
southern
Red
Sea
(Table
1). These
studies
con-
centrated
on
the
Chaetodontidae
(butterflyfishes),
Pomacanthidae
(angelfishes),
Pomacentridae
(damselfishes),
Acanthuridae
(surgeonfishes)
and
Balistidae
(triggerfishes).
At
each
site
underwater
visual
census
(UVC)
transects
of
pomacanthid
and chaetodontid
fishes
were
carried
out.
Transects
were
250
m
in
length,
following
the
depth
contour,
and
all
pomacanthid
and
chaetodontid
fishes
within
5
m
of
the
central
line
of
the
transect
were
identified
to
species
and
recorded
on
prepared
re-
cording
sheets
printed
on
waterproof
paper.
Transects
were
initially
measured
using
a
50
m
tape,
to
provide
a
baseline.
Subsequently
transect
lengths
were
estimated
by
timing
them
(at
5
min
per
50
m),
and
were
re-measured
after
every
ten
or
twelve
transects
in
order
to
ensure
that
transect
lengths
were
being
estimated
consistently.
Habitat
characterisation
was
carried
out
along
the
line
of
each
UVC
transect,
using
five
replicate
quadrats
spaced
at
50
m
intervals
along
the
first
200
m
of
each
transect.
Habitat
characterisation
consisted
of
estimated
percentage
cover
of
17
categories
of
substrate,
including
life-forms
of
living
hard
and
soft
corals,
in
5
x
5
m
quadrats
(KEMP
&
BENZONI
2000).
In
addition
to
the
quantitative
transect,
all
pomacentrid,
balistid
and
acanthurid
species
oc-
curring
at
each
site
were
recorded,
along
with
any
additional
chaetodontid
and
pomacanthid
species
observed
outside
the
quantitative
transect
area.
Thus
a
species
list
for
every
survey
site
was
compiled
for
each
of
these
five
families.
As
a
secondary
task,
a
record
of
all
other
fish
species
positively
identi-
fied
in
each
of
the
four
survey
areas
was
compiled.
No
collection
of
fishes
was
possible,
so
all
identifi-
cations
presented
are
photographic
or
sight
records,
and
uncertain
identifications
have
been
omitted.
Cluster
analysis
(Ward's
method
of
hierarchical
agglomerative clustering)
was
used
to
assess
rela-
tionships
between
species
assemblages
of
the
five
principal
families
studied,
in
all
areas
visited
during
the
1998
expedition
(Fig.
3).
This
cluster
analysis
is
based
only
on
presence/absence
data
for
each
region,
with
no
weighting
for
species
abundance.
Ward's
method
calculates
the
squared
Euclidean
distance
to
the
cluster
means
for
each
case,
and
sums
them
for
all
cases.
At
each
step
the
clusters
which,
when
merged,
give
the
smallest
increase
in
the
sum
of
squared
within-cluster
distances,
are
merged.
Cluster
analysis
was
carried
out
on
the
statistics
package
SPSS
for
Windows,
Version
6.0.
RESULTS
New
records
Chaetodon
trifasciatus
Park,
1797
Plate
3
Chaetodon
trifasciatus
Park,
1797.
—
Transactions
of
the
Linnean
Society
3:
34.
Type
locality:
Sumatra.
Remarks:
A
single
small
subadult
(6-7
cm
total
length)
was
observed
on
the
northern
side
of Sikha Island,
in
approximately
1
m
of
water
in
a
shallow
sheltered
bay
with
very
high
cover
of

298
J.M.
KEMP
healthy
living
coral.
This
individual
was
closely
associated
with
subadults
of
the
locally
very
abun-
dant
close
relative
Chaetodon
melapterus
Guichenot,
1862,
an
Arabian
endemic
species
(RANDALL
1994)
which
ranges
from
the
Arabian
Gulf
around
the
Arabian
Peninsula
to
the
southern
Red
Sea.
Distribution
(Fig.
2):
Chaetodon
trifasciatus,
one
of
four
members
of
the
obligate
coralli-
vorous
chaetodontid
subgenus
Corallochaetodon
Burgess,
1978,
is
commonly
distributed
through-
out
the
coral-rich
regions
of
the
Indian
Ocean
(BURGESS
1 978,
BLUM
1 989),
with
the
exception
of
Arabia
and
the
Gulf
of
Aden.
It
is
replaced
in
the
Pacific
by
Chaetodon
lunulatus
Quoy
&
Gaimard,
1824
(KUITER
1995).
Around
Arabia
C.
trifasciatus
is
replaced
by
C.
melapterus
in
the
Arabian
Gulf,
Gulf
of
Oman,
Arabian
Sea
coast,
Gulf
of
Aden,
Socotra
Archipelago,
and
the
ex-
treme
southern
Red
Sea
(RANDALL
1 994,
1996;
KEMP
1998
b).
Within
the
Red
Sea
C.
melapterus
is
replaced
by
C.
austriacus
Riippell,
1836,
which
is
common
in
the
northern
two
thirds
of
the
sea
(ROBERTS
et
al.
1992),
and
has
recently
been
reported
to
be
common
at
several
locations
in
the
extreme
south
of
the
Red
Sea
(WATT
1996,
BRODIE
e t
al.
in
press),
where
it
is
sympatric
with
C.
melapterus.
Waifs
of
C.
austriacus
are
recorded
from
as
far
afield
as
Oman
(RANDALL
1996).
Chaetodon
zatizibarensis
Playfair,
1866
Plate
4
Chaetodon
zanzibarensis
Playfair,
1866. —
In:
The
fishes
of
Zanzibar:
33.
Type
locality:
Zanzibar.
Remarks:
Four
adult
Chaetodon
zanzibarensis
were
observed
and
photographed
over
a
two-
week
period
at
Sikha
Island.
Three
were
consistently
observed
among
or
near
very
large
Porites
cor-
als
in
a
sheltered
bay
on
the
south
coast
of
the
island,
and
one
was
observed
on
one
occasion
only,
among
Porites
co rals
in
the
northern
bay.
This
species
was
not
observed
anywhere
else
in
the
re-
gion.
All
four
individuals were
fully
grown
adults.
Distribution:
Western
and
central
Indian
Ocean.
This
species
has
been
recorded
through-
out
East
Africa
as
far
north
as
Mombassa,
and
in
the
Seychelles,
Mascarenes
and
the
Chagos
Ar-
chipelago
(BURGESS
19 78,
BLUM
19 89,
WINTERBOTTOM
et
al.
1989,
TMRU
1994).
It
is
not
yet
re-
corded
from
the
Maldives
(RANDALL
&
ANDERSON
1993)
or
the
Socotra
Archipelago
(KEMP
1998
b).
Halichoeres
cosmetus
Randall
&
Smith,
1982
Plate
5
Halichoeres
cosmetus
Randall
&
Smith,
1982.
—
Ichthyological
Bulletin
45:
15.
Type
locality:
Maldives.
Remarks:
Several
individuals
of
this
species
were
seen
amongst
hard
and
soft
corals
in
shel-
tered
sites
at
Sikha
Island,
between
depths
of
3
and
8
m.
One
was
photographed
in
3-4
m
of
wa-
ter
in
a
sheltered
shallow
bay
on
the
northern
side
of
Sikha,
amongst
massive
Porites
and
scattered
branching
hard
and
soft
corals
on
sand.
Distribution:
Western
Indian
Ocean
including
the
Seychelles,
Maldives, Mascarenes,
Chagos
Archipelago
and
Comores
and
East
Africa
from
Natal
to
northern
Kenya
(RANDALL
&
SMITH
1982).
RANDALL
&
SMITH
( 1982)
explicitly
exclude
the
Gulf
of
Aden,
Red
Sea
and
Arabian
Gulf
from
this
species'
range.
Considerable
further
work
since
1982,
particularly
surveys
of
the
ichthyofauna
of
the
southern
Red
Sea,
south-western
Gulf
of
Aden
and
Oman
(RANDALL
1 994;
MCCLANAHAN
&
OBURA
1 997;
RANDALL
1996)
has
failed
to
record
it
in
Arabian
waters.
Thalassoma
hardwicke
(Bennett,
1830)
Plate
6
Sparus
hardwicke
Bennett,
1830.
—
A
selection
of
rare
and
curious
fishes
found
upon
the
coast
of
Ceylon
6:
12.
Type
lo-
cality:
Sri
Lanka.
Remarks:
At
least
four
individuals
of
this
species
were
observed,
and
two
photographed,
in
1-3
m
of
water
in
the
very
shallow
coral-rich
area
of
the
northern
bay
at
Sikha
Island.
The
speci-
men
pictured
is
one
of
the
two
largest,
at
approximately
17-18
cm
total
length.
Two
others
were

Zoogeography
of
coral
reef
fishes
of
the
Gulf
of
Aden
299
|40° |50°
|60°
|70°E
t,
/
1
^
/
5
i
^
#
Chaetodon
austriacus
y
kjg,
\
•
Chaetodon
melapterus
A
Chaetodon
trifasciatus
30
N
—
*
*'
20_
—
o:
10°
1 1 1
IS
Fig.
2:
North-western
Indian
Ocean
distributions
of
three
species
of
the
obligate
corallivorous
chaetodontid
subgenus
Corallochaetodon
Burgess,
1978.
Each
of
the
three
out-liers
(C.
melapterus
in
the
Seychelles,
C.
trifasciatus
in
Yemen
and
C.
austriacus
in
Oman)
are
isolated
records
of
waifs
(this
paper;
RANDALL
1994,
1996).
The
distribution
of
C.
austriacus
on
the
Afri-
can
side
of
the
Red
Sea
probably
follows
the
distribution
on the
Arabian
side.
Both
C.
austriacus
and
C.
melapterus
are
rare
in
the
southern
Red
Sea,
and
southern
Red
Sea
rarity
may
have
been
severely
exacerbated
by
recent
(early
1990s)
massive
bleaching-
related
mortality
of
shallow
scleractinian
corals
throughout
the
Yemen
Red
Sea
region
(J.
Kemp,
unpublished
data).
Sources:
AL-
BAHARNA
19 86
(Bahrain);
BARRATT
&
MEDLEY
1990
(Djibouti);
T.
Burkitt
&
A.
Dawson-Shepherd,
pers.
comm.
(Sudan);
BUR-
GESS
1 978
(Seychelles);
BLUM
1 989
(Ras
al-Hadd,
Oman);
CARPENTER
e t
al.
1997
(Kuwait);
D.
Fabian,
pers.
comm
(Asseb,
Eritrea);
FRASER-BRUNNER
1950
(Aden);
KEMP
1 998
b
(Socotra
Archipelago);
F.
Krupp,
pers.
comm.
(Jubail,
Saudi
Arabia);
ORMOND
e t
al.
1984
(Red
Sea,
Saudi
Arabia);
RANDALL
1 994
(Yemen
Red
Sea);
RANDALL
1 996
(southern
Oman);
RANDALL
&
ANDERSON
1 993
(Maldives);
SMITH
et
al.
1987
(Arabian
Gulf);
WATT
1 996
(Bab
al-Mandab);
WINTERBOTTOM
e t
al.
1993
(Chagos
Archipelago);
J.
Kemp,
unpublished
data
(Gulf
of
Oman,
Musandam,
eastern
Gulf
of
Aden,
Aden
[Ras
Imran],
south-
ern
Red
Sea
[Kamaran Islands]).
smaller
(13-14
cm).
All
were
observed
only
within
a
single
50
x
100
m
area
of
corals
composed
of
mixed
branching
Acropora
and
Stylophora
and
foliose
and
branching
Montipora.
Distribution:
Throughout
the
Indo-West
Pacific,
excluding
the
Red
Sea,
Oman,
and
the
Arabian
Gulf.
Not
recorded
from the
Socotra
Archipelago.

300
J.M.
KEMP
Thalassoma
quinquevittatum
Lay
&
Bennett,
1839
Plates
7,
8
Thalassoma
quinquevittatum
Lay
&
Bennett,
1839.
—
In:
Zoology
of
Captain
Beechey's
voyage
to
the
Pacific
and
Behrings
Straits
[...]:
66.
Type
locality:
Loo
Choo
Islands.
Remarks:
Observed
in
large
numbers
at
between
0.5
and
5
m
depth,
on
the
south-western
side
of
Sikha
Island.
The
site
was
a
coral-free
rocky
headland,
highly
exposed
to
waves
and
swell,
and
densely
covered
in
algal
turf,
barnacles
and
small
invertebrates.
DOR
(1984)
cites
records
of
this
species
from
inside
the
Red
Sea,
but
RANDALL
&
EDWARDS
(1 984)
state
that
it
does
not
extend
its
range
there.
GOREN
&
DOR
(1994)
do
not
record
this
species
inside
the
Red
Sea.
In
particular,
records
of
the
species
from
the
northern
Red
Sea,
at
Tiran
and
elsewhere
in
the
vicinity
of
Sinai
(see
DOR
1984)
are
likely
to
be
a
result
of
confusion
with
Thalassoma
klunzingeri
Fowler
&
Steinitz,
1956,
a
Red
Sea
endemic
species
which
is
extremely
abundant
in
shallow
reef
habitats
throughout
the
northern
and
central
Red
Sea,
and
which
is
a
sister
species
to
T.
quinquevittatum
(RANDALL
&
EDWARDS
19 84,
ORMOND
&
EDWARDS
19 87).
This
confusion
may
arise
from
the
fact
that
some
specimens
of
T.
klunzingeri
have
in
the
past
been
misidentified
as
T.
guentheri
(see
com-
ments
in
RANDALL
&
EDWARDS
1984).
Julis
guentheri
Bleeker,
1862
is
a
junior
synonym
of
T.
quinquevittatum.
The
record
of
T.
quinquevittatum
at
Sikha
Island
is
thus
the
first
confirmation
of
the
species
in
Arabian
waters.
Most
individuals
observed
at
Sikha
were
very
closely
associated
with
the
rocky
substrate,
although
many
were
also
engaged
in
spawning
in
the
high
energy
surge
zone
at
0.5-3.0
m
depth.
Ecsenius
lineatus
Klausewitz,
1962
Plate
9
Ecsenius
lineatus
Klausewitz,
1962.
—
Senckenbergiana
biologica
43
(2):
145.
Type
locality:
Madewaru
Island,
FadifFulu
Atoll,
Maldives.
Remarks:
One
individual
of
this
species
was
photographed
at
Sikha
Island,
in
a
coral-rich
area
of
the
northern
bay,
in
approximately
5
m
of
water.
Another
was
observed
at
a
depth
of
3
m
at
Belhaf,
in
an
area
of
very
large
colonies
of
Porites.
Distribution:
Central
and
eastern
Indian
Ocean
and
western
Pacific,
from
the
Maldives
and
Mauritius
to
Taiwan
and
the
Ryukyu
Islands.
Not
known
from
East
Africa,
from
the
Indo-
Malay
archipelago
anywhere
east
of
Sumatra,
or
from
eastern
Australia
(SPRINGER
1 988).
Acanthurus
leucocheilus
Herre,
1927
Plate
10
Acanthurus
Leucocheilus
Herre,
1927.
—
Philippines
Journal
of
Science
34
(4):
419.
Type
locality:
Philippines.
Remarks:
Several
adults
(approximately
30
cm
length)
were
observed
on
the
exposed
east
and
south
coasts
of
Sikha
Island.
All
were
in
1-4
m
of
water,
browsing
on
exposed
rocky
surfaces
with
very
low
coral
cover,
and
a
high
cover
of
algal
mat
or
turf,
as
shown
in
the
photograph.
The
photograph
does
not
show
the
fish
very
clearly,
but
the
species was
identified
on
the
basis
of:
a
dark
brown
overall
colour
with
a
white
caudal
blade
and
white
or
pale
bar
across
the
caudal
pe-
duncle,
white
mouth,
variably
pale
to
white
chin-strap,
tail
paler
than
the
colour
of
the
body,
moderately
to
strongly
lunate
and
with
a
blue-grey
margin.
Distribution:
Indo-Pacific.
In
the
north-western
Indian
Ocean
at
the
Maldives,
Chagos
Ar-
chipelago,
Sri
Lanka
(DEBELIUS
1993,
RANDALL
&
ANDERSON
1 993,
WINTERBOTTOM
&
ANDERSON
1997).
Plates
1-8:
1:
Shallow
coral
community
dominated
by
branching
corals
at
Bir
Ali,
Shabwa
Province.
2:
Coral
community
domi-
nated
by
massive
Porites
corals
at
Bir
Ali.
3:
Subadult
Chaetodon
trifasciatus
with
juvenile
and
subadult
C.
melapterus
at
Sikha
Island,
Shabwa
Province.
4:
Adult
Ckaetodon
zanzibarensis
at
Sikha
Island.
5:
Halichoeres
cosmetus
at
Sikha
Island.
6:
Thalassoma
hardwicke
at
Sikha
Island.
7:
Male
Thalassoma
quinquevittatum
at
Sikha
Island.
8:
Female
Thalassoma
quinquevittatum
at
Sikha
Island.

302
J.M.
KEMP
Acanthurus
triostegus
(Linnaeus,
1758)
Chaetodon
triostegus
Linnaeus,
1758.
—
Systema
Naturae
10
(1):
274.
Type
locality:
"Indies".
Remarks:
Adults
of
this
species
were
observed
at
al-Mukalla
in
Yemen,
and
at
the
Hallaniyat
(Kuria
Muria)
Islands
in
Oman
(17°30'N
56°19'E).
In
both
cases
only
rare
individuals
were
re-
corded,
at
shallow
rocky
inshore
sites.
At
al-Mukalla
two
were
seen
at
one
site
to
the
east
of
the
town,
and
at
the
Hallaniyat
Islands
single
individuals
were
seen
at
each
of
two
sites,
approximately
1.5
km
apart.
No
photographs
were
taken
of
this
species,
but
it
is
large,
conspicuous
and
unmis-
takable.
Distribution:
Indo-Pacific,
from
East
Africa,
the
Seychelles,
Maldives
and
Chagos
Archi-
pelago
to
the
eastern
Pacific.
Recently
recorded
at
the
Socotra
Archipelago
(KEMP
1 998
b).
Further
species
records
from
Hadramaut
and
Shabwa
A
preliminary
checklist
of
all
species
of
shallow
coastal
fishes
recorded
throughout
the
survey
in
eastern
Yemen
is
presented
in
Table
2
(Appendix).
Because
no
collection
of
fishes
was
possible,
there
is
a
bias
in
the
species
identified
in
this
study
towards
larger,
diurnal
and
non-cryptic
species.
Lists
for
the
five
families
which
were
central
to
zoogeographic
studies
and
which
were
always
iden-
tified
(Chaetodontidae,
Pomacanthidae,
Pomacentridae,
Acanthuridae
and
Balistidae)
are
probably
quite
comprehensive
for
the
area.
The
checklists
for
all
other
families
listed
were
compiled
as
a
secondary
task,
and
should
be
regarded
as
incomplete.
Further
surveys
will
certainly
extend
this
checklist
considerably.
DISCUSSION
The
benthic
communities
of
shallow
sublittoral
hard
substrates
in
the
Hadramaut/Shabwa
region
are
dominated
by
scleractinian
corals
(KF.MP
&
BENZONI
2000),
with
extensive,
healthy
and
diverse
coral
communities
being
widespread
throughout
the
region.
Although
biogenic
reef
structures
are
very
uncommon
in
the
region,
the
fish
assemblages
associated
with
these
coral
communities
are
dominated
by
characteristically
coral
reef
associated
groups
such
as
chaetodontids,
pomacanthids,
scarids,
labrids,
acanthurids
and
balistids
(for
discussion
of
definitions
of
coral
reef
fishes
see
CHOAT
&
BELLWOOD
1 991;
BELLWOOD
1 996,
1998;
ROBERTSON
1 998).
RANDALL
(1996)
lists
seven
different
zoogeographic
components
of
the
ichthyofauna
of
the
coast
of
southern
Oman,
a
region
contiguous
with
the
coast
of
Hadramaut
and
Shabwa
but
600
km
to
the
east.
These
components
are:
cosmopolitan
in
warm
seas;
Indo-Pacific;
Indian
Ocean;
Red
Sea
and
Gulf
of
Aden;
Gulf
of
Oman;
southern
Africa;
Oman
endemics.
All
but
one
of
the
new
records
presented
here
(Chaetodon
Zanzibarensis)
belong to
the
broadly
distributed
Indo-Pacific
group,
although
this
is
the
first
record
of
Ecsenius
lineatus
from
the
western
margin
of
the
Indian
Ocean.
The
cosmopolitan
species
group,
for
instance
Aetobatus
narinari
(Euphrasen,
1790)
and
Aluterus
scriptus
(Osbeck,
1765),
is
present in
Hadramaut/Shabwa,
but
does
not
pro-
vide
any
significant
zoogeographic
information,
and
will
not
be
discussed
further
here.
All
of
the
other
components
of
the
Oman
assemblage
identified
by
RANDALL
(1996)
are represented
in
the
Hadramaut/Shabwa
assemblages,
but
each
takes
a
slightly
different
form
from
the
equivalent
group
in
Oman.
The
Indo-Pacific,
Indian
Ocean
and
Red
Sea
/
Gulf
of
Aden
groups
are
more
speciose
as
well
as
more
generally
abundant
in
Hadramaut/Shabwa
than
in
Oman.
Conversely,
although
the
Oman
endemic
and
Gulf
of
Oman
assemblages
are
present
-
e.g.
Cirrhitichthys
calliurus
Regan,

Zoogeography
of
coral
reef
fishes
of
the
Gulf
of
Aden
303
1905,
Chaetodon
dialeucos
Salm
&
Mee,
1989
and
Ecsenius
pulcher
(Murray,
1887)
-
they
are
greatly
reduced
in
diversity.
RANDALL'S
(1996)
southern
African
group
is
represented
in
Hadramaut/
Shabwa
by
just
one
taxon
(Diplodus
sargus
capensis
Smith,
1844).
The
almost
complete
absence
of
the
southern
African
assemblage
from
Hadramaut/Shabwa
may
be
significant.
RANDALL
( 1996)
re-
marks
that
the
link
between
southern
Oman
and
southern
Africa
may
be
environmental,
being
related
to
the
presence
of
cold
monsoon
upwelling
in
Oman
(CURRIE
et
al.
1973;
BARRATT
e t
al.
1984,
1986;
SAVIDGE
e t
al.
1990),
and
RANDALL
&
HOOVER
(1995)
note
the
existence
of
a
centre
of
endemism
on
the
Arabian
Sea
coast
of
Oman
which
may
be
related
to
the
same
seasonal
upwelling
event.
The
Hadramaut/Shabwa
area
lies
at
the
western
edge
of
the
effects
of
the
upwelling,
and
if
RANDALL'S
hy pothesis
is
correct
the
effects
may
not
be
pronounced
enough
in
Hadramaut/Shabwa
to
allow
many
of
the
southern
African
species
to
establish
successfully.
There
are
three
principal
distributional
features
of
the
fish
species
assemblages
of
the
Hadramaut
and
Shabwa
area,
at
varying
geographic
scales,
which
become
apparent
from
this
study.
Firstly,
there
is
a
pronounced
overlap
of
ichthyofaunas
with
different
zoogeographic
affinities.
Secondly,
and
closely
related
to
the
first
point,
there
is
a
clear
difference
between
fish
assemblages
of
al-
Mukalla
and
Bir
Ali,
just
100
km
apart.
Thirdly,
the
fish
assemblage
of
Sikha
Island,
the
only
lo-
cation
of
six
of
the
eight
new
records,
is
h ighly
unusual
both
locally
and
regionally.
The
pronounced
overlap
of
zoogeographically
distinct
species
assemblages
in
Hadramaut/
Shabwa
gives
rise
to
previously
unrecorded
sympatry
between
sister
species,
particularly
in
the
Chaetodontidae,
a
family
with
high
levels
of
endemism
around
Arabia
(ORMOND
&
EDWARDS
1987,
BLUM
1 989,
KLAUSEWITZ
1989).
Two
Red
Sea
and
Gulf
of
Aden
endemic
butterflyfishes,
Chaetodon
fasciatus
Forsskal,
1775
and
Heniochus
intermedins
Steindachner,
1893,
are
sympatric
here
with
their
Indo-West
Pacific
sister
taxa
C.
lunula
(Lacepede,
1802)
and
H.
acuminatus
(Linnaeus,
1758),
respectively.
The
C.
fasciatus
and
C.
lunula
pair
were
only sympatric
at
Sikha,
where
an
apparently
stable
heterospecific
pair
was
observed
repeatedly
and
photographed
over
a
two-week
period
(Plate
11),
while
the
Heniochus
were
sympatric
throughout
the
region.
In
the
Balistidae
the
Indo-West
Pacific
species
Sufflamen
chrysopterus
(Bloch
&
Schneider,
1801)
and
its
Red
Sea
and
Gulf
of
Aden
endemic
sister
species
S.
albicaudatus
(Riippell,
1829)
are
sympatric
at
Sikha.
The
blenniid
genus
Ecsenius
provides
a
further
example
of
overlap
of
zoogeographic
ranges,
although
not
between
sister
taxa.
In
this
genus
the
Arabian
Gulf
and
northern
Arabian
Sea
species
Ecsenius
pulcher
(Murray,
1887)
and
the
Red
Sea
species
Ecsenius
frontalis
(Ehrenberg,
1836)
are
both
common
in
Shabwa.
Both
of
these
records
are
considerable
range
extensions,
with
E.
fronta-
lis
previously
only
known
from
the
Red
Sea
and
Djibouti
(SPRINGER
1988)
and
E.
pulcher
from
the
Arabian
Gulf,
Pakistan
and
Oman
(SPRINGER
1 988,
RANDALL
1996),
although
KEMP
(1998
b)
records
it
from
Socotra.
Zoogeographic
trends
between
Shabwa
Province
and
al-Mukalla
Over
the
relatively
short
100
km
distance
between
the
Bir
Ali
area
and
al-Mukalla,
zoogeographic
trends
consistent
with
the
larger
scale
east-west
divergence
between
Oman
and
Hadramaut/Shabwa
are
apparent.
A
significant
part
of
the
divergence
between
Oman
and
Yemen
described
above
is
due
to
the
species
assemblage
at
Bir Aii
(including
Sikha
Island),
with
the
assemblage
of
al-Mukalla
being
intermediate
between
those
of
Oman
and
Bir
Ali.
The
influences
of
the
Red
Sea
and
Indian
Ocean
species
assemblages
are
more
apparent
throughout
the
Bir
Ali
area,
both
mainland
and
islands,
than
at
al-Mukalla.
The
chaetodontid
as-
semblage
of
Bir
Ali
is
more
heavily
dominated
by
Red
Sea
species
(22.2
%
at
Shabwa,
13.3
%
at

304
J.M.
KEMP
al-Mukalla)
with
the
Red
Sea
species
Chaetodon
semilarvatus
Cuvier,
1831
and
C.
larvatus
Cuvier,
1831
both
common
at
Bir
Ali
but
absent
or
very rare
at
al-Mukalla.
Similarly,
four
Indian
Ocean
or
Indo-West
Pacific
chaetodontid
species
recorded
at
Bir
Ali
were
not
present
at
al-Mukalla
and
are
not
recorded
from
Oman
(Chaetodon
lineolatus
Cuvier,
1831,
C.
melannotus
Bloch
&
Schnei-
der,
1801,
C.
trifasciatus
and
C.
zanzibarensis).
In
other
families
the
Red
Sea
species
Larabicus
quadrilineatus
(Riippell,
1835)
(Labridae),
Neopomacentrus
xanthurus
Allen
&
Randall,
1981
(Pomacentridae)
and
Sufflamen
albicaudatus
(Balistidae)
are
all
common
throughout
the
Bir
Ali
area,
but
were
not
recorded
at
al-Mukalla.
The
Red
Sea
scarid
Chlorurus
genazonatus
(Randall
&
Bruce,
1983)
(Plate
12)
was
common
at
Sikha,
but
was
not
recorded
at
al-Mukalla.
Four
Indo-
West
Pacific
balistids
and
two
acanthurids
which
extend
their
ranges
from
the
Indian
Ocean
around
the
Horn
of
Africa
into
the
Red
Sea,
but
not
eastwards
to
Oman
(a
distribution
common
to
many
families,
KEMP
1 998
b)
were
present
at
Bir
Ali,
but
not
at
al-Mukalla.
The
reverse
of
this
is
also
true,
although
to
a
less
marked
degree,
with
some
species,
such
as
Pomacanthus
semicircu-
latus
(Cuvier,
1831),
which
are
common
in
southern
Oman
being
present
at
al-Mukalla
but
not
at
Bir
Ali.
The
damselfish
Amphiprion
sp.
(Plate
13),
present
at
al-Mukalla,
may
represent
a
Yemen
sister
taxon
to
Amphiprion
omanensis
Allen
&
Mee,
1991.
Although
the
status
of
the
al-Mukalla
Amphiprion
remains
to
be
ascertained,
it
very
closely
resembles
Amphiprion
omanensis
in
all
re-
spects
of
size,
general
shape
and
coloration,
except
for
the
width
of
the
two
white
bars,
which
are
wider
than
those
found
in
Oman
populations
of
A.
omanensis.
The
divergence
between
the
fish
assemblages
of
al-Mukalla
and
the
Bir
Ali
area
may
be
due
to
the
occurrence
of
a
significant
faunal
break
between
the
two
areas.
This
is
illustrated
by
the
results
of
a
hierarchical
cluster
analysis
(Ward's
method),
illustrated
in
Fig.
3.
This
shows
the
relationship
between
the
species
assemblages
of
five
families
of
fishes
(Chaetodontidae,
Pomacanthidae,
Pomacentridae,
Acanthuridae
and
Balistidae),
totalling
80
species,
in
all
regions
of
southern
and
eastern
Arabia
visited
during
the
1998
expedition.
The
al-Mukalla
species
assemblage
for
these
five
families
more
closely
resembles
that
of
southern
Oman
600
km
to
the
east
than
it
does
that
at
Shabwa
less
than
100
km
to
the
west.
The
dendrogram
reveals
that
the
Bir
Ali
assemblage
is
a
Gulf
of
Aden
fauna,
clustering
with
the
assemblage
from
Ras
Imran
to
the
west.
The
species
assemblage
of
Sikha
Island
is
deeply
separated
from
the
Bir
Ali
/
Ras
Imran
cluster.
The
occurrence
of
this
zoogeographic
change,
from
a
Gulf
of
Aden
fish
species
assemblage
to
one
more
closely
resembling
that
of
southern
Oman,
along
only
100
km
of
coastline
is
at
first
sight
surprising.
However,
ROBERTS
(1986)
and
ROBERTS
et
al.
(1992)
described
a
similarly
pro-
nounced
change
in
coral
reef
fish
assemblages
at
approximately
20°N
in
the
southern
Red
Sea,
at-
tributing
the
difference
to
oceanographic
and habitat
changes.
An
examination
of
the
oceanogra-
phy
of
the
eastern
Gulf
of
Aden
reveals
a
possible
explanation
for
the
Bir
Ali
-
al-Mukalla
discontinuity.
This
region
lies
at
the
extreme
western
edge
of
the
Arabian
Sea
upwelling,
with
raised
nutrient
levels,
high
primary
productivity
and
low
water
temperatures
in
the
Arabian
Sea
to
the
east
during
summer,
and
warmer
and
more oligotrophic
waters
in
the
Gulf
of
Aden
to
the
Plates
9-16:
9:
Ecsenius
lineatus
at
Sikha
Island,
Shabwa
Province.
This
species
was
also
present
at the
nearby
mainland.
10:
Acanthurus
leucocheilus
at
Sikha
Island.
See
text
for
description.
11:
Heterospecific
pair
of
Chaetodon
lunula
and C.
fasciatus
at
Sikha
Island.
This
pair
was
observed
on
several
occasions
over
a
two-week
period.
12:
The
'Red
Sea
endemic'
scarid
Chlorurus
genazonatus
at
Sikha
Island.
13:
Unidentified
Amphiprion
sp.,
bearing
a
close
resemblance
to
Amphiprion
omanensis
in
all
respects
except
for
the
width
of
the
two
white
bars
(see
text)
at
al-Mukalla.
14:
Pseudanthias
marcia.
This
species
is
extremely
abundant
on
Porites-dominated
slopes
at
Sikha
Island.
15:
Pseudanthias
townsendi
at
Sikha
Island.
16:
The
Oman
butterflyfish
Chaetodon
dialeucos
at
Sikha
Island.

Zoogeography
of
coral
reef
fishes
of
the
Gulf
of
Aden
305

306
J.M.
KEMP
Rescaled
distance
o
5
10
15
20
25
Site
i
ia o
11111
cu
i
uccp
BirAli
shal
BirAli
deep
Sikha
shal
Sikha
deep
Oman
shal
Oman
deep
al-Mukalla
shal
al-Mukalla
deep
3
2
1
Fig.
3:
Dendrogram
(Ward's
method)
of
species
assemblages
for
five
families
of
coral-associated
fishes
(Chaetodontidae,
Pomacanthidae,
Pomacentridae,
Acanthuridae
and
Balistidae),
totalling
80
species,
in
six
areas
on
the
coast
of
southern and
east-
ern
Arabia.
Shallow
assemblages
(shal)
were
at
1-3
m
depth,
and
deep
assemblages
(deep)
were
at
8-12
m
depth.
The
dendrogram
reveals
three
major
clusters
of
species
assemblages
(labelled
1,
2
and
3),
and
illustrates
the
divergence
between
the
al-Mukalla
assemblage
and
those
of
the
Bir
Ali
mainland
shore
and
Sikha
Island.
The
assemblage
of
al-Mukalla
is
more
closely
related
to
that
of
southern
Oman,
700
km
to
the
east,
than
it
is
to
that
of
Bir
Ali,
100
km
to
the
west.
The
three
clusters
are:
(1)
the
Kamaran
Islands,
southern
Red
Sea,
(2)
the
Gulf
of
Aden
and
Arabian
Sea coast
of
Yemen
and
Oman,
from
al-Mukalla
to
the
Hallaniyat
(Kuria
Muria)
Islands,
and
(3)
the
Gulf
of
Aden
from
Aden
(Ras
Imran)
to
Bir
Ali.
west.
Upwelling
systems
are
unstable
environments
in
which
physical,
chemical
and
biological
characteristics are
subject
to
continuous
change,
a
feature
which
creates
a
relatively
stressful
envi-
ronment
for
marine
organisms
(SAKKO
19 98).
In
Oman
and
eastern
Yemen
the
Arabian
upwelling
causes
reduced
water
temperatures
and
raised
productivity
from
June
to
September,
during
the
summer
monsoon
(SHEPPARD
et
al.
1992).
Steep
clines
in
temperature
and
primary productivity
occur
between
al-Mukalla
and
Bir
Ali
during
the
upwelling,
with
al-Mukalla
generally
exposed
to
more
pronounced
upwelling
effects
than
Bir
Ali.
Sea
surface
temperatures
(SST)
at
Bir
Ali
are
commonly
between
1
and
2
°C
higher
during
the
summer
monsoon
upwelling
than
at
al-Mukalla
(NOAA
data
provided
by
the
Climate
Diagnostics
Center
at
www.cdc.noaa.gov,
SLUTZ
et
al.
1985,
WOODRUFF
et
al.
1993).
Shallow
sub-surface
(4
m
depth)
temperatures
follow
similar
patterns,
with
temperatures of
19-20
°C
at
al-Mukalla
from
August
to
September
1984,
and
25-27
°C
in
the
Bir
Ali
area
at
the
same
time
(STIRN
1 985,
cited
in
WATT
1996).
Over
the
same
period pri-
mary
productivity,
as
measured
by
sea
surface
colour,
typically
demonstrates
a
similarly
pro-
nounced
cline
(Plate
17),
with
phytoplankton
pigment
concentration
falling
from
as
high
as
10
mg/m3
in
the
al-Mukalla
area
to
as
low
as
2
mg/m3
in
the
Bir
Ali
area.
The
areas
of
lower
tem-
perature
and
higher
primary
productivity
correspond
to
the
areas
of
more
intense
monsoon
upwelling
(CURRIE
et
al.
1973,
SAVIDGE
et
al.
1990).
These
areas
in
turn
correspond
closely
to
the
centre
of
endemism
identified
in
Oman
by
RANDALL
&
HOOVER
(1995)
and
to
disjunct
Arabian
fish
distributions
described
below.
If
the
effects
of
monsoon
upwelling
are
significant
direct
or
in-
direct
factors
determining
the
distributions
of
fish
species
and
the
composition
of
fish
communi-
ties
in
southern
and
eastern
Arabia,
then
the
distributions
of
these
environmental
variables
may
explain
the
clustering
pattern
of
species
assemblages
in
Fig.
3.
The
closer
relationship
of
the
al-Mukalla
species
assemblage
to
that
of
southern
Oman
is
not
completely
consistent
across
all
families.
In
the
Pseudochromidae,
Pseudochromis
aldabraensis
Bauchot-Boutin,
1958
is
abundant
in
Oman,
from
Musandam
in
the
north
to
Salalah
in
the
south
(RANDALL
19 96,
Kemp
personal
observation),
but
is
absent
from
Hadramaut
and
Shabwa.
Here
it

Zoogeography
of
coral
reef
fishes
of
the
Gulf
of
Aden
307
Plate
17:
Coastal
Zone
Colour
Scanner
image
of
phytoplankton
pigment
concentration
in
the
north-western Indian
Ocean
re-
gion
in
summer
1979
(July-August-September),
showing
the
areas
of
upwelling
(yellow,
orange
and
red)
along
the
Indian
Ocean
coast
of
Somalia
and
the
Arabian
Sea
coasts
of
Yemen
and
Oman.
The
relatively
low
productivity
in
the
Gulf
of
Aden
is
con-
spicuous.
Bir
Ali
and
al-Mukalla
lie
either
side
of
the
most
pronounced
cline
in
upwelling
along
the
mainland
of
Arabia, where
the
intensity
of
upwelling
in
the
Arabian
Sea
rapidly
declines
moving
westwards
into
the
Gulf
of
Aden.
(Data
from
http://seawifs.gsfc.nasa.gov/SEAWIFS/IMAGES/CZCS_DATA.html).
is
replaced
by
the
locally
abundant
Red
Sea
/
Gulf
of
Aden
species
P.
sankeyi
Lubbock,
1975.
These
two
species
occupy
similar
habitats,
both
being
most
commonly
found
in
small
groups
closely
as-
sociated
with
vertical
rocky
faces
and
overhangs.
In
the
Serranidae,
the
Oman
species
Pseudanthias
marcia
Randall
&
Hoover,
1993
(Plate
14)
is
extremely
abundant
on
steeper
coral-rich
slopes
at
Sikha,
but
was
not
recorded
at
al-Mukalla.
The
Arabian
Gulf and
Oman
species
Pseudanthias
townsendi
(Boulenger,
1897)
was
also
present
at
Sikha
Island,
but
in
very
low
numbers,
with
only
one
male
and
less
than
half
a
dozen
females
recorded
at
one
site
(Plate
15).
Rare
individuals
of
the
Oman
butterflyfish
Chaetodon
dialeucos
were
also
present
at
Sikha
Island
(Plate
16),
but
were
re-
corded
nowhere
else
in
Yemen.
Disjunct
Arabian
distributions
and
the
Oman
area
of
endemism
The
southern
Oman
centre
of
endemism
noted
by
RANDALL
&
HOOVER
(1 995)
is
a
significant
fea-
ture
of
fish
species
distributions
in
eastern
Arabia.
In
addition
to
high
levels
of
endemism
in
this
region,
RANDALL
&
HOOVER
(1995)
and
RANDALL
(1996)
noted
the
occurrence
of
Indian
Ocean
or Indo-West
Pacific
species
here
which
are
otherwise absent
from
Arabia.
The
opposite
is
also
the
case:
a
number
of
species
have
markedly
disjunct
distributions
in
eastern
Arabia,
being
common
either
side
of
the
Oman
area
of
endemism,
but
rare
or
absent
within
it.
This
distributional
feature
is
well
illustrated
by
two
species
of
Pomacanthus
in
Oman
and
Yemen,
P.
semicirculatus
and
P.
m aculosus
(Forsskal,
1775).
Pomacanthus
semicirculatus,
a
wide-
spread
Indo-West
Pacific
species,
appears
to
replace
P.
maculosus
in
the
area
of
most
pronounced

308
J.M.
KEMP
upwelling,
approximately
from
Masirah
Island
in
Oman
to
the
eastern
Gulf
of
Aden
in
Yemen.
Pomacanthus
maculosus
is
very
common
in
the
Gulf
of
Aden
and
the
Gulf
of
Oman
to
either
side,
where
P.
semicirculatus
is
absent
or
very rare
(KEMP
2000).
Pomacanthus
semicirculatus
was
absent
at
Bir
Ali,
but
was
sympatric
with
P.
mac ulosus
at
al-Mukalla
(KEMP
2000).
Other
species
which
appear
to
have
similar
Arabian
distributions
include
the
pomacentrid
Pomacentrus
tricbourus
Playfair
&
Giinther,
1867,
the
balistid
Rbinecanthus
assasi
(F orsskal,
1775),
and
the
acanthurid
Acanthurus
sohal
(Forsskal,
1775),
amongst others.
Such
species
are
rare
in
southern
Oman
but
common
in
the
Gulf
of
Oman
or
Arabian
Gulf
to
the
north,
and
the
Red
Sea
and
Gulf
of
Aden
to
the
west.
The
unusual
ichthyofauna
of
Sikha
Island
A
significant
feature
of
the
eight
new
records
presented
here
is
that
seven
come
from
the
very
small
island of
Sikha.
In
spite
of
extensive
surveys
of
nearby
coral
communities
fringing
the
mainland
shore,
and
at
nearshore
islands,
six
of
these
species
were
not
recorded
anywhere
else
(Ecsenius
lineatus
was
recorded
at
both
Sikha
Island
and
the
Bir
Ali
mainland).
The
fish
community
of
Sikha
is
highly
unusual
in
the
entire
Hadramaut/Shabwa
area,
and studies
of
charts
of
the
area
(Admi-
ralty
Chart
#
6,
Gulf
of
Aden,
1993)
reveals
that
there
are
no
further
sites
in
the
northern
Gulf
of
Aden
which
resemble
Sikha
(islands
more
than
1
km
offshore,
in
more
than
40
m
of
water).
Of
a
total
of
267
species
of
fish
listed
in
Table
2
(Appendix),
five
are
included
as
photographic
records
for
the
region
(from
DEBELIUS
1998).
Of
the
remaining
262
species
identified
in
Hadramaut
and
Shabwa
during
the
1998
expedition,
50
(=
19
%)
were
only
recorded
at
Sikha.
This
contrasts
with
12
species
(=4.5
%)
only
recorded
at
al-Mukalla,
and
21
species
(=8.0
%) only
recorded
at
coastal
and
nearshore
sites
(including
al-Mukalla),
and
not
recorded
at
Sikha
Island.
Diversity of
the
five
target
families
in
Hadramaut
and
Shabwa
is
high
in
comparison
to
many
other
regions
of
Arabia,
and
most
of
this
diversity
comes
from
Sikha
Island.
The
most
striking
ex-
ample
of
this
is
in
the
Chaetodontidae.
Eighteen
species
of
chaetodontids
were
recorded
at
Sikha,
a
total
unprecedented
for
any
other
region
of
Arabia
(Fig.
4).
With
less
than
4
km
of
coastline
Sikha
Island
has
a
higher
species
richness
of
butterflyfishes
than
southern
Oman,
the
Gulf
of
Oman,
the
Arabian
Gulf,
or
any
section
of
the
Red
Sea
(the
entire
Red
Sea
has
15
confirmed
spe-
cies).
At
a
more
local
scale,
eight
of
these
butterflyfish
species
(44
%)
were
not
recorded
anywhere
else
in
Hadramaut
or
Shabwa.
Only
one
butterflyfish
species
present
in
Hadramaut/Shabwa
was
not
recorded
at
Sikha
Island
(Chaetodon
leucopleura
Playfair
&
Giinther,
1867,
recorded
at
al-
Mukalla).
In
the
Acanthuridae,
five
of
15
species
(=
33
%)
were
only
present
at
Sikha.
In
the
Balistidae
and
Pomacentridae
the
figures
are
40
%
and
15
%,
respectively.
The
new
records
are
thus
just
one
feature
of
a
generally
unusual
ichthyofauna
at
this
island.
The
higher
diversity
at
Sikha,
and
lower
diversity
elsewhere,
is
not
a
result
of
sampling
bias.
Twenty
hours
were
spent
SCUBA
diving
at
Sikha
Island,
approximately
half
of
the
total
time
spent
SCUBA
diving
at
all
other
areas
of
Hadramaut
and
Shabwa
(41
hours).
Approximately
equal
amounts
of
time
(6-8
hours)
were
spent
snorkelling
in
each
area.
The
new
records
are
of
species
with
broad
distributions
in
the
Indian
Ocean.
Most
are
known
from
all
of
the
areas
surrounding
Arabian
seas
to
both
south
and
east,
including
East
Africa,
the
Seychelles,
the
Chagos
Archipelago
and
the
Maldives.
With
the
exception
of
Acanthurus
triostegus
none
of
the
new
records
have
yet
been
recorded
from
the
Socotra
Archipelago
(A.
triostegus
was
also
the
only
species
among
the
new
records
which
was
present
at
al-Mukalla
and
in
southern
Oman,
but
not
in
Shabwa).
Although
both
Hadramaut/Shabwa
and
Socotra
are
dominated
by

Zoogeography
of
coral
reef
fishes
of
the
Gulf
of Aden
309
<
25
E
O
E
O
Fig.
4:
Species
richness
of
butterfiyfishes
(Chaetodontidae)
in
different
regions
of
Arabian
seas.
With
approximately
4
km
of
coastline
Sikha
Island
is
more
speciose
than
any
other
single
large
region.
similar
characteristically
South
Arabian
species
(for
instance,
in
the
Chaetodontidae
the
Arabian
endemic
taxa
Cbaetodon
vagabundus
pictus
Fraser-Brunner,
1950
and
C.
melapterus
are
very
domi-
nant
in
both
areas),
in
some
respects
the
ichthyofaunas
of
the
two
areas
differ
considerably
from
each
other.
The
assemblage
of
distinctively
Indian
Ocean
or
Indo-West
Pacific
species
present
at
Socotra
but
absent
from
Arabia
(KEMP
1998
b)
is
completely
different
from
the
analogous
assem-
blage
at
Sikha.
A
number
of
Indo-West
Pacific
and
Indian
Ocean
species
present
or
even
common
at
Socotra
(KEMP
1998
b)
were
not
recorded
anywhere
in
Hadramaut/Shabwa,
e.g.
Chaetodon
kleinii
Bloch,
1790,
Dascyllus
carneus
Fischer,
1885,
Acanthurus
lineatus
Linnaeus,
1758,
Balistoides
conspicillum
(Bloch
&
Schneider,
1801)
and
Ostracion
meleagris
Shaw,
1796.
Conversely,
none
of
the
Shabwa
new
records
have
yet
been
recorded
from
Socotra.
The
Red
Sea
influence,
in
the
form
of
Red
Sea
/
Gulf
of
Aden
endemic
species,
is
minimal
at
Socotra
in
comparison
to
both
Bir
Ali
(Shabwa
Province)
and
al-Mukalla
(Hadramaut
Province).
A
similarity
between
Socotra
and
Hadramaut/Shabwa,
and
one
both
areas
share
with
Oman,
is
the
apparent
absence
of
several
widespread
Indo-West
Pacific
fish
species
which
are
also
found
in
the
Red
Sea.
These
include
species
such
as
the
pomacentrids
Dascyllus
aruanus
(Linnaeus,
1758)
and
Pomacentrus
sulphureus
Klunzinger,
1871,
and
the
pomacanthid
Pygoplites
d iacanthus
(Boddaert,
1772).
This
supports
the
observation
of
KEMP
( 1998
b)
that
such
species
may
have
disjunct
distri-
butions,
being
present
in
the
Red
Sea
and
extreme
west
of
the
Gulf
of
Aden
and
in
most
of
the
Indian
Ocean,
but
absent
from
the
intervening
central
and
eastern
Gulf
of
Aden,
Oman,
Socotra
and
the
northern Horn
of
Africa.
This
is
likely
to
have
significant
implications
for
gene
flow,
evo-
lution
and
conservation
of
these
species.

310
J.M.
KEMP
Long-distance
planktonic
dispersal
of
fishes
to
and
from
Arabia
The
nature
of
the
fish
assemblage
of
Sikha
has
implications
for
understanding
of
the
relationship
between
larval
dispersal
and
the
distribution
of
fishes
at
a
zoogeographic
scale
throughout
the
north-western
Indian
Ocean
region.
The
only
species
of
the
new
records
which,
on
the
basis
of
the
1998
survey,
can
be
unequivocally
said
to
have
an
established
Arabian
breeding
population
(sensu
WILLIAMSON
1996)
is
Thalassoma
quinquevittatum,
observed
spawning
in
large
numbers
at
Sikha
Island.
Most
of
the
other
species
are
very
rare
in
the
Bir
Ali
area
and
may
successfully
spawn
here
rarely
or
not
at
all.
PYLE
&
RANDALL
( 1994)
suggest
that
locally
rare
species
(such
as
species
at
or
near
the
edges
of
their
ranges)
may
have
very
low
levels
of
reproductive
success.
For
most
of
the
new
records
presented
here,
and
other
locally
rare
species,
the Gulf
of
Aden
is
likely
to
be
a
sink
rather
than
a
source
of
larvae.
It
is
thus
possible
that
at
least
some
of
these
species
are
only
repre-
sented
in
Shabwa
by
widely
dispersed
products
of
spawning
events
outside
Arabian
seas,
where
es-
tablished
populations
are
known
to
occur.
Adults
of
the
majority
of
tropical
reef
fishes
are
territorial
or
site-attached
(SALE
1980),
but
most
species
go
through
a
pelagic
planktonic
phase
as
eggs
and/or
larvae
(LEIS
1 991).
It
is
during
this
phase
that
long-distance
dispersal
is
believed
to
occur,
principally
by
passive
advection
by
cur-
rents.
The
duration
of
the
larval
phase
varies
between
and
within
families,
ranging from
as
little
as
nine
to
over
100
days,
and
dispersing
larvae
over
distances
ranging
from
a
few
meters
to
thousands
of
kilometres
(LEIS
1 991).
At
the
end
of
this
time
the
larvae
settle
onto
a
benthic
habitat,
and
be-
fore,
during
or
after
settlement
metamorphose
into
the
adult
form
(VICTOR
1991).
The
Arabian
Sea
coast
of
Arabia
is
swept
by
two
major
currents
through
the
course
of
the
year
(Fig.
5).
These
currents
are
driven
by
the
Indian
Ocean
monsoon
winds,
and
may
disperse
fish
larvae
of
many
species
to
and
from
the
Arabian
Peninsula.
From
November
to
March
the
north-
east
monsoon
current
flows
westwards
across
the
Arabian
Sea,
past
Arabia
and
southwards
along
the
African
coast.
This
pattern
is
reversed
between
April
and
October
during
the
South-west
monsoon,
when
the
Somali
current
flows
north
along
the
African
and
Arabian
coasts
before
turn-
ing
eastwards
in
the
Arabian
Sea
towards
India
and
the
Maldives.
Several
instances
of
long-distance
dispersal
of
Arabian
endemic
species
via
these
currents,
to
areas
outside
their
normal
ranges,
have
been
recorded.
AHL
(1923)
recorded
a
single
juvenile
of
Chaetodon
melapterus
at
the
Seychelles,
and
RANDALL
&
ANDERSON
(1 993)
reported
the
occurrence
of
a
single
adult
Zebrasoma
xanthurum
(Blyth,
1852)
in
the
Maldives.
RANDALL
(1996)
remarks
that
juveniles
of
this
latter
species
appear
in
the
Gulf
of
Oman
in
the
summer.
This
is
at
the
time
when
the
prevailing
currents
in
the
Arabian
Sea
are
moving
in
an
easterly
direction.
Thus,
the
ob-
served
occurrence
of
juveniles
in
the
Gulf
of
Oman
coincides
with
the
only
time
of
year
when
larvae
could
be
transported
from
Arabia
to
the
Maldives,
the
only
non-Arabian
location
where
the
species has
been
recorded,
and
a
distance
of
at
least
2200
km.
The
dispersal
of
the
juvenile
C.
melapterus
from
Arabia
to
the
Seychelles
must
have
occurred
between
November
and
March,
when
the
monsoon
currents
are
reversed,
flowing
from
Arabia
southwards
past
East
Africa,
and
then
eastwards
towards
the
Seychelles,
a
minimum
straight-line
distance
of
1900
km.
The
indirect
route
the
winter
currents
actually
follow
from
Arabia
to
the
Seychelles
means
that
the
true
distance
trav-
elled
by
this
individual
is
likely
to
have
been
close
to
3000
km.
Isolated
records
such
as
these
pro-
vide
significant
information
about
the
dispersal
abilities
of
reef
fishes,
and
confirm
the
proposi-
tion
of
LEIS
( 1991)
that
the
larval
range
of
many
reef
fish
is
likely
to
be
significantly
greater
than
that
of
established
adult
populations.
This
raises
the
question
of
where
the
original
source
of
the
very
isolated
populations
of
non-Arabian
species
recorded
at
Sikha
Island
is
likely
to
have
been,
and
why
these
fish
settled
and
survived
at
Sikha
but
not
elsewhere.

Zoogeography
of
coral
reef
fishes
of
the
Gulf
of
Aden
311
Fig.
5:
Prevailing
currents
in
the
Arabian
Sea
and
north-western
Indian
Ocean
during
the
north-east
(winter)
monsoon
(left)
and
the
south-west
(summer)
monsoon
(right).
The
bold
arrows
indicate
the
direction
of
prevailing winds
and
surface
currents
in
the
Gulf
of
Aden.
The
possibility
of
dispersal
of
larvae
over
long
distances
in
the
northern
Indian
Ocean
is
al-
ready
demonstrated
by
the
two
non-Arabian
records
of
Arabian
endemics
described
above.
Of
the
Shabwa
records,
Chaetodon
zanzibarensis
is
not
known
from
the
Maldives
and
Laccadives,
and
so
the
Sikha
population
is
most
likely
to
have
originated
in
east
Africa
or
the
Seychelles,
requiring
transport
via
the
Somali
current
during
the
period
of
the
upwelling.
In
contrast,
Ecsenius
lineatus
is
unknown
from
elsewhere
on
the
western
Indian
Ocean
margin,
and
the
closest
record
to
Arabia
prior
to
that
presented here
is
from
the
Maldives
(SPRINGER
1988).
Thus
the
fish
community
of
the
Bir
All
area
provides
evidence
that
dispersal
of
fishes
to
the
eastern
Gulf
of
Aden
from the
In-
dian
Ocean
occurs
via
both
the
summer
and
the
winter
monsoon currents.
Evidence
from
south-
ern
Oman
indicates
that
the
same
is
true
of
the
Arabian
Sea
coast
of
Arabia,
where
isolated
records
of
Centropyge
acanthops
(Norman,
1922)
from
East
Africa,
and
of
Chaetodon
decussatus
Cuvier,
1831
from
the
Sri
Lanka
/
Maldives
region,
have
been
made
(RANDALL
19 96,
DEBELIUS
19 98).
The
nutrient-rich
water
of
the
summer
monsoon
upwelling
produces
an
area
of
high
produc-
tivity
along
the
Indian
Ocean
coast
of
Somalia
and
the
Arabian
Sea
coast
of
the
Arabian
Peninsula
(CURRIE
et
al.
1973,
SAVIDGE
e t
al.
1990).
Under
these
conditions
survival
of
coral
reef
fish
larvae
may
be
greatly
reduced
(ROBERTS
1 991),
and
oceanographic
conditions
prevailing
throughout
the
duration
of
the
summer
monsoon
may
act
as
a
severe
limitation
on
dispersal
of
fishes
from
East
African
coral
reef
areas
to
Arabia
(KEMP
1998
b).
It
is
thus
possible
that
dispersal
to
Arabia
via
this
route
is
a
relatively
rare
event,
and
the
records
of
East
African
species,
such
as
Chaetodon
zanzi-
barensis
and
Centropyge
acanthops,
are
exceptions
to
the
rule.
Hence,
Arabian
populations
of
many
Indian
Ocean
or
Indo-West
Pacific
species,
such
as
Chaetodon
lunula,
C.
auriga
setifer
Ahl,
1923,
Acanthurus
triostegus
and
Acanthurus
leucosternon
Bennett,
1832,
whose
Arabian
distributions
are
restricted
to
Oman
and
the
Gulf
of
Aden,
may
recruit
principally
during
the
winter
monsoon,

312
J.M.
KEMP
originating
from
the
Maldives/Laccadives
region.
A
consequence
of
this
may
be
unidirectional
gene
flow,
in
the
Arabian
Sea
region,
for
some
species
of
fish.
Two
other
factors
related
to
the
pronounced
seasonality
of
the
monsoon
currents
may
also
re-
sult
in
unidirectional
dispersal
and
gene
flow
for
many
marine
taxa
in
the
Arabian
Sea
and
the
Gulf
of
Aden.
Firstly,
seasonality
of
spawning
in
reef
fishes
is
widespread,
although
with
wide
geo-
graphic
and
taxonomic
variation
(ROBERTSON
1 991).
Seasonality
of
spawning
of
any
reef
fish
spe-
cies
in
the
north-western
Indian
Ocean
region
will
have
a
profound
effect
upon
direction
of
dis-
persal
of
those
species.
Species
spawning
during
the
summer
monsoon
will
disperse
from
Africa
towards
Arabia,
and
from
the
Maldives
away
from
Arabia.
Spawning
during
the
winter
monsoon
will
result
in
the
opposite
situation.
Secondly,
within
the
Gulf
of
Aden
during
the
summer
monsoon,
when
the
Somali
current
flows
northwards
past
the
Gulf
of
Aden
(Fig.
5),
wind-driven
surface
currents
within
the
Gulf
of
Aden
flow
from
west
to
east
(EDWARDS
1 987),
making
it
unlikely
that
fish
larvae
arriving
from
East
Africa
via
the
Somali
current
will
be
able
to
disperse westwards
into
the
Gulf
of
Aden
(further
emphasising
the
low
probability
of
frequent
arrival
of
East
African
and
Seychelles
species,
such
as
Chaetodon
zanzibarensis,
inside
the
Gulf
of
Aden).
Dispersal
of
Indian
Ocean
species
into
the
Gulf
of
Aden,
and
thus
to
Bir
All
and
Sikha
Island,
is
likely
to
occur
more
frequently
during
the
winter
monsoon,
when
westward-flowing
surface
currents
in
the
Gulf
of
Aden
(EDWARDS
1987,
SHEPPARD
et
al.
1992)
would
tend
to
carry
larvae,
arriving
at
Arabia
from
the
Maldives/Laccadives
region
via
the
north-east
monsoon
current,
into
the
Gulf
of
Aden,
and
consequently
towards
the
Red
Sea.
This
is
the
only
route
by
which
Ecsenius
lineatus
can
have
arrived
at
the
Bir
Ali
area,
and
it
is
a
hypothesis
which
suggests
that
populations
of
many
non-endemic
Gulf
of
Aden
and
Red
Sea
fish
species
may
be
more
closely
related
to
those
of
the
Maldives
and
Sri
Lanka
region
than
they
are
to
East
African
populations.
Strong
seasonality
of
Arabian
Sea
currents,
combined
with
the
unusual
oceanographic
feature
of
the
Somali
and
Arabian
upwelling,
may
impose
strong
directionality
on
dispersal
to
and
from
Arabia,
and
consequently
on
gene
flow
in
marine
taxa
of
the
north-western
Indian
Ocean
region.
Identification
and
confirmation
of
such
source/sink
patterns
of
population
and
gene
flow
is
of
increasing
significance
for
development
of
regional
conservation
plans
and
net-
works
of
protected
areas
(ROBERTS
1997),
and
underlines
the
interdependence
of
apparently
far-
flung
locations,
at
a
time
when
complacency
about
the
resilience
of
widespread
and
widely-dis-
persing
marine
taxa
to
local
or
global
extinction
is
rapidly
coming
to
an
end
(ROBERTS
&
HAWKINS
1999,
ROBERTS
et
al.
in
press).
The
coast
of
Oman
is
exposed
to
both
the summer
and
winter
monsoon
currents,
and
larvae
of
the
Sikha
Island
and
Bir
Ali
species,
although
unknown
in
Oman,
must
pass
through
Omani
waters
as
larvae
en
route
from
the
Maldives.
The
lack
of
records
of
these
species
from
Oman
may
be
due
to
a
lack
of
settlement
by
larvae,
or
post-settlement
mortality,
or
a
combination
of
the
two
(although
a
paucity
of
sampling
and
survey
effort
in
the
south
of
Oman
means
that
at
least
some
Indian
Ocean
species
not
yet
known
from
Arabia
will
almost
certainly
be
recorded
there
in
fu-
ture).
Recruits
of
many
non-Arabian
species
may
occur
in
Oman
during
the
winter
monsoons,
only
for
the
majority
to
be
killed
off
by
conditions
during
the
subsequent
summer
monsoon
upwelling.
The
reduced
intensity
of
the
upwelling
in
Shabwa
Province
will
allow
many
of
these
species,
when
settling
from
the
plankton
in
the
Bir
Ali
area,
to
survive
the
summer.
This
hypoth-
esis
is
testable
by
detailed
studies
of
juvenile
settlement
and
mortality
on
the
Arabian
Sea
coast
of
Oman,
at
the
Socotra
Archipelago,
and
within
the
Gulf
of
Aden.
A
number
of
factors
may
contribute
to
the
observed
differences
between
assemblages
of
In-
dian
Ocean
origin
at
Socotra,
and
at
Sikha.
The
Sikha
species
may
be
present
at
Socotra,
but
not
yet
recorded
due
to
limited
survey
and
sampling.
Only
one
study
of
the
fishes
of
Socotra
has
been

Zoogeography
of
coral
reef
fishes
of
the
Gulf
of
Aden
313
completed
to
date
(KEMP
1 998
b),
on
the
basis
of
studies
at
a
total
of
21
sites.
However, sites
sur-
veyed
throughout
the
Socotra
Archipelago
included
habitats
very
similar
to
those
of Sikha
Island.
The
Sikha
new
records
are
all
of
large
and
conspicuous
fish,
and
if
any
are
present
at
Socotra
they
are
likely
to
be
rare.
Alternatively,
KEMP
(1 998
b)
argues
that
the
'pseudo-high
latitude'
effect
aris-
ing
from
the
monsoon
upwelling
of
the
Somali
coast
and
the
Arabian
Sea
coast of
Oman
may
pro-
duce
conditions
which
preclude
settlement
or
survival
of
many
Indian
Ocean
reef
fish
species
at
Socotra.
The
markedly
lower
intensity
of
the
upwelling
conditions
at
Bir
Ali
in
comparison
to
al-
Mukalla
has
already
been
suggested
in
this
paper
as
an
explanation
for
the
differences
between
the
Bir
Ali
and
al-Mukalla
fish
assemblages.
It
follows
from
this
that
the
Socotra
Archipelago,
which
experiences
greater
exposure
to
the
effects
of
upwelling
than
Bir
Ali,
would
be
unlikely
to
support
fish
species
which
are
present
at
Bir
Ali
and
Sikha
but
do
not
settle
successfully
or
survive
at
al-
Mukalla.
Implications
of
the
new
records
for
understanding
the
role
of
planktonic
dispersal
and
settlement
site
selection in
Arabian
reef
fish
zoogeography
The
closest
high-cover
coral
communities
to
Sikha
Island
are
along
the
mainland
coast
at
Bir
Ali,
less
than
10
km
distant.
The
absence
of
six
of
the
seven
Sikha
new
records
from
these
closely
neighbouring
coral
areas
in
spite
of
extensive
surveys
clearly
does
not
indicate
that
larvae
of
these
species
do
not
arrive
at
the
mainland
areas,
but
rather
that
the
majority
of
them
probably
do
not
settle
or
successfully
colonise
anywhere
other
than
Sikha.
The
fact
that
the
fish
observed
were
of
different
ages
(subadult
Chaetodon
trifasciatus,
adult
C.
zanzibarensis,
co-occurrence
of
different
size
classes
of
Thalassoma
hardwicke)
further
indicates
that
arrival
of
these
travellers
is
not
infre-
quent.
Differences
in
intensity
of
upwelling
may
explain
the
observed
differences
between
Bir
Ali
and
al-Mukalla,
but
they
are
unlikely
to
explain
the
differences
between
the
Bir
Ali
mainland
and
Sikha
Island.
In
addition
to
six
of
the
new
records,
a
total
of
44
other
species
in
17
families
were
restricted
to
Sikha
Island.
Twenty-three
of
these
species
are
at
or
near
the
geographical
limit
of
their
ranges,
including
Red
Sea
species
(Chaetodon
fasciatus,
Chlorurus
genazonatus,
etc.),
and
a
greater
number
of
Indian
Ocean
or
Indo-Pacific
species
which
do
not
appear
to
extend
their
ranges
any
further
north-east
into
Oman
[Caesio
xanthonota
Carpenter,
1987,
Chaetodon
lineolatus,
C.
melannotus,
Naso
brevirostris
(Valenciennes,
1835),
N.
fageni
Morrow,
1954,
Balistapus
undulatus
(Park,
1797),
Pseudobalistes
fuscus
(Bloch
&
Schneider,
1801)].
This
unusual
fish
community
is
likely
to
be
a
result
of
differential
settlement
from
the
plank-
ton
rather
than
post-settlement
migration,
because,
with the
exception
of
pelagic
and
epi-pelagic
species,
post-settlement
movement
of
shallow
reef
fish
between
the
mainland
and
Sikha
is
u nlikely.
Some
studies
have
shown
post-settlement
migration
to
be
significant
at
smaller
scales
(e.g.
LEWIS
1997),
but
migration
of
the
shallow
water
species
of
Sikha,
many
of
which
are
closely
associated
with
coral-rich
habitats,
across
the
several
kilometres
of
deep
water
between
Sikha
and
the
main-
land,
or
vice
versa,
is
unlikely.
This
suggests
that
there
may
be
a
feature,
or
features,
of
the
Sikha
environment
which
differs
from
nearby
coastal
habitats,
and
which
enables
successful
settlement
and
survival
of
species
at
the
extremes
of
their
ranges.
Certainty
about
the
environmental
charac-
teristics
which
give
rise
to
this
is
not
possible
at
this
stage,
but
some
obvious
possibilities
exist.
Diversity
of
habitats:
Sikha
is
the
only
relatively
deep
water
island
in
the
northern
Gulf
of
Aden.
Species
associated
with
steep,
current-swept
coral
slopes
at
Sikha
(e.g.
Pseudanthias
marcia)
are
un-

314
J.M.
KEMP
likely
to
find
this
kind
of
habitat
anywhere
else
in
the
Hadramaut/Shabwa
area.
Similarly,
the
only
very
shallow,
very
high
cover
areas
of
healthy
branching
corals
located
during
the
recent
survey
were
those
at
Sikha.
In
close
proximity
at
Sikha
are
exposed
low
coral
cover,
high
algal
cover
rocky
slopes,
extensive
areas
of
high
cover
branching
and
massive
corals,
large
expanses
of
soft
corals,
and
very
diverse
mixtures
of
all
of
these,
and
all
at
a
wide
range
of
depths
-
a
feature
locally
unique
to
this
island.
An
offshore
location
with
considerably
lower
turbidity
than
the
mainland
coral
communities:
The
gross
level
habitat
differences
described
above
cannot
account
for
the
presence
of
all
the
Sikha
species.
For
instance,
Chaetodon
zanzibarensis,
Halichoeres
cosmetus
and
Acanthurus
leucocheilus
at
Sikha
Island
were
all
associated
with
habitat
types
which
were
also
present
at
nearby
mainland
sites
(respectively:
extensive
areas
of
massive
Pontes
corals;
mixed
hard
and
soft coral
areas;
exposed
rocky
shores
with
low
coral
cover).
A
conspicuous
difference
between
Sikha
Island
and
the
inshore
areas
was
turbidity.
Turbid
conditions
inshore
at
Bir
Ali
were
noticeably
more
frequent
and
severe
than
at
Sikha
during
the
1998
survey
period.
Studies
inside
the
Red
Sea
have
revealed
marked
differences,
often
of
a
nature
resembling
zoogeographic
differences,
between
the
fish
communities
of
closely
adjacent
turbid
and
clear-wa-
ter
sites.
ROBERTS
e t
al.
(1992)
found
significant
differences
between
fish
assemblages
of
turbid
in-
shore
and
clear-water
offshore
reefs
in
the
southern
Red
Sea.
In
the
central
Red
Sea
at
Rabigh
(Saudi
Arabia),
the
pomacanthid
Pomacanthus
asfur
(Forsskal,
1775)
is
common
in
turbid
lagoon
environments
reminiscent
of
the
southern
Red
Sea
(where
it
is
abundant),
but
is
absent
from
the
clear-water
seaward
reef
slopes
and
offshore
patch
reefs
(J.
Kemp,
personal
observation).
The
characteristically
central
and
southern
Red
Sea
butterflyfish
Chaetodon
larvatus
is
uncommon
in
the
northern
Red
Sea
except
for
localised
abundance
at
inshore
areas
of
high
turbidity
(C.
Roberts,
pers.
comm.).
In
Shabwa
Province
this
species
is
almost
six
times
more
abundant
at
mainland
hard
coral
sites
than
it
is
at
similar
sites
at
Sikha.
It
is
thus
possible
that
differences
in
turbidity
of
the
mainland
and
of
Sikha
Island
impose
different
selective
pressures
on
the
fish
assemblages
at
the
two
sites.
Differential
settlement
of
fish
larvae,
due
to
environmental
and
habitat
differences
between
Sikha
and
the
adjacent
mainland,
may
explain
some
of
the
observed
differences
between
fish
as-
semblages
of
the
two
areas.
BOOTH
&
WELLINGTON
(1998)
suggest
that
strong
habitat
preferences
in
reef
fishes
at
the
time
of
settlement
from
the
planktonic
phase
may
decouple
the
relationship
between
larval
supply
and
recruitment.
From
the
time
of
settlement
fish
exhibit
strong
preferences
for
particular
habitats
(SALE
1980).
Habitat
selection
by
larval
or
juvenile
coral
reef
fish
at
the
time
of
settlement
is
increasingly
recognised
as
a
significant
factor
structuring
fish
communities
at
a
range
of
scales,
from
preferences
between
individual
coral
colonies,
to
selection
between
distinct
zones
in
large
reef
systems
(e.g.
MILICICH
&
DOHERTY
1994,
DOHERTY
et
al.
1996,
LIGHT
&
JONES
1997,
BOOTH
&
WELLINGTON
1998).
This
has
been
documented
up
to
large
scales
in
a
range
of
different
circumstances,
such
as
a
failure
of
juveniles
of
some
families
of
fish
to
settle in
areas
of
corals
destroyed
by
storm
damage,
coral
bleaching,
or
crown-of-thorns
starfish
(see
review
by
JONES
&
SIMS
1998).
In
the
light
of
the
proposition
by
LEIS
( 1991)
that
larval
fish
ranges
may
be
considerably
greater
than
the
ranges
of
adult
populations
this
is
a
possibility
which
may
have
pro-
found
implications
for
studies
of
reef
fish
zoogeography
and
ecology.
Whether
the
patterns
of
fish
distribution
at
Sikha
and
Bir
Ali
are
the
result
of
settlement
pref-
erences
or
differential
post-settlement
survival,
or
some
combination
of
the
two,
is
not
clear,
but
whichever
is
the
case
the
results
of
this
study
give
a
clear
indication
that
pre-settlement
mortality

Zoogeography
of coral
reef
fishes
of
the
Gulf
of Aden
315
is
probably
not
as
significant
in
this
case,
at
least
for
some
species,
as
processes
occurring
at
or
soon
after
the
time
of
settlement.
RANDALL
&
HOOVER
(1995)
suggest
that
the
occurrence
of
the
unu-
sual
ichthyofauna
of
the
Arabian
Sea
coast
of
Oman
may
be
due
to
physical
or
biological
param-
eters
related
to
the
presence
of
seasonal
monsoon-driven
upwelling
of
cold
nutrient-rich
water
along
this
coast,
which
may
isolate
southern
Oman
fish
populations.
The
findings
of
this
study
support
part
of
this
hypothesis,
namely
that
the
upwelling
directly
or
indirectly
affects
the
distri-
butions
of
coastal
fishes
in
southern
and
eastern
Arabia.
However,
there
is
reason
to
doubt
whether
the
effect
is
entirely
due
to
creation
of
barriers
to
dispersal
of
fish
larvae.
The
evidence
from
the
fish
assemblage
of
the
Bir
Ali
area,
and
particularly
Sikha
Island,
suggests
that
habitat
effects,
ei-
ther
at
settlement
or
immediately
post-settlement,
may
be
as
significant
as
larval
dispersal
in
de-
termining
the
distribution
of
fish
species
and
the
composition
of
fish
communities
at
both
zoogeographic
and
local
scales
along
the
Arabian
Sea
and
Gulf
of
Aden
coast
of
Arabia.
Settlement
preferences
and
post-settlement
processes
may
at
least
partly
determine
the
very
large-scale
distri-
bution
of
tropical
reef
fish
species.
Unusual
environmental
conditions
and
habitats
at
a
range
of
scales,
both
local
and
regional,
appear
to
give
rise
to
a
'zoogeographically
displaced'
Indian
Ocean
component
of
the
fish
fauna
at
Bir
Ali,
and
particularly
at
Sikha
Island.
This
component
probably
originates
largely
from
the
Maldives/Laccadives
region,
although
part
of
it
is
probably
of
East
African
origin.
Identification
of
such
locations
is
likely
to
provide
an
unusual
opportunity
to
examine
the
effects
of
settlement
preferences
of
larval
reef
fishes,
and
the
effects
of
pre-
and
post-settlement
processes,
at
very
large
zoogeographic
scales.
ACKNOWLEDGEMENTS
Fieldwork
throughout
Oman
and
Yemen
in
early
1998
could
not
have
been
successfully
carried
out
without
the
logistical
support
and
help
of
Jonathan
Ali
Khan
and
other
members
of
the
Ara-
bian
Seas
Expedition.
Dr.
V.G.
Springer
of
the
National
Museum
of
Natural
History,
Smithsonian
Institution,
Washington
D.C.,
and
Dr.
J.E.
Randall
of
the
Bernice
P.
Bishop
Museum,
Hawaii,
provided
assistance
with
identification
of
photographed
fishes,
and
Dr.
A.C.
Gill
of
the
Natural
History
Museum,
London,
provided
advice
and
assistance
with
research
on
collections
held
there.
P.J.
Hogarth,
C.
Dytham
and
A.V.
Morris,
all
of
the
University
of
York,
provided
constructive
criticism
of
the
manuscript.
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YOl
5DD,
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e-mail:
jmkl00@york.ac.uk

Zoogeography
of
coral
reef
fishes
of
the
Gulf
of
Aden
319
APPENDIX
Table
2:
A
preliminary
checklist
of
reef
fish
species,
Hadramaut
and
Shabwa
provinces.
Locations:
BA
=
Bir
Ali
(Shabwa
main-
land)
only;
M
=
al -Mukalla
only;
S
=
Sikha
Island
only;
SH
=
Shabwa
(mainland
and
Sikha)
only.
Abundances:
1
=
o ne
only;
a
=
abundant;
c
=
common;
r
=
rare.
Other:
•
=
p hotographed;
**
=
f rom
DEBELIUS
(1 998).
All
others
widespread
in
the
region.
Torpedinidae
—
Torpedo
rays
Torpedo
panthera
Olfers,
1831
•
S,
1
Dasyatidae
—
Stingrays
Dasyatis
sp.
[ref
Randall
1996:
44]
BA,
c
Taeniura
lymma
(Forsskal,
1775)
•
c
Himantura
uarnak
(Forsskal,
1775)
M,
1
Hypolophis
sephen
(Forsskal,
1775)
BA,
1
Myliobatidae
—
Eagle
Rays
Aetobatus
narinari
(Euphrasen,
1790)
c
Mobulidae
—
Devil
rays
Mobula
thurstoni
(Lloyd,
1908)
•
S,
r
Muraenidae
—
Moray
eels
Enchelycore
partialis
(Temminck
&
Schlegel,
1846)
•
M,
r
Gymnothorax
favagineus
(Bloch
&
Schneider,
1801)
•
c
Gymnothorax
flavimarginatus
(Riippell,
1830)
c
Gymnothorax nudivomer
(Playfair
&
Giinther,
1867)
BA,
1
Scuticaria
tigrina
(Lesson,
1829)
**
Siderea
grisea
(Lacepede,
1803)
•
r
Ophichthidae
—
Snake
eels
Myrichthys
maculosus
Cuvier,
1816
•
M,
1
Chanidae
—
Milkfishes
Chanos
chanos
Forsskal,
1775
c
Synodontidae
—
Lizardfishes
Synodus
dermatogenys
Fowler,
1912
•
c
Holocentridae
—
Squirrelfishes
Myripritis
murdjan
(Forsskal,
1775)
•
c
Neoniphon
sammara
(Forsskal,
1775)
c
Sargocentron
caudimaculatum
(Riippell,
1838)
c
Sargocentron
rubrum
(Forsskal,
1775)
M,
r
Sargocentron
seychellense
(Smith
&
Smith,
1963)
BA,
1
Sargocentron
spiniferum
(Forsskal,
1775)
•
r
Fistulariidae
—
Cornetfishes
Fistularia
commersonii
Riippell,
1838
r
Scorpaenidae
—
Scorpionfishes
Pterois
antennata
(Bloch,
1787)
•
r
Pterois
miles
(Bennett,
1828)
r
Scorpaenopsis
barbatus
(Riippell,
1838)
•
c
Scorpaenopsis
diabolus
(Cuvier,
1829)
•
c
Serranidae
—
Groupers
Pseudanthias
marcia
Randall
&
Hoover,
1993
•
S,
a
Pseudanthias
townsendi
(Boulenger,
1897)
•
S,
r
Pseudanthias
sp.
3
(small
?
9
only,
P.
squamipinnis•)
r
Aethaloperca
rogaa
(Forsskal,
1775)
c
Cephalopholis
argus
Bloch
&
Schneider,
1801
•
c
Cephalopholis
hemistiktos
(Riippell,
1830)
r
Cephalopholis
miniata
(Forsskal,
1775)
•
c
Epinephelus
chlorostigma
(Valenciennes,
1828)
•
c
Epinephelus
fasciatus
(Forsskal,
1775)
•
c
Epinephelus
malabaricus
(Bloch
&
Schneider,
1801)
r
Epinephelus
stoliczkae
(Day,
1875)
•
a
Epinephelus
summana
(Forsskal,
1775)
r
Epinephelus
tukula
Morgans,
1959
r
Pseudochromidae
—
Dottybacks
Pseudochromis
linda
Randall
&
Stanaland,
1989
•
c
Pseudochromis
nigrovittatus
Boulenger,
1897
•
r
Pseudochromis
sankeyi
Lubbock,
1975
•
a
Priacanthidae
—
Bigeyes
Priacanthus
blochii
Bleeker,
1853
c
Priacanthus
hamrur
(Forsskal,
1775)
c
Cirrhitidae
—
Hawkfishes
Cirrhitichthys
calliurus
Regan,
1905
•
c
Cirrhitichthys
oxycephalus
(Bleeker,
1855)
S,
r
Cirrhitus
pinnulatus
(Bloch
&
Schneider,
1801)
r
Teraponidae
—
Terapons
Kuhlia
mugil
(Forster
&
Schneider,
1801)
c
Apogonidae
—
Cardinalfishes
Apogon
aureus
(Lacepede,
1802)
•
c
Apogon
cyanosoma
Bleeker,
1853
•
c
Apogon
exostigma
(Jordan
&
Seale,
1906)
•
r
Apogon
fraenatus
Valenciennes,
1832
•
c
Archamia
fucata
(Cantor,
1850)
•
c
Cheilodipterus
macrodon
(Lacepede,
1802)
•
c
Cheilodipterus
quinquelineatus
Cuvier,
1828
•
c
Malacanthidae
—
Tilefishes
Malacanthus
latovittatus
(Lacepede,
1802)
•
S,
r
Echeneidae
—
Remoras
Echeneis
naucrates
Linnaeus,
1758
S,
1
Carangidae
—
Jacks
Carangoides
bajad
(Forsskal,
1775)
•
c
Carangoides
ferdau
(Forsskal,
1775)
c
Caranx
heberi
(Bennett,
1828)
•
BA,
r
Caranx
ignobilis
(Forsskal,
1775)
c
Caranx
sexfasciatus
Quoy
&
Gaimard,
1824
c
Elegatis
bipinnulata
(Quoy
&
Gaimard,
1824)
S,
r
Gnathodon
speciosus
(Forsskal,
1775)
•
c
Trachinotus
baillonii
(Lacepede,
1801)
•
M,
c
Trachinotus
blochii
(Lacepede,
1801)
S,
r
Gerreidae
—
Moj
arras
Gerres
oyena
(Forsskal,
1775)
c
Lutjanidae
—
Snappers
Lutjanus
argentimaculatus
(Forsskal,
1775)
S,
r
Lutjanus
bengalensis
(Bloch,
1790)
•
a
Lutjanus
bohar
(Forsskal,
1775)
c
Lutjanus
coeruleolineatus
(Ruppell,
1838)
•
r
Lutjanus
ehrenbergi
(Peters,
1879)
c
Lutjanus
fulviflamma
(Forsskal,
1775)
c
Lutjanus
fulvus
(Forster
&
Schneider,
1801)
r
Lutjanus
gibbus
(Forsskal,
1775)
r
Lutjanus rivulatus
(Cuvier,
1828)
*c
Caesionidae
—
Fusiliers
Caesio
lunaris
Cuviet,
1830
•
c
Caesio
varilineata
Carpenter,
1987
•
c

320
J.M.
KEMP
c
c
BA,
r
Caesio
xanthonota
Carpenter,
1987
•
S,
r
Haemulidae
—
Grunts
Diagramma
pictum
(Thunberg,
1792)
Plectorhinchus
flavomaculatus
(Cuvier
1830)
Plectorhinchus
gaterinus
(Forsskal,
1775)
Plectorhinchus
gibbosus
(Lacepede,
1802)
Plectorhinchus
playfairi
(Pellegrin,
1914)
Plectorhinchus
pictus
(Tortonese,
1835)
Plectorhinchus
schotaf{Forsskal,
1775)
Pomadasys
aheneus
McKay
&
Randall
1995
**
Nemipteridae
—
Breams
Scolopsis
ghanam
(Forsskal,
1775)
Scolopsis
taeniatus
Cuvier,
1830
Scolopsis
vosmeri
(Bloch,
1792)
Lethrinidae
—
Emperorfishes
Lethrinus
mahsena
(Forsskal,
1775)
S,
Lethrinus
nebulosus
(Forsskal,
1775)
Lethrinus
obsoletus
(Forsskal,
1775)
Sparidae
—
Seabreams
Acanthopagrus
bifasciatus
(Forsskal,
1775)
Diplodus
sargus
capensis
(Smith,
1844)
Rhabdosargus
sarba
(Forsskal,
1775)
Mugilidae
—
Mullets
Crenimugil
crenilabis
(Forsskal,
1775)
Mullidae
—
Goatfishes
Mulloidichthys
flavolineatus
(Lacepede,
1801)
Mulloidichthys
vanicolensis
(Valenciennes,
1831)
•
Parupeneus
barberinus
(Lacepede,
1801)
•
Parupeneus
bifasciatus
(Lacepede,
1801)
Parupeneus
cyclostomus
(Lacepede,
1801)
Parupeneus
forsskali
(Fourmanoir
&
Gueze,
1976)
Parupeneus
indicus
(Shaw,
1803)
Parupeneus
macronemus
(Lacepede,
1801)
Upeneus
tragula
Richardson
1846
M,
Pempheridae
—
Sweepers
Pempheris
vanicolensis
Cuvier,
1831
Monodactylidae
—
Monos
Monodactylus
argenteus
(Linnaeus,
1758)
Kyphosidae
—
Sea
chubs
Kyphosus
cinerascens
(Forsskal,
1775)
Chaetodontidae
—
Butterflyfishes
Chaetodon
collare
Bloch,
1787
Chaetodon
dialeucos
Salm
&
Mee,
1989
Chaetodon
fasciatus
Forsskal,
1775
Chaetodon
gardineri
Norman,
1939
Chaetodon
larvatus
Cuvier,
1831
•
c
(rare
Chaetodon
leucopleura
Playfair
&
Gunther,
1867
Chaetodon
lineolatus
Cuvier,
1831
Chaetodon
lunula
Lacepede,
1802
Chaetodon
melapterus
Guichenot,
1862
Chaetodon
melannotus
Bloch
&
Schneider,
1801
Chaetodon
auriga
setifer
Ahl,
1923
Chaetodon
semilarvatus
Cuvier,
1831
•
Chaetodon
trifascialis
Quoy
&
Gaimard,
1823
Chaetodon
trifasciatus
Park,
1797
Chaetodon
vagabunduspictus
Fraser-Brunner,
1950
Chaetodon
zanzibarensis
Playfair,
1866
Heniochus
acuminatus
(Linnaeus,
1758)
Heniochus
diphreutes
Jordan,
1903
S,
c
•
c
S,
r
•
S,
r
•
c
at
M)
M,
1
•
S,
r
•
c
•
a
•
S,
1
•
S,
r
SH,
c
•
c
•S,
1
•
a
•S,
r
•
c
S,
r
Heniochus
intermedius
Steindachner,
1893
Pomacanthidae
—
Angelfishes
Apolemichthys
xanthotis
Fraser-Brunner,
1950
Pomacanthus
imperator
(Bloch,
1787)
Pomacanthus
maculosus
(Forsskal,
1775)
Pomacanthus
semicirculatus
(Cuvier,
1831)
Pomacentridae
—
Damselfishes
Abudefduf
notatus
(Day,
1969)
Abudefduf
sexfasciatus
(Lacepede,
1801)
Abudefduf
sordidus
(Forsskal,
1775)
Abudefduf
vaigiensis
(Quoy
&
Gaimard,
1825)
Amphiprion
sp.
Chromis
dimidiata
(Klunzinger,
1871)
Chromis
flavaxilla
Randall,
1994
Chromis
pembae
(Smith,
1960)
Chromis
weberi
Fowler
&
Bean,
1928
Chrysiptera
unimaculata
(Cuvier,
1830)
Dascyllus
marginatus
(Ruppell,
1829)
Dascyllus
trimaculatus
(Rttppell,
1829)
Neopomacentrus
cyanomos
(Bleeker,
1856)
Neopomacentrus
miryae
Dor
&
Allen,
1977
Neopomacentrus
xanthurus
Allen
&
Randall,
1981
Pomacentrus
aquilus
Allen
&
Randall,
1980
Pomacentrus
caeruleus
Quoy
&
Gaimard,
1825
Pomacentrus
leptus
Allen
&
Randall,
1980
Pomacentrus
trichourus
Playfair
&
Gunther,
1867
Pomacentrus
trilineatus
Cuvier,
1830
Labridae
—
Wrasses
Anampses
lineatus
Randall,
1972
Anampses
meleagrides
Valenciennes,
1840
Bodianus
axillaris
(Bennett,
1831)
Bodianus
diana
(Lacepede,
1801)
Bodianus
macrognathos
(Morris,
1974)
Cheilinus
abudjubbe
(Ruppell,
1835)
Cheilinus
lunulatus
(Forsskal,
1775)
Coris
aygula
Lacepede,
1801
Coris
caudimacula
(Quoy
&
Gaimard
1834)
Coris
frerei
Playfair
&
Gunther,
1867
Gomphosus
caeruleus
Lacepede,
1801
Halichoeres
cosmetus
Randall
&
Smith,
1982
Halichoeres
hortulanus
(Lacepede,
1801)
Halichoeres
iridis
Randall
&
Smith,
1982
Halichoeres
marginatus
(Ruppell,
1835)
Halichoeres
nebulosus
(Valenciennes,
1839)
Halichoeres
scapularis
(Bennett,
1831)
Halichoeres
zeylonicus
(Bennett,
1832)
Hemigymnus
melapterus
(Bloch,
1792)
Hemigymnus
fasciatus
(Bloch,
1792)
Hologymnosus
annulatus
(Lacepede,
1801)
Hologymnosus
doliatus
(Lacepede,
1801)
Labroides
bicolor
Fowler
&
Bean,
1928
Labroides
dimidiatus
(Valenciennes,
1839)
Larabicus
quadrilineatus
(Ruppell,
1835)
Macropharyngodon
bipartitus
Smith,
1957
Novaculichthys
taeniourus
(Lacepede,
1801)
Pseudocheilinus
hexataenia
(Bleeker,
1857)
Stethojulis
albovittata
(Bonnaterre
1788)
Thalassoma
hardwicke
(Bennett,
1828)
Thalassoma
lunare
(Linnaeus
1758)
•
a
•
r
•
c
•
M,
c
•S,
r
S,
c
r
•
a
•
M,
r
S,
1
•
a
•
c
•
c
•
c
•
c
c
•
c
•SH,
c
•SH,
c
r
•
c
•
a
•S,
r
S,
1
S,
c
c
r
r
S,
r
•
c
•
c
c
•S,
r
c
c
c
c
r
S,
r
r
•
r
S,
r
S,
r
c
•
c
1
SH ,
c
c
c
c
•
S,
c
•
S,
r
c

Zoogeography
of
coral
reef
fishes
of
the
Gulf
of
Aden
321
Thalassoma
lutescens
(Lay
&
Bennett,
1839)
•
c
Thalassoma
quinquevittatum
(Lay
&
Bennett,
1839)
•
S,
c
Scaridae
—
Parrotfishes
Chlorurus
sordidus
{Forsskal,
1775)
c
Chlorurus
genazonatus
(Randall
&
Bruce,
1983)
*
S,
r
Chlorurus
strongylocephalus
(Bleeker
1854)
*
S,
c
Scarus
ferrugineus
Forsskal,
1775
•
a
Scarus
fremitus
Lacepede,
1802
•
c
Scarus
ghobban
Forsskal,
1775
•
c
Scarus
niger
Forsskal,
1775
c
Scarus
rubroviolaceus
Bleeker,
1847
•
c
Pinguipedidae
—
Sandperches
Parapercis
hexophthalma
(Cuvier,
1829)
c
Parapercis
robinsoni
Fowler,
1932
S,
1
Trypterygiidae
—
Triplefins
Helcogramma
steinitzi
Clark
1979
**
Blenniidae
—
Blennies
Atloblennius
pictus
(Lotan,
1969)
•
SH,
c
Cirripectes
filamentosus
(Alleyne
&
Macleay,
1877)
•
c
Ecsenius
frontalis
(Ehrenberg,
1836)
•
SH,
r
Ecsenius
lineatus
Klausewitz,
1962
•
SH,
r
Ecsenius
nalolo
Smith,
1959
•
c
Ecsenius
pulcher
(Murray,
1887)
SH,
c
Plagiotremus
rhinorynchos
(Bleeker,
1852)
c
Plagiotremus
townsendi
(Regan,
1905)
c
Gobiidae
—
Gobies
Asterropteryx
semipunctatus
Riippell,
1835
•
c
Ctenogobiops
maculosus
(Fourmanoir,
1955)
c
Cryptocentrus
fasciatus
(Playfair
&
Giinther,
1867)
c
Cryptocentrus
lutheri
(Klausewitz,
1960)
c
Eviota
guttata
Lachner
&
Karnella,
1978
•
c
Eviota
sebreei
Jordan
&
Seale,
1906
•
c
Lotilia
graciliosa
Klausewitz,
1960
r
Gnatholepis
anjerensis
(Bleeker,
1850)
•
c
Gobiodon
citrinus
(Ruppell,
1838)
r
Istigobius
decoratus
(Herre,
1927)
•
c
Valenciennia
helsdingenii
(Bleeker,
1858)
•
r
Valenciennia
puellaris
(Tomiyama,
1956)
•
c
Valenciennia
sexguttata
(Valenciennes,
1837)
•
c
Microdesmidae
—
Dartfishes
Ptereleotris
arabica
Randall
&
Hoese,
1985
S,
r
Ptereleotris
evides
(Jordan
&
Hubbs,
1925)
S,
r
Callionymidae
—
Dragonets
Syncbiropus
sechellensis
Regan
1908
**
Soleidae
—
Soles
Pardachirus
marmoratus
(Lacepede,
1802)
•
c
Sphyraenidae
—
Barracudas
Spbyraena
barracuda
(Walbaum,
1792)
c
Scombridae
—
Tunas
and
mackerels
Rastrelliger
kanagurta
(Cuvier,
1817)
•
c
Ephippidae —
Spadefishes
Platax
orbicularis
(Forsskal,
1775)
c
Platax
teira
(Forsskal,
1775)
•
c
Siganidae
—
Rabbitfishes
Siganus
argenteus
(Quoy
&
Gaimard, 1825)
c
Zanclidae
—
Moorish
idols
Zanclus
cornutus
Linnaeus,
1758
•
c
Acanthuridac
—
Surgeonfishes
Acanthurus
dussumieri
Valenciennes,
1835
S,
r
Acanthurus
gahhm
(Forsskal,
1775)
r
Acanthurus
leucocheilus
Herre,
1927
•
S,
r
Acanthurus
leucosternon
Bennett,
1832
•
M,
r
Acanthurus
mata
(Cuvier,
1829)
•
c
Acanthurus
sohal
(Forsskal,
1775)
c
Acanthurus
tennentii
Giinther,
1861
•
S,
r
Acanthurus
triostegus
(Linnaeus
1758)
M,
r
Ctenochaetus
striatus
Quoy
&
Gaimard,
1825)
c
Zebrasoma
desjardinii
(Bennett,
1835)
SH,
a
Zebrasoma
xanthurum
(Blyth,
1852)
•
c
Naso
brevirostris
(Valenciennes,
1835)
•
S,
r
Naso
lituratus
(Schneider,
1801)
c
Naso
fageni
Morrow,
1954
S,
r
Naso
unicornis
(Forsskal,
1775)
c
Balistidae
—
Triggerfishes
Balistapus
undulatus
(Park,
1797)
S,
c
Balistoides
viridescens
(Bloch
&
Schneider,
1801)
r
Melichthys
indicus
Randall
&
Klausewitz,
1973
c
Odonus
niger
(Ruppell,
1836)
•
a
Pseudobalistes
flavimarginatus
(Ruppell,
1829)
S,
r
Pseudobalistes
fuscus
(Bloch
&
Schneider,
1801)
S,
c
RJoinecanthus
assasi
(F orsskal,
1775)
SH,
r
Sufflamen
albicaudatus
(Ruppell,
1829)
•
SH,
c
Sufflamen
chrysopterus
(Bloch
&
Schneider,
1801)
•
S,
1
Sufflamen
fraenatus
(Latreille,
1804)
a
Monacanthidae
—
Fileflshes
Aluterus
scriptus
(Osbeck,
1765)
c
Cantherines
partialis
(Ruppell,
1837)
c
Ostraciidae
—
Trunkfishes
Lactoria
cornuta
(Linnaeus
1758)
**
Ostracion cubicus
Linnaeus,
1758
c
Ostracion
cyanurus
Ruppell,
1828
c
Tetrasoma
gibbosus
(Linnaeus,
1758)
BA,
1
Tetraodontidae
—
Pufferfishes
Arothron
meleagris
(Bloch
&
Schneider,
1801)
r
Arothron
nigropunctatus
(Bloch
&
Schneider,
1801)
•
c
Arothron
stellatus
(Bloch
&
Schneider,
1801)
r
Canthigaster
solandri
(Richardson,
1844)
•
c
Canthigaster
valentini
(Bleeker,
1853)
•
c
Diodontidae
—
Porcupinefishes
Diodon
holocanthus
(Linnaeus, 1758)
r
Diodon histrix
(Linnaeus,
1758)
c
Diodon
liturosus
Shaw,
1804
r