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Oecologia (2004) 139: 23–29
DOI 10.1007/s00442-004-1489-3
POPULATION ECOLOGY
Andrew S. Hoey
.
Mark I. McCormick
Selective predation for low body condition at the larval-juvenile
transition of a coral reef fish
Received: 10 June 2003 / Accepted: 19 December 2003 / Published online: 6 February 2004
# Springer-Verlag 2004
Abstract Mortality is known to be high during the
transition from larval to juvenile life stages in organisms
that have complex life histories. We are only just
beginning to understand the processes that influence
which individuals survive this period of high mortality,
and which traits may be beneficial. Here we document a
field experiment that examines the selectivity of predation
immediately following settlement to the juvenile popula-
tion in a common tropical fish, Pomacentrus amboinensis
(Pomacentridae). Newly metamorphosed fish were tagged
and randomly placed onto replicated patches of natural
habitat cleared of resident fishes. After exposure to
transient predators for 3 days, fish were recollected and
the attributes of survivors from patch reefs that sustained
high mortality were compared to individuals from patch
reefs that experienced low mortality. Seven characteristics
of individuals, which were indicative of previous and
present body condition, were compared between groups.
Predation was found to be selective for fish that grew
slowly in the latter third of their larval phase, were low in
total lipids, and had a high standardized weight (Fulton’s
K). Traits developed in the larval phase can strongly
influence the survival of individuals over this critical
transition period for organisms with complex life cycles.
Keywords Metamorphosis
.
Condition at settlement
.
Selective mortality
.
Larval growth history
.
Growth-
mortality hypothesis
Introduction
The selective loss of individuals from a population is the
foundation of the theory of natural selection (Roff 1992).
As an organism grows, its habits change, as do the
mortality agents that influence selection and, conse-
quently, the species’ patterns of abundance. Understanding
the selective loss of individuals throughout their life cycle
is fundamental to our understanding of population regu-
lation.
Processes influencing which individuals survive to
reproduce are complicated by a major transitional stage
in organisms that have complex life histories (e.g. many
plants, insects, marine invertebrates and fish, and
amphibians; Werner 1988; Pechenik et al. 1998). This
transition between developmental stages is often rapid and
is typically accompanied by morphological, physiological
and behavioural changes as the organism adapts to its new
environment (Wilbur 1980; McCormick and Makey 1997;
McCormick et al. 2002). These changes are energetically
costly and bring a new set of challenges for developing
organisms, which may influence their probabilities of
survival. Typically, only a very small fraction of the total
offspring produced actually survives the larval or propa-
gule stage to metamorphose into juveniles (Jansen 1971;
Bailey and Houde 1989; Morgan 1995). Hence, small
changes in the way mortality agents act can greatly
influence the number of individuals reaching the juvenile
phase (Houde 1987; Pepin and Myers 1991), and the
phenotypes of those individuals. Despite this, few studies
have examined the strength and direction of selective loss
of individuals at this crucial transition between larval and
juvenile developmental stages.
Most marine reef fishes have complex life cycles, where
a relatively sedentary reef-associated adult produces larvae
that spend a number of weeks in the plankton, prior to
settling onto the reef to join the juvenile population.
Although mortality is almost absolute in the larval phase
(Leis 1991), those that do survive suffer high losses
immediately following settlement (Webster 2002). Up-
wards of 57% of juvenile coral reef fishes may die within
the first 2 days after settlement (Webster and Almany,
submitted). Of those that survive this initially high
mortality, few survive through to maturity (e.g. Jones
1990). Selective forces are therefore strongest in the larval
A. S. Hoey (*)
.
M. I. McCormick
School of Marine Biology and Aquaculture,
James Cook University,
Townsville, Queensland 4811, Australia
e-mail: andrew.hoey1@jcu.edu.au
Tel.: +61-747-815729
Fax: +61-747-251570
stage and immediately after settlement to the reef,
suggesting that the transition between stages is a critical
period (McCormick 1998; Searcy and Sponaugle 2001;
McCormick and Hoey 2004).
Clearly all fish larvae do not have an equal chance of
survival, instead varying in traits that may influence their
susceptibility to mortality (Ferron and Leggett 1994). This
variation is initially driven by parental contributions,
which may be modified by environmental conditions
experienced throughout the life cycle. If this initial
variation is maintained, then fast-growing larvae will be
larger and thus potentially less vulnerable to predators than
slower-growing larvae of the same age (the “bigger-is-
better” hypothesis; Miller et al. 1988; Bailey and Houde
1989). Consequently, they will be the first to achieve
juvenile form and settle, reducing the period they are
exposed to planktonic predators (the “stage-duration”
hypothesis; sensu Leggett and Deblois 1994). Advantages
obtained in the larval phase are believed to extend into the
juvenile phase to influence an individual ’s probability of
survival (Sogard 1997). Recent studies of tropical reef
fishes have suggested that advantages gained prior to
hatching are positively correlated to larval growth and
dictate survival in later life stages (Vigliola and Meekan
2002). Variations in larval growth rates have also been
demonstrated to influence the number of larvae surviving
up to settlement (Bergenius et al. 2002; Wilson and
Meekan 2002). However, few studies have examined
selection at the larval-juvenile transition for reef fishes
(but see Searcy and Sponaugle 2001; Shima and Findlay
2002). We explore this issue for a common coral reef fish.
Characteristics that may be influential in determining
survival during and immediately after the settlement
transition include size (Booth 1995; McCormick and
Hoey 2004), prior growth history (Shima and Findlay
2002), lipid content (Booth and Hixon 1999; Booth and
Alquezar 2002), sensory development (McCormick 1993)
and burst swimming speed (McCormick and Molony
1993). All of these traits have been found to display high
levels of variability within a species on a range of spatial
and temporal scales (Wellington and Victor 1989;
McCormick and Molony 1993; McCormick 1994; Spo-
naugle and Cowen 1994, 1997; Kerrigan 1996; Searcy and
Sponaugle 2000). It is upon this phenotypic variation
amongst individuals that selective processes act. If mor-
tality at settlement is selective with respect to some aspects
of individual quality, then settlers in better condition
should contribute proportionately more to the juvenile
population than those in poor condition (Suthers 1998).
The present study examines the selectivity of mortality
immediately following settlement in a common tropical
damselfish, Pomacentrus amboinensis (Pomacentridae).
Here we use a short-term experiment to examine whether
mortality is selective with respect to seven measures of
fish quality. Results indicate that prior growth history,
manifested as growth rate and lipid levels, strongly affects
the survival of fishes in a patch reef habitat.
Materials and methods
Study site and species
The study was conducted at Lizard Island (14°38′S, 145°28′E) on
the northern Great Barrier Reef, Australia during November 1998.
The model species was Pomacentrus amboinensis, a ubiquitous
pomacentrid that typically settles in high numbers to a variety of
habitats, from sheltered lagoons to exposed windward reefs, on the
northern Great Barrier Reef (Kerrigan 1994). P. amboinensis has a
pelagic larval duration of 15–23 days and settles at 10.3–15.1 mm
standard length (Wellington and Victor 1989; Kerrigan 1996) with
its juvenile body plan largely complete, and undergoes a rapid (less
than 12 h) change in body pigmentation (McCormick and Makey
1997; McCormick et al. 2002). P. amboinensis is found at highest
densities when associated with small patch reefs at the base of
shallow reefs and, once settled, these omnivorous pomacentrids are
relatively site-attached, making them ideal for field experiments.
Field experiment design
To determine the selectivity of mortality immediately following
settlement, a field experiment was conducted on 15 patch reefs
(approximately 0.7×0.7×0.7 m) on the leeward side of Lizard Island.
A random sample of newly metamorphosed fish was placed on
patch reefs surrounded by sand and exposed to natural predation.
After 3 days, the period of highest mortality for this species
(McCormick and Hoey 2004), fish were recollected and the body
condition of individuals from patch reefs that sustained high
mortality was compared to those that sustained low mortality.
Newly metamorphosed P. amboinensis were caught using light
traps as they came into the vicinity of the reef to settle (for design
see Stobutzki and Bellwood 1997). Traps were anchored on the
leeward side of Lizard Island in approximately 16 m of water,
positioned so that the collection slots were 1 m below the surface.
Fish were removed from the traps at 0730 hours, returned to the
laboratory and maintained in 40 l aquaria with running seawater for
4 h. Three hundred individuals captured in a single night were each
transferred to a small clip-seal plastic bag to avoid scale damage and
tagged through the bag with a fluorescent subcutaneous elastomer
tattoo (Northwest Marine Technologies Inc.) using a 29-gauge
hypodermic needle. A detailed study of this tagging technique
showed that tagging had no significant effects on mortality or
growth over a 2-week period, and that tags had a 100% retention
rate (Hoey 1999).
The patch reefs used in the experiment were of similar size and
structural complexity, and composed of a combination of live and
dead Pocillopora damicornis, known to be a preferred habitat for the
species (Öhman et al. 1998). These were positioned on a sand flat in
3 m of water, 15 m from the edge of the nearest reef. Reefs were
arranged in a five by three matrix with adjacent reefs being
separated by 8 m. Immediately prior to releasing the tagged fish, the
patch reefs were cleared of all fishes and potential invertebrate
predators using a fence net, small hand nets and clove oil.
Twenty randomly selected, tagged fish were released onto each of
the 15 patch reefs. This density is representative of the natural levels
observed during settlement pulses at Lizard Island, where densities
on similar-sized patches may reach up to 65 recruits (McCormick,
unpublished data). Newly settled fish on adjacent reefs were tagged
with a different colour so that migration between reefs, or settlement
of new individuals, could be detected. A visual census shortly after
releasing the fish revealed that all individuals were associated with
their experimental patch reef. Only two individuals were found to
have migrated to an adjacent patch reef during the 3-day experiment.
No tagged individuals were observed during a census of the adjacent
contiguous reef at the conclusion of the experiment.
After 3 days, reefs were re-censused and were categorized
according to the survival of tagged fish: high (>75% survival; range
80–95%,
n=4); intermediate (50–75% survival; n=7); or low (<50%
survival; range 25–45%, n=4). There was no spatial gradient in
24
survivorship among the patch reefs with respect to distance from the
contiguous reef or position within the patch reef matrix. Due to the
lack of resident predators, mortality among reefs was a consequence
of action by transient piscivores. These predators include lizardfish
(Synodus spp.) and juvenile lutjanids (primarily Lutjanus gibbus),
which are known to prey on recently settled reef fishes (Sweatman
1984, 1993) and were observed in the vicinity of patch reefs during
censuses. Fish from four reefs classified as having high survivorship
(>75% survival) and four reefs classified as having low survivorship
(<50% survival) were collected using a fence net, small hand nets
and clove oil, before being killed by cold shock and subsequently
frozen prior to processing. Fish from the high survivorship patch
reefs were used as a ‘control’ group, representing a random sample
of the fish released onto the reefs, followed by 3 days of growth.
Fish from the low survivorship reefs represent a subset of the initial
sample, which had been exposed to high levels of predation.
Condition measures
The selectivity of mortality was assessed with respect to seven
measures of morphology and body condition: standard length (SL,
mm); wet weight (mg); Fulton’s condition index [K=(wet weight,
kg)/(SL, m)
3
]; sagittal otolith radius at settlement (a proxy for
relative size at settlement; μm); pre-settlement growth (mean width
of the last seven increments prior to the settlement mark; μm day
−1
);
post-settlement growth (mean width of the three increments after the
settlement mark; μm day
−1
); and total lipid content (mg g
−1
dry
body weight). Otolith increment width was used as a proxy for fish
growth, which is based on the assumption that there is a strong
relationship between somatic and otolith growth. This is a generally
held assumption that is supported by a number of studies (e.g.
Suthers 1998; Campana 1999), and a positive linear relationship
between otolith radius and standard length has been demonstrated
for Pomacentrus amboinensis (11.3–18.4 mm SL, n=292, r=0.86;
Hoey 1999). Cross-sections of the sagittal otoliths were produced
following the protocol of Wilson and McCormick (1997). Increment
measurements were made along the longest axis of the otolith, from
the nucleus to the outer-most complete ring, using a high power
compound microscope with polarized transmitted light, linked to a
computer image analysis system (Sigma Scan). Furthermore, the
formation of daily otolith increments has been validated in recently
settled P. amboinensis (Pitcher 1988) and it is assumed that pre-
settlement increments are also deposited on a daily basis. A
conspicuous settlement mark, which is formed in this species
(Wilson and McCormick 1997), was used as a reference point for
the division between larval and post-settlement increments.
The total lipid content of each fish was determined gravime-
trically using chloroform-methanol extraction. Fish were freeze-
dried and weighed to the nearest 0.1 mg then homogenized in 2 ml
of distilled water. Lipid was extracted from duplicate 500 μl aliquots
of each sample of homogenate using the methods of Bligh and Dyer
(1959) and Mann and Gallagher (1985). Aliquots of 1 ml solvent
extract were dried to a constant weight at 60°C and weighed to the
nearest 0.01 mg. The mean of the duplicates was expressed as total
lipid in mg g
−1
dry weight. The coefficient of variation between
duplicates was less than 14% for all samples.
Analyses
The frequency distributions of condition measures from fish within
low survival patch reefs were compared to those from the high
survival patch reefs using Kolmogorov-Smirnov two-sample tests
(K-S test). Frequency distributions were compared, rather than mean
values, as selective processes operate on trait distributions and are
not always reflected in changes in the mean value of the trait (Miller
1997). Correlations and partial correlations (controlling for standard
length) among the seven condition measures were also examined.
Results
Variability in condition
The total lipid content of Pomacentrus amboinensis
collected from control reefs was the most variable of the
seven condition measures (Table 1). Wet weight, post-
settlement otolith growth rate and Fulton’s K displayed
moderate levels of variation. In contrast, both measures of
fish length (standard length and otolith radius at settle-
ment) were the least variable among fish (Table 1).
Selectivity of early post-settlement mortality
A comparison of the frequency distributions of individual
traits between high (control) and low survivorship reefs
suggested that mortality had been selective toward three
attributes: total lipid content, pre-settlement otolith growth
rate and Fulton’s K (Table 2). The frequency distributions
for standard length, wet weight, relative size at settlement
(i.e. otolith size at settlement) and post-settlement growth
rates did not differ between treatments, suggesting that
predators were not selective for these traits in this habitat
(Table 2).
A comparison of the distributions of total lipid content
between treatments suggested that individuals that had low
lipid levels were selectively preyed upon (Table 2;
Fig. 1a). The proportion of fish with total lipid content
less than 150 mg g
−1
dry weight was substantially greater
for high survival (52.2%) than low survival (13.3%) reefs.
Similarly, predation appeared to be selective towards fish
with low pre-settlement otolith growth rates (Table 2;
Fig. 1b). High survivorship reefs had a greater proportion
of individuals with pre-settlement otolith growth rates
below 19 μm day
−1
than low survivorship reefs (41.8%
and 23.3% respectively).
Table 1 Summary of the vari-
ability in seven measures of
body condition for Pomacentrus
amboinensis that have been
settled on patch reefs for 3 days
and sustained low levels of
mortality ( n=67)
Condition measure Mean Range CV
Standard length (mm) 12.4 11.3–13.7 4.0
Wet weight (mg) 63.5 36.4–110.5 25.4
Fulton’s K 32.7 21.6–43.1 16.5
Otolith radius at settlement (μm) 247.7 201.7–282.0 6.3
Pre-settlement otolith growth rate ( μm day
−1
) 19.6 16.7–25.0 9.1
Post-settlement otolith growth rate (μm day
−1
) 6.0 3.7–8.9 17.8
Total lipid (mg g
−1
) 155.9 45.1–373.3 43.5
25
In contrast, fish from the low survivorship reefs had
lower values of Fulton’s K than those from high
survivorship reefs (Fig. 1c). The proportion of fish with
Fulton’s K greater than 33.0 was substantially greater for
high survival (49.3%) than low survival (20.0%) reefs.
This suggests that the P. amboinensis that survived high
predation pressure were those of lower bulk.
Comparison of measures of condition
Correlations among the seven measures of condition were
generally weak, with the exception of relationships
between morphological measures and their derivative,
Fulton’s K (Table 3). Total lipid content of P. amboinensis
was negatively related to standard length (Table 3),
suggesting that smaller recruits had a tendency to have a
higher proportion of lipid than larger recruits. Not
surprisingly, there was a strong relationship between pre-
settlement growth and relative size at settlement (i.e.
otolith size at settlement). Interestingly, there was no
relationship between pre- and post-settlement otolith
growth. However, there was a negative relationship
between relative size at settlement and post-settlement
otolith growth, suggesting that there may be some
compensatory growth occurring. The relationships
among condition measures remained relatively unchanged
after removing the effects of standard length (Table 3).
Discussion
Mortality of Pomacentrus amboinensis was found to be
selective at settlement. In this patch reef habitat, it appears
that transient predators selectively removed individuals
with lower lipid levels, slower pre-settlement growth and
higher Fulton’s K. Thus, processes that affect the condition
of individuals during the pelagic larval phase not only
influence the strength of cohorts (e.g. Bergenius et al.
2002; Wilson and Meekan 2002) but also the survival
probabilities of settling individuals within a cohort.
The absence of different post-settlement growth rates
between reefs, together with the short duration of the
experiment, suggests that the observed differences in
condition between high and low survival populations were
present at settlement and were not simply the result of a
density-dependent reduction in competition in the low
survival populations. The growth of juvenile coral reef
Table 2 Comparison of the frequency distributions of seven
measures of body condition for P. amboinensis between two groups
of fish from the same settlement cohort: one that sustained high
mortality (n=30), the other that sustained low mortality (n=67). The
results of Kolmogorov-Smirnov two-sample tests are summarized
Condition measure D statistic Kolmogorov-SmirnovZ Significance level
Standard length (mm) 0.121 0.553 0.920
Wet weight (mg) 0.290 1.320 0.061
Fulton’s K 0.326 1.483 0.025*
Otolith size at settlement (μm) 0.178 0.809 0.530
Pre-settlement otolith growth rate ( μm day
−1
) 0.306 1.395 0.041*
Post-settlement otolith growth rate (μm day
−1
) 0.193 0.876 0.426
Total lipid (mg g
−1
) 0.498 2.267 6.9×10
−5
***
*P< 0.05; **P<0.01; ***P< 0.001
Fig. 1a–c Comparison of the frequency distributions of three
measures of body condition between newly settled Pomacentrus
amboinensis exposed to high levels of predation (open bars, n=30)
and those exposed to low levels of predation (solid bars , n=67). a
Total lipid content (mg g
−1
dry body weight); b otolith growth rates
(μm day
−1
) for the 7 days prior to settlement; c Fulton’s condition
index (weight/length
3
)
26
fishes has been shown to be density dependent within
naturally occurring densities, but these effects are only
evident weeks to months after settlement (e.g. Doherty
1982; Victor 1986; Jones 1987; Forrester 1990). Further-
more, food deprivation experiments have shown that there
is a considerable lag in the response of various condition
measures, including total lipid content and Fulton’s K,in
both juvenile (Weber et al. 2003) and adult fishes (Molony
and Sheaves 1998). The generality of this time lag in the
response of lipid content and Fulton’s K to feeding levels
suggests that the present results are likely to be the
consequence of selective mortality.
Few previous studies have examined the selectivity of
mortality immediately after settlement, particularly with
respect to body condition. Searcy and Sponaugle (2001)
used the width of the metamorphic band in the otolith of
two Caribbean wrasse species (Halichoeres bivittatus and
Thalassoma bifasciatum) as a measure of body condition
at settlement. The width of this band is thought to
represent growth during a 3- to 5-day period of non-
feeding whilst individuals are buried in the sand
metamorphosing, a common phenomenon amongst
wrasses (Sponaugle and Cowen 1997). By comparing
newly settled fish with fish 6 or more days after
settlement, they suggested that mortality was selective
for body condition. Similarly, higher total lipid content
increased the survival of a Caribbean damselfish,
Stegastes partitus for the period 7–17 days after settlement
(Booth and Hixon 1999). The lipid levels of recently
settled individuals were manipulated in aquaria by feeding
them either a high or low ration diet for a period of 7 days.
Fish fed a high-ration diet exhibited higher survivorship
than individuals from the low-ration diet when exposed to
a piscivorous fish in an aquarium or released onto a reef
for 10 days (Booth and Hixon 1999). These findings
suggest that if the differences in condition of individuals at
settlement are maintained, the advantages gained in the
larval phase may extend several weeks after settlement. In
contrast, experimental trials have shown predation by
lizardfish, Synodus variegatus, on newly settled goatfish,
Upeneus tragula, to be non-selective with respect to total
lipid content (McCormick and Kerrigan 1996). This lack
of selectivity was attributed to the ambush capture strategy
employed by the predator (Sweatman 1984). In general it
appears that body condition, in the form of available or
excess energy, is important for reef fish at settlement and
may determine which individuals survive this period of
high selection.
Our findings support recent studies from a range of reef
systems that have found that larval growth is important for
survival immediately after settlement. Higher larval
growth rates have been shown to increase the survival
probability of a temperate serranid Paralabrax clathratus
during the first 5 days after settlement (Shima and Findlay
2002). High pre-settlement growth rates have also been
found to enhance survival of one Caribbean wrasse (H.
bivittatus) but not another (T. bifasciatum) during their
first 2 weeks on the reef (Searcy and Sponaugle 2001).
Furthermore, the results of a caging experiment that
manipulated access by different size classes of predators to
newly settled P. amboinensis suggested that, in almost all
cases, predation was selective for individuals with low
pre-settlement growth (McCormick and Hoey 2004). Pre-
settlement growth appears to play an important role in
post-settlement survival in most species studied to date.
Interestingly, P. amboinensis with higher Fulton’s K
suffered greater mortality than those that had lower weight
to length ratios. This result is surprising as Fulton’s K is a
starvation-dependent index, with higher K values thought
to represent fish in better condition (Suthers 1998). In
contrast to the present study, Booth and Hixon (
1999)
reported a positive relationship between Fulton’s K and
survivorship for recently settled S. partitus. This incon-
sistency may be related to a difference in growth form
between the two species, exposure to predators who
exhibit different prey preferences, or simply by the actions
of selective predation targeted toward one or more traits
that have negative associations with Fulton’s K. Irrespec-
tive of the process, the effectiveness of Fulton’s K as a
measure of condition at developmental boundaries is
questionable.
Our study found no obvious advantage to being large at
settlement. Evidence to date suggests that size does not
always influence the survival probabilities of newly settled
fishes. Larger initial size was found to increase survival of
recently settled domino damselfish, Dascyllus albisella in
one year of a 2-year study (Booth 1995). McCormick and
Hoey (2004) monitored the fate of naturally settled P.
Table 3 Correlations among seven measures of condition ofP. amboinensis recruits from low mortality patch reefs 3 days after settlement.
Pearson correlation coefficients are given. Partial correlations controlling for standard length are given in parentheses. n=67
Wet weight Fulton’s K Size at
settlement
Pre-settlement
growth
Post-settlement
growth
Total
lipid
Standard length 0.831*** 0.519*** 0.337*** 0.092 −0.007 −0.355**
Wet weight 0.898***(0.982***) 0.164( − 0.222) −0.012(−0.161) 0.092(0.156) −0.221(0.143)
Fulton’sK 0.026(−0.185) −0.100(−0.174) 0.135(0.162) −0.064(0.150)
Size at settlement 0.544***(0.547***) − 0.276*(− 0.291*) −0.153(−0.038)
Pre-settlement growth 0.052(0.052) −0.153(−0.129)
Post-settlement growth −0.110(− 0.120)
*P<0.05; **P <0.01; ***P<0.001
27
amboinensis on a contiguous reef and showed that
individuals who were slightly larger at settlement
(<1 mm SL difference) had improved survival probabil-
ities. In contrast, Searcy and Sponaugle (2001) found that
otolith length at settlement (a proxy for size at settlement)
did not influence survival of two wrasses, H. bivittatus and
T. bifasciatum. Predation by lizardfish, S. variegatus,on
newly settled goatfish, U. tragula, has also been found to
be non-selective for size (McCormick and Kerrigan 1996).
These contrasting results suggest that predation is not
always directed toward size, and that the relationships
among the various morphological and biochemical aspects
of condition that influence survival may determine
whether size is found to be important or not.
Generally, studies have found poor relationships
between measures of condition, suggesting that selection
with respect to one trait has little influence on the patterns
of variability in other traits (McCormick and Molony
1993; Kerrigan 1996). Morphological measures of condi-
tion, including Fulton’s K, have been found to be both
positively (Booth 1995; Booth and Hixon 1999) and
negatively (McCormick and Molony 1993, present study)
related to total lipid content in coral reef fishes at
settlement. In addition, Kerrigan (1996) found that the
relationships among morphological variables and total
lipid levels changed among three recruitment seasons and
between species for two congeneric damselfish, P.
amboinensis and P. nagasakiensis. These relationships
are not surprising, given the different ecological functions
of growth, tissue energy and morphological indices.
However, these studies do suggest that caution is required
in inferring the significance of selection toward a trait (e.g.
size) in relation to other measures of condition, particu-
larly when the relationships among body condition
measures are unknown.
Our present inability to assess biochemical and phys-
iological measures of condition non-destructively or in
retrospect has restricted our focus to using readily
measurable morphological traits as indicators of condition
(but see Booth and Hixon 1999; Booth and Alquezar
2002). The importance of size at a particular developmen-
tal stage has been emphasized in the literature, with the
extension of the ‘bigger-is-better’ hypothesis, developed
from larval research (Leggett and Deblois 1994), to the
juvenile phase (Sogard 1997). This importance of size
pervades the literature of many other organisms that
exhibit complex life cycles (e.g. tadpoles: Tejedo 1993;
marine snails: Moran and Emlet 2001). Part of this
emphasis on size is that many performance characteristics
have been related to size (Bailey and Houde 1989; Fuiman
and Higgs 1997). However, these relationships can break
down once developmental stage is accounted for (e.g.
Neilson et al. 1986; McCormick and Molony 1993). In the
present study, size and the proxy for size at settlement
(otolith radius at settlement) were the least variable of the
traits measured, with measures of body condition (i.e. lipid
levels, pre- and post-settlement growth and Fulton’s K)
showing 2–10 times as much variability. A re-examination
of a similar dataset for newly metamorphosed goatfish, U.
tragula (McCormick and Molony 1993), shows the same
trend in variability, with the lowest variability in standard
length (5.5% CV), and 3–
6 times as much variability in
measures of body condition and performance (total lipid
content 31.4% CV, Fulton’s K 17.6% CV, burst speed
24.4% CV). It may be that selectivity directed toward
other aspects of body condition and performance may be
more important than size, but size is the only variable
measured under the usually untested and possibly
unfounded assumption that other measures of quality
will be positively correlated with size.
This study indicates that the condition of coral reef fish
at settlement has important ramifications for their
subsequent survival and recruitment to the adult popula-
tion. Although total lipid content and pre-settlement
growth rates influenced the survival of newly settled P.
amboinensis, the poor correlation between condition
measures suggests that no single measure comprehen-
sively describes the quality of an individual at settlement
(Ferron and Leggett 1994). Predator—prey and competi-
tive interactions tend to be species-specific and may
respond differently to particular components of condition.
Therefore, when assessing condition it is necessary to
consider a variety of measures to adequately describe the
relative fitness of an individual.
Acknowledgements Thanks to S. Stoute, J. Pit, S. Holst and D.
Wilson for their assistance in the field and laboratory. We are
grateful to C. Fulton, J. Hoey and S. Smith for comments on a draft
of the manuscript. Two anonymous reviewers provided useful
comments on the manuscript. We are indebted to the staff at the
Lizard Island Research Station, a facility of the Australian Museum,
for their assistance with the project. This project was funded through
a CRC Augmentative grant to A.S.H. and an Australian Research
Council grant to M.I.M. This study was conducted under the
approval of the James Cook University ethics board.
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