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Considerazioni su Polybius henslowi, Leach (Crustacea, Brachyura)
... Henslow's swimming crab (Polybius henslowii) is a benthic species with pelagic phases, and is distributed from the British Isles to Morocco and the Mediterranean (Della Croce, 1961;Hayward and Ryland, 1995). In Galicia, trawled samples show that this crustacean could account for more than 90% of decapod crab biomass of the continental shelf (González-Gurriarán and Olaso, 1987). ...
... Furthermore, Harris (1965) includes the velvet crab (Necora puber) amongst the prey items of the herring gull. Shoals of Polybius in coastal waters seem to be found mainly in the Iberian Atlantic and adjacent waters (Della Croce, 1961). It is not surprising, then, that the only recorded instances of Polybius as an important food for gulls come from yellow-legged gull populations in Portugal (Luis, 1982) and the Cantabrian Sea (Alvarez-Laó and Méndez, 1995), as well as from wintering lesser black-backed gulls in Portuguese waters (Tait, 1924). ...
... On the continental shelf, maximum values reached 201 459 crabs (2.5 t biomass) per trawling hour (González-Gurriarán and Olaso, 1987), while at sampling stations in coastal waters, average densities ranged from 0.21 to 16.6 crabs 100 m 2 (Romero et al., 1982;Iglesias and González-Gurriarán, 1984;González-Gurriarán, 1987;González-Gurriarán et al., 1991) with maximum values of 157.5 crabs 100 m 2 . However, Henslow's swimming crabs seem to be very susceptible to predation by large gulls, because they often live very close to the surface (Della Croce, 1961;González-Gurriarán and Méndez, 1986), allowing their capture by plunging, dipping, and surface seizing (pers. obs.). ...
An analysis of the contents of 2562 pellets sampled from 1987 to 1993 at breeding colonies and roosting sites showed that
Henslow's swimming crabs (Polybius henslowii) are by far the most important marine prey for yellow-legged gulls (Larus cachinnans) on the coasts of Galicia (north-western Spain), occurring in 36.4% of pellets. The results also suggest that yellow-legged
gulls in Galicia are to a great extent marine foragers. Galicia has one of the largest yellow-legged gull populations in western
Europe, largely dominating the seabird community. Polybius henslowii is the most abundant decapod crab over the continental shelf of Galicia. It enters coastal waters in large shoals and frequently
stays close to the sea surface. Compared with the diets of other yellow-legged gull populations or any of the other closely
related gull species, such as the herring (L. argentatus) and the lesser black-backed gull (L. fuscus), Polybius henslowii appears as a characteristic and even exclusive prey of yellow-legged gull populations in the Iberian Atlantic. There is also
some evidence that the regular irruption of large Polybius henslowii shoals is a phenomenon peculiar to Iberian Atlantic waters.
... Characterization of portunoid swimming capacity have been combined with a simplified phylogenetic scheme of portunoids based on the present phylogenetic reconstruction with some additions from Schubart and Reuschel (2009), i.e. relationships of Liocarcinus holsatus and Polybius henslowii (Fig. 7). We also indicated there a phylogenetic origin of "perfect swimmers" in certain portunoid taxa, i.e. the species that spend considerable part of their lifetime in the water column: Polybius henslowii (Della Croce, 1961;Hartnoll, 1971;González-Gurriarán, 1987), Charybdis (Goniohellenus) smithii MacLeay, 1837 (Couwelaar et al., 1997;Türkay and Spiridonov, 2006), and Euphylax dovii Stimpson, 1860 (Jerde, 1967;Norse and Fox-Norse, 1977). Our comparison indicates that swimming construction types I, II and III are associated with different major clades of portunoids which also include non-swimming or rarely swimming forms. ...
Cheliped construction, in particular the teeth pattern on chelae fingers is considered as most important character suit (along with burrowing/swimming apparatus) for the diagnosis of Portunoidea. Heterochelic and heterodontic chelipeds with the molariform tooth in the larger chela and multi-lobed serial teeth are presumably ancestral and most common pattern for the group. New material (mostly species of Thalamitinae Paulson, 1875, Lupocyclus Adamd and White, 1848 and Portunus Weber, 1795 sensu lato) have been combined with the existing sequences from the GenBank to produce molecular phylogenetic reconstructions based on the histone H 3 gene fragment and a multi-gene tree (for smaller set of species) based on partial sequences of H3, D 1 region of 28 S gene and mitochondrial CO I gene. These reconstructions have not provided necessary support to the monophyly of Portunoidea sensu lato but indicated the presence of several monophyletic lineages, i.e. Portunidae sensu stricto, Polybiidae + Thiidae + Carcinidae + Pirimelidae, Benthochascon + Geryonidae (to lesser extent), and Ovalipes. Monophyly of the Portunidae sensu stricto is supported by both the H 3 and multigene trees and morphological evidence. Swimming capacity probably evolves as a result of parallel evolution in at least three different lineages of portunoids. A new version of the family level classification of Portunoidea and a key to their families are provided with the following taxa: Geryonidae (Geryoninae + Benthochasconinae subfam. nov.), Ovalipidae fam. nov., Brusiniidae Števčić, 1991, Thiidae, Pirimelidae, Carcinidae McLeay, 1838 (Carcininae + Portumninae Ortmann, 1893), Polybiidae Ortmann, 1893, and Portunidae Rafinesque, 1815 sensu stricto. The most radical change in the systematics of Portunidae sensu stricto is the final recognition of the polyphyly of Portunus sensu lato and the need for revalidization and re-diagnozing of several taxa that were synonymized by Stephenson and Campbell (1959) and Stephenson (1972) under Portunus. While some subfamilies of the Portunidae (Podophthalminae Dana, 1851, Thalamitinae, and Lupocyclinae Alcock, 1895) are well supported by molecular phylogenies and the presence of morphological synapomorphies, the other need re-assessement.
A community of decapod crustaceans (Brachyura) was sampled seasonally (October 1978–July 1979) from three habitats (raft, middle and beach) in the Ría de Muros e Noia (North-West Spain), with the purpose of studying spatial and temporal changes in the community and comparing with communities in the neighbouring Ría de Arousa, which supports an intense mussel (Mytilus edulis)-raft culture. The Portunidae family dominated the decapod community. Polybius henslowi, a species with pelagic stages, which enters the rías periodically in large numbers, was the dominant species at all the stations throughout the sampling period, attaining densities of 1.6 individuals m-2 (18.7 g wet wt m-2) in summer. Macropipus depurator and M. puber were the next most important species at the raft station, M. depurator at middle stations, and M. vernalis and Carcinus maenas at beach stations. The highest population densities were recorded in summer, due to the great abundance of Polybius henslowi at this time. When the data were reconsidered omitting p. henslowi, highest densities were in autumn and winter in the inner ría. In general, the nature of the substratum, the presence of mussel rafts, depth and salinity were the main factors determining the structure of the community. Density and biomass in the Ría de Muros e Noia (P. henslowi omitted) were lower than in the Ría de Arousa (up to six times lower in some areas). The Ría de Muros lacks the extensive number of mussel rafts present in the Ría de Arousa which constitute an important food resource for decapods.
A dense population of Polybius henslowi Leach was recorded at the surface of the sea 15 miles off the north coast of Spain. The depth of water at this point was 1740 m. Visual observations of the swimming behaviour show that Polybius tends to swim with the body facing diagonally and backwards against the current. The space between individuals appears to be maintained deliberately and was never less than 6 ft. during daylight. Measurements show that there are at least two sizegroups present. Females represent 40% of the total of 251 animals collected, and these were at approximately the same reproductive state with the ova maturing. The males are on average 2·3 mm longer than the females. No food was found in the stomach of any of the animals taken.
The crab community in the Ra de Arousa, North-West Spain, was studied for 2 yr (1974–1975; 1975–1976), firstly to detect any differences due to mussel (Mytilus edulis) raft aquaculture; secondly to study temporal changes in spatial distributions in beach, raft and non-raft areas throughout the ra. Portunid crabs dominated the fauna, the dominant species being Macropipus puber and M. depurator in the raft areas, M. depurator in non-raft subtidal areas, and M. arcuatus in beach stations. No substantial seasonal changes were observed in species composition throughout the ra. In general, the highest densities occurred in fall and winter. Raft stations showed the highest values of abundance, up to 0.47 individual per m2, and 8.20 g wet wt m-2. The food resource provided by the rich epifauna associated with the mussel rafts, and changes in the sediment due to shell deposits could account for the high density values in raft areas. Raft areas (polygons) cover about 10% of the surface of the Ra de Arousa and, thus, the raft aquaculture of mussels significantly increases crab production.
The orientational behaviour of the neritic mysid Neomysis mirabilis in a swarm is considered under natural and experimental conditions. In nature, the swarms exhibit elements of inner integration, such as homogeneous age structure, collective behaviour, and relative constancy of inter-individual spacing. The mysids are guided by combined optomotor and vibrotactile cues, determining their disposition in aquaria of different shapes. Maximum accuracy of spatial arrangement is observed in round vessels. It is suggested that the stress encountered in an aquarium produces responses comparable to those elicited by the presence of a predator. The rigid spatial arrangement at the supra-individual level is interpreted as evolutionally-optimized prey strategy. These elements in the geometrical distribution of individuals in mysid swarms are inherent in other pelagic crustaceans also, and are not controlled by random taxes stimulated by hydrological factors.
Variations in embryo size and fatty acid (FA) dynamics during embryogenesis were evaluated in deep-sea pandalids and portunid
swimming crabs from the Portuguese continental margin and Madeira Island slope and compared with previous data on neritic
and deep-sea lobsters and shrimps (collected between February 2001 and March 2004). Inter-specific variations in embryo size
seem to be dictated primarily by phylogeny rather than by differences in reproductive or early life history traits. FA reserves
were significantly correlated with embryo size (P<0.001). Principal component analysis revealed differences among three groups (1—neritic caridean shrimps, 2—deep-sea pandalids
of the genus Plesionika, and lobsters, 3—portunid crabs and the deep-sea pandalid Chlorotocus crassicornis, Costa 1871). Group 1 was clearly separated by PC1 mainly due to the higher percentage of essential C18 (linoleic and linolenic acids) and C20 (namely eicosapentaenoic) polyunsaturated FA (specific markers of primary producers). PC2 separated Group 2 from Group 3
due to differences in the percentage of several saturated FA (including odd-numbered FA—bacterial markers) and C18 monounsaturated FA (namely 18:1n−9, a general marker of carnivory). Therefore, these differences among groups seem to result from distinctions in diet and
ecological niche. Intra-specific differences in FA composition between western and southern Plesionika martia martia (A. Milne-Edwards, 1883) populations may reflect higher water temperatures on the south sub-tropical coast. Lobster embryonic
development was more demanding of lipid energy than that of the other decapod species, which may reflect an evolutionary trend
in decapod taxa related to an increasing degree of lecithotrophy. However, a lower FA catabolism can be interpreted as an
enhanced independence of the newly hatched larvae from external energy sources. Higher FA content at hatching and, as a consequence,
a greater independence from the external environment should increase the chances of larval survival.
1 - The authors study and compare the biovolumes of 69 samples taken with the Isaacs-Kidd midwater trawl during the Polymède expedition on the N. O. "Jean Charcot" (May and June, 1970) in the western Mediterranean and in the vicinity of Cap Finisterre. 2 - The authors, having assembled the measurements of physical oceanographers, have prepared a diagram of the deep-current issuing from the Mediterranean into the Atlantic North- East. It is possible to superimpose on this diagram the route used by the young albacore (Thunnus alalunga) during their annual summer migration. This correspondance suggests an inter-relation between the two phenomena provided by intermediate trophic levels. [NOT CONTROLLED OCR] 1 - Les auteurs étudient et comparent les biovolumes de 69 prélèvements effectués au chalut Isaacs-Kidd pendant la campagne Polymède du N. O. "Jean Charcot" (mai et juin 1970) en Méditerranée occidentale et dans les parages du Cap Finisterre. 2 - Les auteurs retracent le schéma de l'extension, en Atlantique Nord-Est, du courant sous-marin issu de Méditerranée. Il est possible de superposer à ce trajet les voies empruntées par les jeunes thons blancs (Thunnus alalunga) pendant leur migration annuelle estivale. Le lien entre ces deux phénomènes dont le développement géographique est identique, est proposé par l'intermédiaire des relations trophiques du germon avec ses proies. [OCR NON CONTRÔLE]
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