Zoogeography of fish parasites of the pearlside (Maurolicus muelleri), with genetic evidence of Anisakis simplex (s.s.) from the Mid-Atlantic Ridge

A total of 200 Maurolicus muelleri from the Mid-Atlantic Ridge (MAR) and the Norwegian Deep (ND) were studied for parasitic helminths. Two different metazoans were isolated from the MAR and five species from the ND. The predominant parasite species in both areas were tetraphyllidean cestode larvae (Scolex pleuronectis) and the anisakid nematode Anisakis simplex sensu stricto (s.s.), the latter being identified using genetic analysis of the internal transcribed spacer (ITS-1, ITS-2) and 5.8S regions of the rDNA. The parasite fauna of M. muelleri from the MAR was less species rich in comparison to ND, due to the deep-sea and oceanic environment. The digeneans Brachyphallus crenatus and Lecithaster confusus as well as the raphidascarid fish nematode Hysterothylacium aduncum were only collected from the ND. This can be explained either by the deep origin of the sampled fish specimens or the lack of suitable intermediate or final hosts in the region. Based on the frequent occurrence of A. simplex (s.s.) around the MAR and the ND, a pelagic life cycle is suggested at both localities, involving baleen and toothed whales as final and pelagic and mesopelagic fish and invertebrates as intermediate or paratenic hosts.     

Distribution of the marine littoral Foraminifera in Argentina,Uruguay and Southern Brazil

Benthic foraminifers collected in the marine littoral zone (sensu lato) of Argentina, Uruguay and Southern Brazil have been studied and compared with the Foraminifera collections from the same area studied previously. Two figures have been prepared, which show the geographical range and relative abundance of the most important species (cosmopolitan and non-cosmopolitan). The following biogeographical conclusions were drawn on the basis of an analysis of these figures. The whole area, from a latitude of about 32° S up to the southern coast of Tierra del Fuego, should be considered as one biogeographical unit (a kingdom of Buccella peruviana, sensu lato). This unit has 2 internal boundaries, which are located approximately at latitudes 41° and 52° S. They divide the whole area into 3 sub-areas which can be called (from North to South): North Patagonian (32° to 41° S), South Patagonian (41° to 52° S) and Malvinian (52° S—southern coast of Tierra del Fuego). With the exception of Buccella peruviana, sensu lato, which is typical of all 3 sub-areas, these sub-areas are characterized by the following faunal features. The North Patagonian sub-area contains abundant numbers of Elphidium discoidale. The South Patagonian sub-area is characterized by abundant numbers of Elphidium macellum. The Malvinian sub-area contains abundant numbers of Elphidium macellum, and also several very typical representatives of the Malvin current water, for instance, Cassidulina crassa, sensu stricto, Angulogerina angulosa, Uvigerina bifurcata, Cassidulinoides parkerianus, Ehrenbergina pupa and others. It is a matter of opinion whether the sub-areas cited be considered biogeographical sub-provinces, or even smaller units. They cannot be interpreted as biogeographical provinces.Contribution No. 62 of the Puerto Deseado Marine Biological Station.     

Association networks in spider monkeys (<Emphasis Type="Italic">Ateles geoffroyi</Emphasis>)

We use two novel techniques to analyze association patterns in a group of wild spider monkeys (Ateles geoffroyi) studied continuously for 8 years. Permutation tests identified association rates higher or lower than chance expectation, indicating active processes of companionship and avoidance as opposed to passive aggregation. Network graphs represented individual adults as nodes and their association rates as weighted edges. Strength and eigenvector centrality (a measure of how strongly linked an individual is to other strongly linked individuals) were used to quantify the particular role of individuals in determining the network's structure. Female–female dyads showed higher association rates than any other type of dyad, but permutation tests revealed that these associations cannot be distinguished from random aggregation. Females formed tightly linked clusters that were stable over time, with the exception of immigrant females who showed little association with any adult in the group. Eigenvector centrality was higher for females than for males. Adult males were associated mostly among them, and although their strength of association with others was lower than that of females, their association rates revealed a process of active companionship. Female–male bonds were weaker than those between same-sex pairs, with the exception of those involving young male adults, who by virtue of their strong connections both with female and male adults, appear as temporary brokers between the female and male clusters of the network. This analytical framework can serve to develop a more complete explanation of social structure in species with high levels of fission–fusion dynamics. This contribution is part of the special issue “Social Networks: new perspectives” (Guest Editors: J. Krause, D. Lusseau and R. James)     

RAPD-PCR investigations of systematic relationships among four species of eels (Teleostei: Anguillidae), particularly Anguilla anguilla and A. rostrata

 We examined the genetic identities of 49 individuals of four species of eels in the genus Anguilla Shaw, A. anguilla, A. japonica, A. reinhardti and A. rostrata, using the random(ly) amplified polymorphic DNA (RAPD)-PCR technique. We used 15 random decamer primers. Out of the 22 148 amplification products detected, 454 markers were evaluated using Nei's distance coefficient, two numerical methods (neighbor-joining, UPGMA), and phylogenetic analysis using parsimony (PAUP). Both numerical and parsimony methods were congruent and confirmed the specific status of all four examined Anguilla species. In all dendrograms, all individuals of each of the species clustered together within four closed groups with highly significant bootstrap values (between 97 and 100%). Additionally 1 to 18 species-specific monomorphic diagnostic fragments were detected in three of the species; none were detected in A. anguilla. Mean interspecific genetic distances ranged from 0.384 to 0.559, with the minimum between A. anguilla and A. rostrata and the maximum between A. anguilla and A. reinhardti. Individuals collected at one locality and belonging to a single species did not cluster together, and neither were any diagnostic monomorphic fragments found for individuals of single localities. This probably reflects a random dispersal of larvae in ocean currents before they reach coastal waters. Among all possible species pairs, only the two Atlantic species were consistently clustered in all dendrograms, with highly significant bootstrap values (100%). Additionally, we detected ten diagnostic markers for this pair of eel species. From RAPD data, we suggest a phylogram which was routed by the descending analysis method: A. reinhardti appears to have been the first species to diverge from a putative common ancestor of the four eel species. Later, A. japonica separated from the hypothetical ancestor of the Atlantic species, which then split recently into A. anguilla and A. rostrata. The close relationship of A. anguilla and A. rostrata is indicated by their low genetic distance (GD = 0.384) and a high degree of shared RAPD fragments (SF = 71.2%); this compares with the following means for all other species pairs: ( = 0.531,  = 44.2%). The prerequisites for using RAPD data for the reconstruction of phylogenies are discussed. Received: 2 September 1999 / Accepted: 8 May 2000     

Interactions among bacterial-feeding nematode species at different levels of food availability

Accurate prediction of the biodiversity–ecosystem functioning relationship requires adequate understanding of the interactions among species in a community. Effects of species diversity on ecosystem functioning are usually considered more pronounced with increasing functional dissimilarity, although species within functional groups may also perform non-identical functions and interact with each other. Here we present results of a laboratory experimental study aimed at elucidating whether interspecific interactions among species within a single nematode trophic group, bacterivores, (1) affect population development and community structure, and (2) depend on food availability. We studied the population growth of Rhabditis (Pellioditis) marina, a rhabditid nematode known to favour very high food densities when in monoculture, and of Diplolaimelloides meyli and D. oschei, congeneric Monhysteridae known to perform better in monocultures at intermediate food availability. Both Diplolaimelloides species showed significantly different patterns of food-density dependence in combination culture compared to monoculture. At very high food availability, the rhabditid nematode facilitated growth of both monhysterid species, probably as a result of down-regulation of bacterial density. At the lowest food availabilities, the presence of even low numbers of monhysterid nematodes lead to exclusion of the rhabditid, which at such low food availability has a very inefficient food uptake. At intermediate food availabilities, abundances of both Diplolaimelloides species were strongly depressed in the combination culture, as a result of food depletion by the rhabditid, indirect inhibitory interactions between the two congeneric species, or both. The complexity of the species interactions render predictions on the outcome and functional consequences of changes in within-trophic-group diversity highly problematic.     

Distribution and abundance of marine nematodes on the kelp Macrocystic integrifolia

The species and distribution of nematodes on the kelp Macrocystic integrifolia Bory, in the Bamfield region of Barkley Sound, British Columbia, Canada were examined. Nine species (belonging to six families) of nematodes were found on the kelp blades. Three species (Monhystera disjuncta, M. refringens and Prochromadorella neapolitana) comprised 91–99% of the nematode fauna and occurred in all monthly samples from July 1978 to November 1979. The three dominant species exhibited seasonal density differences. P. neapolitana occurred mostly in the summer, M. refringens abundance peaked from July to October and M. disjuncta was relatively abundant throughout the year. The other species contributed little to the overall abundance and distribution patterns. All three species occurred in greatest abundance on the lower and middle blades of M. integrifolia in the deep end of the kelp bed. Very few individuals occurred on the upper blades. Nematode distribution on M. integrifolia appeared to be related to blade age and the associated food sources on the blade.     

Mosaic horizontal distributions of three species of copepods in the subarctic Pacific during spring

 Continuous abundance estimates (510 m resolution) of the copepods Neocalanus cristatus, N. flemingeri and Metridia pacifica were obtained with an electronic particle counter along cruise tracks in the subarctic western North Pacific in spring. For all three species, the number of patches decreased exponentially with increasing patch size. Most patches (63 to 83%) were dominated by one species, and patches of the same species more closely spaced than patches of different species. The patches of M. pacifica tended to coexist with those of N. cristatus. In contrast, patches of N. flemingeri rarely co-occurred with those of other copepods. These patterns were more clearly observed in fine-scale observations with sampling intervals of <31 m. Coherence analysis of copepod species pairs showed no characteristic scale at 2 to 50 km wave lengths. At shorter wave lengths (<2 km), frequent positive correlations were observed between N. cristatus and M. pacifica. Thus, the distribution of copepods appears to be a mosaic assemblage of patches of each copepod species. These results suggest that copepods have a mechanism to form species-specific aggregations, and the aggregation and segregation processes are maintained at a scale of <2 km. Received: 24 February 1999 / Accepted: 25 April 2000     

Genetic differentiation among populations of a broadcast spawning soft coral, Sinularia flexibilis, on the Great Barrier Reef

The genetic structure of 12 reef populations of the soft coral Sinularia flexibilis (Octocorallia, Alcyoniidae) was studied along the Great Barrier Reef (GBR) at a maximum separation of 1,300 km to investigate the relative importance of sexual and asexual reproduction, genetic differentiation and gene flow among these populations. S. flexibilis is a widely distributed Indo-Pacific species and a gamete broadcaster that can form large aggregations of colonies on near-shore reefs of the GBR. Up to 60 individuals per reef were collected at a minimum sampling scale of 5 m at two sites per reef, from December 1998 to February 2000. Electrophoretic analyses of nine polymorphic allozymes indicated that genotypic frequencies in most populations and loci did not differ significantly from those expected from Hardy–Weinberg predictions. Analysis of multi-locus genotypes indicated a high number of unique genotypes (N _go) relative to the number of individuals sampled (N) in each reef population (range of 0.69–0.95). The maximum number of individuals likely to have been produced sexually (N*) was similar to the number of individuals sampled (i.e. N*:N ˜ 1), suggesting that even repeated genotypes may have been produced sexually. These results demonstrated a dominant role of sexual reproduction in these populations at the scale sampled. Significant genetic differentiation between some populations indicated that gene flow is restricted between some reefs (F _ST=0.026, 95% CI= 0.011 − 0.045) and even between sites within reefs (F _ST=0.041, 95% CI=0.027 − 0.055). Nevertheless, there was no relationship between geographic separation and genetic differentiation. Analyses comparing groups of populations showed no significant differentiation on a north-south gradient in the GBR. The pattern in the number of significant differences in gene frequencies in pairwise population comparisons, however, suggested that gene flow may be more restricted among inner-shelf reef populations near to the coast than among mid/outer-shelf populations further from the coast. Received: 10 July 2000 / Accepted: 5 October 2000     

Allozyme electrophoresis indicates high gene flow between populations of Holothuria (Microthele) nobilis (Holothuroidea: Aspidochirotida) on the Great Barrier Reef

 Genetic variation in 15 Holothuria (Microthele) nobilis (Selenka, 1867) populations on the Great Barrier Reef was studied at seven polymorphic allozyme loci. Although populations were separated by distances up to 1300 km, there were no apparent restrictions to gene flow (F _ST values were not significantly different from 0) and the maximum Nei's unbiased genetic distance was 0.003. Populations were in Hardy–Weinberg equilibrium at all loci. The estimated maximum sexual input [this is the ratio of the number of sexually produced individuals (N*) to the sample size (N _i )] and the minimum sexual input [this is the ratio of the number of genotypes (N _go ) over the sample size (N _i )] were used as estimators for the amount of asexual reproduction. Both parameters suggested that H. nobilis reproduces solely by sexual means (N*:N _i : = 1; N _go :N _i  = 0.74 to 1). The allozyme data indicated high gene flow between populations, but the possibility that allozyme frequencies may not be at equilibrium means that it was not possible to distinguish whether the patterns reflect present-day dispersal or dispersal that occurred in the past. Received: 27 March 2000 / Accepted: 29 June 2000     

Genetic structure,lack of sex-biased dispersal and behavioral flexibility in the pair-living fat-tailed dwarf lemur, <Emphasis Type="Italic">Cheirogaleus medius</Emphasis>

Mating system and dispersal patterns influence the spatio-genetic structure within and between populations. Among mammals, monogamy is rare, and its socio-genetic consequences have not been studied in detail before. The goal of our study was to investigate population history, demographic structure, and dispersal patterns in a population of pair-living fat-tailed dwarf lemurs, Cheirogaleus medius, a small, nocturnal primate from western Madagascar, and to infer their underlying behavioral mechanisms. Tissue samples for DNA extraction were obtained from a total of 140 individuals that were captured in two subpopulations about 3 km apart. Analyses of mtDNA variability at the population level revealed very low levels of genetic variability combined with high haplotype diversity, which is indicative of a recent population bottleneck. We found no evidence for spatial clustering of same-sexed individuals with identical haplotypes within each of two subpopulations but significant clustering between them. Thus, a high level of local subpopulation differentiation was observed (F _ST = 0.230). The sexes showed equal variances in the number of individuals representing each haplotype, as well as equal levels of aggregation of identical haplotypes. Hence, both sexes disperse from their natal area, one pattern expected in a pair-living mammal. There is a possibility of behavioral and social flexibility in this species, however, because we documented pronounced differences in density and sex ratio between the two subpopulations, suggesting that single study sites or populations may not be representative of a given local population or even species.     

Phylogeography and Limited Genetic Connectivity in the Endangered Boring Giant Clam across the Coral Triangle

Abstract: The Coral Triangle is the global center of marine biodiversity; however, its coral reefs are critically threatened. Because of the bipartite life history of many marine species with sedentary adults and dispersive pelagic larvae, designing effective marine protected areas requires an understanding of patterns of larval dispersal and connectivity among geographically discrete populations. We used mtDNA sequence data to examine patterns of genetic connectivity in the boring giant clam (Tridacna crocea) in an effort to guide conservation efforts within the Coral Triangle. We collected an approximately 485 base pair fragment of mtDNA cytochrome c oxidase 1 (CO1) from 414 individuals at 26 sites across Indonesia. Genetic structure was strong between regions (φ_ST=0.549, p < 0.00001) with 3 strongly supported clades: one restricted to western Sumatra, another distributed across central Indonesia, and a third limited to eastern Indonesia and Papua. Even within the single largest clade, small but significant genetic structure was documented (φ_ST=0.069, p < 0.00001), which indicates limited gene flow within and among phylogeographic regions. Significant patterns of isolation by distance indicated an average dispersal distance of only 25–50 km, which is far below dispersal predictions of 406–708 km derived from estimates of passive dispersal over 10 days via surface currents. The strong regional genetic structure we found indicates potent limits to genetic and demographic connectivity for this species throughout the Coral Triangle and provides a regional context for conservation planning. The recovery of 3 distinct evolutionarily significant units within a well‐studied taxonomic group suggests that biodiversity in this region may be significantly underestimated and that Tridacna taxa may be more endangered than currently recognized.     

Similar soft-bottom polychaete diversity in Arctic and Antarctic marine inlets

The diversity of soft-bottom polychaete assemblages in one Antarctic (Admiralty Bay) and two Arctic (Kongsfjord and van Mijenfjord) localities was compared. The data sets included 79 (Admiralty Bay), 80 (Kongsfjord) and 44 (van Mijenfjord) samples collected with use of 0.1 m² van Veen grab. The number of species per sample in Kongsfjord (mean 19.9 ± 8.0 SD) was higher than that in Van Mijenfjord (13.7 ± 8.3) or Admiralty Bay (15.7 ± 9.4). The differences in species numbers reflected differences in numbers of individuals in samples: 310.4 ind/0.1 m² ± 178.0 in Kongsfjord, 132.7 ind/0.1 m² ± 88.7 in Van Mijenfjord and 138.9 ind/0.1 m² ± 91.5 in Admiralty Bay. The Hurlbert diversity for 50 individuals (ES _[50]) was similar at all sites: 10.7 ± 3.4 in Kongsfjord, 9.7 ± 4.2 in van Mijenfjord, 10.5 ± 4.9 in Admiralty Bay. The shape of species accumulation curves was also similar for all localities. There was no significant difference (at P < 0.05) either in the total number of species or in species richness as estimated by Chao1 and Chao2 estimators. The generic and family richness at three sites was also similar. We found no substantial differences in the distribution of species among families. At both poles Terebellidae, Ampharetidae, Maldanidae, Spionidae and Polynoidae were dominant in terms of species numbers. The similarity of infaunal polychaete diversity at the polar sites studied contrasts with the substantial differences reported for epi-megafauna. Our study suggests that the patterns of diversity of polar benthic communities are shaped by patterns of habitat heterogeneity which appears to mask any historical processes.     

Females go where the food is: does the socio-ecological model explain variation in social organisation of solitary foragers?

The socio-ecological model (SEM) links ecological factors with characteristics of social systems and allows predictions about the relationships between resource distribution, type of competition and social organisation. It has been mainly applied to group-living species but ought to explain variation in social organisation of solitary species as well. The aim of this study was to test basic predictions of the SEM in two solitary primates, which differ in two characteristics of female association patterns: (1) spatial ranging and (2) sleeping associations. Beginning in August 2002, we regularly (re-)captured and marked individuals of sympatric populations of Madame Berthe's and grey mouse lemurs (Microcebus berthae, Microcebus murinus) in Kirindy Forest (Madagascar). We recorded data on spatial patterns, feeding and social behaviour by means of direct observation of radio-collared females. The major food sources of M. berthae occurred in small dispersed patches leading to strong within-group scramble competition and over-dispersed females with a low potential for female associations. In contrast, M. murinus additionally used patchily distributed, high-quality (large) resources facilitating within-group contest competition. The combined influence of less strong within-group scramble and contest as well as between-group contest over non-food resources allowed females of this species to cluster in space. Additionally, we experimentally manipulated the spatial distribution of food sources and found that females adjusted their spatial patterns to food resource distribution. Thus, our results support basic predictions of the SEM and demonstrated that it can also explain variation in social organisation of solitary foragers.     

Patterns in the spatial arrangements of polychaetes and bivalves in intertidal sandflats

Spatial autocorrelation correlograms based on Moran's coefficient were constructed for common polychaetes (Goniada emerita, Heteromastus filiformis, Macroclymenella stewartensis, Boccardia spp. and Magelona? dakini)_and bivalves (Nucula hartvigiana, Soletellina siliqua and Tellina liliana) collected from intertidal sandflats of Manukau Harbour (New Zealand) during October, 1987. Patterns of heterogeneity on a scale smaller than inter-sample distance, homogenous density patches (5 to 30 m radius) and gradients in abundance running through sample sites (9 000 m²) were identified. Patterns could be defined even for species with distributions which, based on the variance: mean ratio test, were not significantly different from random. The possible influence on two of the study sites of sediment disturbances generated by feeding rays is discussed. Identification of spatial patterns is considered an important aspect of the design of surveys and manipulative field experiments.     

A molecular approach to the ecology of a mussel (Mytilus edulis – M. trossulus) hybrid zone on the east coast of Newfoundland, Canada

Mytilus trossulus Gould and M. edulis L. coexist in mixed populations in Atlantic Canadian waters. Although there is evidence that the two species hybridize in natural populations and that hybrids produce progeny through backcrosses, no study of the microgeographic distribution of the two forms and their hybrids has been made. Here we examine subtidal samples of mussels taken in July 1997 from two locations in eastern Newfoundland (Canada) and from wave-exposed and protected environments within each location. Shell lengths ranged from 15 to about 90 mm. Mussels were classified as pure forms or hybrids (F₁, F₂ and from backcrosses) based on four diagnostic markers, two allozyme loci (Mpi and Est-D) and two nuclear PCR-based DNA markers (ITS and Glu-5). In addition, a PCR-based mtDNA marker (COIII) was used to characterize the distribution of mtDNA mitotypes among pure and hybrid individuals. There were differences in the proportions of pure M. edulis and M. trossulus between sites and between environments at one location. M. trossulus was the predominant species at one of the two exposed sites. In all four samples, M. trossulus was also the predominant form among small individuals. The frequency of hybrids was 26% overall and did not differ among samples. Hybrids consisted mostly of backcrosses that were M. trossulus-biased among small mussels and M. edulis-biased among large ones. We conclude that both intrinsic genetic factors and extrinsic environmental factors influence the relative frequency of M. edulis, M. trossulus and their hybrids. Received: 29 June 1998 / Accepted: 4 November 1998     

Using a combined approach to explain the morphological and ecological diversity in <Emphasis Type="Italic">Phanogenia gracilis</Emphasis> Hartlaub, 1893 (Echinodermata: Crinoidea) <Emphasis Type="Italic">sensu lato</Emphasis>: two species or intraspecific variation?

Phanogenia gracilis sensu lato is a shallow-water crinoid distributed throughout the Indo-western Pacific. The taxonomy of P. gracilis s.l. is clouded by the presence of two distinct morphotypes, each differing in morphology and ecology. The goal was to determine the taxonomic status of P. gracilis s.l. using partial gene sequences of two mitochondrial DNA genes, cytochrome oxidase c subunit I and NADH dehydrogenase subunit II, in conjunction with morphological and ecological data. The molecular phylogenies revealed three lineages separated by 5.0–6.6% corrected genetic distance, which is consistent with the genetic distances among other echinoderm species. Neither morphotype was monophyletic, nor was any examined morphological character exclusive to any one lineage. Discriminant function analysis (DFA) of the morphological and ecological data yielded significant results when grouping P. gracilis by morphotype and by clades recovered in the phylogenetic analyses, but grouping by sample locality was rejected. Although DFA results of grouping by clade were significant, jackknife support was weak, while only correctly grouping specimens by their respective clades 65% of the time. The results suggest the possibility of cryptic species, but additional molecular and morphological data are needed to confirm this. This study demonstrates the need to reevaluate the taxonomy of crinoid species and their respective diagnostic characters.     

Communication ecology of webbing clothes moth: 4. Identification of male- and female-produced pheromones

Summary. We investigated the hypothesis that aggregation signals produced by male webbing clothes moths (WCM), Tineola bisselliella (Hum.) (Lepidoptera: Tineidae), and close-range male attractant signals produced by females have a pheromonal basis, at least in part. Gas chromatographic-electroantennographic detection (GC-EAD) and GC-mass spectrometric analyses of bioactive methanolic extracts of male WCM disclosed three candidate pheromone components: hexadecanoic acid methyl ester (16:Ester), (Z)-9-hexadecenoic acid methyl ester (Z9—16:Ester), and octadecanoic acid methyl ester (18:Ester). In bioassay experiments in a large Plexiglas™ arena, a blend of synthetic 16:Ester plus Z9—16:Ester was attractive to male and virgin (but not mated) female WCM; the 18:Ester was inactive. GC-EAD analyses of pheromone gland extracts from female WCM revealed (E,Z)-2,13-octadecadienal (E2Z13—18:Ald) and (E,Z)-2,13-octadecadienol (E2Z13—18:OH) as candidate sex pheromone components. In arena bioassay experiments, 1—5 female equivalents of synthetic E2Z13—18:Ald (0.2 ng) and E2Z13—18:OH (0.1 ng) were more attractive to male WCM than were two virgin female WCM. We anticipate that the combination of aggregation and sex pheromones, male-produced sonic aggregation signals, and habitat-derived semiochemicals will be highly effective in attracting male and female WCM to commercial traps. Received 12 January 2001; accepted 8 June 2001.     

Composition and temporal fluctuations of inshore juvenile fish populations in the Kornati Archipelago, eastern middle Adriatic

Temporal fluctuations of species composition and abundance of fish juveniles in the National Park Kornati were studied over 12 months from January to December 1992. A total of 40 168 individuals, representing 24 families and 69 species, were collected using a 50 m long beach seine. The community was dominated numerically by a few species: Atherina hepsetus (45.90%), Sarpa salpa (21.21%), Diplodus vulgaris (10.49%), and Symphodus ocellatus (6.98%), constituting over 84.58% of the total catch. Similarity between patterns in the abundance of the 17 most common species were examined using correlation matrix-based principal component analysis. Results were compared to the abiotic factors leading to the conclusion that only a low amount of variation in the abundance field can be explained by temperature, salinity and dissolved oxygen. Received: 23 March 1997 / Accepted: 11 April 1997     

Growth parameters of deep-water decapod crustaceans in the Northwestern Mediterranean Sea: a comparative approach

 Relative and absolute growth were studied in 17 species of deep-water decapod crustaceans, spanning nine families of six different infra-orders, in the Northwestern Mediterranean Sea. The overall maximum abundance of these species lay between 200 m and 750 m (i.e. upper- and mid-slope species). Relative and absolute growth rates were compared by contrasting the slopes of the size–weight relationships for the different species and calculating the von Bertalanffy growth-equation parameters asymptotic length (L _∞ ) and growth rate (k). The size–weight relationships differed significantly as function of the species' life habits. The results revealed a significant decrease in weight relative to size in mesopelagic species (which carry out diel vertical migrations), an almost isometric relationship between size and weight in the less mobile nektobenthic species, and a significant increase in weight relative to size in strictly benthic species. The mean allometric coefficient for each group increased significantly from mesopelagic to benthic species. However, no general trend was observed in the growth-performance index, Φ (an index used to compare absolute growth rates between species, as a function of habit and depth of maximum abundance for all species combined), suggesting that the deep-water decapod crustaceans studied have similar absolute growth rates. Nevertheless, comparison of growth-parameter and growth-performance index values within families did reveal differences. Mesopelagic species of the families Sergestoidae and Pasiphaeidae showed slightly increased growth rates with increasing depth of distribution. Nektobenthic species of the genus Plesionika followed a trend opposite to that shown by mesopelagic species, with a higher growth rate for the shallowest-dwelling species (P. heterocarpus) than the deepest-dwelling species (P. acanthonotus). Taking growth as one of the major components of an organism's energy budget, the growth rates for the decapod crustacean species in this study were significantly lower than those reported in the literature for shallow-water penaeid crustacean species (which are distributed in higher-temperature habitats than deep-water Mediterranean crustaceans) and higher than those reported for mesopelagic myctophid fish species. Hence, the well-defined growth trends shown by deep-water decapod crustacean species in the Northwestern Mediterranean Sea, compared to the less well-defined trends in the other taxa, is discussed in the framework of the overall dynamics of their ecosystem. Received: 25 May 1998 / Accepted: 27 September 1999