Genetic divergence and phylogenetic inferences in five species of Mugilidae (Pisces: Perciformes)

Allozyme electrophoresis was used to compare the genetic divergence of global populations of Mugil cephalus Linnaeus, 1758 and two congeneric [M.␣curema Cuvier & Valenciennes, 1836; M. gyrans (Jordan & Gilbert, 1885)] and two more distantly related [Liza ramada (Risso, 1826); Xenomugil thoburni (Jordan & Starks, 1896)] species on the basis of 18 enzyme loci. The amount of genetic divergence among the species examined is in agreement with their present systematic status, the differences being larger among non-congeneric species than among species of the same genus. Intraspecific genetic distances in M. cephalus (average Nei's D= 0.154), although higher than those reported for conspecific populations of fish, appear to be small when compared to the interspecific values among mugilid species (0.821 ≤ Nei's D ≤ 1.744). Phylogenetic trees obtained by genetic distance methods and discrete character parsimony analysis were of similar topology, except for the relationships within the genus Mugil and for the arrangement of M. cephalus populations. Received: 7 April 1997 / Accepted: 4 February 1998     

Genetic structure of populations of two species of Chthamalus (Crustacea: Cirripedia) in the north-east Atlantic and Mediterranean

Protein electrophoresis on starch gels was used to investigate population genetic structure of the barnacles Chthamalus montagui Southward and C. stellatus (Poli) over their north-east Atlantic and Mediterranean ranges. In each species, a single locus exhibited marked differentiation of allele frequencies between Atlantic and Mediterranean localities; in C. stellatus, genetic differentiation between the two basins had not previously been noted. In both species, mean heterozygosity per locus appeared higher in the Mediterranean samples than in the Atlantic, and Mediterranean populations had more alleles at the loci studied. Possible explanations for the differentiation between the Atlantic and the Mediterranean populations are discussed. Received: 30 May 1996 / Accepted: 17 September 1996     

Genetic structure and allozyme variation of sea bass (Dicentrarchus labrax and D. punctatus) in the Mediterranean Sea

This paper reports data on 28 allozyme loci in wild and artificially reared sea bass (Dicentrarchus labrax) samples, originating from either coastal lagoon or marine sites in the Mediterranean Sea. F _ST analysis (θ estimator) indicated strong genetic structuring among populations; around 34% of the overall genetic variation is due to interpopulation variation. Pairwise θ estimates showed that, on average, the degree of genetic structuring was much higher between marine populations than between samples from lagoons. Six polymorphic loci showed differences in allele frequencies between marine and lagoon samples. Multivariate analyses of individual allozymic profiles and of allele frequencies suggested that different arrays of genotypes prevail in lagoons compared to marine samples, particularly at those loci that, on the basis of previous acclimation experiments, had been implicated in adaptation to freshwater. On the other hand, variation at “neutral” allozyme loci reflects to a greater extent the geographic location of populations. Allozyme differentiation was also studied in a D. labrax population from the Portuguese coast. Average genetic distance between this population and the Mediterranean populations was quite high (Nei's D = 0.236) and calls into question the taxonomic status of the Portuguese population. Finally, genetic relationships between D. labrax and D. punctatus were evaluated. Average Nei's D was 0.648, revealing high genetic differentiation between the two species, even for two sympatric populations of these species in Egypt; thus gene flow was not indicated between species. Received: 24 October 1996 / Accepted: 27 November 1996     

Gene flow at three spatial scales in a coral reef fish, the three-spot dascyllus, Dascyllus trimaculatus

Dispersal in coral reef fishes occurs predominantly during the larval planktonic stage of their life cycle. With relatively brief larval stages, damselfishes (Pomacentridae) are likely to exhibit limited dispersal. This study evaluates gene flow at three spatial scales in one species of coral reef damselfish, Dascyllus trimaculatus. Samples were collected at seven locations at Moorea, Society Islands, French Polynesia. Phylogenetic relationships and gene flow based on mitochondrial control region DNA sequences between these locations were evaluated (first spatial scale). Although spatial structure was not found, molecular markers showed clear temporal structure, which may be because pulses of settling larvae have distinct genetic composition. Moorea samples were then compared with individuals from a distant island (750 km), Rangiroa, Tuamotu Archipelago, French Polynesia (second spatial scale). Post-recruitment events (selection) and gene flow were probably responsible for the lack of structure observed between populations from Moorea and Rangiroa. Finally, samples from six Indo-West Pacific locations, Zanzibar, Indonesia, Japan, Christmas Island, Hawaii, and French Polynesia were compared (third spatial scale). Strong population structure was observed between Indo-West Pacific populations. Received: 26 May 2000 / Accepted: 10 October 2000     

Effects of contrasting modes of larval development on the genetic structures of populations of three species of prosobranch gastropods

 In south-eastern Australia, the prosobranch gastropods Morula marginalba (Blainville), Cominella lineolata (Lamarck) and Bedeva hanleyi (Angas) have similar fine-scale distributions, but appear to possess very different dispersal capabilities due to contrasting modes of larval development. M.marginalba produce planktonic larvae, whereas C. lineolata and B. hanleyi undergo direct development in benthic egg capsules and emerge as crawling juveniles. To test for possible effects of contrasting life histories on levels of genetic variation within and among populations, a survey was conducted of allozyme variation at six polymorphic loci in 8 to 9 local populations of each species. Collections of snails were made between June 1992 and November 1993. Sampling ranges spanned between 162 and 180 km of coast. Regardless of larval type, proportions of single-locus genotypes in each collection were consistent with the recruitment of offspring which had been generated through random mating. However, genotypic diversity was lower in those species that undergo direct development. Loci surveyed in C. lineolata and B. hanleyi were polymorphic (i.e. frequency of most common allele <95%) in fewer populations than those examined for M.␣marginalba (P <0.001) and, where polymorphisms occurred, also possessed significantly fewer alleles (P <0.001). Consequently, average levels of expected heterozygosity were greater in populations of M. marginalba than in those of either of the other species (P <0.001). Genetic variation among populations, expressed as the standardised variance in allele frequencies (F _ST ), was inversely related to expected larval dispersal capability. The nine collections of M. marginalba showed little overall differentiation (F _ST  = 0.017; P <0.001), reflecting the ability of planktonic larvae to interconnect local populations, and so limit divergence due to drift and natural selection. In contrast, there were high levels of allelic heterogeneity among the nine collections of C. lineolata (F _ST  = 0.523; P <0.001) and eight collections of B. hanleyi (F _ST  = 0.140; P <0.001). These data imply that for species which undergo direct development, local populations are effectively closed and evolve largely independent of one another. Received: 3 May 1996 / Accepted: 12 July 1996     

Allozyme variation in global populations of striped mullet, Mugil cephalus (Pisces: Mugilidae)

The striped mullet, Mugil cephalus Linnaeus, 1758, is one of the few species of marine shore fish with a worldwide circumtropical distribution. Because of this distribution and the dependency of M. cephalus on coastal waters during various phases of its life cycle, as well as nearshore living habits, questions have been raised regarding levels of genetic divergence and gene flow among transoceanic populations. To cast more light on this, allozyme variation at 27 presumptive gene loci was investigated in ten globally diverse populations. The observed heterozygosity ranged from 0.018 (Hawaii) to 0.081 (Florida), averaging 0.050. The proportion of polymorphic loci showed a similar trend. Several populations were characterised by fixed allelic differences. Estimated gene diversities were very high, the allele frequency variation among populations was found to be 68%; genetic distances reached 0.242, with an average of 0.117. Estimated rates of gene flow were high among Mediterranean populations (Nm = 7.26), and between Mediterranean and East Atlantic populations (Nm= 2.86), but extremely low between non-contiguous populations within the Indian, Pacific and Atlantic Oceans, where Nm ranged from 0.03 to 0.05. Received: 7 April 1997 / Accepted: 4 February 1998     

Population genetics of the Antarctic heteronemertean Parbolasia corrugatus from the South Orkney Islands

An allozyme survey, using starch-gel electrophoresis, was carried out on eight populations of the Antarctic nemertean worm Parborlasia corrugatus (McIntosh, 1876) collected from locations around the South Orkney Islands, Antarctica. These populations were separated by distances in the order of tens of kilometres. Genetic variation was estimated over 22 enzyme loci for all populations examined, giving an observed heterozygosity of 0.142. This was much lower than the expected heterozygosity (H _e  = 0.201), and it was found that there was a significant deficiency of het‐erozygotes across four enzyme loci ( p ≤ 0.01). A more detailed examination of this deficiency of heterozygotes was undertaken for the six populations and six variable enzyme loci for which the most complete data sets existed. A significant deficiency of heterozygotes was found at the enzyme locus Odh-1 for four of the six populations examined ( p ≤ 0.01). Mean F _is (0.240) indicated a significant ( p ≤ 0.01) within-population component of the heterozygote deficiency estimated for the six populations sampled, and this was mainly due to the␣Ap-1, Odh-1 and Pgm-1 loci. The mean F _st value (0.036) was also significant ( p ≤ 0.01), indicating a degree of genetic differentiation between populations. The observed levels of genetic differentiation between populations of P. corrugatus and the significant heterozygote deficiencies were unexpected, because this species has been reported to have a long-lived planktotrophic larva. It is hypothesised that recruitment of P. corrugatus in the South Orkney Islands originates from genetically distinct populations located in the Weddell Sea and to the west of the Antarctic Peninsula. Shifts in the relative position of the Weddell Sea Front, Weddell–Scotia Confluence and Scotia Front, relative to the South Orkney Islands, provide a mechanism for variation in the origin of recruits over time. Received: 24 July 1997 / Accepted: 31 October 1997     

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     

Evidence of limited gene flow in three species of coral reef fishes in the lagoon of New Caledonia

Allozyme variation was used to investigate the genetic structure of the coral reef fishes Stegastes nigricans, Epinephelus merra and Acanthurus triostegus around New Caledonia. Each species was sampled from each of three sites in the ≃1000 km circumference of the lagoon of New Caledonia. Allelic variation was recorded for each species at 14, 13 and 17 loci, respectively, and heterozygosity diversity (H s) was 0.082, 0.065 and 0.116, respectively. Analysis of genetic differentiation between sites produced inconsistent results between species, with spatial heterogeneity in two species (S. nigricans, F st  = 0.038; A. triostegus, F st = 0.049) and homogeneity in one species (E. merra, F st = 0.000). Hydrological and climatic data from the lagoon suggest that the eastern and western sides of the lagoon are isolated, since they lie in water masses of different origin. This may explain the genetic differentiation and restricted gene flow found at a local scale for S. nigricans and A. triostegus. Homogeneity in populations of E. merra is discussed in relation to its low genetic diversity and its reproductive behaviour. Received: 23 April 1997 / Accepted: 25 September 1997     

Genetic heterogeneity among adult and recruit red sea urchins, Strongylocentrotus franciscanus

Allozyme electrophoresis was used to characterize genetic variation within and among natural populations of the red sea urchin Strongylocentrotus franciscanus. In 1995 to 1996, adult urchins were sampled from twelve geographically separated populations, seven from northern California and five from southern California (including Santa Rosa Island). Significant population heterogeneity in allelic frequencies was observed at five of six polymorphic loci. No geographic pattern of differentiation was evident; neighboring populations were often more genetically differentiated than distant populations. Northern and southern populations were not consistently distinguishable at any of the six loci. In order to assess within-population genetic variation and patterns of recruitment, large samples were collected from several northern California populations in 1996 and 1997, and were divided into three size classes, roughly representing large adults (>60 mm), medium-sized individuals (31 to 60 mm, “subadults”) and individuals <2 yr of age (≤30 mm test diam, referred to as “recruits”). Comparisons of allelic counts revealed significant spatial and temporal differentiation among size-stratified population samples. Recruit samples differed significantly from adult samples collected at the same locale, and showed extensive between-year variation. Genetic differentiation among recruit samples was much higher in 1997 than in 1996. Between-year differences within populations were always greater for recruits than for adults. Potential explanations for the differentiation of recruit samples include pre- and post-settlement natural selection and high interfamily variance in reproductive success or “sweepstakes” recruitment. Unless recruit differentiation can be attributed to an improbable combination of strong and spatially diverse selection, such differentiation across northern California populations indicates that the larval pool is not well mixed geographically (even on spatial scales <20 km), despite long planktonic larval duration. Received: 6 July 1999 / Accepted: 25 January 2000     

Genetic variation and clonal structure in the scleractinian coral Pocillopora damicornis in the Ryukyu Archipelago, southern Japan

Samples of the scleractinian coral Pocillopora damicornis were collected from six sites located around four islands in the Ryukyu Archipelago, southern Japan, and subjected to allozyme electrophoresis. Seven polymorphic loci were examined for their allelic patterns. The ratio of observed to expected genotypic diversity (0.30 < G _o :G _e  < 0.64), the ratio of the observed number of genotypes to the number of individuals (0.47 < N _g :N _i  < 0.75), and deviations from Hardy–Weinberg equilibrium indicated that asexual reproduction plays a major role in the maintenance of established populations. However, populations were not completely dominated by a single or a few clones, and most clones were represented by only a few individual samples. The high frequency of typhoons in the region suggests that, in P. damicornis, fragmentation caused through occasional exposure to powerful waves is a major mode of asexual reproduction, but asexual production of planulae may also be contributing to the maintenance of populations. A significant genetic differentiation (F ST) was found between the six populations examined (0.027 < F ST < 0.092, average F ST = 0.056). The moderate gene flow is discussed according to characteristics of the larval stage of the species, and to circulation patterns in the region. Received: 7 August 1998 / Accepted: 18 May 1999     

Population structure of the common sole (<Emphasis Type="Italic">Solea solea</Emphasis>) in the Northeastern Atlantic and the Mediterranean Sea: revisiting the divide with EPIC markers

Spatial and temporal population genetic structures of the common sole, Solea solea, were studied in Northeastern Atlantic and Mediterranean Sea populations, using three polymorphic exon-primed intron-crossing (EPIC) markers. Results demonstrated significant multilocus differentiation among Eastern Mediterranean and a group composed by Western Mediterranean and Atlantic populations (θ = 0.150, P < 0.001), but also suggested unrecorded genetic differentiation of the Adriatic Sea population. No pattern of isolation-by-distance was recorded across the range covered by sampling, from the Kattegat to the Aegean Sea. Conversely to genetically structured Mediterranean populations, Atlantic populations ranging from Denmark to Portugal could be considered as representative of the same panmictic unit (θ = 0.009, not significant). Results further demonstrated stability of multilocus genetic structure among temporarily replicated cohort samples [0+, 1+, subadults] from several coastal and estuarine locations from Bay of Biscay, excepted for the amylase locus Am2B3-2 at one location (Pertuis d’Antioche). Despite coherence of such observed patterns of multilocus differentiation with previous allozymic surveys in sole, and with patterns generally obtained for other marine fish species, single-locus results from EPICs indicated divergent coalescence schemes supporting a complex response to ecology and history of sole’s populations. Results stress the use of nuclear genes such as EPIC markers to investigate population structure, but also historical, demographic, and possibly selective processes in marine fishes.     

Genetic variation in seven goby species (Perciformes: Gobiidae) assessed by electrophoresis and taxonomic inference

Data on the electrophoretic patterns of 20 enzyme loci were used to investigate relationships among seven Mediterranean goby species. The study evidenced different levels of genetic variability among the species. On the whole, the degrees of genetic differentiation were consistent with the current taxonomic recognition of species and genera. Phenetic and phylogenetic analyses agreed in clustering the samples in three groups, i.e. the Gobius (including Zosterisessor ophiocephalus), the Lesueurigobius species and Pomatoschiarua minutus. The taxa analysed probably evolved following the complex geological and climatic events that have been affecting the Mediterranean basin ever since the Miocene. Received: 20 June 1998 / Accepted: 5 February 1999     

Genetic structure of the flounders Platichthys flesus and P. stellatus at different geographic scales

The genetic structure of the flounders Platichthys flesus L. and P. stellatus Pallas was investigated on different spatial scales through analysis of allozyme variation at 7 to 24 polymorphic loci in samples collected from different regions (Baltic Sea, North Sea, Brittany, Portugal, western Mediterranean, Adriatic Sea, Aegean Sea and Japan) in 1984 to 1987. No geographic variation was evident within a region. Some pattern of differentiation by distance was inferred within the Atlantic, while the Mediterranean comprised three geographically isolated populations and was itself geographically isolated from the Atlantic (fixed allele differences at up to three loci were found among P. flesus populations from the Atlantic, the western Mediterranean, the Adriatic Sea, the Aegean Sea and also P. stellatus from the coast of Japan). Sea temperature during the reproductive period probably acts as a barrier to gene flow between populations. Genetic distances among European flounder populations (P. flesus) were higher than, or of the same magnitude as, the genetic distance between Pacific (P. stellatus) and European flounder populations, suggesting that P. flesus is paraphyletic and/or there is no phylogenetic basis to recognising P. stellatus as a different species. The divergence between P. flesus and P. stellatus was thus inferred to be more recent than the divergence between the present P. flesus populations from the NE Atlantic and eastern Mediterranean. The eastern Mediterranean populations are thought to originate from the colonisation of the Mediterranean by a proto-P. flesus/P. stellatus ancestor, whereas the present western Mediterranean population has undergone a more recent colonisation event by P. flesus. Patterns of mitochondrial DNA variation, established on a smaller array of P. flesus samples, were in accordance with the geographic patterns inferred from the allozyme survey. In addition, they supported the hypothesis of a two-step colonisation of the western Mediterranean. These results contribute to our understanding of the biogeography of the Mediterranean marine fauna, especially the group of boreal remnants to which P. flesus belongs. Received: 7 February 1997 / Accepted: 26 March 1997     

Sequence divergence of mitochondrial DNA indicates cryptic biodiversity in Octopus vulgaris and supports the taxonomic distinctiveness of Octopus mimus (Cephalopoda: Octopodidae)

DNA sequence diversity of octopods was investigated using the mitochondrial cytochrome oxidase III gene (mtCOIII). DNA was obtained from ethanol- or formalin-fixed tissue of 15 specimens belonging to Octopus mimus Gould, 1852, Octopus vulgaris Cuvier, 1797 and Scaeurgus unicirrhus d'Orbigny, 1840, from coastal waters of the Mediterranean (France), the southwestern Atlantic (Brazil), the Caribbean (Costa Rica) and the southeastern/tropical Pacific (north Chile/Costa Rica). A 612 bp fragment of the mtCOIII gene was sequenced and aligned to the orthologous sequences available from northeastern Pacific Octopus species. Possible phylogenetic relationships were reconstructed. The mtCOIII gene tree revealed two main clusters, one comprised O. rubescens, O. dofleini and O. californicus, while the other included all O. vulgaris specimens, O. bimaculatus, O. bimaculoides and O. mimus. With one exception all South American haplotypes including O. bimaculatus and O. bimaculoides appeared as the sister group of the Mediterranean haplotype of O. vulgaris, indicating that most of the South American O. vulgaris specimens investigated would not belong to the recently redescribed species O. vulgaris restricted to the Mediterranean and eastern Atlantic. The treatment of O. mimus as a species distinct from Mediterranean O. vulgaris is supported by a high nucleotide divergence of 12.7%. Based on the mtCOIII gene tree the existence of cryptic species among O. vulgaris-like octopods is suggested. Received: 15 January 1999 / Accepted: 15 October 1999     

Genetic protein variation in red mullet (Mullus barbatus) and striped red mullet (M. surmuletus) populations from the Mediterranean Sea

Starch-gel electrophoresis of allozymes was used to differentiate the two red mullet species (Mullus barbatus L. and M. surmuletus L.) in the Mediterranean Sea and, further, to investigate the genetic stock structure of M. barbatus in the eastern Mediterranean area. Twenty putative enzyme-coding loci were examined in eight M. barbatus samples caught in the Aegean and Ionian Seas (Greece) and in the Gulf of Lion (France), and two M. surmuletus samples caught in the Aegean and Gulf of Lion. A high degree of genetic polymorphism was found in both species. Species-specific electrophoretic patterns were found in PGI* and PGM*. Estimates of variance of allele frequencies among samples (F _ST) and ² analyses both revealed significant differences (P < 0.05) among the M. barbatus samples. Most of the genetic variation was among samples regardless of region. The mean value of Nei's genetic distance between the two species was 0.329. Genetic distance among M. barbatus samples was low (maximum Nei's D = 0.012), with the sample from Platania differing most from other M. barbatus samples. This is probably be due to founder effects existing at this area. These results suggest that allozyme analysis may provide important information on the genetic structure of the red mullet to ensure sustainable management of this species. Received: 7 May 1997 / Accepted: 13 October 1997     

Genetic differentiation in Hediste diversicolor (Polychaeta: Nereididae) for the North Sea and the Baltic Sea

Genetic differentiation between North Sea and Baltic Sea Hediste diversicolor (O.F. Müller, 1776) (Polychaeta: Nereididae) populations was studied by allozyme electrophoresis on starch gel. Thirteen loci were analyzed in eight populations. The level of genetic variation was very low (mean H _o = 0.000 to 0.015). Differentiation between H. diversicolor populations is quite high (F _ST = 0.892) and reflected by three enzyme loci (MDH-I*, MDH-II*, IDH-I*). The reduced gene flow (N _m<1) may be explained by the limited dispersal capacity of the species. Regardless of whether found in the North Sea or Baltic Sea, there appear to be two different genetic types which are parapatric or sympatric in some places. The two types hybridize at three localities, but no signs of hybridization have been found at one (Tallinn). Received: 26 June 1997 / Accepted: 10 September 1997     

Is Syllis gracilis (Polychaeta: Syllidae) a species complex? An allozyme perspective

The genetic relationships between morphologically indistinguishable marine and brackish populations of Syllis gracilis Grube, 1840 (Polychaeta: Syllidae) were studied by means of allozyme electrophoresis. Samples of S. gracilis from marine coastal and brackish-water habitats were examined for variation at 13 presumptive loci. In addition, a sample of the closely related species S. prolifera (Krohn, 1852) was analysed. Five loci were multiallelic in at least one population of S. gracilis and eight loci in S. prolifera. Low to moderate levels of within-population genetic variability were found, with average expected heterozygosity values ranging from H = 0.068 (±0.043 SE) to 0.187 (±0.069 SE) in the populations of S. gracilis; higher values were found in S. prolifera (H = 0.325 ± 0.076). The presence of various private alleles indicated a marked genetic divergence among populations of S. gracilis, with Nei's genetic distances ranging from D = 0.000 to 0.833 and a highly significant F _ST value. Furthermore, evidence for strong genetic heterogeneity between two sympatric marine populations was found. UPGMA cluster analysis and multidimensional scaling pointed out a clear genetic divergence between brackish and marine populations. At least two genetically divergent entities occurred in marine and brackish habitats. This could be due to local adaptation of individuals coming from marine populations to brackish habitats, but more presumably to the occurrence of a species complex within S. gracilis. Received: 6 June 1999 / Accepted: 7 February 2000     

The amphipod Corophium multisetosum (Corophiidae) in Ria de Aveiro (NW Portugal). II. Abundance, biomass and production

 The abundance and biomass of Corophium multisetosum Stock, 1952 were determined from benthic corer samples collected monthly over 1 yr in the upper reaches of Canal de Mira (Ria de Aveiro, Portugal). Both density and biomass over the sampling period were negatively correlated with water temperature and positively correlated with chlorophyll a concentration in the sediment. C. multisetosum density was significantly negatively correlated with plant biomass and positively correlated with salinity. The nature of the sediment, favourable environmental conditions, high availability of food and low interspecific competition allowed the population to reach a maximal density of 200 × 10³ individuals m⁻² and a maximal biomass (ash-free dry wt, AFDW) of 62 g_AFDW m⁻². The population was highly productive, especially during the autumn/winter period. Production, estimated by two different methods (Hynes method: 251 g_AFDW m⁻² yr⁻¹; Morin–Bourassa method: 308 g_DW m⁻² yr⁻¹), was much higher than the values reported for other Corophium species. The annual P:Bˉ ratio (10) was high, but similar to values reported for Swedish populations of C. volutator and lower than the values estimated from Mediterranean populations of C. insidiosum. Received: 8 October 1999 / Accepted: 22 June 2000     

Larval bloom of the oviparous sponge Cliona viridis: coupling of larval abundance and adult distribution

 We performed an intensive year-round sampling with the aim of studying the abundance of sponge larvae in four Mediterranean benthic communities: photophilic algae, sciaphilous algae, semi-obscure (i.e. low light-intensity) caves and sandy bottoms. We record here for the first time, a larval bloom of Cliona viridis (Schmidt 1862), the most common excavating sponge in the Mediterranean, which took place simultaneously in several rocky communities of the Blanes sub-littoral (NE Spain), and discuss the role of restricted larval dispersal in the distribution of adult sponges. In the communities studied, C. viridis larvae bloomed synchronously once, in June. Spawning and consequent embryo development presumably occurred in May, when water temperature was 16 °C. The free larva is a small, evenly ciliated, weakly swimming parenchymella with low dispersal capabilities. The number of larvae m⁻³ and sponge abundance (as percent cover and biomass) were significantly higher in the community of sciaphilous algae than in the other communities studied. Because of limited larval dispersal, larval and adult abundance in the communities were positively correlated. Larvae developed into juvenile sponges 10 to 15 d after settlement. Settlers displayed distinctive features: a peripheral cuticle, vacuolar etching-like cells at the sponge base, absence of oscular chimneys, and the presence of zooxanthellae, which were presumably transmitted during oocyte maturation. Received: 24 January 2000 / Accepted: 4 July 2000