Demographic plasticity in tropical reef fishes

We use age-based analyses to demonstrate consistent differences in growth, mortality, and longevity of coral reef fishes from similar habitats (exposed reef crests) 20 km apart. On outer-shelf reef crests of the northern Great Barrier Reef (GBR), size in four taxa of reef fishes (Chlorurus sordidus, Scarus frenatus, and S. niger and the acanthurid Acanthurus lineatus) was systematically and significantly smaller when compared with the same taxa on adjacent mid-shelf reef crests. Differences in size could be attributed to differences in growth between habitats (shelf positions). On outer reef crests the species examined had consistently lower size at age profiles and also reduced life spans compared with populations from mid-shelf reefs. To confirm this relationship, two of the most abundant species (C. sordidus and S. frenatus) were selected for more detailed spatial analysis of demographic patterns. Sampling adults of both taxa from reef crests on three mid- and three outer-shelf reefs revealed that most of the variation in growth was explained by shelf position, although C. sordidus also displayed differences in growth among mid-shelf reefs. We conclude that differences in body sizes across the continental shelf of the northern GBR are primarily determined by these trends in growth. Strong spatial patterns also existed in the mean ages of populations and longevity estimates for C. sordidus and S. frenatus between shelf positions. Both species on outer-shelf reefs displayed less variable cohort sizes, significantly reduced mean ages, and foreshortened longevity compared with populations on mid-shelf reefs. Furthermore, differences in these parameters were rare among replicate reefs within mid- and outer-continental-shelf positions. Age-based catch curves suggested that rates of S. frenatus natural mortality on the outer shelf were nearly twice as high as on the mid shelf. Visual surveys indicated that total scarid densities on outer-shelf reef crests are on average fourfold higher than for equivalent mid-shelf habitats. This fact, coupled with significantly reduced growth rates, reduced mean ages, and increased mortality rates, suggests that density-dependent processes may be responsible for observed differences among localities.     

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     

Mitochondrial DNA analysis of the genetic relationships among populations of scad mackerel (Decapterus macarellus, D. macrosoma, and D. russelli) in South-East Asia

The genetic relationships among South-East Asian populations of the scad mackerels Decapterus macarellus, D. macrosoma and D. russelli (Pisces: Carangidae) were investigated. In 1995 and 1996, 216 fish were sampled in seven localities spanning the seas of Indonesia and were examined for restriction-site polymorphisms using ten restriction enzymes for the mitochondrial (mt) DNA control region, amplified by the polymerase chain-reaction. The inferred phylogeny of haplotypes led to the recognition of three distinct mitochondrial lineages or phylads consistent with the distinctions of current taxonomy. All 15 mtDNA haplotypes found in D. macarellus and all 9 haplotypes found in D. macrosoma were arranged as star-like clusters, suggesting recent evolutionary history. In contrast, the phylad formed by 6 haplotypes in D. russelli from the Sulawesi Sea exhibited diffuse topology, suggesting that ancestral lineages of this species have been retained to the present. Average nucleotide-divergence estimates between haplotypes of different phylads were between 0.042 and 0.135, suggesting ancient separation, in consistency with published allozyme data. High levels of haplotype diversity, but no geographical heterogeneity, was detected within D. macarellus from the Molucca Sea and the Banda Sea. Populations of D. macrosoma exhibited both significant differences between adjacent regions (Sunda Strait and Java Sea), and broadscale genetic homogeneity from the South China Sea to the Sulawesi Sea via the Java Sea and Makassar Strait. The geographic isolation of the D. macrosoma population sampled in the Sunda Strait suggests that this region constitute a sharp transition zone between the Indian Ocean and the Sunda Shelf. Near-monomorphism of haplotypes and low nucleotide diversity (d _X) were observed in the samples of D. macrosoma from the continental shelf (haplotype-diversity estimates, h, = 0.00 to 0.25 ± 0.08 and d _X = 0.000 to 0.002). This was in contrast to the comparatively high haplotype and nucleotide diversities observed in other pelagic fish species including D. macarellus (h = 0.82 ± 0.05, d _X = 0.012 to 0.015) and D. russelli (h = 0.63 ± 0.12, d _X = 0.016), and in the oceanic D. macrosoma population sampled in the Sunda Strait (h = 0.67 ± 0.31, d _X = 0.005). We hypothesise that this may be the consequence of recent and perhaps repeated bottleneck events that have affected the D. macrosoma population sampled on the continental shelf. Received: 29 September 1997 / Accepted: 3 September 1999     

Phylogeography of the ocean quahog (Arctica islandica): influences of paleoclimate on genetic diversity and species range

The ocean quahog, Arctica islandica (Linnaeus, 1767), is a commercially important bivalve found on continental shelves throughout much of the North Atlantic. To assess genetic subdivision in this species, we sequenced 385 nucleotides of the mitochondrial cytochrome b (cyt b) gene from 83 specimens collected from 12 localities between September 1998 and July 1999 (based on preliminary data, the Internal Transcribed Spacers, ITS, of the nuclear ribosomal repeat were not useful). The cyt b data delimited 11 haplotypes with 0.26 to 8.1% nucleotide difference (coded by 36 variable nucleotide positions) among them. Only three haplotypes were detected in 39 specimens collected along the USA coastline, compared to five haplotypes from nine Icelandic individuals. The western Atlantic populations ranging from Penobscot Bay (Maine, USA) to southern Virginia showed relatively low diversity and appeared genetically similar in that region. Based on the presence of shared haplotypes, AMOVA analyses, and phylogenetic reconstructions, Icelandic populations appear to be more genetically similar to western Atlantic populations than eastern Atlantic populations. Specimens from the Faroe Islands (n=4) show mixed affinities. These data are consistent with the hypothesis that a warm Holocene climatic optimum (ca. 7,500 years BP), and not glacial refugia, shaped the present-day genetic structure in A. islandica. Received: 18 January 2000 / Accepted: 26 June 2000     

Genetic relationships of the colour morphs of Acanthochromis polyacanthus (Pomacentridae) on the northern Great Barrier Reef

Acanthochromis polyacanthus is an unusual tropical damselfish because it lacks pelagic larvae and has lost the capacity for broad-scale dispersal among coral reefs. On the modern Great Barrier Reef, this fish has multiple colour morphs and we have previously described steep genetic clines in the central region between three colour morphs. A similar transition of colour morphs has been found in the far northern region (Latitude 11°S), where at least five colour morphs and intergrading hybrids were found during a survey of 14 locations on nine adjacent reefs. On two of these reefs, monochromatic white and bicoloured morphs coexist, partitioning the reef slope vertically when sympatric, but occupying the full depth range elsewhere. In areas of overlap, they interbreed, producing hybrids of intermediate colour. Although the discriminatory power of our genetic analysis was weakened by the low level of variability in these populations (only four polymorphic loci), allozyme electrophoresis revealed significant genetic differentiation within and among reefs. There was neither simple linkage between colour and protein variation, nor correlation between genetic similarity and proximity of sampled populations. We suggest that the observed chaotic structure is the result of differences among the founding populations, although the two colour-based stocks have been homogenized through a long history of introgression during multiple episodes of isolation and secondary contact. Despite genetic mixing, phenotypic diversity (i.e. colour morphs) seems to have been preserved in these populations by sexual selection, perhaps reinforced by natural selection. The long-term stability of this outcome, however, is suggested by the presence of unique morphs on two reefs that are detached from the continental shelf and surrounded by very deep water. The strong identity of these populations can be attributed to long occupation of these isolated sites compared with those on the continental shelf which have only been established in the last 15 000 yr and still retain differences arising from the initial founder events. Received: 15 January 1997 / Accepted: 15 August 1997     

Low-temperature adaptation of deep-sea bacteria isolated from the Japan Trench

Montastraea annularis, M. faveolata, and M.␣franksi are three recently separated species that together dominate reefs of the tropical western Atlantic. Despite morphological, life-history, ecological and genetic differences, the legitimacy of their status as separate species has been questioned. This controversy stems from both the scarcity of unambiguous, diagnostic differences among them, and from the possibility of extensive hybridization associated with their approximately synchronous reproduction in sympatry. Here we report on fertilization trials and the timing of spawning, both of which suggest that the potential for hybridization may be limited. Crosses between M. faveolata (the most genetically distinctive taxon) and the other two species were largely unsuccessful, as were selfed matings for all three species. M. annularis and M. franksi showed no evidence of fertilization barriers, but the timing of spawning typically differed between them by 1 to 2 h. We also found that spawning times in the field of M. annularis and M. faveolata were non-overlapping in 1995, and that the timing of spawning in M. annularis could be experimentally shifted forward by simulating earlier than natural sunsets. These findings from Panamá and Honduras, particularly given their consistency with comparable observations and experiments elsewhere, provide evidence of reproductive isolation and support the separate species status of these three taxa. Some hybridization may occur under natural conditions at these sites, particularly between M. annularis and M.␣franksi. Rampant genetic interchange among these taxa in Central America seems unlikely, however, in the light of the concordant associations between morphology, reproductive biology and other characters which are observed. Received: 22 July 1996 / Accepted: 2 October 1996     

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.     

Genetic relationships within and between clonal and solitary forms of the sea anemone Anthopleura elegantissima revisited: evidence for the existence of two species

Along the temperate Pacific coast of North America, the actiniarian sea anemone Anthopleura elegantissima exhibits two discrete life-history phenotypes. Although both forms sexually produce planula larvae, the clonal morph can also asexually propagate by fission, whereas the solitary morph does not. Whether the two forms constitute one or two species has long been contested. Hand originally designated the two forms as conspecifics, whereas Francis – on the basis of differences in microhabitat, biogeographic range and phenotypic frequencies – argued that the two forms constituted a sibling-species pair. From the results of an electrophoretic survey in which they pooled allelic frequencies across several geographic locations, Smith and Potts subsequently argued that the two forms were not genetically differentiated, and therefore represented a single species. We re-examined the relationship between the forms electrophoretically, substantially extending the geographic range and doubling the sample sizes beyond those used by Smith and Potts, and not pooling allelic frequencies in our analyses. Our analysis of patterns of genetic variation at ten highly polymorphic allozyme loci shows that although no fixed genetic differences distinguish the two forms, there are significant differences in allele frequencies between clonal and solitary A.␣elegantissima at every site we sampled throughout their range of sympatry (over 1000 km); within each form, however, there is little detectable genetic differentiation among populations. We therefore conclude that the two forms represent recently reproductively isolated taxa, and propose that the clonal form retain the binomial A. elegantissima (Brandt, 1835), whereas the solitary form be described and named a new species, Anthopleura sp. Received: 28 August 1996 / Accepted: 25 September 1996     

Protection of Genetic Diversity and Maintenance of Connectivity among Reef Corals within Marine Protected Areas

Abstract: High‐latitude coral reefs (HLRs) are potentially vulnerable marine ecosystems facing well‐documented threats to tropical reefs and exposure to suboptimal temperatures and insolation. In addition, because of their geographic isolation, HLRs may have poor or erratic larval connections to tropical reefs and a reduced genetic diversity and capacity to respond to environmental change. On Australia's east coast, a system of marine protected areas (MPAs) has been established with the aim of conserving HLRs in part by providing sources of colonizing larvae. To examine the effectiveness of existing MPAs as networks for dispersal, we compared genetic diversity within and among the HLRs in MPAs and between these HLRs and tropical reefs on the southern Great Barrier Reef (GBR). The 2 coral species best represented on Australian HLRs (the brooding Pocillopora damicornis and the broadcast‐spawning Goniastrea australensis) exhibited sharply contrasting patterns of diversity and connectedness. For P. damicornis, the 8‐locus genetic and genotypic diversity declined dramatically with increasing latitude (N_a= 3.6–1.2, H_e= 0.3–0.03, N_g:N = 0.87–0.06), although population structure was consistent with recruitment derived largely from sexual reproduction (G_o:G_e= 1.28–0.55). Genetic differentiation was high among the HLRs (F_ST[SD]= 0.32 [0.08], p < 0.05) and between the GBR and the HLRs (F_ST= 0.24 [0.06], p < 0.05), which indicates these temperate populations are effectively closed. In contrast for G. australensis, 9‐locus genetic diversity was more consistent across reefs (N_a= 4.2–3.9, H_e= 0.3–0.26, N_g:N = 1–0.61), and there was no differentiation among regions (F_ST= 0.00 [0.004], p > 0.05), which implies the HLRs and the southern GBR are strongly interconnected. Our results demonstrate that although the current MPAs appear to capture most of the genetic diversity present within the HLR systems for these 2 species, their sharply contrasting patterns of connectivity indicate some taxa, such as P. damicornis, will be more vulnerable than others, and this disparity will provide challenges for future management.     

Variability in reproductive output across a water quality gradient for a tropical marine sponge

To establish a complete understanding of reproductive variability, larval supply and ultimately population demographics of a species it is important to determine reproduction across a broad spectrum of environmental conditions. This study quantified sexual reproduction of the brooding, gonochoristic sponge Rhopaloeides odorabile from populations across the shelf reefs of the central Great Barrier Reef (GBR). Histological sections of reproductive sponges collected at increasing distances from the coast were used to determine if numbers of reproductive sponges, reproductive output (using a reproductive output index), size at sexual maturity, and sex ratios varied according to their location (distance) from the coastline and therefore from influences of terrigenous/riverine discharge. Significantly higher proportions of reproductive sponges occurred with increasing distance from the coast. The proportion of all reproductive sponges (both male and female) on offshore reefs ranged from 77 to 90%, during November and December, the peak reproductive months of this sponge, compared to 47 to 50% for sponges occurring on coastal reefs. Levels of female reproduction increased with increasing distance from the coastline on two levels. First, oocytes from offshore sponges were significantly larger than oocytes from coastal sponges. Second, sponges from offshore reefs showed a reproductive index (proportions of oocytes, embryos and larvae mm⁻²) approximately 15 times higher than coastal reef sponges. Therefore, both numbers of oocytes, embryos and larvae in conjunction with larger oocytes contribute to a higher reproductive output index for offshore sponges. The production of spermatic cysts in males was consistent across the GBR. Sex ratios for coastal reef sponges showed a male bias while offshore sponges showed approximate equal sex ratios. The effect of terrigenous riverine input from coastal fluvial plains to the inner GBR is well established and is likely to contribute to the lower levels of reproduction associated with female sponges inhabiting coastal reefs of the central GBR.     

Are mangroves and seagrasses sources of organic carbon for penaeid prawns in a tropical Australian estuary? A multiple stable-isotope study

The vertical distribution of the larvae of shelf-dwelling fish species that spawn in the NW Mediterranean Sea in spring was studied in relation to environmental data. Two sampling cycles were carried out at fixed stations on the continental shelf in May and June 1992. Three patterns of larval vertical distribution for the various taxa represented in the samples were observed. The larvae of most species (e.g. Boops boops, Diplodus sargus) were mainly located in the surface layer (10 m), others (e.g. Arnoglossus sp.) had broader distributions in the upper 40 m of the water column, and but a few (e.g. Gobiidae) were present in large concentrations at greater depths. The vertical distribution patterns of the various species showed no variations, despite high hydrographic variability during the study. The vertical distribution of only a few species (e.g. Arnoglossus sp., Crystallogobius linearis and Engraulis encrasicolus) varied over the diel cycle. The possible influence of the vertical distribution of fish larvae on their horizontal distribution patterns is discussed. Received: 10 March 1997 / Accepted: 4 April 1997     

Phylogeographic structure of false clownfish, Amphiprion ocellaris, explained by sea level changes on the Sunda shelf

The phylogenetic structure of the anemonefish Amphiprion ocellaris was established based on sequence data generated for the 5′ end of the cytochrome b (cytb) gene at 11 sites throughout Southeast Asia. Considerable genetic structuring was observed throughout the range of A. ocellaris. The region has a complex geography, with the Sunda shelf having been exposed during the lower sea levels associated with periods of glaciation. The direction of subsequent flooding of the Sunda shelf, as a direct consequence of the retreating glacial sheets, can be predicted based on the major river drainage systems in the region. Much of the phylogeographic structure, including levels of intra-site genetic variation, can be explained in terms of the “seeding” of sites on the Sunda shelf, by those on the shelf rim, as sea levels rose. We often found surface ocean currents in the region, which should influence larval dispersal, to be poorly correlated with phylogeographic structure. Several geographically close sites, which appear to be connected by surface currents, showed significant genetic stratification. We hypothesise that the phylogeographic structure of A. ocellaris is more reminiscent of the Pleistocene sea level changes than surface currents. The high contribution of sea level changes to the phylogeographic structure was also supported by several missing haplotypes in the generated spanning network. Cytb DNA sequences generated for recently recruited A. ocellaris individuals sampled from Singapore indicate that, on a local scale, there is a directional inflow of recruits, which is dependent on the monsoon seasons. The nature of dispersal and genetic structure of reef fish species found on the Sunda shelf is clearly complex, and should take into consideration past phylogeographic events. Received: 13 November 1999 / Accepted: 12 July 2000     

Effects of kinship on growth of a live-bearing reef fish

The influence of genetic relatedness on the individual performance (e.g. growth, development) of animals is often tied to agonistic or cooperative behaviors among conspecifics, and studies of the effects of kinship have produced mixed results. To explore genetic relatedness independent of these behaviors, we investigated the effects of kinship on the growth of the kelp perch Brachyistius frenatus, a live-bearing, planktivorous marine reef fish that is capable of only limited dispersal. Although juveniles occur in aggregations and compete for food resources, they do not exhibit overt aggressive or cooperative behavioral interactions. We hypothesized that under competition and in the absence of these behaviors, sibling and non-sibling groups of juvenile B. frenatus raised at the same densities in the field would not differ in average growth, but that siblings would exhibit lower variation in growth, simply due to genetic similarities in inherent growth rates. Pregnant, female kelp perch were collected and placed in cages until parturition was complete. Groups of young, recently born from the same mother or from different mothers, were then raised in the field for 9 wk. Our results revealed that average growth rates were similar between sibling and non-sibling treatments. While variation in growth increased initially in non-siblings, siblings showed little such variation. This divergence, however, was not consistent over the duration of the experiment, and variation in the growth of siblings ultimately converged with that of non-siblings. Effects of genetic relatedness would be most likely to manifest themselves early after birth, before environmental factors exert their influence, and this may explain the initial separation but eventual convergence in variation in growth between sibling and non-sibling treatments. For B. frenatus and other organisms that will encounter relatives and compete for resources without overt behavioral interactions, the degree of kinship may play a minor role in the demography of local populations. Received: 26 January 1998 / Accepted: 30 September 1998     

Morphological and fluorescence analysis of the Montastraea annularis species complex in Florida

The taxonomic status of the Montastraea annularis species complex is unclear. Much evidence has been accumulated to support the separation into 3 species, but the presence of intermediate morphotypes and the apparent lack of effective reproductive barriers in some areas are yet unexplained. Several authors have made a call for the introduction of new traits that can be used to resolve differences among closely related coral species. We collected skeletal and tissue samples from corals within the M. annularis species complex (15 each of M. annularis, M. faveolata, and M. franksi) and 10 morphological intermediates from several reefs in the Florida Keys. Multivariate analysis of corallite skeletal measurements supported the separation of the species complex into three taxa. We detected two main fluorescence emission peaks at 480 nm (turquoise) and 515 nm (green) that were not distributed equally among the three species. Every M. annularis colony had a major turquoise fluorescence peak. Some had a weak green secondary fluorescence peak. Colonies of M. faveolata and M. franksi had either the green or turquoise fluorescence peak, but at significantly different frequencies. The intermediate morphotypes proved to be highly heterogeneous with respect to both micromorphology and fluorescence, and their nature could not be fully explained. We were not able to separate the three species using fluorescence characters alone, however this new trait does increase our understanding of the taxonomic structure within the M. annularis species complex. Received: 21 January 2000 / Accepted: 1 September 2000     

Genetic structure across the GBR: evidence from short-lived gobies

The Great Barrier Reef (GBR) exhibits distinct cross-shelf zonation. These patterns are particularly well documented in reef fishes and have been attributed to either environmental gradients (e.g. wave energy, oceanography) or barriers to gene flow. This study examined the extent to which barriers to gene flow contribute to cross-shelf patterns by examining the mitochondrial DNA of gobies (genus Eviota). The genus Eviota was selected due to its extreme life history characteristics (shortest vertebrate lifespan) and cross-shelf distribution patterns (E. queenslandica, inner- and mid-shelf, and E. albolineata mid- and outer-shelf). Although cross-shelf barriers to gene flow were predicted, this study found no population structure between shelf locations. However, a genetically distinct population of E. queenslandica (the inner-shelf species) was observed at North Direction Island (Phi_st = 0.088, P = 0.004). As no comparable structure was observed in E. albolineata (the outer-shelf species) it may be that habitat type (E. queenslandica = reef lagoon, E. albolineata = reef crest) is a significant factor driving the structure observed in E. queenslandica. Larval behaviour, olfactory or auditory senses and reef selection at settlement could be assisting larvae to return to reefs similar to natal reefs. We suggest that ecological gradients are more important than barriers to gene flow in structuring cross-shelf distributions within Eviota.     

Relationship between depth, sediment, latitude, and the structure of benthic infaunal assemblages on the mainland shelf of southern California

A regional benthic survey was conducted in 1994, and the data were used to assess the relationship among three habitat factors (depth, sediment grain size, and latitude) and the distribution of benthic infaunal assemblages on the southern California coastal shelf. Benthic samples were collected with a 0.1 m² Van Veen grab from 251 sites on the continental shelf (10–200 m deep) from Point Conception, California, to the United States–Mexico international border. The relationship between habitat and assemblages was investigated by conducting a Q-mode cluster analysis to define groups of stations with similar species composition and then examining whether differences were present in physical habitat attributes among those groups of stations. Analysis of data from 175 uncontaminated sites yielded four habitat-related benthic infaunal assemblages along the southern California coastal shelf: a shallow-water assemblage from 10–32 m, a mid-depth assemblage between 32 and 115 m, and two deep-water (115–200 m) assemblages, one in fine and one in coarse sediments. These empirically defined points in the depth and sediment grain size gradients can be used to define reference habitats for the development of biocriteria. Benthic abundance and diversity were greatest in the mid-depth assemblage, conforming to predictions for benthic assemblages in regions of upwelling. Within the 500 km of coastline examined, latitude was not an important factor in defining assemblages. Received: 3 December 1999 / Accepted: 9 October 2000     

Megabenthic decapod crustacean assemblages on the Galician continental shelf and upper slope (north-west Spain)

The structure of megabenthic decapod crustacean assemblages on the Galician (north-west Spain) continental shelf (100 to 200 depth) and upper slope (200 to 500 m) was analyzed based on surveys carried out in autumn and spring, from 1980 to 1987. Forty species belonging to 19 families were caught. The portunid crab Polybius henslowii, a species with pelagic phases, was the most abundant species, but displayed strong spatial and temporal fluctuations. Other dominant species were the Norway lobster Nephrops norvegicus, the portunid Liocarcinus depurator, the galatheids Munida intermedia and M. sarsi, and the shrimps Solenocera membranacea, Plesionika heterocarpus, Pasiphaea sivado and Dichelopandalus bonnieri. Total abundance and biomass (average values excluding Polybius henslowii = 255 individuals and 2.06 kg/30 min tow) and species richness and diversity, H′ (6.85 species and H′ = 1.45 per tow) displayed a significant positive correlation with depth, and strong interannual fluctuations. The factors determining community organization were depth and, to a lesser extent, spatial structure. There was clear evidence of bathymetric zonation, differentiating between species characteristic of the slope (D. bonnieri and Pasiphaea sivado), shelf-slope edge (Macropipus tuberculatus, Pontophilus spinosus, Munida sarsi, S. membranacea, Processa spp.) and shelf (L. depurator, Macropodia tenuirostris, Paguridae and Chlorotocus crassicornis). The spatial zonation was related to changes in oceanography and sediment along the continental margin. Goneplax rhomboides, N. norvegicus, C. crassicornis and Alpheus glaber are benthic species which generally exhibit burrowing behaviour, and they were found mainly in the southern area where there are fine sediments due to the outwelling from the Rías Baixas. Different benthopelagic shrimps (Pontophilus spinosus, Plesionika heterocarpus,Processa spp. and Pasiphaea sivado) were typical of the zone just north of Fisterra, characterized by a convergence of water masses bringing about an increase in productivity due to upwelling. The benthic anomuran and brachyuran crabs Munida intermedia, M.␣sarsi, L.␣depurator and Macropipus tuberculatus were characteristic of the northwestern zone between Fisterra and Estaca, where the infauna reaches high biomass despite coarser sediments with a lower concentration of organic material than in the southern area. Lastly, both the Paguridae and Macropodia tenuirostris were species typically found in the waters in the northern shelf. Based on interannual changes in assemblage structure, two periods could be distinguished: between 1980 and 1984, when Polybius henslowii, D. bonnieri and Pasiphaea sivado had abundance peaks; and another period from 1985 to 1987 when L. depurator, Munida intermedia, M.␣sarsi and Macropipus tuberculatus increased in abundance. Received: 21 May 1996 / Accepted: 9 August 1996     

Distribution and diversity of mtDNA lineages among southern right whales (Eubalaena australis) from Australia and New Zealand

Using a biopsy dart system, samples of skin tissue were collected from southern right whales (Eubalaena australis) in 1995 on two wintering grounds, southwest Australia (n = 20) and the Auckland Islands of New Zealand (n = 20); and on offshore feeding grounds at Latitudes 40 to 43°, south of Western Australia (n = 5). A variable section of the mitochondrial DNA control-region (289 nucleotides) was amplified and sequenced from these 45 individuals (21 males, 20 females and 4 of unknown sex), distinguishing a total of seven unique sequences (i.e. mtDNA haplotypes). Two haplotypes were found on both wintering grounds (including a common type representing 45% of each sample), and five types were unique to only one wintering ground. An analysis of variance adapted for molecular information revealed significant genetic differentiation between the two wintering grounds (p = 0.017). The feeding-ground sample was too small for statistical comparison with the wintering grounds, but included two haplotypes found only in the Auckland Islands as well as the common haplotype found on both wintering grounds. The nucleotide diversity and differentiation of mtDNA among the right whales was similar to that among humpback whales (Megaptera novaeangliae) from the same regions (Baker et al. 1998), but haplotype diversity was significantly reduced, perhaps as a result of more intensive hunting during the last century and continued illegal hunting during this century. Received: 16 March 1998 / Accepted: 18 December 1998     

Does the composition of the demersal fish assemblages in temperate coastal waters change with depth and undergo consistent seasonal changes?

The aim of this study was to determine whether the composition of the demersal fish fauna in coastal marine waters in temperate Australia changes markedly with increasing water depth and distance from the shore and whether the composition of the fish fauna in water depths of 5 to 35 m undergoes cyclic, seasonal changes. Samples of demersal fishes were therefore collected by trawling over the predominantly sandy substrate at nine sites located in water depths of 5 to 15 m or 20 to 35 m and within 20 km of the shore in four regions along ∼200 km on the lower west coast of Australia. The sampling regime involved trawling for fishes at each site at night in seven consecutive seasons between the summer of 1990/1991 and winter of 1992. A total of 72 435 fishes, representing 77 families, 143 genera and 172 species was caught. The compositions of the fish faunas in offshore waters with depths of 5 to 35 m were shown to differ markedly from those previously recorded for nearshore marine waters in the same regions. However, as some species, such as Sillago burrus, S. vittata, S. bassensis and Rhabdosargus sarba, increase in size, they move out from their nursery areas in nearshore waters into deeper and more offshore waters, where spawning occurs. Ordination showed that, in each of the four regions, the composition of the fish fauna in depths of 5 to 15 m differs from that in depths of 20 to 35 m. This difference is attributable to the fact that some species, such as  S. burrus, S. vittata and Upeneichthys lineatus, are far more abundant in depths of 5 to 15 m, whereas other species, such as S. robusta, U. stotti and Lepidotrigla modesta, occur predominantly in depths of 20 to 35 m. However, the samples collected from the single site that was inshore but in deeper water demonstrate that the composition of the fish fauna is influenced by distance from shore as well as by water depth. The compositions of the fish faunas differed with latitude, largely due to the fact that some subtropical species, such as Polyspina piosae, S. burrus and  S. robusta, did not extend down into the more southern regions. Ordination also showed that the composition of the fish faunas at all but one of the nine sites underwent pronounced and consistent cyclic, seasonal changes. This seasonal cyclicity at the different sites was attributable to sequential patterns of immigrations and emigrations by a number of fish species during the course of the year. These seasonal migrations involved, inter alia (1) movements of certain species from their nursery areas into these deeper waters, e.g.  S. bassensis and Scobinichthys granulatus; (2) migrations into and off the sandy areas of the inner continental shelf, e.g. Arnoglossus muelleri; (3) migrations to spawning areas, e.g. Sillago robusta; and (4) movements into areas where detached macrophytes accumulate in winter, e.g. Cnidoglanis macrocephalus and Apogon rueppellii. Received: 21 August 1998 / Accepted: 9 February 1999     

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