Distribution of final stage phyllosoma larvae and free-swimming pueruli of Panulirus japonicus around the Kuroshio Current off southern Kyusyu, Japan

The distribution of the phyllosoma larvae and free-swimming pueruli of the Japanese spiny lobster Panulirus japonicus (von Siebold, 1824) has been studied off the south coast of Kyusyu Island. From 1992 to 1995, four research cruises were conducted on board the R.V. “Yoko-maru”. Cruises were mainly carried out over the new moon period between June and August along transect lines that cross the Kuroshio Current. In total, 89 later stage Form F phyllosoma (body lengths ≥20 mm) and 43 free-swimming pueruli of P. japonicus were caught; 94.4% of the later stage phyllosoma larvae were in the final stage. The phyllosoma were distributed widely in and south of the Kuroshio Current, where high-salinity (34.8) water exists at depths below about 80 m. Highest densities of the final phyllosoma larvae were observed in or near the  Kuroshio Current, and molting to the puerulus stage also occurred in the same area. Free-swimming pueruli were mainly sampled in and north of the Current. It is suggested that the pueruli of P. japonicus swim across the Kuroshio Current to settle in coastal areas. Received: 9 December 1996 / Accepted: 25 September 1998     

Variation in concentrations of trace elements in otoliths and eye lenses of a temperate reef fish, Parma microlepis, as a function of depth, spatial scale, and age

 Territorial Parma microlepis (Günther) (Pomacentridae) were collected at different depths, at three sites in each of four estuaries near Sydney, Australia. Element concentrations were measured by induc- tively-coupled–plasma mass spectrometry. Significant differences in concentrations of Mn and Ba were found in the otoliths of fish sampled in different depth strata, with concentrations generally greatest in fish found in water <4 m deep. Depth-related differences varied among estuaries (e.g. 0 to 1.2 μg Ba g⁻¹ otolith). In most estuaries there was a negative linear relationship between concentrations of Mn and Ba in otoliths and actual depth. Great variation was found within an estuary among sites separated by 0.5 to 3 km. In the eye lenses, concentrations of Rb differed according to depth of capture of fish. The age of fish (1+ to 34 yr) had no influence on the concentrations of elements in otoliths or lenses. Multivariate comparisons of elemental composition (= fingerprints) detected significant differences among depth strata. Fish collected from shallow water had the clearest multivariate classification according to depth. There was a close match between our shallow strata and the average depths reached by low-salinity/high-temperature estuarine plumes. The element composition of whole otoliths and lenses represents average concentrations experienced by the fish. The temporal resolution of differences in ambient conditions is likely to be coarse in the fish (i.e. months to years). Received: 9 April 1999 / Accepted: 29 February 2000     

Identification of settling and early postlarval stages of mussels (Mytilus spp.) from the Pacific coast of North America, using prodissoconch morphology and genomic DNA

 Detailed inventories of the benthos and field studies of the settlement and recruitment processes of marine benthic invertebrates require accurate identification of newly settled larvae and early juvenile stages. We provide morphological criteria, visible under a good quality dissecting stereomicroscope, by which to discriminate between species of the settling larval and early postlarval stages (∼250 to 700 μm shell length) of mussels of the genus Mytilus on the west coast of Vancouver Island and Southern California. Compared to the bay mussel (M. trossulus), the sea mussel (M. californianus) has: (i) a shallower and flatter umbo, the latter corresponding to a significantly less pronounced prodissoconch I (PI) curvature and (ii) a greater PI length; as well as (iii) a wider separation between the provincular lateral teeth (PLT). The PLT distance is a new term denoting the separation between the midpoint of two reddish pigment spots of the provinculum (larval hinge apparatus) region of settling larvae and early postlarvae of Mytilus spp. from the East Pacific Coast. These spots mark the larger provincular lateral teeth, situated at either end of the provinculum. We confirmed the validity of morphological criteria by comparing PCR products of genomic DNA of provisionally identified postlarvae. Furthermore, measurements of PI lengths and PLT distance from well-preserved postlarvae of sea mussels (M. californianus) and of bay mussels (M. galloprovincialis) from Southern California indicate that the PI morphology and morphometry, and PLT distance criterion apply for that region as well. The criteria presented here can also apply to the advanced (competent) veliger stages, as the latter may settle (i.e. become the “settling” stage) upon encountering a suitable substrate. Our present and previously published work provide economical and effective identification methods that can be used to discriminate among early life history stages (∼250 μm to 5.0 mm shell length) of Mytilus spp. along the west coast of North America. Received: 10 November 1999 / Accepted: 6 September 2000     

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 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     

Reproductive dynamics of endeavour prawns, Metapenaeus endeavouri and M. ensis, in Albatross Bay, Gulf of Carpentaria, Australia

 The spawning patterns of two penaeid prawns, Metapenaeus endeavouri (Schmitt) and M. ensis (De Haan), were examined from data collected at 45 stations between March 1986 and March 1992. An index of population fecundity based on the abundance, proportion and fecundity of sexually mature females was used as a measure of spawning output of the prawn stock. The population fecundity index for M. ensis was higher than that for M. endeavouri. The monthly population fecundity index for M. endeavouri varied markedly among years, while that for M. ensis was consistent among years. Spawning of M. endeavouri occurred year-round, while that of M. ensis was concentrated mainly in spring (September to November). For M. endeavouri, a minor spawning, derived from a relatively small number of summer spawners, occurred in the 20 to 30 m offshore waters in summer. In early summer (after May), the major spawning group consisted of large females from the winter-spawning cohort, and the spawning area shifted to depths of 30 to 60 m. In winter (July), the major spawning, derived from the winter-spawning cohort, occurred at depths of 20 to 40 m. For M. ensis, the major spawning, derived from the spring-spawning cohort, was observed in depths <50 m and was concentrated particularly in inshore waters (<20 m) in spring. In autumn, the spawning output was mainly from the autumn-spawning cohort, which comprised but a small number of individuals. In winter, the major spawning group again consisted of the large females from the spring-spawning cohort, and spawning increased in the oceanic waters (>50 m). These results suggest that mature female M. endeavouri and M. ensis move offshore (>40 m) by May and July, respectively, and return to shallow waters (<35 m) in July and November, respectively. The monthly reproduction patterns of both species in the “effective spawning” area showed that the major spawning season for M. endeavouri is August to October and that for M. ensis is September to December. Received: 19 February 1999 / Accepted: 18 June 2000     

Why do snakes have eyes? The (non-)effect of blindness in island tiger snakes (Notechis scutatus)

Large (to >1 m), diurnally active tiger snakes (Notechis scutatus) are abundant on Carnac Island, near the coast of Western Australia. Our behavioural and mark-recapture studies provide the first ecological data on this population, and reveal a surprising phenomenon. Many adult tiger snakes have had their eyes destroyed, apparently during nest defence, by silver gulls (Larus novaehollandiae). This loss of vision did not reduce the snakes' body condition (mass relative to length), or their rates of growth or survival (measured over a 12-month period). Blind male snakes trail-followed females, and mated successfully. Thus, destruction of a major sensory modality had no detectable effect on these predators. This result is strongly counter-intuitive, but mirrors an earlier report of congenital blindness (without ill-effects) in American viperid snakes. Similarities between the two systems (island populations, highly venomous snakes, reliance on sessile prey) clarify the circumstances under which the loss of vision does not reduce an organism's viability. These natural experiments support Gans' hypothesis of “momentarily excessive construction” in that the snakes possess a complex organ system that they do not actually require for successful feeding, survival or reproduction. Received: 30 November 1998 / Received in revised form: 24 April 1999 / Accepted: 9 May 1999     

Relationships between diet and body size, mouth morphology, habitat and movements of six sillaginid species in coastal waters: implications for resource partitioning

The dietary compositions and breadths of sequential 50 mm size classes of the six whiting species found in nearshore (<1.5 m), shallow inner-shelf (5 to 15 m) and/or deep inner-shelf (20 to 35 m) waters of the lower west coast of Australia were determined. Comparisons between the results of principal components analysis of head and mouth dimensions and the dietary compositions of Sillago bassensis, S. vittata, S. burrus, S. schomburgkii, S. robusta and Sillaginodespunctata suggests that any differences in the dietary composition of similar-sized representatives of different species, when they occur in the same habitat, are more likely to be due to differences in foraging behaviour than mouth morphology. Classification, ordination and Schoener's overlap indices showed that, in nearshore waters, the juveniles of Sillago bassensis, which colonise relatively exposed areas, have a different diet to those of the smallest representatives of the other whiting species that occupy more sheltered habitats. S. bassensis consumes mainly amphipods, whereas the smaller representatives of S. vittata, S. burrus, S. schomburgkii and Sillaginodes punctata ingest large volumes of copepods, which are typically abundant in protected nearshore waters. Although the mouth dimensions of S. punctata tend to be smaller than those of Sillago schomburgkii, the larger individuals of the former species ingest greater quantities of larger prey, such as crabs and carid shrimps. As S. bassensis, S. vittata and S. burrus increase in size and migrate out into shallow inner-shelf waters, the latter two species tend to concentrate more on benthic prey, while the former species ingests fauna that is more epibenthic. The largest S. bassensis subsequently migrate out into deep inner-shelf waters, where they co-occur with S. robusta, which is restricted to those waters. In these waters, S. bassensis feeds to a far greater extent on large benthic prey, whereas S. robusta consumes a greater quantity of small epibenthic crustaceans, differences that reflect the far larger lengths of the former species in that region. The above data emphasise that the distribution and ontogenetic movements of the six abundant species of whiting play a major role in facilitating a partitioning of food resources amongst these species found in coastal waters of the lower west coast of Australia. Received: 7 October 1996 / Accepted: 31 January 1997     

In situ swimming and settlement behaviour of larvae of an Indo-Pacific coral-reef fish, the coral trout Plectropomus leopardus (Pisces: Serranidae)

Late larvae of the serranid coral trout Plectropomus leopardus (Lacepède), captured in light traps, were released during the day both in open water and adjacent to two reefs, and their behaviour was observed by divers at Lizard Island, northern Great Barrier Reef. Coral trout larvae (n = 110) were present in light-trap catches from 18 November to 3 December 1997, including new moon (30 November). The swimming speed of larvae in open water or when swimming away from reefs was significantly greater (mean 17.9 cm s⁻¹) than the speed of larvae swimming towards or over reefs (mean 7.2 cm s⁻¹). Near reefs, larvae swam at average depths of 2.7 to 4.2 m, avoiding 0 to 2 m. In open water, swimming depth varied with location: larvae >1 km east of Lizard Island swam steeply downward to >20 m in 2 to 4 min; larvae >1 km west oscillated between 2.6 and 13 m; larvae 100 to 200 m east of Lizard Island oscillated between 0.8 and 15 m. Nearly all larvae swam directionally in open water and near reefs. In open water, the average swimming direction of all larvae was towards the island, and 80% (4 of 5) swam directionally (p < 0.05, Rayleigh's test). Larvae swam directionally over the reef while looking for settlement sites. The frequency of behaviours by larvae differed between two reefs of different exposure and morphology. Depending on site, 26 to 32% of larvae released adjacent to reefs swam to open water: of these, some initially swam towards or over the reef before swimming offshore. In some cases, offshore-swimming seemed to be due to the presence of predators, but usually no obvious cause was observed. Depending on the reef, 49 to 64% of the larvae settled. Non-predatory reef residents aggressively approached 19% of settlers. Between 5 and 17% of the larvae were eaten while approaching the reef or attempting to settle, primarily by lizardfishes but also by wrasses, groupers and snappers. A higher percentage of larvae settled in the second week of our study than in the first. Average time to settlement was short (138 s ± 33 SE), but some larvae took up to 15 min to settle. Average settlement depth was 7.5 to 9.9 m, and differed between locations. No settlement took place on reef flats or at depths <4.2 m. Larvae did not appear to be selective about settlement substrate, but settled most frequently on live and dead hard coral. Late-stage larvae of coral trout are capable swimmers with considerable control over speed, depth and direction. Habitat selection, avoidance of predators and settlement seem to rely on vision. Received: 7 July 1998 / Accepted: 26 January 1999     

Patterns of seagrass (Posidonia oceanica) flowering in the Western Mediterranean

The intensive reconstructive sampling (1957–2004, 39 localities), a systematic direct observation (1992–2004, 1 locality) and particular direct observations (66 localities) of Posidonia oceanica meadows were analysed together with temporal series of flowering available in the literature (19 localities). This allowed the examination of temporal and spatial variability in annual flowering prevalence (FP, the fraction of meadows flowering in a given year) and of annual meadow flowering intensity (FI, number of inflorescences per shoot) for the period 1979–2004 across the Western Mediterranean, as well as spatial variability of flowering frequency (FF, the fraction of years that a given meadow has flowered) and shoot flowering probability (Pf, fraction of flowering stalks appeared per annual segment). Each year, on an average 17% of the investigated meadows flowered, ranging from 3 to 86% of meadows among the years. The highest annual FP and FI values were obtained in 2003 (FP=0.86 and mean FI=0.23±0.03 inflorescences shoot⁻¹). A secondary peak of FP and mean FI occurred 9 years earlier, in 1994 (FP=0.44 and mean FI=0.08±0.02). Both peaks of flowering occurred after hot summers. Flowering synchrony in particular years across the Western Mediterranean and clines of increased meadow flowering frequency towards the North and East, suggests the existence of large-scale environmental mechanisms controlling the floral induction. On the other hand, meadow FF and Pf were highly heterogeneous among and within the meadows, indicating that local factors also may play a significant role in flowering induction. When flowering, the Western Mediterranean meadows showed an average 0.11±0.02 inflorescences shoot⁻¹, but FI greatly varied among and along the series (from 0.002 to 0.54 inflorescences shoot⁻¹) and decreased significantly with depth but was independent of meadow shoot density and meadow latitude or longitude. The shoot flowering probability was quite low (0.007±0.002 inflorescences shoot⁻¹ year⁻¹) and exponentially increased with shoot age.     

Age and growth of the fan mussel Pinna nobilis from south-east Spanish Mediterranean seagrass (Posidonia oceanica) meadows

The calcitic and aragonitic shell of the fan mussel Pinna nobilis L. contains a record of the environmental changes experienced during its growth. Stable-isotope analyses of oxygen (¹⁸O:¹⁶O) in shell carbonate from the calcitic outer shell-layer have been used to validate the periodicity of clearly defined concentric rings on the aragonitic posterior adductor-muscle scar and to estimate the age and growth of fan mussels growing in Posidonia oceanica (L.) meadows at four locations on the south-east Spanish Mediterranean coast. The stable oxygen-isotope records obtained at intervals along a profile across the shell surface enabled seasonal changes in water temperature to be established, and hence seasonal patterns of shell growth to be inferred. Muscle-scar rings were found to be deposited annually in the shell in the spring and early summer (a period of increasing water temperatures), and represent an interruption in the migration of the posterior adductor muscle along the inner surface of the shell. In small pinnids (<25 cm) accretion of the shell is rapid during the first year, but in the second year it is distinctly slower than at the same time the previous year. This slowing down in growth during the second year coincides with the appearance of the “first” distinct muscle-scar ring, indicating that Pinna nobilis does not form a muscle-scar ring during its first year of shell growth. Maximum growth rates were recorded amongst pinnids from Carboneras, where they achieved a length of 59 cm in 8 yr, whilst those from Aguamarga were estimated to be the oldest (attaining a length of 45 cm in 13 yr). Received: 26 January 1998 / Accepted: 8 October 1998     

A comparison of two cartographic exposure methods using Fucus vesiculosus as an indicator

Morphological variation and vertical distribution of Fucus vesiculosus were quantified at several sites in the Finnish archipelago (Baltic Sea). F. vesiculosus samples were obtained from skerries at geographical distances of 1 km or more (large scale) and at intervals of ca 100 m around a single island (small scale). The results were examined in relation to wave exposure, calculated by Baardseth and effective fetch cartographic methods. Despite the fact that the exposure indices were calculated differently they correlated strongly. Vegetative morphological characteristics of F. vesiculosus illustrate the morphological differences both within and between exposure gradients. The tallest and widest F. vesiculosus plants were found at the sheltered end of the large-scale exposure gradient. Those from equally sheltered sites of the island were smaller in all respects. Thus, the trend from small narrow plants to large wide sheltered plants was expressed differently over the different geographical scales. Consequently localities with similar exposure indices may have morphologically different F. vesiculosus populations. Shores with similar cartographic exposure indices can be different in nature. Underwater topography and shore locations, either close to the mainland or at the outermost sites of the archipelago, affect the exposure. Although a sheltered shore is indicated, the sublittoral zone may be quite exposed to the movements of water. In contrast, in an open shore environment underwater rocks, boulders and shallow water areas can provide sheltered habitats. The depth range of the F. vesiculosus belt exhibited two distinctive patterns. At sheltered sites, around islands in the outermost reaches of the archipelago F. vesiculosus can grow to a maximum depth of 5 m. In exposed habitats the belt becomes narrower, reaching a maximum depth of 3 m. Closer to the mainland F. vesiculosus is found at exposed sites to a maximum depth of 5 m; the depth range at sheltered sites is narrower, only reaching depths of 2 m or less. In conclusion, the changes in plant morphology and in the vertical belt distribution are similar to each other along both gradients at the exposed ends of the wave action spectrum; however, the two gradients diverge at the sheltered ends of the spectrum. Received: 10 August 1998 / Accepted: 11 January 1999     

Microstructure of settlement-marks in the otoliths of tropical reef fishes

The morphology and ultrastructure of the otolith settlement-mark was examined in 44 tropical reef-fish species spanning nine families. A classification scheme based on similar otolith characteristics is presented. Three major categories are identified based on changes in increment width and optical qualities of the settlement-mark. Of the 44 species examined, 39 possessed “abrupt” settlement-marks (Type I) characterised by a rapid decrease in increment width (up to 50% reduction) over settlement. Type I settlement-marks were found in all nine families examined. The 39 species spanned the whole range of possible larval durations (Pomacentrus moluccensis, 15 d ± 0 SE; Naso hexacanthus, 91.2 d ± 2.97 SE). Four of the 44 species possessed “zonal” settlement-marks (Type II), featuring a band of increments that are wider than pre-settlement increments. Species in this category are the labrids Corisaygula, Thalassoma bifasciatum, T. lunare and an unidentified acanthurid (Acanthurus sp. 2). One species of acanthurid (N. brevirostris) possessed a “gradual” settlement-mark (Type III), manifest as a gradual decrease in increment width during the settlement period. A possible fourth type was identified from the literature. Gnatholepis thompsoni and Coryphopterus glaucofraenum possessed a settlement-mark with increment widths that increased post-settlement. Available data suggest a poor relationship between the structure of the settlement-mark and the magnitude of metamorphosis (previously reported as internal and external morphological change). Evidence suggests that the increment profile over early development and the increment transitions associated with the settlement event are taxon-specific and may enable late-larval stage fishes to be identified to species level. Received: 21 May 1997 / Accepted: 3 February 1999     

Differences in the early life history of the Australasian shortfinned eel Anguilla australis from Australia and New Zealand, as revealed by otolith microstructure and microchemistry

Otolith microstructure and microchemistry were examined in juveniles of Australasian shortfinned eel, Anguilla australis, from Australia and New Zealand. Patterns in otolith increment widths were similar in these two stocks. A marked increase in otolith increment width was found from age 138 to 198 d (mean ± SD: 164 ± 18.6 d) from Australia, 161 to 208 d (185 ± 17.3 d) from the western coast of New Zealand and 161 to 211 d (187 ± 18.9 d) from the eastern coast. These changes coincided with a drastic decrease in otolith Sr:Ca ratios, suggesting that metamorphosis began at these ages in each species. The duration of metamorphosis estimated from otolith microstructure was the same in the different stocks, 17 to 41 d (mean ± SD: 27 ± 5.4 d). Ages at recruitment were 186 to 239 d (mean ± SD: 208 ± 17.4 d) from Australia, 214 to 263 d (232 ± 19.8 d) from the western coast of New Zealand and 208 to 266 d (237 ± 20.0 d) from the eastern coast. There was a significant difference in the age between the Australian stock and the two stocks from New Zealand. No significant difference was found in the age between the latter two stocks. The difference in the period for the recruitment between Australian and New Zealand stocks seems to reflect their geographical separation. Received: 1 March 1999 / Accepted: 19 July 1999     

Variability over space and time in the genetic structure of the winged kelp Alaria marginata

The genetic structure of Alaria marginata Postels & Ruprecht was investigated spatially and seasonally using amplified-fragment length polymorphisms (AFLP). Using one primer, 206 scoreable bands were produced. Individual plants that were separated by as little as a few decimeters to >100 km could be distinguished, and followed an isolation-by-distance model. Genetic similarity (average April data) ranged from 76% for patches (a few decimeters in diameter), to 71% for individual kelp stands (15 m across) and 67% for a group of stands separated by 185 km. Greater genetic similarity of patches occurred at a wave-sheltered site than at a wave-exposed site. The lower wave action may limit meiospore dispersal, resulting in patches of related sporophytes. Genetic similarities between A. marginata stands indicated a pattern of gene flow that is consistent with local currents. In one stand, genetic similarities were markedly different between seasons. This seasonal pattern may be the result of different age groups dominating the sampled stands over time. The genetic structure of A. marginata comprises local scale (patch and within-stand) heterogeneity and larger scale (between-stands) homogeneity. Received: 30 September 1998 / Accepted: 26 October 1999     

Mating system and alternative male mating tactics in the grass goby Zosterisessor ophiocephalus (Teleostei: Gobiidae)

 Peculiar fertilization dynamics, with males releasing sperm in mucous trails lasting several hours, characterize some demersal spawning fish. The mating system was investigated in a natural population of one of these species: the grass goby Zosterisessor ophiocephalus (Pallas, 1814), a large coastal goby inhabiting seagrass meadows in shallow brackish water. Adult males ranged in size from 7.4 to 23 cm total length, but only larger ones were observed to dig and defend a burrow, where they performed parental care on eggs laid by one to several females. Field observations together with analyses of age, sperm production, trail sperm content and sperm competition tests indicated the occurrence of alternative male mating tactics, likely the expression of an ontogenetic gradient. Larger males are older than smaller ones, and while the former are territorial, the latter “sneak” territorial male spawns. The ejaculate characteristics indicate that grass goby males have functionally polymorphic spawns: in fact sperm trails of larger males last longer and release fewer sperm than those of smaller males. Sperm production over several days is more constant in larger than in smaller males, but the total number of sperm released is higher in the latter. The influence of seminal fluid in the functional intraspecific variability in sperm release in this species is discussed. Received: 30 December 1999 / Accepted: 31 July 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     

Restricted gene flow and evolutionary divergence between geographically separated populations of the Antarctic octopus Pareledone turqueti

Samples of the Antarctic octopus Pareledone turqueti were taken from three locations on the Scotia Ridge in the Southern Ocean. The genetic homogeneity of these populations was investigated using isozyme electrophoresis. Whilst panmixia appeared to be maintained around South Georgia (F _ST = 0) gene flow between this island and Shag Rocks, an island only 150 km away but separated by great depths, was extremely limited (F _ST = 0.74). These results are examined with respect to the discontinuous distribution of P. turqueti throughout Antarctica. An estimate of effective population size was also calculated (N _e = 3600). Received: 7 March 1997 / Accepted: 27 March 1997     

Microgeographic genetic differentiation in a colonial ascidian (Botryllus schlosseri) population

Limited gene flow via the restricted dispersal of larvae and gametes is expected to result in the genetic differentiation of populations of clonal invertebrates on small spatial scales. However, occasional dispersal events over greater distances may generate sufficient gene flow to maintain genetic homogeneity. We applied a spatial autocorrelation approach that does not require a priori definitions of subdivision boundaries to examine genetic differentiation within a continuous population of the colonial ascidian Botryllus schlosseri (Pallas) at two allozyme and five polychromatism loci. Colonies were sampled in July 1992, on a 12 by 18 m grid superimposed on a shallow subtidal (1 to 3 m) population in the Damariscotta River estuary in Maine, USA. Low but significant levels of positive autocorrelation were detected over very small spatial scales (<5 m), with negative autocorrelation occurring on larger scales (>8 m). This pattern indicates significant genetic differentiation over distances of 8 to 21 m, and is consistent with genetic drift and inbreeding creating small scale genetic structure. Received: 18 October 1999 / Accepted: 11 July 2000     

Comparative population genetic structure of marine gastropods (Littorina spp.) with and without pelagic larval dispersal

 Population genetic theory predicts that marine animal species with planktonic larvae will have less genetic structure than those with direct development. We compared the genetic structure of four species of littorinid snails – two with planktonic egg capsules that hatch as planktonic larvae and two with benthic egg masses that hatch as crawl-away juveniles. We used DNA sequencing and single stranded conformational polymorphism (SSCP) to assess sequence variation in a 480 bp fragment of the mitochondrial cytochrome b gene and then used an analysis of molecular variance (AMOVA) to estimate Φ_st for populations from the northeastern Pacific coast. One of the two direct-developing species, Littorina subrotundata, had a moderate amount of population structure (Φ_st=0.209) as expected but the other direct-developing species, L. sitkana, was nearly fixed for a single haplotype that made it impossible to precisely estimate Φ_st. One of the two planktonic-developing species, L. scutulata, did not show any significant population structure (Φ_st=0.004). In contrast to our expectations, the other planktonic-developing species, L. plena, showed some weak but statistically significant population structure (Φ_st=0.052). We discuss how differences in population genetic structure between species with the same type of development may reflect differences in their historical demography. Received: 22 December 1999 / Accepted: 24 July 2000