Influence of habitat on the reproductive biology of the deep-sea hydrothermal vent limpet <Emphasis Type="Italic">Lepetodrilus fucensis</Emphasis> (Vetigastropoda: Mollusca) from the Northeast Pacific

Habitat selection by the hydrothermal vent limpet, Lepetodrilus fucensis, in Northeast Pacific hydrothermal vent ecosystems, may influence its reproductive output, as it occupies habitats with varying physico-chemical conditions that reflect the availability of nutritional resources. Histological techniques were used to determine size at first reproduction, gametogenesis, reproductive output, and fecundity in relation to shell length (SL), through examination of the gonads of male and female L. fucensis, collected from five different hydrothermal vent habitat types with different temperature anomalies and hydrothermal fluid flow vigour: vigorous (VIG), diffuse (DIF), tubeworm bushes (TWB), peripheral (PER), and senescent areas (SEN). Both male and female L. fucensis exhibited early maturity, with the first reproductive event occurring at 3.8 and 3.9 mm shell length, respectively. All stages of gamete development were present in the gonads of males and females, suggesting continuous gametogenesis and asynchronous reproduction in this species. Gametogenic maturity of limpets did not vary among actively venting habitats (VIG, DIF, TWB, and PER), but was significantly lower in males and females from SEN habitats. Mean oocyte diameter was largest in females from VIG habitats, and smallest in females from SEN habitats, than in those from the other habitats (DIF, TWB, and PER). Females from actively venting habitats also had greater actual fecundity than those from senescent habitats. While the gametogenic pattern of L. fucensis appears phylogenetically constrained, selection of actively venting habitats by L. fucensis maximizes its reproductive output. The multiple feeding strategies of L. fucensis may allow for a constant supply of energy to be allocated to reproduction in any habitat except senescent vents. Early maturity, high fecundity, and continuous production of gametes suggest a reproductive strategy characteristic of an opportunistic species, and may be contributing to the extremely abundant populations of L. fucensis observed in the Northeast Pacific vent ecosystem.     

Persistence,morphology, and nutritional state of a gastropod hosted bacterial symbiosis in different levels of hydrothermal vent flux

The limpet, Lepetodrilus fucensis McLean, is found in prominent stacks around hydrothermal vents on the Juan de Fuca Ridge. L. fucensis hosts a filamentous episymbiont on its gill lamellae that may be ingested directly by the gill epithelium. To assess the persistence of this symbiosis I used microscopy to examine the gills of L. fucensis from sites representing its geographic range and different habitats. The symbiosis is present on all the specimens examined in this study, including both sexes and a range of juvenile and adult sizes. Next, I aimed to determine if patterns in bacterial abundance, host condition, and gill morphology support the hypotheses that the bacteria are chemoautotrophic and provide limpets with a food resource. To do so, I compared specimens from high and low flux locations at multiple vents. My results support the above hypotheses: (1) gill bacteria are significantly less abundant in low flux where the concentrations of reduced chemicals (for chemoautotrophy) are negligible, (2) low flux specimens have remarkably poor tissue condition, and (3) the lamellae of high flux limpets have greater surface area: the blood space and bacteria-hosting epithelium are deeper and have more folds than low flux lamellae, modifications that support higher symbiont abundances. I next asked if the morphology of the lamellae could change. To test this, I moved high flux limpets away from a vent and after 1 year the lamellar depth and shape of the transplanted specimens resembled low flux gills. Last, I was interested in whether bacterial digestion by the gill epithelium is a significant feeding mechanism. As bacteria-like cells are rarely apparent in lysosomes of the gill epithelium, I predicted that lysosome number would be unrelated to bacterial abundance. My data support this prediction, suggesting that digestion of bacteria by the gill epithelium probably contributes only minimally to the limpet’s nutrition. Overall, the persistence and morphology of the L. fucensis gill symbiosis relates to the intensity of vent flux and indicates that specimens from a variety of habitats may be necessary to characterize the morphological variability of gill-hosted symbioses in other molluscs.     

Scarred limpets at hydrothermal vents: evidence of predation by deep-sea whelks

The chaotic physical and chemical environment at deep-sea hydrothermal vents has been associated with an ecosystem with few predators, arguably allowing the habitat to provide refuge for vulnerable species. The dominance of endemic limpets with thin, open-coiled shells at north Pacific vents may support this view. To test their vulnerability to predation, the incidence of healed repair scars, which are argued to reflect non-lethal encounters with predators, were examined on the shells of over 5,800 vent limpets of Lepetodrilus fucensis McLean (1988) that were collected from 13 to 18 August 1996. Three vent fields on the Juan de Fuca Ridge at ca. 2,200 m depth were sampled, two within 70 m of 47°56.87′N 129°05.91′W, and one at 47°57.85′N 129°05.15′W with the conspicuous potential limpet predators, the zoarcid fish Pachycara gymninium Anderson and Peden (1988), the galatheid crab Munidopsis alvisca Williams (1988), and the buccinid snail Buccinum thermophilum Harasewych and Kantor (2002). Limpets from the predator-rich vent were most often scarred, a significant difference created by the high incidence of scars on small (<4 mm long) limpets in this sample. Collected with the limpets were small (median shell diameter 4.4 mm) buccinids. They, rather than the larger, more conspicuous mobile fishes and crabs are argued to be the shell-damaging predator. Electronic supplementary material The online version of this article (doi:) contains supplementary material, which is available to authorized users.     

Evolution of habitat use by deep-sea mussels

Previous phylogenetic studies proposed that symbiont-bearing mussels of the subfamily Bathymodiolinae (Bivalvia: Mytilidae) invaded progressively deeper marine environments and evolved from lineages that decomposed wood and bone to specialized lineages that invaded cold-water hydrocarbon seeps and finally deep-sea hydrothermal vents. To assess the validity of the hypotheses, we examined two nuclear (18S and 28S rRNA) and two mitochondrial genes (COI and ND4) from a broad array of bathymodiolin species that included several recently discovered species from shallow hydrothermal seamounts. Bayesian phylogenetic analysis and maximum-likelihood estimates of ancestral character states revealed that vent species evolved multiple times, and that reversals in vent and seep habitat use occurred within the sampled taxa. Previous hypotheses regarding evolution from wood/bone-to-seeps/vents are supported in that mid-ocean hydrothermal vent species may represent a monophyletic group with one noticeable reversal. Earlier hypotheses about progressive evolution from shallow-to-deep habitats appear to hold with a few instances of habitat reversals.     

Field distribution and sulphide tolerance of Capitella capitata (Annelida: Polychaeta) around shallow water hydrothermal vents off Milos (Aegean Sea). A new sibling species?

The cosmopolitan polychaete Capitella capitata, known as a complex of opportunistic sibling species, usually dominates the macrobenthos of polluted or unpredictable environments. A population of C. capitata, termed Capitella sp. M, was found in a shallow water hydrothermal vent area south of Milos (Greece). Here, this population occurs close to vent outlets (termed the “transition zone”), an environment with steep gradients of temperature, salinity and pH and increased sulphide concentrations of up to 710 μM. The field distribution of C. capitata in relation to sulphide concentrations around the vent outlets was investigated and sulphide tolerance experiments were conducted on laboratory-cultured worms to elucidate possible adaptations of Capitella sp. M to these extreme environmental conditions. In order to investigate whether the population from the Milos hydrothermal vent area can be considered a distinct sibling species within the C. capitata complex, crossbreeding experiments and analysis of general protein patterns were conducted with Capitella sp. M and three other C. capitata populations of different ecological ranges. Capitella sp. M showed high resistance (median survival time: 107 ± 38 h) to anoxia plus high sulphide concentrations of 740 μM. It seems that the ability to survive high-sulphide conditions in combination with reduced interspecific competition enables the polychaete to maintain a continuous population in this rigorous habitat. From the extremely high tolerance to anoxia and sulphide, shown in both the crossbreeding experiments and the analysis of total proteins, it can be concluded that Capitella sp. M from the Milos hydrothermal vent area represents a separate sibling species within the C. capitata complex. Received: 3 March 1997 / Accepted: 12 September 1997     

Reproductive traits of pioneer gastropod species colonizing deep-sea hydrothermal vents after an eruption

The colonization dynamics and life histories of pioneer species determine early succession at nascent hydrothermal vents, and their reproductive ecology may provide insight into their dispersal and population connectivity. Studies on the reproductive traits of two pioneer gastropod species, Ctenopelta porifera and Lepetodrilus tevnianus, began within a year after an eruption on the East Pacific Rise (EPR) that eliminated vent communities near 9°50′N from late 2005/early 2006. Standard histology was used to examine gamete release, instantaneous female fecundity, and time to maturation. Both species exhibited two-component oocyte size–frequency distributions indicating quasi-continuous reproduction with high fecundity. In samples collected in December 2006, both C. porifera and L. tevnianus individuals were reproductively mature. The smallest reproducing C. porifera were 4.2 mm (males) and 5.4 mm (females) in shell length, whereas reproductive L. tevnianus were smaller (2.3 and 2.4 mm in males and females, respectively). Most C. porifera were large (>6.0 mm) compared to their size at metamorphosis and reproductively mature. In contrast, most L. tevnianus were small (<1.0 mm) and immature. Reproductive traits of the two species are consistent with opportunistic colonization, but are also similar to those of other Lepetodrilus species and peltospirids at vents and do not fully explain why these particular species were the dominant pioneers. Their larvae were probably in high supply immediately after the eruption, due to oceanographic transport processes from remote source populations.     

Ecological implications of the presence of the tube-building polychaete <Emphasis Type="Italic">Lanice conchilega</Emphasis> on soft-bottom benthic ecosystems

The common tube-building polychaete Lanice conchilega is known as a habitat structuring species and can form dense aggregations. The effects of L. conchilega on the surrounding benthic community have received little attention, especially in subtidal areas. Therefore, the presence of L. conchilega in different habitats in the North Sea and its effect on the abundance, species richness, diversity and community structure in these habitats are evaluated in the present paper, based on data from the ICES North Sea Benthos Survey of 2000. Lanice conchilega has a wide geographical distribution and a low habitat specialization, but optimally occurs in shallow fine sands. In the present study, the presence of L. conchilega resulted in a density increase and a significant (positive) correlation of the benthos density with the density of L. conchilega. Furthermore, the species richness (number of species) increased with increasing density of L. conchilega. This trend was, however, not consistent: the number of species reached more or less an asymptotic value or even decreased after reaching a critical density of L. conchilega (>500–1,000 ind/m2), as observed in shallow fine sands. The same overall pattern was detected concerning the expected number of species. The N ₁-diversity index showed similar or slightly higher values in L. conchilega patches compared to patches without L. conchilega. From the results of the community analysis, it can be concluded that the species, which were responsible for the increase of the diversity, belonged to the overall species-pool of that habitat. The effects on density and diversity differed between the four discerned habitats (shallow muddy sand, shallow fine sand, shallow medium sand and deep fine sand), and were most pronounced in shallow fine sands. These patterns can be attributed to the habitat structuring capacity of L. conchilega. The mechanisms responsible for the increase of the habitat quality in patches of L. conchilega can be summarized as (1) changes in the hydrodynamics, (2) increases of the habitat stability and oxygen supply, and (3) a creation of habitat heterogeneity in a uniform environment. In this way, L. conchilega alters the habitat characteristics and affects other organisms, and can therefore even be considered as an ecosystem engineer. In other words, L. conchilega patches are responsible for an increased habitat quality in an otherwise uniform habitat, which results in a higher survival of the surrounding benthic species.     

Geographic clines and stepping-stone patterns detected along the East Pacific Rise in the vetigastropod Lepetodrilus elevatus reflect species crypticism

Three different molecular markers (i.e. seven allozyme loci, two nuclear gene loci and, mtCOI DNA sequences) were used to assess the genetic structure of the vent gastropod Lepetodrilus elevatus collected from three vent fields along the East Pacific Rise (13°N, 9°50′N and 17°S). While allozymes and nuclear loci suggested a strong stepping-stone pattern, a multivariate analysis performed on allozymic frequencies showed the presence of two distinct evolutionary lineages: the first situated in the north from 13°N to 9°50′N and the second in the south from 9°50′N to 17°S. The analysis of mitochondrial DNA sequences confirmed the separation of L. elevatus into two distinct clades with a divergence of 6.5%, which is consistent with the interspecific level of sequence variation in other vent species. A divergence time of 6–14 Mya was estimated between the two clades from previous clock calibrations. Our results suggest that these taxa followed an allopatric speciation between the northern and southern parts of the EPR with a recent demographic expansion of the southern clade to the north and a subsequent secondary contact (clade hybridisation). This speciation was probably reinforced by a habitat specialisation of the two cryptic species because the southern clade was mainly found associated with mussel-dominated communities and the northern clade with tubeworm-dominated communities. However, the analysis of shell morphology failed to separate the two cryptic species based on this sole criterion although they differed from Lepetodrilus elevatus galriftensis (Galapagos population) by a higher shell elevation. Within each clade, genetic differentiation was not related to the distance across populations and could be within vent field as important as between fields. While both clades appear to be in expansion since their speciation, significant excesses in heterozygotes suggest a very recent and local bottleneck at 17°S, probably due to massive site extinction in this region.     

POM in macro-/meiofaunal food webs associated with three flow regimes at deep-sea hydrothermal vents on Axial Volcano,Juan de Fuca Ridge

Deep-sea hydrothermal vent ecosystems host both symbiotic and non-symbiotic invertebrates. The non-symbiotic vent fauna is generally assumed to rely on free-living chemoautotrophic bacteria as their main food source but other sources such as detritus have recently been suggested to be a part of the invertebrate diets. Little is known about how food availability influences the distribution of vent organisms on a small scale. In addition, the feeding ecology and role of small, often numerically dominant invertebrates, the meiofauna is poorly understood at vents. In this study, we used stable carbon and nitrogen isotopic analysis to investigate the role of particulate detritus in the diets of macro- and meiobenthic invertebrates within three vent assemblages at Axial Volcano, Juan de Fuca Ridge, and Northeast Pacific. Particulate organic matter of a detrital origin became more important in the diet of invertebrates in assemblages typically associated with low-hydrothermal flow intensities. Meiobenthic species occupied several different feeding guilds and trophic levels in the assemblages investigated. We conclude that small-scale spatial variability in food sources is an important feature of vent food webs and that spatial patterns observed here and elsewhere are shaped by variations in hydrothermal discharge.     

Abundance,distribution and prey composition of scyphomedusae in the southern North Sea

The annual cycle of abundance and distribution of the scyphozoan medusae Aurelia aurita, Cyanea lamarckii, C. capillata and Chrysaora hysoscella were studied in the southern North Sea in 2004 and 2005. Three different patterns of seasonal occurrence of medusae were distinguished: (1) the early occurring C. lamarckii (February–August), (2) C. capillata and A. aurita (April–August) and (3) the late appearing C. hysoscella (July/August–September). Cyanea lamarckii was the most frequently encountered species in this study; its highest mean abundance was 1.8 ± 2.7 ind. 100 m⁻³. The prey spectra of C. lamarckii, C. capillata and C. hysoscella contained several copepod and other crustacean species and thus make them potential competitors with fish larvae. Medusae in this study also consumed fish eggs and larvae, including clupeids, in all months analysed. Although peak spawning of sprat (Sprattus sprattus) coincides with the maximum abundance of medusae (May–June) the relative low abundance of all medusae species in this study makes jellyfish predation unlikely to be a factor controlling sprat recruitment in the time frame investigated.     

Coexistence of nine anemonefish species: differential host and habitat utilization, size and recruitment

The region of Madang, Papua New Guinea, has the highest reported species diversity of both anemonefishes (nine species) and their host anemones (ten species). To determine which factors may allow so many anemonefish species to coexist at this location, we studied their patterns of distribution, abundance, and recruitment. Population surveys at three replicate reef sites within four zones situated at varying distances from the mainland (nearshore, mid-lagoon, outer barrier, and offshore) indicated that each species of host anemone and anemonefish lived within a particular range of zones. Each species of anemonefish lived primarily with one species of host. Anemonefish species that lived with the same host species usually had different distribution patterns among zones (e.g., Amphiprion percula occupied Heteractis magnifica in nearshore zones, while A. perideraion occupied H. magnifica in offshore zones). Monitoring of natural populations showed that there were few changes (losses or recruitment) in the number or species of fishes associated with each individual anemone over periods ranging from 3 to 9 months. Recruitment was monitored on anemones with and without residents (resident fishes were removed) within each of three zones (nearshore, mid-lagoon, outer barrier). Significantly more anemonefishes recruited to anemones without resident fishes than to anemones with resident fishes. Each anemonefish species recruited to particular host species and zones. The distribution and abundance of the recruits of each fish species among zones were positively correlated with the distribution and abundance of resident fishes in the benthic habitat. This suggests that the spatial patterns of recruitment among zones strongly determined the distribution and abundance patterns of the benthic populations, and they were not the result of post-recruitment mortality or movement. Coexistence of the nine anemonefish species on the limited anemone resource was considered possible because of niche differentiation (i.e., differences in host and habitat utilization among zones), and the ability of two small species (i.e., Amphiprion sandaracinos and A. leucokranos) to cohabit individual anemones with other anemonefish species. Received: 29 July 1999 / Accepted: 1 September 2000     

Trophic relationships among invertebrates at the Kairei hydrothermal vent field (Central Indian Ridge)

Exploration of hydrothermal vent systems in locations remote from well-studied sites allows ecologists to determine the degree of site-specific variation in trophic relationships among communities. A preliminary outline of the trophic structure of the Kairei hydrothermal vent community on the Central Indian Ridge (25°19.23′S; 70°02.42′E) is provided here, based on analysis of collections from an April 2001 expedition. Invertebrate biomass at Kairei is dominated by organic carbon with a δ¹³C isotopic value of about –13‰, due to the abundance of primary consumers (shrimp: Rimicaris aff. exoculata) and secondary consumers (anemones: Marianactis n. sp.) with this isotopic composition. Filamentous thiotrophic episymbionts on shrimp have been interpreted to be the major diet items of the shrimp and hence are the dominant primary producers within the community. Free-living autotrophic microorganisms are implicated as the dietary base for other invertebrate species. Four trophic groups are identified within the Kairei invertebrates based on carbon- and nitrogen-isotope ratios, but these groups do not always define discrete trophic levels. Ontogenetic shifts in diet are documented for R. aff. exoculata and brachyuran crabs (Austinograea n. sp.). Diets of symbiont-bearing mussels (Bathymodiolus aff. brevior) and two species of gastropods are isotopically constant throughout the range of sizes analyzed. There is a consistent but unexplained pattern of increasing nitrogen isotopic composition with increasing carbon isotopic composition in vent communities from geographically disjunct oceanic regions. Given the assumptions associated with interpretations of isotopic data, there remains a missing pool of carbon (presumably unsampled bacterial biomass) that contributes to the maintenance of the ¹³C- and ¹⁵N-enriched primary consumers in these ecosystems.     

Transparent exopolymer particles in a deep-sea hydrothermal system: Guaymas Basin,Gulf of California

This is the first report of transparent exopolymer particle (TEP) concentrations within deep-sea hydrothermal vent systems using colorimetric methods, measuring TEP in supernatants of sediments surrounding the vents, in fluids emanating directly from hydrothermal vents and in neutrally buoyant hydrothermal plumes. Samples were collected at Guaymas Basin (Gulf of California), a sedimented hydrothermal system. TEP concentrations within the hydrothermal fluids were significantly greater than the only other report of TEP in deep water. The range of values for TEP abundance were 8–6,451 μg/L of gum xanthan equivalents, the highest values being associated with supernatants of microbial mat-covered sediments. The potential sources and significance of the high concentrations of TEP observed in this deep-sea hydrothermal environment are discussed.     

Slowest of the slow: latitudinal insensitivity of burrowing capacity in the bivalve <Emphasis Type="Italic">Laternula</Emphasis>

Low temperature limits the rate of biochemical reactions and aerobic scopes of cold water ectotherms. To compensate for this limiting effect, animals living in cold environments often possess physiological or morphological adaptations to maintain vital functions. Cross-latitudinal comparison of aerobic capacities is one method to test which factors constrain activity in thermally distinct environments particularly when congeneric studies are carried out on related species with conservative ecology and habitat. Burrowing is a major aerobic activity of bivalve molluscs that is described here for the first time for the tropical mangrove species Laternula truncata and Laternula boschasina and then compared with their Antarctic congener Laternula elliptica. About 80% of L. truncata (16.3–46.1 mm shell length) and 63% of L. boschasina (11.3–27.7 mm shell length) buried within 24 h at 28°C. The burrowing rate index (BRI = [³√wet weight/time to bury]×10⁴) ranged between 1.1 and 20.2 for L. boschasina and 1.1–32.9 for L. truncata. These values are 2–3 orders of magnitude less than other tropical bivalve molluscs and are amongst the lowest recorded for any bivalve. Comparisons with the Antarctic L. elliptica showed little or no differences in BRI (Q ₁₀ of 1.0–1.2 for specimens of the same size). This is contrary to the general pattern over a wide range of bivalves, where BRI increases with a Q ₁₀ of between 2.9 and 6.4 between high latitudes and the equator. L. elliptica has 25–30% longer relative foot length than tropical congeners of the same size, which could be a morphological adaptation compensating for reduced burrowing speeds in a colder environment. Burrowing rates within the genus Laternula could, however, also be maintained by differing habitat, ecological and physiological constraints on burrowing capability.     

Megafaunal-habitat associations at a deep-sea coral mound off North Carolina,USA

Deep-sea corals provide important habitat for many organisms; however, the extent to which fishes and other invertebrates are affiliated with corals or other physical variables is uncertain. The Cape Fear coral mound off North Carolina, USA (366–463 m depth, 33° 34.4′N, 76° 27.8′W) was surveyed using multibeam sonar and the Johnson-Sea-Link submersible. Multibeam bathymetric data (2006) were coupled with in situ video data (2002–2005) to define habitat associations of 14 dominant megafauna at two spatial scales. Results suggested greater habitat specificity of deep-reef fauna than previously documented, with fishes showing greater affinity for certain habitat characteristics than most invertebrates. High vertical profile, degree of coral coverage, and topographic complexity influenced distributions of several species, including Beryx decadactylus, Conger oceanicus, and Novodinia antillensis on the smaller scale (30 × 30 m). On the broad scale (170 × 170 m), several suspension feeders (e.g., N. antillensis, anemones), detritivores (Echinus spp.), and mesopelagic feeders (e.g., Beryx decadactylus, Eumunida picta) were most often found on the south-southwest facing slope near the top of the mound. Transient reef species, including Laemonema barbatulum and Helicolenus dactylopterus, had limited affiliations to topographic complexity and were most often on the mound slope and base. Megafauna at deep-water reefs behave much like shallow-water reef fauna, with some species strongly associated with certain fine-scale habitat attributes, whereas other species are habitat generalists. Documenting the degree of habitat specialization is important for understanding habitat functionality, predicting faunal distributions, and assessing the impacts of disturbance on deep-reef megafauna.     

Size–frequency dynamics of NE Pacific abyssal ophiuroids (Echinodermata: Ophiuroidea)

The 17-year time-series study at Station M in the NE Pacific has provided one of the longest datasets on deep-sea ophiuroids to date. Station M is an abyssal site characterized by low topographical relief and seasonal and interannual variation in surface-derived food inputs. From 1989 to 2005, over 31,000 ophiuroid specimens were collected. Size–frequency distributions of the four dominant species, Ophiura bathybia, Amphilepis patens, Amphiura carchara and Ophiacantha cosmica, were examined for recruitment and the role of surface-derived food supplies on body size distributions. Juveniles were collected in sediment traps and used to investigate settlement patterns and seasonality. Trawl samples showed no indication of seasonal changes in recruitment to larger size classes; however, there was evidence of seasonal settling of juveniles. Interannual differences in median disk diameters and size distributions of trawl-collected adults are greater than those at the seasonal scale. Three of the four species, O. bathybia, A. patens and O. cosmica, had co-varying monthly median disk diameters, suggesting they may have a similar factor(s) controlling their growth and abundance. Interannual differences in monthly size distributions were generally greater than those between seasons. Cross-correlations between the particulate organic carbon (POC) flux (food supply) and size distribution indices for O. bathybia, A. patens and O. cosmica all were significant indicating that increases in food supply were followed by increases in the proportion of smaller size classes after approximately 17–22 months. These findings suggest that food inputs are indeed an important factor influencing deep-sea ophiuroid populations on interannual time scales, more generally supporting the long-hypothesized connection between food availability and population size structure in the deep sea. Electronic supplementary material  The online version of this article (doi:) contains supplementary material, which is available to authorized users.     

Larvae of benthic invertebrates in hydrothermal vent plumes over Juan de Fuca Ridge

Larvae of benthic invertebrates collected in the water column above Juan de Fuca Ridge show distinct variations in abundance and composition in, and away from, the neutrally-buoyant hydrothermal plume emanating from underlying vents. Larvae of vent gastropods (Lepetodrilus sp. and two peltospirid species) occur in significantly higher abundances in the plume than away from it (mean abundance=21.0 individuals 1000 m^?3 vs 1.4 individuals 1000 m^?3), and larvae of vent bivalves (Calyptogena? sp.) occur exclusively in the plume (mean abundance=0.5 individuals 1000 m^?3). Larvae from other benthic taxa known not to be endemic to Juan de Fuca vent communities, such as anthozoans, pholad clams, bryozoans and echinoderms, are less abundant in the plume than away (mean abundance=47.5 vs 16.9 individuals 1000 m^?3) at comparable depths and heights above the bottom. These results support the hypothesis that larvae of vent species are entrained into buoyant hydrothermal plumes and transported at the level of lateral spreading several hundred meters above the seafloor. The discovery of vent-associated larvae in the plume suggests that models used to predict hydrodynamic processes in the plume will also be useful for modeling larval dispersal. Advanced imaging and new molecular-based approaches will be required to resolve taxonomic uncertainties in some larval groups (e.g. certain polychaete families) in order to distinguish vent species and make comprehensive flux estimates of all vent larvae in the neutrally-buoyant plume.     

Habitat modification affects recruitment of abalone in central New Zealand

The habitat experienced during early life-history stages can determine the number and quality of individuals that recruit to adult populations. In a field experiment, biogenic habitat complexity was manipulated (presence or absence of foliose macroalgae) at two depths (2–3 m and 5–6 m) and the habitat-dependent effects on recruitment of the black foot abalone (Haliotis iris) were examined at three field sites along the south coast of Wellington, New Zealand (41°20′S, 174°47′E), between July and November 2005. Recruit density (<5 weeks post-settlement) was measured on cobbles covered with crustose coralline algae. Habitats of low complexity (barrens treatments) had consistently greater densities of recruits than habitats of high complexity (algae treatments). However, recruits in algae habitats were larger, and for deep habitats, there was greater survival in algae habitats compared with barrens habitats. While depth had no significant effect on early recruit (<2 weeks post-settlement) density, late recruit (<5 weeks post-settlement) density was greater in shallow habitats, and so it seems recruit survival was greater in shallow habitats. In this experiment, algal habitat complexity had strong effects on early recruit abundance, but habitat-dependent variations in recruit growth and survival may modify initial patterns of abundance and determine recruitment to adult abalone populations.     

Population structure and reproductive biology of two sympatric hydrothermal vent polychaetes,Paralvinella pandorae and P. palmiformis

The alvinellid polychaetes Paralvinella pandorae Desbruyères and Laubier and P. palmiformis Desbruyères and Laubier occur at deep-sea hydrothermal vents along the Juan de Fuca and Explorer Ridges in the northeast Pacific Ocean. The population structure and reproductive biology of both species were studied in samples taken from three vent sites during six cruises in 1983 and 1984. Size-frequency analyses of two P. pandorae populations produced unimodal histograms, suggesting continuous or semi-continuous juvenile recruitment; in a third population two possible size classes were evident. Histograms of P. palmiformis displayed size-class peaks, which most likely reflected periodic recruitment of juveniles. Both species are gonochoric and gametes develop free in the coelom. Due to the simultaneous presence of a full range of gametogenic stages in P. pandorae populations, including spermatozoa in males, and to the continuous or semi-continuous recruitment pattern suggested by the size-frequency histograms, continuous reproduction is proposed for this species. In P. palmiformis a discrete, possibly synchronized, breeding cycle is thought to occur. Although maximum fecundity of P. pandorae is very low, continual reproduction over a long period of time could enhance its reproductive potential. The estimate of maximum fecundity for P. palmiformis is comparable to estimates for other polychaetes that undergo non-planktotrophic larval development. Maximum observed oocyte size was 215 and 260 m in P. pandorae and P. palmiformis, respectively. It is proposed that P. pandorae broods its young, while P. palmiformis probably undergoes demersal lecithotrophic larval development. The continual production of brooded young by P. pandorae could maintain a vent population, but severely limit dispersal to other vents. Demersal lecithotrophic larvae of P. palmiformis could repopulate vents, and potentially be carried by bottom currents to other vent sites.