Clam Beds Research Articles

Induced spawning, larval rearing, and innate diet analysis of Indian black clam, Villorita cyprinoides: An alternative to resource restoration through aquaculture

Villorita cyprinoides (Gray, 1825) also called the Indian black clam is a native species from the Indian peninsula directly related to the livelihood of many beneficiaries. The wild population of this Cyrenid clam is confronted with substantial challenges, including various climatic stressors and anthropogenic pressures such as overfishing and habitat destruction. A balance between capture fisheries and aquaculture through the development of hatchery technology is inevitable for ensuring the sustainable use of resources. The declining population of V. cyprinoides underscores the urgency of standardizing breeding protocols and implementing proper farming practices to foster a sustainable black clam fishery, given that Villorita is a potential candidate species for aquaculture. This paper describes the first successful induced spawning of the clam with successful rearing of larvae up to the umboned veliger stage and evaluates the efficacy of induced spawning through combined physical and chemical stimuli. Furthermore, our study employs eDNA metabarcoding to analyze plankton dynamics in waters from native clam beds. This sheds light on the potential microalgal dietary preferences of the species, which can be valuable in preparing diets for larval development and aquaculture in the future.

Fluctuations in abundance of the striped venus clam Chamelea gallina in the southern Adriatic Sea (Central Mediterranean Sea): knowledge, gaps and insights for ecosystem-based fishery management

An assessment on the fluctuations in abundance of the striped venus clam (Chamelea gallina) in the southern Adriatic Sea (Central Mediterranean Sea), and the northern Gargano area, has been conducted through both historical information and recent data from monitoring surveys during the period 1997–2019. Production trends, conditions of the commercial stock biomass, and depth distribution pattern of juveniles and commercial sizes were analysed testing temporal differences. Moreover, the exploitation of the clam beds and recruitment events were investigated in 2018–2019. Changes in abundance were analysed using non-parametric tests for both juvenile (length class, LC < 22 mm) and commercial (LC ≥ 22 mm) fractions. Hydrodynamic changes, temperature and salinity variations were explored using a 3D hydrodynamic numerical model (MIKE 3 FM-HD) and statistical analysis, as well as changes in benthic assemblages impacted by hydraulic dredges were investigated through PERMANOVA and other multivariate analysis.The results showed a temporal decline of production and biomass of C. gallina during the 1997–2019 period, and a regression of the depth limit in the clams’ distribution towards shallower waters. A significant reduction in juveniles was observed during 2018–2019 with a very limited recruitment. The fishing exploitation showed high impacts on the commercial stock and benthic assemblages in the summer of 2018. Overall, water currents were predominantly directed offshore in 2018, during the C. gallina spawning period. This could affect the larval dispersal and settlement on unsuitable bottoms. Anomalies in temperature (high peaks in August 2018, > 28 °C) and salinity (low values in spring 2018, < 37 PSU) could have induced stress and mortality events on the entire clam bed in the study area. This first study highlights the need to integrate environmental information in the assessment of commercial stocks of clams in the Adriatic Sea, to better understand climate change effects on the fluctuations and to support effective ecosystem-based fishery management.

The stress response of the seagrassZostera nolteiand three commercial clam species to low salinity associated with heavy rainfall

AbstractThe maintenance of stocks of estuarine species strongly depends on the ability of the species to cope with environmental stress. In NW Spain, commercial clam beds, which are usually co-occupied by the seagrass Zostera noltei, are often exposed to reduced salinity caused by intense rainfalls. Our goals were to evaluate the effects of low salinity events on both juvenile clams and Z. noltei, including their interactions. A mesocosm experiment was performed to simulate three salinity decreases (35–35, 25–10, and 20–5), and several indicators of clam and seagrass performance were measured after 3 and 6 days of exposure and again after a recovery period of 4 days. No differences were observed in the non-native clam Ruditapes philippinarum, while oxygen consumption, clearance rate and growth decreased significantly in the native clams R. decussatus and Venerupis corrugata in response to low salinity stress. Zostera noltei indicators did not vary in response to low salinity exposure, except the sucrose content, which decreased. Moreover, the seagrass buffered juvenile clams from salinity fluctuations in the short term, although the interactions were weak. The species-specific sensitivity to low salinity should be a major concern in future management plans for the shellfish beds in the context of climate change.

Seascape ecology in the vicinity of a Blake Ridge cold seep

Systematic surveys of the distribution of epibenthic megafaunal species relative to one another and to environmental variables in the deep sea can lead to inferences and testable hypotheses regarding factors that influence their distributions. Here we use a seascape approach to provide insight into the character and spatial extent of the influence of a chemosynthetic seep on the distribution of epibenthic megafauna and the nature of transition zones (ecotones). Faunal distributions were determined from georeferenced images of the seabed collected during a systematic survey (~ 400 m x 400 m) by the Autonomous Underwater Vehicle Sentry in the vicinity of a newly discovered methane bubble plume on the Blake Ridge Diapir. The survey area was found to include both seep and non-seep habitats. The sphere of influence of seep productivity on the surrounding benthic megafaunal assemblage was limited—on the order of 10’s of meters—based on ecotone analysis. Small but detectable redox anomalies in the water column (5 m above bottom) in the study area occurred on a similar horizontal scale. Distributions of background megafaunal taxa were non-random for many morphotypes and included both positive and negative associations between morphotypes and the seep habitat. Subtle variations in depth (&amp;lt;6 m) correlated with distributions of seep-associated vesicomyid clams, which occupy shallow depressions in the seabed. The seep habitat itself, comprising a patchy mosaic of megafaunal sub-communities (e.g., clam bed, mussel bed, background soft-sediment bathyal taxa) and transition zones, was at least as diverse as the surrounding non-seep habitat and contributes seep endemic morphotypes to regional biodiversity. While seep productivity may support prey fields for deep-diving beaked whales, any relationship between the seeps and whale feeding areas remains intriguing speculation. Like many other regions of the deep sea, Blake Ridge South has accumulated marine litter, including litter likely originating from scientific endeavors. The suite of observations and analyses deployed here underscore the importance of seep habitats in enriching regional biodiversity, provide a glimpse of the non-random complexity of species distributions from a seascape perspective, and establish ecological baselines against which future studies may measure natural and anthropogenic changes in the seascape.

Using the Pumped Area Method for the Assessment of Recreational Razor Clam, Siliqua patula Populations in Washington State

Since 1898, the Pacific razor clam, Siliqua patula has represented an important resource for commercial and recreational diggers and has been an important source of economic revenue to coastal communities in the Pacific Northwest from central California to southern Alaska. In 1996, Washington State adopted the Pumped Area Method as the preferred method to accurately assess populations of razor clams on coastal beaches. The Pumped Area Method utilizes a water pump and a series of hoses to draw water out of the surf to liquefy the clam bed exposing clams so they can be measured and recorded. This method relies on a fixed stratified random sampling of transects across all managed beaches to produce a robust estimate of the total population of clams. The Pumped Area Method has been adopted by state and tribal management agencies along the west coast to determine the total allowable catch in each management area but never been formally described. This method in conjunction with a biweekly sampling of toxic algae abundance supports the sustainable harvest of razor clams, providing up to 40 million dollars annually in economic income to the state of Washington for the last 25 y.

Mega- and macrofauna of the hydrothermally active submarine Piip Volcano (the southwestern Bering Sea)

Benthic communities of the hydrothermally active submarine Piip Volcano (55°445 N, 167°263 E, 368–495 m, the southwestern Bering Sea) were explored during the 75th and 82nd cruises of the RV Akademik M.A. Lavrentyev using the ROV Comanche 18. The Piip Volcano is the northernmost hydrothermal region in the Pacific. Macrofauna composition and community structure were investigated based on qualitative and relative abundance samples along with still images and video records. In total, 130 species of macro- and megafauna were found, of which ∼25% are new to science. Of the fauna, 9 species (7%) are obligate or potentially obligate to environments with access to reduced chemicals. These species are the bivalve Calyptogena pacifica (Vesicomyidae: Pliocardiinae), the gastropods Parvaplustrum wareni (Parvaplustridae) and Provanna sp. (Provannidae), the amphipod Onesimoides sp. (Tryphosidae), the leptostracan Nebalia piipensis (Nebaliidae), the isopod Eurycope andreyi (Munnopsidae), and the polychaetes Neosabellides uschakovi (Ampharetidae), Ophryotrocha beringiana (Dorvilleidae) and Harmothoe globosa (Polynoidae).The total species richness of the Northern and Southern summits was almost identical (90 species and 85 spp respectively), but the number of species on sites without bacterial mats on the Northern Summit (81 spp) was almost 1.5 times higher than on the Southern Summit (57 spp). At the same time the species richness was almost twice higher in habitats with bacterial mats and/or clam beds on the Southern Summit (58 spp) compared to the Northern one (32 spp). The main faunal difference was the absence of Calyptogena pacifica on the Northern Summit. The factors that may explain differences of the faunal communities of the Northern and Southern summits are discussed.The distinctive features of macro- and megafaunal communities of the Piip Volcano were the significant number of taxa, obligate for reducing habitats, of different taxonomic levels including family and subfamily levels and plentiful abundances of sedentary organisms, including the sea anemone Corallimorphus cf. pilatus, the demosponge Vulcanella koltuni, calcareous sponges and benthopelagic Trachimedusa, all of them presumably utilizing the rich food resources of reducing habitats.

Strategy of micro-environmental adaptation to cold seep among different brittle stars’ colonization

Diffusing fluid from methane seepage in cold seep field creates zones with physicochemical gradients and divergent ecosystems like the mussel beds and clam beds. Three species of brittle stars (Ophiuroidea) were discovered in the Haima cold seep fields, of which Ophiophthalmus serratus and Histampica haimaensis were found on top of or within mussel beds and clam beds, whereas Amphiura sp. was only collected from muds in the clam bed assemblage. Here, we evaluated the genetic signatures of micro-environmental adaptation of brittle stars to cold seep through the comparison of mitogenomes. This study provided two complete mitogenome sequences of O. serratus and Amphiura sp. and compared with those of H. haimaensis and other non-seep species. We found that the split events of the seep and non-seep species were as ancient as the Cretaceous period (∼148–98 Mya). O. serratus and H. haimaensis display rapid residue mutation and mitogenome rearrangements compared to their shallow or deep-sea relatives, in contrast, Amphiura sp. only show medium, regardless of nucleotide mutation rate or mitogenome rearrangement, which may correlate with their adaptation to one or two micro-ecosystems. Furthermore, we identified 10 positively selected residues in ND4 in the Amphiura sp. lineage, suggesting important roles of the dehydrogenase complex in Amphiura sp. adaptive to the cold seep environment. Our results shed light on the different evolutionary strategies during colonization in different micro-environments.

Methane seep communities on the Koryak slope in the Bering Sea

Methane seep communities on the Koryak slope in the Bering Sea were discovered in 2018 during the 82nd cruise of the RV Akademik M.A. Lavrentyev using ROV Comanche 18. Methane seeps found between 400 m and 695 m depth are the northernmost chemosynthesis-based habitats (∼61°N) known to date in the Pacific. Macrofauna species composition and community structure of methane seep and background benthic communities were investigated at three depth horizons: 400–402 m, 417–429 m and 647–695 m.A total of 335 macrofaunal species were identified. At the depth 647–695 m the species richness in the methane seep communities was 265 species and 72 species in the background. The deepest seep communities were characterized by the highest species richness, relatively high evenness and strong variations in the composition and structure. At shallower depths the species richness was low: 33–34 species at methane seeps and 66–71 in the background. The methane seep communities at shallow depths showed relatively low evenness and low diversity of community structure. The highest species richness at the greatest depth can be related in part to increased habitat heterogeneity associated with carbonate crusts and vesicomyid clam beds occurring only at deeper methane seeps. The deepest methane seep communities were dominated by the chemosymbiotrophic pliocardiine Calyptogena pacifica; dominant in the background was the ophiuroid Ophiophthalmus normani. At shallower methane seeps only single specimens of C. pacifica were found. The shallower methane seeps were dominated by the background species despite numerous extensive bacterial mats and high potential toxicity of the environment. The seep community at 417–429 m was dominated by the echinoid Brisaster latifrons with population density on the bacterial mat four times higher than in the background. Four chemosymbiotrophic species were recorded at 647–695 m and only one was found at shallower depths. Potentially obligate to reducing habitats polychaetes of the genus Neosabellides and Ophryotrocha occurred in methane seep communities at all depths. Further geochemical, geological and microbiological studies are required to better characterize differences of methane seeps at different depths and reasons of these differences.

Once-iconic Pismo clams persist in southern California at low intertidal population densities and with variable recruitment

The Pismo clam (Tivela stultorum) has experienced substantial population decline in California over the past century, extinguishing most public participation in a once-iconic recreational fishery before the end of the 20th century. A subsequent decrease in data collection has led to uncertainty about the current population status of this species. We conducted 6 years of intertidal Pismo clam population assessment surveys in Orange, San Diego, and southern Los Angeles Counties to provide a current dataset that could help guide research and management efforts in southern California. Pismo clams were observed at 19 out of 27 study sites during 57 days of surveys. Average clam bed density was low (mean 2.0 ± 1.1 clams/m2, median 0.1 ± 0.7 clams/m2, n = 21 sites), especially when considering larger clams ≥ 35 mm (mean 0.3 ± 0.1 clams/m2, median 0.1 ± 0.4 clams/m2), and varied greatly between sites (0.0–98.5 clams/m2), with Orange County densities approximately one order of magnitude lower than those in San Diego County. Juvenile recruitment was generally low or undetectable, except for consistent recruitment within a &lt; 10 km beach area in San Diego County and a much larger, widespread recruitment event in 2022. Multi-year observations at several sites failed to indicate any consistent seasonal or inter-annual population trends. Densities and abundances were similar to recent historic data (&lt; 30 years old), but are substantially lower than populations prior to the 1980s. We conclude that the Pismo clam persists on many southern California beaches at generally low densities and that recruitment is occurring throughout the southern California region with high spatial and temporal variability. This study provides foundational data to help inform Pismo clam conservation management decisions and to which additional monitoring, ecological research, and fishery data collection should be added.

Barkley Canyon Gas Hydrates: A Synthesis Based on Two Decades of Seafloor Observation and Remote Sensing

Barkley Canyon is one of the few known sites worldwide with the occurrence of thermogenic gas seepage and formation of structure-II and structure-H gas hydrate mounds on the seafloor. This site is the location of continuous seafloor monitoring as part of the Ocean Networks Canada (ONC) cabled observatory off the west coast off Vancouver Island, British Columbia, Canada. We combine repeat remotely operated vehicle (ROV) seafloor video observations, mapping with an autonomous underwater vehicle (AUV), ship-, ROV-, and AUV-based identification of gas flares, as well as seismic and Chirp data to investigate the distribution of fluid migration pathways. Geologically, the site with the prominent gas hydrate mounds and associated fluid seepage is covering an area of ∼0.15 km2 and is situated on a remnant of a rotated fault block that had slipped off the steep flanks of the north-east facing canyon wall. The gas hydrate mounds, nearly constant in dimension over the entire observation period, are associated with gas and oil seepage and surrounded by debris of chemosynthetic communities and authigenic carbonate. The formation of gas hydrate at and near the seafloor requires additional accommodation space created by forming blisters at the seafloor that displace the regular sediments. An additional zone located centrally on the rotated fault block with more diffuse seepage (∼0.02 km2 in extent) has been identified with no visible mounds, but with bacterial mats, small carbonate concretions, and clam beds. Gas venting is seen acoustically in the water column up to a depth of ∼300 m. However, acoustic water-column imaging during coring and ROV dives showed rising gas bubbles to much shallower depth, even &amp;lt;50 m, likely a result of degassing of rising oil droplets, which themselves cannot be seen acoustically. Combining all observations, the location of the gas hydrate mounds is controlled by a combination of fault-focused fluid migration from a deeper reservoir and fluid seepage along more permeable strata within the rotated slope block. Fluids must be provided continuously to allow the sustained presence of the gas hydrate mounds at the seafloor.

A preliminary study of macrofaunal communities and their carbon and nitrogen stable isotopes in the Haima cold seeps, South China Sea

The macrofaunal community in the Haima cold seeps of the South China Sea was investigated, and trophic relationships were evaluated using carbon and nitrogen stable isotope signatures (δ13C and δ15N). A total of 30 macrofaunal species were identified in this study, most of which were collected from the Gigantidas haimaensis mussel beds. Only four macrofaunal species were collected from the Calyptogena marissinica clam beds, where the environment may not be suitable for the survival of most macrofauna. The bush of slim tubeworms (Sclerolinum sp.) might be an important nursery ground for mussels. G. haimaensis was the predominant species, and its average δ13C and δ15N values were −52.7‰ and 0.6‰, respectively. Compared with the stable isotope signatures of particulate organic matter (POM), it suggested that the food source of macrofauna in the Haima cold seeps was mainly originated from chemosynthetic autotrophs. In the mussel bed, most of the macrofauna had a large δ13C isotopic distance compared with G. haimaensis, suggesting that G. haimaensis was not a direct food source for most cold-seep macrofauna in the mussel bed. The variation in stable isotope signatures of macrofauna might be attributed to different proportions of methanotrophic and thiotrophic endosymbionts. Neolithodes brodiei and Bathynomus jamesi showed the highest δ13C and δ15N values. However, the large isotopic distance indicated that N. brodiei and B. jamesi might just occasionally visit the cold-seep ecosystem and their food sources were mainly from the upper ecosystem relying on photosynthesis. Overall, our results suggested that there was no significant predator-prey relationship among these macrofaunal species in the Haima cold seeps. This study provided important baseline data of stable isotope signatures for further studies to elucidate the trophic interaction among seep organisms.

Comparative evidence for harvesting-driven enhancement of clam beds in northeastern New Brunswick, Canada

Populations of infaunal clams can be affected by natural and anthropogenic factors. Two such factors include sediment porewater pH and clam harvesting. To date, however, the potential effects of clam harvesting on sediment pH conditions and corresponding clam densities remain understudied. To fill this knowledge gap, we sampled sediment pH conditions and the densities of three clam species (Mya arenaria spat, and all life stages of Macoma balthica and Gemma gemma) in harvested and non-harvested areas at two sites (Miramichi and Point aux Carr) in eastern New Brunswick, Canada. Within sites, sediment pH conditions were higher within harvested areas and correlated with significantly higher clam densities compared to non-harvested areas. Between sites, clam abundances were significantly higher at the site with lower pH conditions, suggesting that reduced clam densities associated with low sediment pH may be restricted to small spatial scales in this region. These results add to a growing body of literature suggesting that, under certain contexts, commercial clam harvesting may enhance habitat suitability and benefit some clam populations. The ways in which commercial clam harvesting affects habitat suitability and clam densities under a wide range of ecological and anthropogenic conditions warrant future investigation.

Spatial ecology of long‐tailed ducks and white‐winged scoters wintering on Nantucket Shoals

AbstractWe examine the long‐term co‐occurrence of long‐tailed ducks (Clangula hyemalis) and white‐winged scoters (Melanitta fusca) wintering at the Nantucket Shoals off Massachusetts, USA, and ask: (1) What oceanographic features attract these aggregations? (2) How are distributions of prey and sea ducks related to one another? and (3) What is the explanation for the spatial association between these two species? A winter concentration of long‐tailed ducks on the order of 3 × 105 birds have been present near Nantucket Island and the Nantucket Shoals since the 1970s, and there is evidence of some concentration there since the late 1800s. Despite the difference in diet, the two duck species overlap in spatial distribution in relation to a prominent tidal front on the west side of Nantucket Shoals where nested swarms of pelagic amphipods and massive clam beds occur in persistent broadscale concentrations. Gammarid amphipods were collected seasonally by bongo tows over 39 yr (1977–2016), and Atlantic surf clams and ocean quahogs were collected by hydraulic dredge over a 34‐yr timescale (1982–2016). Long‐tailed ducks and white‐winged scoters were counted during systematic low‐level aerial surveys. Both long‐tailed ducks and white‐winged scoters associated with amphipod and clam aggregations at similar scales, and tracked amphipod and clam concentrations at larger spatial scales, up to ~30 km. These multi‐scalar nested associations suggest that the sea ducks foraged within a hierarchical patch system structured by the tidal regime, and concentrated in areas of spatially anchored recurring prey, with highest densities in southwest areas. Enhanced concentrations of prey within a relatively narrow zone on Nantucket Shoals provide a predictable food resource to wintering sea ducks whose populations are in decline. As supported by our generalized additive models, we propose that the positive spatial associations among these species are at least partly explained by local enhancement or facilitation, whereby each species of duck derives foraging benefit from noting the location of aggregations of the other. This interaction will be important to the designation of marine protected areas.

Building a set of criteria for selection of natural clam beds (&lt;i&gt;Lutraria rhynchaena&lt;/i&gt;, Jonas 1844) as broodstock source for seed production and gene conservation in Cat Ba - Ha Long bay

Building on a set of criteria used as a scientific basis for conservation zoning of natural marine resources is essential. In this study, we propose the set of criteria to select the suitable natural clam beds of Lutraria rhynchaena for protection priority from 16 sites in Cat Ba - Ha Long bay. Research results have built a set of 13 different criteria, including area, density, benthic substrate, food organisms, turbidity, water flow, water depth, predators, salinity, benthic organisms, pollution, area location and zoning conflicts. The criteria are divided into 5 groups, in which the area and density have the highest coefficent of 5, followed by the zoning conflict with the coefficient of 4, the pollution with the coefficient of 3, the efficient of benthic substrate and water flow is 2, the remaining criteria have a same coefficient of 1. The highest points are evaluated at Tung Sau bed (station 12) with a score of 254 points, followed by Van Boi beach (station 7) with a score of 235 points, the bed is in Trinh Nu Cave (Station 13) with a score of 229 points, which are proposed to be prioritized sites for conservation.

Application of a fish finder system to spatial distribution mapping for the razor clam Solen gordonis: Case study from coastal waters, northwestern Kyushu, Japan

Effective spatial management planning for sedentary fishery resources requires accurate spatial distribution mapping of a focal stock including both fished and associated unfished populations. This study focuses on (sub-)adult razor clams (Solen gordonis), with shell lengths ≥25 mm, in Sasebo Bay and Omura Bay, northwestern Kyushu, Japan. They are commercially harvested, but little is known about their spatial distribution pattern. The objective was to estimate the spatial distribution and configuration of clam beds existing within an area of ca. 12 km2. For this, clam and sediment sampling by scuba-equipped divers, acoustic bathymetric surveys using a recreational-grade fish finder (single-beam acoustic) system, and presence–absence modelling using generalized linear models were performed. For the collected clams, catch per unit effort (CPUE; number of clams collected/h) was calculated and used as a proxy for clam individual density. The results showed that the presence–absence variation in the spatial distribution of (sub-)adult clams was associated with the bottom sediment type. (Sub-)adult clams occurred frequently in the sediments with higher gravel (particles with diameters ≥2 mm, mainly shell fragments) and lower mud (diameters <0.063 mm) contents than the sediments of the absence sites. Acoustic signals of the fish finder system were backscattered more intensely from gravel-sand beds (i.e., typical of the presence sites) than from muddy sand beds (i.e., absence sites). Using the relationships among the presence–absence variation of (sub-)adult clams, sediment type, and backscatter strength, spatial distribution of clams was predicted with high accuracy. The presence probability of (sub-)adults (= x; continuous values from 0 to 1) predicted from the results was significantly regressed on CPUE (= y) [i.e., y = exp(−0.7984 + 4.9350x) − 0.05]. Using this relationship, a map for the relative abundance of (sub-)adult clams was obtained. This map depicted several clam beds including both exploited and unexploited ones. The latter beds virtually conform to no-take zones in the razor clam fishery.

Fine-scale infaunal community and food web patch mosaics from Barkley methane hydrates (British Columbia, Canada): The role of food quality

In order to assess the influence of organic matter patchiness on deep-sea biodiversity, we examined organic matter patchiness and macrofauna at small spatial scales (meters – 100 s of meters) in a chemosynthetic environment (Barkley methane hydrates, British Columbia continental slope, ~900 m depth). Specifically, we assessed quantity, quality, and sources of organic matter and their influence on the associated infaunal community and food web structure (feeding guild composition) at the methane outcrop, as well as at sites 20 m and 600 m away. We found greater patchiness in food composition at the outcrop site (containing clam beds) than the more distant locations. Trophic diversity (ES[10]) was significantly greater at the outcrop compared to that at the 20 m site, suggesting that the outcrop added rather than replaced trophic niche opportunities. Diversity (ES[10]) was lower at the outcrop compared to the other two sites, although not significantly so. We re-analysed the community data at higher spatial resolution (5–10 m, and lower replication) to identify the distance of influence of the hydrates habitat and found a transition from outcrop to background at 9 and 15 m away from the most active site, with greater similarity in the communities at 28 m to those at 600 m than the outcrop itself. Although not major controlling factors, food quality (i.e., nutritional value for benthic organisms) and source played a significant role in determining food web structure, outweighing the influences of food quantity and sediment type. However, our distance-based linear model (distLM) using all variables, food quality, or topography explained only 33.56%, 33.54%, and 33.18% respectively of the total variation in feeding guild composition, suggesting important roles for other environmental variables. We conclude that the higher food patchiness in Barkley Hydrates compared to ambient sediments likely contributed to increased trophic niche opportunities. We emphasize the importance of sampling at adequate spatial scales to detect the limits of the influence of methane hydrates in infaunal communities and food webs.

Heterogeneity of methane seep biomes in the Northeast Pacific

Methane seeps provide biogeochemical and microbial heterogeneity in deep-sea habitats. In the Northeast (NE) Pacific Ocean recent studies have found an abundance of seeps at varying spatial separations and within distinct biogeochemical environments ranging in oxygen, depth, and temperature. Here, we examine eight newly discovered seeps and two known seeps covering 800km and varying across 2000m water depth to identify: (1) novel megafaunal communities in this geographical region; (2) variations in the microbiome of seep habitats across the margin; (3) spatial and biogeochemical drivers of microbial diversity at seeps. In addition to authigenic carbonates, clam beds, microbial mats, and exposed hydrates - we also observed Siboglinidae tube worm bushes and an anomalous deep-sea barnacle adding to the overall habitats known from the NE Pacific. The microbial communities showed high variability in their spatial distribution and community structure. The seep communities formed distinct groups that included multiple groups of anaerobic methane oxidizing Archaea (ANME; 1, 2ab, 2c, and 3), often co-occurring within one site – however, there were also other sites with clearly dominant members (e.g. ANME-1s at Nehalem Bank). Sulfide oxidizers were dominated by the non-mat forming Campylobacterales and even though vertical gradients in redox potential typify seep sediments, in two cases there was not a significant change in community structure across the top fivecm of sediment. We posit that these patterns were driven by ‘bubble-turbation,’ and bioirrigation by megafauna. A surprising latitudinal trend was observed in species diversity and richness with increasing richness significantly correlated to increasing latitude. Overall, our results demonstrate that heterogeneity is ubiquitous in the seep biome, spanning all faunal classes, and that the understanding of seeps and the drivers of the community structure can be improved by studying seeps at a range of spatial scales.

Correction to: Effects of clam dredging on benthic ecology of two cultivated northern quahog beds with different harvest histories and sediment grain sizes

In Connecticut, cultivation of the northern quahog, or hard clam, Mercenaria mercenaria L., relies on hydraulic dredging. After harvesting, leased shellfish beds remain fallow for varying durations to facilitate natural reseeding and to allow small clams to reach harvestable size. The interval between dredging events, or harvest history, may influence benthic ecology and response of communities to further dredging. Two clam beds with different harvest histories, located near Milford, Connecticut, were studied from July through October 2012. These leased beds, fallowed for 3 and 8 years, respectively, were subdivided into two plots. One plot on each bed was commercially harvested in July while the other remained not dredged. Sediment sampling was conducted on alternate weeks using Smith MacIntyre grabs and sediment cores to compare ecology of benthic communities and chemistry of marine sediments on newly dredged and not dredged plots within leases. Main effects of lease (harvest history), dredging treatment (dredged versus not dredged plots), mean sediment phi size (ɸ), and season (sampling date) significantly affected benthic community structure. Newly settled bivalves, including early successional pioneer species, occurred in high abundance on 3-year beds. Diversity, evenness, and number of species were high on the 8-year beds, while abundance of individuals was low, more typical of later successional equilibrium communities. Differences among a subset of species on the 8-year beds were observed between dredged and not dredged plots while no community differences were observed between dredging treatments on 3-year beds. Significantly more individuals were observed on dredged versus not dredged plots on the 8-year beds only. Our results suggest that harvest frequency and/or sediment ɸ size may explain differences in benthic assemblages between leased areas with different dredging histories, while dredging had no measurable effect on sediment chemistry.

The vesicomyid bivalve habitat at cold seeps supports heterogeneous and dynamic macrofaunal assemblages

The high biodiversity found at cold seeps, despite elevated concentrations of methane and hydrogen sulfide, is attributed to multiple sources of habitat heterogeneity. In addition to geological and geochemical processes, biogenic habitats formed by large symbiont-bearing taxa, such as bivalves and siboglinid tubeworms, or by microbial mats drive the biodiversity of small-sized fauna. However, because these habitat-forming species also depend on geochemical gradients, the respective influence of abiotic and biotic factors in structuring associated macrofaunal communities is often unresolved. The giant pockmark Regab located at 3200m depth on the Congo margin is characterized by different fluid-flow regimes, providing a mosaic of the most common biogenic habitats encountered at seeps: microbial mats, mussel beds, and vesicomyid clam beds; the latter being distributed along a gradient of environmental conditions from the center to the periphery of the pockmark. Here, we examined the structure of macrofaunal communities in biogenic habitats formed in soft sediment to (1) determine the influence of the habitats on the associated macrofaunal communities (inter-habitat comparison), (2) describe how macrofaunal communities vary among vesicomyid clam beds (intra-habitat comparison) and (3) assess the inter-annual variation in vesicomyid beds based on repeated sampling at a three-year interval. The highest densities were found in the microbial mat communities in intermediate fluid-flow areas, but they had low diversity — also observed in the sediment close to mussel beds. In contrast, vesicomyid beds harbored the highest diversity. The vesicomyid beds did not show a homogeneous macrofaunal community across sampled areas; instead, density and composition of macrofauna varied according to the location of the beds inside the pockmark. The clam bed sampled in the most active, central part of the pockmark resembled bacterial mat communities by the presence of highly sulfide-tolerant species living at the sediment surface, along with vesicomyid juveniles. This similarity suggests a gradual change in community composition from mats to clam beds. Inter-annual comparisons of the different clam beds highlighted that the most active central site had a more variable community than its peripheral counterparts. Finally, a rapid shift in community structure, particularly in polychaete families, in experimentally reduced oxygen concentrations in the central part of Regab, suggests that high beta-diversity communities can withstand intense variation in geochemical conditions. These community dynamics are likely related to the diversity and to the plasticity of the vesicomyids themselves, because they can cope with high spatial and temporal environmental variability at a very local scale.

Impact of the clam Arca zebra artisanal fishery upon the population of the neogastropod Voluta musica in eastern Venezuela

120 An important ark clam ( Arca zebra ) artisanal fishery takes place in the east region of Venezuela. Besides the target species, trawling extracts a significant bycatch of several mollusk species including the gastropod Voluta musica, a threatened species according to the Venezuelan Red List of Endangered Species. In this paper we evaluate: 1) the composition of mollusk species in the bycatch, 2) the number of individuals of V. musica caught as bycatch and, 3) the abundance and size structure of the exploited population. Each fishing night, about 27,830 m2 are trawled by each boat extracting on the average 607 kg of A. zebra meat and 19 kg of V. musica (whole shelled animal). This fishery activity potentially captures ~30,000 kg of ark clam meat and 922 kg of V. musica in one week (~95 snails/fishing night/boat). The size structure of the V. musica population at the ark clam bed is significantly smaller than in other nearby sites not impacted by trawling fishing activities. Non-targeted species extracted in the bycatch but consumed by the local inhabitants include the gastropods Chicoreus brevifrons , Phyllonotus margaritensis , P. pomum , Fasciolaria tulipa , Strombus pugilis , a few Trochidae species, and the bivalves Pinctada imbricata , Spondylus americanus , Anadara floridana , A. notabilis , and Trachicardium muricatum . Individuals of V. musica along with several invertebrates are discarded. We recommend that V. musica should not be neglected as a conservation target, and despite that A. zebra fisheries are considered “artisanal”, that more strict regulations should be established on it. Normal 0 false false false EN-US X-NONE X-NONE /* Style Definitions */ table.MsoNormalTable {mso-style-name:Table Normal; mso-tstyle-rowband-size:0; mso-tstyle-colband-size:0; mso-style-noshow:yes; mso-style-priority:99; mso-style-parent:; mso-padding-alt:0in 5.4pt 0in 5.4pt; mso-para-margin:0in; mso-para-margin-bottom:.0001pt; mso-pagination:widow-orphan; font-size:10.0pt; font-family:Times New Roman,serif;}