Clinocardium Nuttallii Research Articles

Population genomics of the basket cockle Clinocardium nuttallii in the southern Salish Sea: Assessing genetic risks of stock enhancement for a culturally important marine bivalve.

Coastal Indigenous communities that rely on subsistence harvests are uniquely vulnerable to declines in nearshore species. The basket cockle Clinocardium nuttallii is among the favored foods of Indigenous people along the northwest Pacific coast of North America, yet localized declines in their abundance have led to interest in stock enhancement efforts. We used a population genomics approach to examine potential risks associated with stock enhancement of C. nuttallii in the southern Salish Sea, a large inland estuary that includes Puget Sound. More than 8000 single nucleotide polymorphisms across 349 individuals at 12 locations were assembled de novo using restriction site‐associated DNA sequencing. Results indicated that C. nuttallii within the southern Salish Sea were distinct from those along the outer Pacific coast (F ST = 0.021–0.025). Within the southern Salish Sea, C. nuttallii populations appear to be well‐connected despite numerous potential impediments to gene flow; Hood Canal, which experiences the lowest flushing rates of all Puget Sound sub‐basins, was a minor exception to this strong connectivity. We found evidence of isolation by distance within the southern Salish Sea, but the slope of this relationship was shallow, and F ST values were low (F ST = 0.001–0.004). Meanwhile, outlier analyses did not support the hypothesis that southern Salish Sea sub‐populations are locally adapted. Estimates of effective population size had no upper bound, suggesting potentially very high adaptive capacity in C. nuttallii, but also making it difficult to assess potential reductions in effective population size resulting from stock enhancement. We present several strategies to augment cockle populations for subsistence harvest that would limit risk to the genetic diversity of wild cockle populations.

Estimating the distribution of harvested estuarine bivalves with natural-history-based habitat suitability models

Habitat suitability models are useful to estimate the potential distribution of a species of interest, particularly in the case of infaunal bivalves. Sampling for these bivalves is time- and cost-intensive, which is increasingly difficult for organizations or agencies that are limited by personnel and funds. Consequently, we developed a framework to identify suitable bivalve habitat in estuaries (FISBHE) – a habitat suitability index (HSI) modeling framework for NE Pacific estuaries that was parameterized with published natural-history information and existing habitat datasets, without requiring extensive field sampling of bivalves. Spatially explicit, rule-based habitat suitability models were constructed in a GIS for five species of bay-clams (Clinocardium nuttallii, Mya arenaria, Tresus capax, Saxidomus gigantea, and Leukoma staminea) that are popular targets for recreational and commercial harvest in estuaries of the U.S. Pacific Northwest. Habitat rasters were produced for Yaquina and Tillamook estuaries (Oregon, USA) using environmental data (bathymetric depth, sediment % silt-clay, wet-season salinity, and burrowing shrimp presence/absence) from multiple studies (1953–2015). These habitat rasters then served as inputs in the final model which produced HSI classes ranging from 0 to 4 (lowest to highest suitability), dependent upon the number of habitat variables that fell within the sensitivity limits for each species of bay-clam. The models were tested with validation analyses and bay-clam occurrence data (reported in benthic community studies, 1996–2012) within each HSI class; logistic regression and Kendall's correlation coefficient both showed correspondence between predicted HSI classes and bay-clam presence/absence. Results also showed that the greatest presence probabilities occurred within habitats of highest predicted suitability, with the exception of M. arenaria in Tillamook Bay. The advantage of FISBHE is that disparate, independent sets of existing data are sufficient to parameterize the models, as well as produce and validate maps of habitat suitability. This approach can be transferred to data-poor systems with modest investment, which can be useful for prioritizing estuarine land-use decisions and could be used to estimate the vulnerability of this valued ecosystem good to changes in habitat quality and distribution.

Intertidal clams exhibit population synchrony across spatial and temporal scales.

Long‐term datasets can be particularly useful for parsing out factors influencing populations, yet few studies have utilized continuous datasets to quantify population dynamics in bivalve molluscs. We used dynamic factor analysis on a clam biomass dataset spanning 28 yr and five distinct regions in the southern Salish Sea to determine (1) if native intertidal clam populations exhibit synchrony and (2) what environmental covariates may be correlated with these population trends. Once covariates were accounted for, the model with the most data support included three predominant trends to describe multidecadal change in clam biomass. Intraspecific synchrony was highest among Saxidomus gigantea and Leukoma staminea populations, with no clear evidence of covariance in Clinocardium nuttallii. Specifically, we quantified a pronounced decadal decline in L. staminea and an increase in S. gigantea biomass on most beaches. No beaches showed synchrony in trends across all three species, indicating that species‐specific trends (regardless of location) were more common than beach‐specific trends (regardless of species). Seven environmental covariates were evaluated in their capacity to explain variability in annual mean biomass. Of these, the North Pacific Gyre Oscillation lagged 4 yr prior to the observation year was most supported by the data in the best fitting model, implying that 4 yr old clam biomass is partially determined by oceanographic processes affecting larval clams. Although results suggest large‐scale density‐independent factors play a role in venerid clam population dynamics, it is also likely local factors account for variability not explained by our model.

Effect of Green Macroalgal Blooms on the Behavior, Growth, and Survival of Cockles (Clinocardium nuttallii) in Pacific NW Estuaries.

Nutrient over-enrichment can produce adverse ecological effects within coastal ecosystems and negatively impact the production of ecosystem goods and services. In small estuaries of the U.S. Pacific Northwest, seasonal blooms of green macroalgae (GMA; Family Ulvaceae) are primarily associated with natural nutrient input, rather than anthropogenic sources. This provided us a unique opportunity to investigate the effects of naturally-stimulated macroalgal blooms on intertidal bivalves. Clinocardium nuttallii (heart cockles) are an important species for shellfisheries in the region. In summer population surveys, we found that cockles emerged from the sediment with greater frequency as GMA biomass increased. Experimental manipulation of GMA biomass in the field showed that GMA elicited emergence, evoked above-ground lateral movement, inhibited shell growth, and increased mortality (by 34.0 ± 15.2%) in cockles. Laboratory experiments revealed that the interaction of a weighted barrier at the sediment surface and GMA presence elicited rapid emergence among cockles. Risk assessment of the emergence response in cockles showed that the in situ emergent population experienced 11.0 ± 8.0% mortality due to gull predation, while laboratory exposure to elevated temperatures (≥34 °C) slowed valve-closure, inhibited reburial, and increased mortality, which could have translated to 7.1 ± 1.5% in situ mortality. We found that cockles avoided mortality due to burial below GMA mats by emerging from the sediment, but that behavior consequently put them at risk of mortality due to heat stress or gull predation. Regardless of nutrient source, our research showed that GMA blooms pose a threat to the survival of intertidal bivalves.

Effects of temperature, diet, and bivalve size on the ingestion of sea lice (Lepeophtheirus salmonis) larvae by various filter-feeding shellfish

Filter-feeding shellfish could act as biological agents in the control of parasitic sea lice (Caligidae) at salmon farms as a benefit of integrated multi-trophic aquaculture. Determining the extent to which various bivalve species ingest sea lice (Lepeophtheirus salmonis) larvae under controlled laboratory conditions was an important first step towards understanding the potential for shellfish to reduce the number of these copepod larvae in the water column at net pens. A series of laboratory experiments examined the effects of temperature (~5, 10, and 15°C), diet (larvae alone or with phytoplankton), and bivalve size (small, medium, and large) on the amount of L. salmonis larvae ingested by basket cockles (Clinocardium nuttallii), Pacific oysters (Crassostrea gigas), mussels (Mytilus spp.), and Pacific scallops (unconfirmed hybrid: Mizuhopecten yessoensis x Patinopecten caurinus). Feeding rate was assessed by placing bivalves individually in 2-l containers holding approximately 450 larvae in 750ml of filtered seawater. Results of the temperature/diet experiments indicated that all four species of bivalves ingested sea lice larvae, regardless of phytoplankton presence or absence, and that temperature had no significant effect on the proportion of larvae ingested. All three sizes of oysters and scallops ingested sea lice larvae, with large shellfish consuming a significantly greater proportion of the larvae than small individuals. Future research, examining the role of bivalves in the control of sea lice, should be continued at a commercial scale at a salmon farm.

Aquaculture potential of the basket cockle (Clinocardium nuttallii). Part 1: effects of stocking density on first year grow-out performance in intertidal and off-bottom suspended culture

The basket cockle (Clinocardium nuttallii) is a candidate species for aquaculture in the northeast Pacific. The aim of the current research was to assess the feasibility of C. nuttallii grow-out, with an emphasis on growth performance and qualities affecting product marketability. In this article, we investigated the combined effects of culture mode (intertidal and off-bottom suspended culture) and initial stocking density (1500, 3000, 10 500 and 21 000 ind m−2) on C. nuttallii survival and growth during the first year of grow-out (May through October). In intertidal culture, cockles exhibited low survival and poor growth rates. In suspended culture, survival was consistently high (>96%) at all stocking densities tested; growth and condition parameters had the highest values at 1500 and 3000 ind m−2. The edible portion (meat yield) exceeded 40% of the whole wet weight at all stocking densities, occurrences of fouled and deformed cockles were <1% and no commensal species were observed. Depending on the minimum harvestable size and stocking density chosen, harvestable proportions constituted from 1.1% to 15.2% by October of the first grow-out year in the suspended system. The effects of stocking density and depth on second year grow-out performance of C. nuttallii are reported in a companion paper (Dunham et al. in this issue).

Aquaculture potential of the basket cockle (Clinocardium nuttallii). Part 2: effects of stocking density and depth on second year grow-out performance of three size cohorts in intertidal and off-bottom suspended culture

We investigated the effects of culture mode (intertidal and off-bottom suspended culture) and initial stocking density (5%, 10%, 35% and 70% bottom cover) on survival, growth and condition indices of three size cohorts (16, 22 and 32 mm initial shell length) of the basket cockle, Clinocardium nuttallii, during a second year of grow-out. In addition, we evaluated the effects of depth (2, 4 and 6 m) in suspended culture. All size cohorts demonstrated significantly higher growth rates, soft-tissue biomass and condition indices in the off-bottom suspended system compared to the intertidal one. In suspended culture, however, C. nuttallii exhibited sub-optimal survival, shell deformities and heavy fouling. For all size cohorts, stocking density had a significant effect on most growth and condition parameters, except meat yield indices, in both culture modes. An initial maximum stocking density of 10% cover is recommended for all size cohorts. Culture depth did not have a consistent statistically significant effect on any of the growth or condition parameters. Depending on the grow-out scenario, stocking density and harvestable size chosen, the cumulative harvestable proportion after the second year of grow-out constituted 15.5–63.1% of the seed planted. Our results could be used to develop and improve culture techniques for C. nuttallii and other cockle species.

Using stocking density modifications and novel growth medium to control shell deformities and biofouling in suspended culture of bivalves

Bivalve aquaculture currently utilizes two main farming practices: intertidal (beach) and deep-water (suspended) culture. Although suspended culture offers a number of advantages during both nursery and grow-out phases, two commonly encountered issues – shell deformities and biofouling – lead to reduced seed and final product quality in some species and preclude other species from being cultured in suspension. None of the existing strategies for controlling these issues is efficient and fully reliable. In this study we tested the efficiency of two new methods for controlling biofouling and shell deformities in suspended culture of bivalves using basket cockle Clinocardium nuttallii as a model species. The first method involved a short-term increase in bivalve stocking density during peak plankton concentrations and biofouling settlement periods. The second method comprised adding artificial growth medium (expanded clay aggregate) to culture enclosures. Both high-density and growth medium treatments significantly reduced the incidence of C. nuttallii shell deformities compared to the control treatment (by 86 and 72%, respectively). This finding suggests that clam shell deformities in suspended culture primarily develop due to the lack of structural support normally offered by the substratum. Both treatments also significantly reduced barnacle fouling rate (by 67 and 83%, respectively). Additionally, growth medium treatment led to a significant reduction in tube worm fouling, as well as combined fouling rate and intensity, but it was less effective in controlling sponge fouling. Overall, both high-density and growth medium treatments showed promise in reducing the incidence of shell deformities and the amount of biofouling on C. nuttallii in suspended culture. These treatments are inexpensive, environmentally-friendly, readily available to shellfish growers, and may be further refined and adapted for a variety of cultured bivalve species. They have the potential to improve the efficiency of suspended grow-out systems and extend the option of suspended culture to bivalve species currently grown on the beach only.

Effects of stocking density, ration, and temperature on growth of early post-settled juveniles of the basket cockle, Clinocardium nuttallii

The effects of stocking density, ration, and temperature on seed growth – from early post-settlement to a size suitable for out-planting ( i.e. ~ 4 mm shell length) – and the effect of stocking density on metamorphic rates were examined for the basket cockle, Clinocardium nuttallii, to determine optimal hatchery rearing conditions for this species. The effect of stocking density on seed growth depended on sampling time. A significant finding of the research was that optimal seed growth can be maintained when less than ~ 100% of the rearing unit's bottom area is covered, regardless of seed size. Metamorphic rates were high (88.2–91.0%) and not significantly affected by stocking density in the tested range (20–320 ind cm −2). Optimal rations were determined for five different size classes of seed fed a bi-algal diet of Chaetoceros muelleri and Isochrysis sp. (Tahitian strain, TISO) and these were, respectively, 3.2, 6.4, 6.4, 12.8, and 25.6 × 10 6 equivalent-TISO cells ind − 1 d − 1 for size classes 1 (initial mean shell length: 0.74 mm), 2 (1.59 mm), 3 (2.10 mm), 4 (2.60 mm), and 5 (3.00 mm). Whilst optimal rations generally increased with an increase in seed shell length, the opposite trend was observed for weight-specific rations. Faster-growing seed built up higher organic matter content in their body than slower-growing individuals, suggesting that satiation feeding for maximum growth should be preferred during hatchery rearing. Due to the rapid growth of seed over a short period of time, frequent adjustments of both stocking density and ration are necessary in order to best utilise available resources ( i.e. space and food) and to maintain maximum growth over time. Seed were grown at various temperatures (range of means: 5.9–26.4 °C) with optimal growth occurring at 18.3 °C.

Effects of stocking density and substratum on the survival, growth, burrowing behaviour and shell morphology of juvenile basket cockle, Clinocardium nuttallii: implications for nursery seed production and field outplanting

The basket cockle, Clinocardium nuttallii, is a candidate species for aquaculture in British Columbia, Canada. Previous research on broodstock conditioning, embryonic development and larval rearing of C. nuttallii demonstrated the potential for reliable hatchery production of cockle seed. In this paper, we investigated the effects of culture density (50% and 150% bottom cover in a monolayer) and substratum (none and fine sand) on cockle seed survival, growth, behaviour and shell morphology to improve the efficiency of the nursery production phase. Low stocking density (50% cover) yielded a shell length increase from 3 to 7 mm over a 4-week period. High stocking density (150% cover) negatively impacted some of the growth and condition parameters studied, but did not have a statistically significant effect on seed survival. Growing seed without substratum did not significantly affect seed survival or growth, but led to shell deformities (at shell length >15 mm) and lower burrowing rates when cockles were subsequently placed on sand. We recommend planting seed for grow-out at a shell length not exceeding 15 mm. Acclimating seed to the substratum before planting may increase the burrowing rates, thereby reducing the risks of seed dislocation and mortality. Additional studies are required to determine optimal substratum acclimation times and techniques.

Effects of stocking density, algal density, and temperature on growth and survival of larvae of the basket cockle, Clinocardium nuttallii

This study determined optimal rearing conditions – stocking density, algal density, and temperature – for hatchery production of the basket cockle, Clinocardium nuttallii, from newly-hatched D-larvae to pediveligers using static rearing systems and discontinuous feeding. The combined effect of initial stocking density (2, 4, and 8 larvae ml − 1 ) and algal density (10, 25, and 50 × 10 3 cells ml − 1 ) on larval growth and survival was examined using a bi-algal diet of Chaetoceros muelleri (CM) and Isochrysis sp. (Tahitian strain, TISO). The effect of algal density (0, 2.5, 5, 10, 20, 40, 60, and 80 × 10 3 cells ml − 1 ) as a single factor was assessed using a single-algal diet of TISO and a fixed stocking density (2 larvae ml − 1 ) held constant throughout the experiment. The effect of temperature (5.9, 10.2, 14.2, 18.2, 21.9, and 26.3 °C) on larval growth and survival was also evaluated. The results showed that, when feeding the bi-algal diet of CM and TISO, an initial stocking density of 2 larvae ml − 1 combined with an algal density of 25 or 50 × 10 3 cells ml − 1 or an initial stocking density of 4 larvae ml − 1 combined with an algal density of 50 × 10 3 cells ml − 1 were optimal conditions for larval growth, and survival rate was significantly better in the treatment with 4 larvae ml − 1 . When feeding the single-algal diet of TISO, optimal larval growth was observed at algal densities of ≥ 40 × 10 3 cells ml − 1 . These optimal rearing conditions translated into minimum food rations of 18.4 and 20 × 10 3 algal cells larva − 1 day − 1 using the bi-algal and single-algal diets, respectively, to support maximum larval growth from newly-hatched D-larvae to pediveligers. Within the tested temperature range of 5.9 to 21.9 °C, larval growth was greater with increasing temperature but survival to settlement stage was not affected by temperature. The larvae failed to survive at the highest tested temperature of 26.3 °C.

Effects of microalgal diets on the growth and survival of larvae and post-larvae of the basket cockle, Clinocardiumnuttallii

The nutritional value of four microalgal species: Chaetoceros muelleri, Pavlova lutheri, Tahitian strain of Isochrysis sp. (TISO), and Thalassiosira pseudonana in single- and bi-species diets was evaluated for larvae and post-larvae of the basket cockle, Clinocardium nuttallii. Larval shell growth and metamorphic rate were found to be the greatest with both single- and mixed-species diets comprising TISO. For the post-larvae, however, optimal shell growth was observed in both single- and mixed-species diets containing Chaetoceros muelleri. In another feeding experiment, the microalga Tetraselmis suecica was tested singly and in combination with TISO. Results showed that the food value of Tetraselmis suecica alone was poor for both larvae and post-larvae. In contrast, the mixed-species diet of Tetraselmis suecica and TISO resulted in significantly improved larval and post-larval growth, similar to the respective best (control) diets as identified in the first experiment. It is concluded that, for the hatchery production of Clinocardium nuttallii seed, a single-species diet of TISO is the best for the larvae and a single-species diet of Chaetoceros muelleri is the best for the post-larvae. A nutritional transition period during which both the microalgal species may be required, is also suggested for the hatchery production of basket cockle seed.

Fertilization and Embryonic Development in the Basket Cockle, Clinocardium nuttallii

Sperm motility, fertilization, and embryonic development were investigated in the hermaphroditic basket cockle, Clinocardium nuttallii. Motility of the sperm was more prolonged over a 2-h storage period at 4C than at 19C. The sperm-to-egg ratio resulting in the highest fertilization rate was 10,000:1, or an equivalent final sperm concentration of 6 3 10 5 cells mL -1 , using a density of 60 eggs mL -1 . However, at least some degree of self-fertilization appeared to be unavoidable during the release of the eggs from the broodstock. The biological zero point, below which embryonic development ceased, was estimated to be 2.8 Ct o 2.9C for C. nuttallii.

Broodstock Conditioning in the Basket Cockle, Clinocardium nuttallii

Factors affecting broodstock conditioning in the hermaphroditic basket cockle, Clinocardium nuttallii, were examined in laboratory experiments. Although a 13-wk experiment conducted at 16°C failed to bring C. nuttallii broodstock into spawning condition under different dietary treatments, initiation of gametogenesis was apparent for those broodstock maintained at 2.5°C. Condition indices were significantly greater when broodstock were fed a combination of Isochrysis galbana (Tahitian strain, T-iso) and Chaetoceros gracilis (CG) or T-iso and Thallasiosira pseudonana (3H) than when fed a combination of Tetraselmis suecica (TS) and 3H or TS and CG, indicating that T-iso may be a better food source than TS for cockle broodstock conditioning.

Malacological insights into the marine ecology and changing climate of the late Pleistocene – early Holocene Queen Charlotte Islands archipelago, western Canada, and implications for early peoples

The first intertidal species to colonize the Queen Charlotte Islands archipelago along the northeastern Pacific margin of Canada after the last glacial maximum (LGM) was Macoma nasuta at 13 210 ± 80 14C years BP. Prior to this time, molluscs were likely excluded where grounded ice extended from the 2 km thick Cordilleran ice sheet on mainland British Columbia. Low water temperatures, high sedimentation rates, high turbidity, dilution, and low primary productivity limited invertebrate colonization subsequent to the LGM, a period of rapid sea-level and climate change. As an adult, M. nasuta is a facultative deposit-suspension feeder that tolerates high turbidity and lowered salinity, and its pediveligers and early juveniles must also have been able to survive these conditions. Subsequently, in addition to M. nasuta, Macoma irus (inquinata), Saxidomus giganteus, Protothaca staminea, Protothaca tenerrima, Hiatella pholadis, Clinocardium nuttallii, and Mytilus trossulus constituted a typical intertidal bivalve assemblage. These findings are explained in terms of the physiology, feeding mechanisms, development, and sediment preferences of living molluscs. The disappearance of most bivalve species between ~11 000 and 10 000 14C years BP indicates the onset of a short interval of low sea-surface temperatures coincident with the Younger Dryas cooling event. Some cold-hardy species persisted, including Clinocardium californiense, Mya truncata, and Serripes groenlandicus. Bivalve species not previously reported as Pleistocene fossils were collected in sediments dating older than 10 000 14C years BP. They include Macoma incongrua, Musculus taylori, Mytilimeria nuttallii, and Tellina nuculoides. Fossil assemblages of intertidal molluscs are used to map ancient shorelines and indicate which species were available as a subsistence resource for early peoples from at least 13 210 ± 80 14C years BP. Intertidal food biomass densities may have reached present commercially harvested levels on southern Moresby Island by 8800 ± 70 14C years BP and on northern Graham Island by 8990 ± 50 14C years BP. When early peoples might have been migrating along the littoral zone, the molluscan productivity of the outer coast was much higher than it is at present.

Pumping Rates, Water Pressures, and Oxygen Use in Eight Species of Marine Bivalve Molluscs from British Columbia

Pumping characteristics and oxygen utilization for Solemya reidi, Yoldia thraciaeformis, Chlamys hastata, Mytilus edulis, Crassostrea gigas, Clinocardium nuttallii, Saxidomus giganteus, and Mya truncata were studied. Pressures were recorded using a Yale A79 spinal tap needle inserted in the pallial cavity or siphonal aperture. Pumping volumes were determined through particulate analysis using a Model B Coulter counter and oxygen consumption by standard Winkler titration modified for small samples. The species chosen were selected to represent progressive increases in gill complexity and siphon length. The minimum pressure differential across the gill (20 Pa) was observed for Y. thraciaeformis while the maximum pressure gradient (600 Pa) was recorded for M. truncata. Pumping rates varied from 1.41 L∙h−1∙g−1 (Y. thraciaeformis) to 4.71 L∙h−1∙g−1 (C. hastata) and species with siphons tended to pump at lower rates. The deeply burrowing M. truncata consumed 3.5 times as much oxygen (0.63 mL O2∙h−1∙g−1) as S. reidi (0.18 mL O2∙h−1∙g−1) which inhabits anoxic environments. For all species, the metabolic cost of pumping was less than 1% of the total oxygen uptake.

INFAUNAL RECOVERY AT EDIZ HOOK FOLLOWING THE ARCO ANCHORAGE OIL SPILL

ABSTRACT The Arco Anchorage crude oil spill occurred near Ediz Hook, in Port Angeles, Washington, in 1985. Following the spill, replicate infaunal sampling was carried out during five summer and winter seasons at a series of transects that ranged from relatively clean and unaffected by the spill to industrialized sites that had received heavy oiling. Average wet weight biomass, abundance, species diversity, and number of species were calculated for all samples. Analysis of variance was used to test for differences in these parameters over time within a transect. A statistically significant increase in average biomass, density, and species diversity was seen at several heavily oiled stations over time. A similar pattern was not seen at an unoiled reference station. Biomass, density, and number of species had significant negative correlations with sediment hydrocarbon concentration. A widespread settlement of bivalves was observed in October 1986 samples. Several species from this settlement (e.g., Macoma nasuta and Clinocardium nuttallii) were present in successively larger sized classes in subsequent samplings. The industrialized nature of Ediz Hook and pollution events unrelated to the oil spill probably limited the degree of recovery and re-colonization documented at several of the transects.

Podocytes in bivalve molluscs: Morphological evidence for ultrafiltration

In representatives from a survey of three major taxa of bivalves the pericardial glands were found in two distinct positions. In protobranches (Acila castrensis) and filibranch bivalves (Glycymeris subobsoleta, Chlamys hastata, Pecten caurinus, Placopecten magellanicus, Mytilus edulis andMytilus californianus) the pericardial glands are located on the auricular surface. In heterodonts (Mercenaria mercenaria, Clinocardium nuttallii andMya arenaria) the pericardial glands are found in an anterodorsal position to the pericardial cavity.

Comparative pumping rates in suspension-feeding bivalves

Pumping rates in undisturbed suspension-feeding bivalves were measured with a thermistor microflowmeter. Pumping rates are related to the dry weight of Clinocardium nuttallii, Macoma nasuta, Mytilus californianus and Chlamys hastata as the following equations: P=0.85 W0.84, P=0.23 W0.855, P=2.216 W0.715, and P=2.419 W0.943 respectively. Pumping rate and gill area increase at the same rate in C. nuttallii, M. californianus and C. hastata. The pumping rate per unit gill area is highest for C. nuttallii (approximately 0.14 cm3/s/cm2), with intermediate values for M. californianus (∼0.08 cm3/s/cm2) and C. hastata (∼0.11 cm3/s/cm2); the lowest rate was found in the deposit-feeder M. nasuta (∼0.0057 to 0.0089 cm3/s/cm2), which also has the smallest gill to body weight. C. nuttallii has the relatively smallest gill of the suspension feeders and the highest pumping rate per unit gill area. The absolute pumping rates, however, were highest for the filibranchs M. californianus and C. hastata. Indications are given that these differences are the results of different fluid-mechanical/ecological strategies to minimize the cost-benefit ratio.

Winter feeding by asteroids on a subtidal sandbed in British Columbia

Abstract The winter feeding of the asteroids Mediaster aequalis, Luidia foliolata, Pisaster brevispinus and Pycnopodia helianthoides on a subtidal sandbed in British Columbia is reported. Bivalve predation and experiments with the latter three species examining size-related predation, sand as a prey refuge and prey escape behavior are reported using the cockle Clinocardium nuttallii. M. aequalis is a small species with a very broad diet and mainly a microphagous feeder which may graze recently settled bivalve larvae. L. foliolata is a burrowing species which specializes in swallowing small infaunal bivalves whose size usually cannot exceed its disc (mouth) diameter of 40 mm. P. brevispinus is large and grazes barnacles on hard substrates, and on sand specializes in excavation of larger bivalves such as the geoduck clam Panope abrupta and the jacknife clam Solen sicarius. P. helianthoides is a large, highly opportunistic predator which grazes epifauna on hard substrates, excavates larger bivalves from sand...