Swarming around Shellfish Larvae

Journal of Shellfish Research, 2018

From the 1980s through 1995, scientists at numerous marine, coastal, estuarine, and freshwater laboratories spawned bivalves to provide larvae for use in identifying species based on larval hinge structures and gross shell morphometry. These larvae were preserved in 95% ethanol and stored in sample vials, many of which dried out over the years. Advantage was taken of 50 of 56 species from this collection (and two additional species that were not in the collection for a total of 52 species) to explore the use of optical techniques (polarized light and a full-wave compensation plate) to highlight birefringence patterns of larval shells to discriminate individual species. Representative images of various developmental stages of 77% (40/52) of the larval bivalve species in the collection were successfully imaged. Similarities across birefringence patterns were observed at the taxonomic ordinal and familial level. Molecular polymerase chain reaction techniques were used in an effort to sequence many of the dried-out specimens and they successfully identified 19% (10/52) of the larval bivalve species with matches in GenBank. Here it has been demonstrated that optical techniques are efficient for imaging dried-out larval bivalve shells for classification purposes and we present successful sequences of 10 species of bivalve larvae from the preserved collection.

Marine Ecology Progress Series, 2012

Physical and biological conditions impact recruitment and adult population structure of marine invertebrates by affecting early life history processes from spawning to post-settlement. We investigated how temperature, salinity and phytoplankton influenced larval abundance and larval size structure for three species of bivalves over two non-consecutive years in Waquoit Bay, MA. Abundance and size of Mercenaria mercenaria (quahog), Anomia simplex (jingle clam), and Geukensia demissa (ribbed mussel) larvae were compared between locations in the bay and with environmental conditions. Shell birefringence patterns using polarized light microscopy were used to distinguish species. Larval abundances for all three species were higher in 2009 than in 2007 and were positively correlated with temperature in both years. Differences in larval abundance and size structure between bay sites were attributed to salinity tolerances and potential source locations. Higher survival in 2009 than in 2007, as determined by number of pediveligers, was likely due to higher temperatures and greater food availability during the peak abundance months of July and August in 2009. Yearly differences in larval growth and survival can have a large impact on recruitment. Knowing the optimal periods and locations for larval abundance and survival can be useful for isolating species-specific patterns in larval dispersal and to aid resource managers in enhancing or restoring depleted populations.

Journal of Plankton Research, 2007

We report the application of a recently developed molecular method, single step nested multiplex PCR (SSNM-PCR) assay and microscopy to identify and investigate temporal patterns of bivalve larvae in a Danish estuary, Isefjord. All samples were collected during the SUSTAINEX program from June to November 2001. Using the molecular assay, larvae could be categorized into six groups: the blue mussel, Mytilus edulis, Ensis spp., species of the Myoidae superfamily (Mya spp.), the common cockle (Cardiidae family), members of the Abra and Macoma genera of the Tellinoidae superfamily and members of the surf clam genera, Spisula spp. A seventh group was composed of unknown larvae. Greater resolution was possible by microscopy, but only for relatively large and intact individuals (.150-200 mm). The molecular approach was capable of differentiating between larvae regardless of shell size. Where it was possible to directly compare identifications based on both methods, concordance was high for M. edulis, Macoma balthica/Abra alba and E. americanus, whereas identification of Myoidae spp. and Cardiids was less consistent. Over the course of the study, two patterns of larval occurrence were observed. Larvae from species known to exhibit a protracted annual spawning period (M. edulis, Myoidae spp., Mysella bidentata and Cardiids) were present in the water column throughout the sampling period, whereas larvae of Abra alba, Barnea candida, E. americanus, Macoma balthica, Musculus marmoratus Scrobicularia plana and Tapes pullastra appeared at clearly defined periods.

Marine Biology, 1997

Epifluorescence microscopy was used to analyze the stomach contents of bivalve larvae collected in the Baie des Chaleurs (western Gulf of St. Lawrence, Canada) in order to document food-particle sizes, compare feeding among taxa, and compare the diet with the in situ phytoplankton community. Stomach contents were mainly composed of small autotrophic flagellates (<5 m) and cyanobacteria (<2 m), reflecting the microbial food web which characterizes these waters. More than half (55%) of all veligers examined contained algal cells of 5 to 15 m, whereas only 3% had cells of 15 to 25 m. Differences in the size ranges of ingested algal cells among similar-sized larvae of different species suggests that veligers actively selected food particles. Among the smallest veligers (185 to 260 m), scallops (Placopecten magellicanus) and mussels (Mytilus edulis) ingested more <5 m and 5 to 15 m algae than clams (Mya arenaria). Among larger veligers (261 to 405 m), clams contained significantly more <5 m cells than mussels, whereas mussels contained significantly more 5 to 15 m algae than clams. Algal cells of 15 to 25 m were preferentially ingested by mussel veligers. Feeding also differed between different-sized veligers within taxa, i.e. the smallest clam veligers ingested fewer of 5 to 15 m algae than the larger size classes. Mussel veligers ingested significantly more 15 to 25 m and fewer <5 m cells as their size increased. The dominance of ultra-plankton in the nearshore waters of Baie des Chaleurs and in the stomach contents suggests that veliger larvae may be an important export path for carbon produced by small phytoplankton.

2012

Physical and biological conditions impact recruitment and adult population structure of marine invertebrates by affecting early life-history processes from spawning to post-settlement. We investigated how temperature, salinity, and phytoplankton influenced larval abundance and larval size structure for 3 species of bivalves over 2 non-consecutive years in Waquoit Bay, Massachusetts, USA. Abundance and size of Mercenaria mercenaria (quahog), Anomia simplex (jingle clam), and Geukensia demissa (ribbed mussel) larvae were compared between locations in the bay and with environmental conditions. Shell birefringence patterns using polarized light microscopy were used to distinguish species. Larval abundances for all 3 species were higher in 2009 than in 2007 and were positively correlated with temperature in both years. Differences in larval abundance and size structure between bay sites were attributed to salinity tolerances and potential source locations. Higher survival in 2009 than in 2007, as determined by number of pediveligers, was likely due to higher temperatures and greater food availability during the peak abundance months of July and August in 2009. Yearly differences in larval growth and survival can have a large impact on recruitment. Knowing the optimal periods and locations for larval abundance and survival can be useful for isolating species-specific patterns in larval dispersal and to aid resource managers in enhancing or restoring depleted populations.

BENTHOS RESEARCH

Six years of data concerning larval recruitment processes,collected from1990to 1995,indicate that there are remarkable seasonal and annual fluctuations in the densities of different life stages of two species of bivalve mollusc(Ruditapes philippinarum and Musculista senhousia)that are common and abundant on Japanese tidal flats.Based on the results of cohort analyses for the two species,we estimated densities of planktonic larvae,new settlers,and recruits by cohort.Then,in order to identify the factors that are vital for determining the dynamics of the benthic populations,we examined the relationships be tween densities of planktonic larvae and new settlers,between the density of new settlers and recruitment success/failure,and between densities of new settlers and recruits.The present study indicates that recruit ment success/failure depends on a matching/mismatching with unpredictable environmental disturbances on the tidal flats.Furthermore,the density of recruits increases with that of new settlers for cohorts that succeed in recruiting,even though density effects were not detectable statistically between the two.Taking into account the results of the present study and our earlier reported findings,we conclude that remarkable seasonal and annual fluctuations in the densities of benthic populations can be caused by a few cohorts that have huge densities of planktonic larvae and new settlers and that subsequently manage to survive and succeed in recruiting.

Journal of Environment & Aquatic Resources, 2011

Lutraria sp., locally known as lapis, is an edible bivalve collected in Taguines Lagoon, Benoni, Camiguin much sought after by local resort visitors for the squid-like flavor and high nutritive value of its meat. Indiscriminate harvesting of this clam through the years had resulted in observable, though undocumented, reduction in its abundance and catch rates. Despite this, no investigations have been made about its habitat, life history, and aquaculture potential. This report presents the findings on the habitat characterization, spawning, fecundity, and larval development of Lutraria sp in Taguines Lagoon conducted in 2007. The substratum of the lagoon consisted predominantly of fine sand with coarse and very fine sand occurring in smaller proportions. Sediment pH was within a narrow range of 8.0-8.5, the organic matter content was low (0.742 -1.490%), salinity was at 33 ppt and water temperature ranged from 28-30 0 C. The diatoms Chaetoceros sp., Thalassiosira sp. and Coscinodiscus sp. dominated the phytoplankton; Calanus sp., Oithona sp. and Acrocalanus sp. were the dominant zooplankton; and nematodes, foraminiferans and bivalves dominated the meiofauna. Adult clams were commonly collected buried 30cm in the substrate although one juvenile was found buried at 12cm deep. Natural spawning under laboratory conditions was attained two months after broodstock conditioning and occurred either on the first quarter, full moon or last quarter phase of the moon. Only two female clams (SL=78.8mm and 89.7mm) survived under laboratory conditions, which released from 250,000 to 9 million eggs upon spawning. The fertilized eggs had a mean diameter of 56µ. Two-cell stage was reached 25 minutes after fertilization and trochophore stage was reached after 6 hours which hatched into D-larvae (SL=90µ) 18 hours later. Four-day old veligers (SL =120µ) became globular as the hinge line began rounding off and reached late umbo stage (SL=160µ) on Day 7. Pediveliger stage (SL= 201.38µ) was attained on Day 8 and began to settle as spats (SL=266.67µ) on Day 10. Research findings are useful in developing a sound and realistic strategy for management of this species, especially in its culture and large-scale seed production to replenish natural stocks and for future commercial utilization.

Palaeogeography Palaeoclimatology Palaeoecology, 1974

Journal of Sea Research, 2014

An individual based population model for bivalves was designed, built and tested in a 0D approach, to simulate the population dynamics of a mussel bed located in an intertidal area. The processes at the individual level were simulated following the dynamic energy budget theory, whereas initial egg mortality, background mortality, food competition, and predation (including cannibalism) were additional population processes. Model properties were studied through the analysis of theoretical scenarios and by simulation of different mortality parameter combinations in a realistic setup, imposing environmental measurements. Realistic criteria were applied to narrow down the possible combination of parameter values. Field observations obtained in the long-term and multistation monitoring program were compared with the model scenarios. The realistically selected modeling scenarios were able to reproduce reasonably the timing of some peaks in the individual abundances in the mussel bed and its size distribution but the number of individuals was not well predicted. The results suggest that the mortality in the early life stages (egg and larvae) plays an important role in population dynamics, either by initial egg mortality, larvae dispersion, settlement failure or shrimp predation. Future steps include the coupling of the population model with a hydrodynamic and biogeochemical model to improve the simulation of egg/larvae dispersion, settlement probability, food transport and also to simulate the feedback of the organisms' activity on the water column properties, which will result in an improvement of the food quantity and quality characterization.

Marine Ecology Progress Series, 2007

Accurate and efficient identification to the species level of early larval stages has long been a problematic step in the study of marine invertebrates, due to the extremely small size of the larvae and their lack of diagnostic morphological characters. It is nonetheless, a prerequisite for any ecological study. As a consequence, a number of molecular approaches, mostly based on the PCR technique, have been developed over the last decade. We developed a method relying on specific rRNA-targeted oligonucleotide probes for in situ molecular hybridization using whole larvae. A colorimetric reaction following the hybridization allows signal detection with a light microscope. A total of 9 probes have been developed, targeting the species that are major components of benthic communities in several European bays. The method can be applied to roughly sorted wild plankton samples, and some steps could be automated. It is relatively inexpensive to implement and does not require costly equipment or expensive staff training. The overall larval morphology is preserved, allowing visual inspection. The quantitative aspect of the approach is another asset. Field-based studies of larval distribution and behaviour are possible applications of the method, as large numbers of samples can be screened to meet the requirements of adequate spatial and temporal coverage. It is also relevant for routine monitoring of target species, such as species of commercial interest, bio-indicators or invasive species.