Hemocyte cell types of the Cortes Geoduck, Panopea globosa (Dall 1898), from the Gulf of California, Mexico.

The geoduck Panopea globosa is an endemic and economic valuable species from the Mexican Northwest coast whose biology has been little studied. No information exists about their hemocytes to date, which is highly important to assess the welfare of wild and cultured organisms. In this study, hemocytes of adult P. globosa were characterized at the morphological, ultrastructural and functional level. The mean number of hemocytes in the hemolymph of P. globosa was 6 × 105 ± 2 × 105 cells mL-1. The cells were identified as granulocytes (Gr) and hyalinocytes (H). The former accounted for 28% of adhered cells in the hemolymph, measured 6-18 µm, showed numerous basophilic granules in the cytoplasm, with round and eccentric nuclei, and a nucleus:cytoplasm ratio of 0.44 ± 0.01. Hyalinocytes were the most abundant cells in the hemolymph of P. globosa (72% adhered cells) and were subdivided, according to their size, in small (Hs) 4-12 µm and large (HL) 6-18 µm. Hyalinocytes were eosinophilic round or ovoid cells with a central or eccentric nucleus, few or no granules in the cytoplasm and similar nucleus:cytoplasm ratio (Hs: 0.63 and HL: 061). Lysosomes and lipids were observed in Gr, while carbohydrates were the most abundant energy substrate in H. Both hemocytic cell types, mainly Gr, were capable to ingest particles and yield superoxide (P > 0.05). The present study shows for the first time the cell types, abundance and immune activities of hemocytes present in the hemolymph of P. globosa. This information provides a useful baseline to carry out further research on the cellular immune response of the clam to potential pathogens or changes in environmental factors.

Ontogenic Changes in Microhabitat Distribution of Juvenile Bay Scallops, Argopecten irradians irradians (L.), in Eelgrass Beds, and Their Potential Significance to Early Recruitment.

Ontogenetic changes in the vertical distribution of a cohort of juvenile bay scallops, Argopecten irradians, on eelgrass, Zostera marina, were followed throughout the summer and early fall in two Long Island embayments (New York, USA). Despite site-specific differences in eelgrass height and density, more than 95% of post-settlement scallops remained attached above the bottom until they reached a shell height of about 11 mm. Over a 5-week period, scallops gradually relocated until, at a mean size of 31 mm, all occurred on the bottom. The decline in percent attachment coincided with a 5-fold increase (from 16 to 84 µmoles min-1 g muscle dry wt-1) in the activity of octopine dehydrogenase (proposed here as an index of the scallops' capacity for burst swimming activity), and in maximum rate of increase in the shell aspect ratio. While attached to eelgrass, scallops were nonuniformly distributed, with greatest concentration at mid-canopy. Following disturbance, they rapidly regained above-ground position, attaining asymptotic heights within 3-10 h. This and prior studies suggest that the climbing behavior of the bay scallop is an adaptive response to high predation pressure at small sizes. Enhanced scope for activity (predator avoidance) may enhance survival of scallops at intermediate sizes, when they become too heavy to maintain elevation but have not yet attained effective refuge in size.