Jennifer H. Alix

Growth of post-set oysters, Crassostrea virginica, on high-lipid strains of algal flagellates Tetraselmis spp.

Abstract Nine microalgal strains from the prasinophyte genus Tetraselmis that were chosen for high total lipid content, and one marine strain of the chlorophyte Chlamydomonas , were compared with Isochrysis sp., strain T-ISO, as diets for oyster spat in a controlled laboratory feeding experiment. Five of these high-lipid Tetraselmis strains supported significantly faster oyster growth than an equivalent ration of T-ISO. Doubling times for oyster weight, volume, and shell height were in the range of 1.5–3 weeks on single daily feedings of the best diets. Tetraselmis strains yielding the most rapid oyster growth contained higher contents of the essential fatty acid 20:5 n − 3 and of the sterols 24-methylcholesterol and/or 24-methylenecholesterol. These data are consistent with our earlier findings that these compounds appear to be deficient in most phytoplankton for optimal growth of Crassostrea virginica spat.

Combined effects of a parasite, QPX, and the harmful-alga, Prorocentrum minimum on northern quahogs, Mercenaria mercenaria

Northern quahogs, Mercenaria mercenaria (L.), frequently are infected with the parasite Quahog Parasite Unknown (QPX, Labyrintohomorpha, Thraustochytriales), which can cause morbidity and mortality of the quahogs. Possible interactions between this parasitic disease and exposure to the harmful dinoflagellate Prorocentrum minimum in M. mercenaria were studied experimentally. Quahogs from Massachusetts with variable intensity of QPX infection were exposed, under controlled laboratory conditions, to cultured P. minimum added to the natural plankton at a cell density equivalent to a natural bloom. After 5 days of exposure, individual clams were diagnosed histologically to assess prevalence and intensity of parasitic infection, as well as other pathological conditions. Further, cellular defense status of clams was evaluated by analyzing hemocyte parameters (morphological and functional) using flow-cytometry. Exposure of quahogs to P. minimum resulted in: a lower percentage of phagocytic hemocytes, higher production of reactive oxygen species (ROS), larger hemocyte size, more-numerous hemocytic aggregates, and increased numbers of hemocytes in gills accompanied by vacuolation and hyperplasia of the water-tubular epithelial cells of the gills. Quahogs had a low prevalence of QPX; by chance, the parasite was present only in quahogs exposed to P. minimum. Thus, the effect of QPX alone on the hemocyte parameters of quahogs could not be assessed in this experiment, but it was possible to assess different responses of infected versus non-infected quahogs to P. minimum. QPX-infected quahogs exposed to P. minimum had repressed percentage of phagocytic hemocytes, consistent with immuno-modulating effect of P. minimum upon several molluscan species, as well as smaller hemocytes and increased hemocyte infiltration throughout the soft tissues. This experiment demonstrates the importance of considering interactive effects of different factors on the immunology and histopathology of bivalve shellfish, and highlights the importance of considering the presence of parasites when bivalves are subjected to harmful-algal blooms.

Physiological and pathological changes in the eastern oyster Crassostrea virginica infested with the trematode Bucephalus sp. and exposed to the toxic dinoflagellate Alexandrium fundyense.

Effects of experimental exposure to Alexandrium fundyense, a Paralytic Shellfish Toxin (PST) producer known to affect bivalve physiological condition, upon eastern oysters, Crassostrea virginica with a variable natural infestation of the digenetic trematode Bucephalus sp. were determined. After a three-week exposure to cultured A. fundyense or to a control algal treatment with a non-toxic dinoflagellate, adult oysters were assessed for a suite of variables: histopathological condition, hematological variables (total and differential hemocyte counts, morphology), hemocyte functions (Reactive Oxygen Species (ROS) production and mitochondrial membrane potential), and expression in gills of genes involved in immune responses and cellular protection (MnSOD, CAT, GPX, MT-IV, galectin CvGal) or suspected to be (Dominin, Segon). By comparing individual oysters infested heavily with Bucephalus sp. and uninfested individuals, we found altered gonad and digestive gland tissue and an inflammatory response (increased hemocyte concentration in circulating hemolymph and hemocyte infiltrations in tissues) associated with trematode infestation. Exposure to A. fundyense led to a higher weighted prevalence of infection by the protozoan parasite Perkinsus marinus, responsible for Dermo disease. Additionally, exposure to A. fundyense in trematode-infested oysters was associated with the highest prevalence of P. marinus infection. These observations suggest that the development of P. marinus infection was advanced by A. fundyense exposure, and that, in trematode-infested oysters, P. marinus risk of infection was higher when exposed to A. fundyense. These effects were associated with suppression of the inflammatory response to trematode infestation by A. fundyense exposure. Additionally, the combination of trematode infestation and A. fundyense exposure caused degeneration of adductor muscle fibers, suggesting alteration of valve movements and catch state, which could increase susceptibility to predation. Altogether, these results suggest that exposure of trematode-infested oysters to A. fundyense can lead to overall physiological weakness that decrease oyster defense mechanisms.

Ocean Acidification Affects Hemocyte Physiology in the Tanner Crab (Chionoecetes bairdi).

We used flow cytometry to determine if there would be a difference in hematology, selected immune functions, and hemocyte pH (pHi), under two different, future ocean acidification scenarios (pH = 7.50, 7.80) compared to current conditions (pH = 8.09) for Chionoecetes bairdi, Tanner crab. Hemocytes were analyzed after adult Tanner crabs were held for two years under continuous exposure to acidified ocean water. Total counts of hemocytes did not vary among control and experimental treatments; however, there were significantly greater number of dead, circulating hemocytes in crabs held at the lowest pH treatment. Phagocytosis of fluorescent microbeads by hemocytes was greatest at the lowest pH treatment. These results suggest that hemocytes were dying, likely by apoptosis, at a rate faster than upregulated phagocytosis was able to remove moribund cells from circulation at the lowest pH. Crab hemolymph pH (pHe) averaged 8.09 and did not vary among pH treatments. There was no significant difference in internal pH (pHi) within hyalinocytes among pH treatments and the mean pHi (7.26) was lower than the mean pHe. In contrast, there were significant differences among treatments in pHi of the semi-granular+granular cells. Control crabs had the highest mean semi-granular+granular pHi compared to the lowest pH treatment. As physiological hemocyte functions changed from ambient conditions, interactions with the number of eggs in the second clutch, percentage of viable eggs, and calcium concentration in the adult crab shell was observed. This suggested that the energetic costs of responding to ocean acidification and maintaining defense mechanisms in Tanner crab may divert energy from other physiological processes, such as reproduction.

IMPACTS OF A CYANOBACTERIUM CONTAMINATING LARGE-SCALE AQUACULTURE FEED CULTURES OF TETRASELMIS CHUI ON SURVIVAL AND GROWTH OF BAY SCALLOPS, ARGOPECTEN IRRADIANS IRRADIANS

Abstract Large-scale, open, microalgal feed cultures for hatchery and nursery production of marine invertebrates inevitably becomes contaminated with various microbes that can affect productivity and usability of the harvested biomass. In the Greenhouse for Research on Algal Mass Production Systems (GRAMPS) at the NMFS Laboratory in Milford, CT, cultures of Tetraselmis chui (PLY429) often become contaminated with a cyanobacterium; preliminary observations suggested that juvenile bay scallops, Argopecten irradians irradians showed reduced performance when the feed culture became contaminated with this cyanobacterium. We isolated a cyanobacterium from a contaminated culture of PLY429 and conducted a feeding study to determine if this isolate affects survival and growth of juvenile bay scallops, either alone or in combination with PLY429, thereby simulating feeding of a contaminated culture. Bay scallops were given a diet of either 100% PLY429, 50% PLY429 with 50% cyanobacteria, 100% cyanobacteria, or starved. There was 100% mortality of bay scallops by week 3 when they were starved, with a significant difference in survival between diets (P < 0.01). At 6 wk the scallops fed only the cyanobacterium had 63% survival, 93% survived in the mixed diet, and 98% survived when fed 100% PLY429. The net growth of bay scallops on the different diets was also significantly different (P < 0.01) with scallops fed 100% PLY429 having the highest shell-growth rate of 198-μm scallop−1 d−1, and growth rates of 82-μm scallop−1 d−1 on the mixed diet, and 65-μm scallop−1 d−1 for the cyanobacterial diet. These findings suggest that the cyanobacterium will not cause instant mortality, but it will not support sustained survival and growth over time scales of weeks.

Short communication: adaptability of the feeding behavior of intertidal ribbed mussels (Geukensia demissa) to constant submersion

The ribbed mussel (Geukensia demissa, Dillwyn 1817) is a dominant benthic filter-feeder in salt marshes along the North American Atlantic Coast. It has been proposed that the cultivation and harvest of ribbed mussels could be used to bioremediate the eutrophication of coastal waters. To accomplish this, mussels would be grown in suspension culture underwater, which is different than this species’ natural, intertidal habitat in which they are exposed to a tidal regime of submersion and emersion. To assess possible effects of constant submersion upon the feeding behavior of G. demissa, we quantified filter-feeding activities of ribbed mussels collected from either an intertidal location or a permanently submerged (2xa0months) population in the same embayment. Filtration measurements to determine clearance rates were conducted in aquaria containing ultra-filtered seawater with cultured phytoplankton. Results show that mussels taken from the intertidal population had significantly higher filtration than the submerged population initially, but after 3xa0days of submersion in the aquaria, this difference disappeared. Moreover, all experimental G. demissa had higher clearance rates during natural low tide than during natural high tide. These results indicate a potential for ribbed mussels to be grown in suspension culture for nutrient bioextraction purposes.