Search

Ploidy manipulation, such as triploidy, in farmed oysters has been used as a tool to enhance oyster quality throughout all seasons because triploid oysters allocate less energy to gametogenesis, and therefore are deemed better performers than fertile diploids. Nevertheless, scientific reports describing no differences between ploidies and, in certain conditions, disadvantages of triploids are not uncommon. As the use of triploid oyster seed increases culture cost for growers, consistency in performance of triploids is considered to be an important goal. Thus, research to assess how ploidy affects physiological processes underlying oyster performance is fundamental for the aquaculture industry. This work was undertaken to assess if ploidy-based differences in performance in the two most commonly cultivated commercial species of oyster in the United States, Crassostrea virginica and Crassostrea gigas, are associated with filtration, feeding, and metabolism. To test this hypothesis, biodeposition measurements were made with oysters exposed to ambient water conditions at locations and seasons providing a variety of environmental conditions. Oysters did not show differences in filtration and feeding associated with ploidy, but physiological feeding variables fluctuated with environmental characteristics associated with spatial and seasonal differences. A preliminarily test of the hypothesis that differences in energy metabolism may account for differences in performance among ploidy levels indicates that basal metabolic rates of diploid, triploid, and tetraploid Eastern oysters are not different.

This study assessed the energy budget for juvenile Atlantic Sea Scallop, Placopecten magellanicus, during a natural drop in temperature (15.6°C to 5.8°C) over an 8-week time period during the fall at three different enrichment levels of carbon dioxide (CO2). Every 2 weeks, individuals were sampled for ecophysiological measurements of feeding activity, respiration rate (RR) and excretion rate (ER) to enable the calculation of scope for growth (SFG) and atomic oxygen:nitrogen ratios (O:N). In addition, 36 individuals per treatment were removed for shell height, dry tissue weight (DTW) and dry shell weight (DSW). We found a significant decrease in feeding rates as CO2 increased. Those rates also were significantly affected by temperature, with highest feeding at 9.4°C. No significant CO2 effect was observed for catabolic energy processes (RR and ER); however, these rates did increase significantly with temperature. The O:N ratio was not significantly affected by CO2, but was significantly affected by temperature. There was a significant interaction between CO2 and temperature for ER and the O:N ratio, with low CO2 levels resulting in a U-shaped response that was not sustained as CO2 levels increased. This suggests that the independent effects of CO2 and temperature observed at low levels are different once a CO2 threshold is reached. Additionally, there were significant differences in growth estimators (shell height and DSW), with the best growth occurring at the lowest CO2 level. In contrast to temperature variations that induced a trade-off response in energy acquisition and expenditure, results from this research support the hypothesis that sea scallops have a limited ability to alter physiological processes to compensate for increasing CO2.

The East River tidal strait, located between New York Harbor and Western Long Island Sound, is characterized by high suspended silt concentrations with low organic content kept in suspension by intense tidal currents. Inorganic nutrients, including nitrate, nitrite, ammonia, and phosphate, were high even during the summer. Dissolved inorganic nitrogen (DIN) concentrations generally were above 20 µM and did not likely limit phytoplankton growth. Despite high nutrient concentrations, median chlorophyll a concentration was only 1.53 µg l−1, making the East River tidal strait a high-nutrient, low-chlorophyll (HNLC) area, likely a result of suspended silt blocking light penetration into the surface water. There were times at which the ratio of mixed layer to depth of the euphotic zone was generally greater than what has been suggested for phytoplankton to produce net primary production. The high-nutrient East River tidal strait is likely one of the sources of nutrients fueling summer phytoplankton production and consequent hypoxia in the Western Long Island Sound as silt settles from surface water in the lower turbulence conditions of the western narrows of Long Island Sound, thereby allowing light penetration and subsequent consumption of dissolved nutrients by phytoplankton.

Mercaldo-Allen, R.; Goldberg, R.; Clark, P.; Kuropat, C.; Meseck, S.L., and Rose, J.M., 2016. Benthic ecology of northern quahog beds with different hydraulic dredging histories in Long Island Sound. This paper evaluates benthic community composition of four shellfish beds in Long Island Sound near Milford, Connecticut, where northern quahog or hard clams, Mercenaria mercenaria (Linnaeus 1758), were harvested by hydraulic dredge. These leased beds reflect a variety of dredging histories; 0 year (dredged just before sampling began), 1 year postharvest, 2 years postharvest, and an inactive clam bed left fallow for at least 10 years. Benthic sediment was sampled at 1- to 2-week intervals from June to October 2011 using a Smith–McIntyre grab. Benthic community composition was significantly influenced by dredging history and sampling month. Abundance of benthic organisms (number of individuals and biovolume) and total organic matter concentrations were significantly greater at the 0-year site than at ...

Gills of marine bivalves, the organs that mediate water flow for feeding and other physiological functions, are exposed to increasing levels of carbon dioxide (CO2) in seawater, in response to ocean acidification (OA). We examined the effects of elevated dissolved CO2 upon filtration and feeding behavior of the blue mussel, Mytilus edulis, under field conditions and in laboratory studies. We further investigated possible changes in cilia beat function in response to elevated dissolved CO2. Physiological filtration and feeding variables measured; included clearance, filtration, organic ingestion, and assimilation rates and selection efficiency, which decreased with increasing CO2. Absorption efficiency was not affected by dissolved CO2. Cilia beat frequency declined in excised lateral cilia (lc) exposed to increasing CO2 levels, which appears to account for decreased clearance rates observed in field and laboratory experiments. Our data suggest that under conditions of increased CO2 blue mussels will experience changes in physiological filtration, feeding rates, and cilia beat function that could have consequences for fitness and performance.

Carbon dioxide (CO2) is the primary substrate for photosynthesis by the phytoplankton that form the base of the marine food web and mediate biogeochemical cycling of C and nutrient elements. Specific growth rate and elemental composition (C:N:P) were characterized for 7 cosmopolitan coastal and oceanic phytoplankton species (5 diatoms and 2 chlorophytes) using low density, nutrient-replete, semi-continuous culture experiments in which CO2 was manipulated to 4 levels ranging from post-bloom/glacial maxima (2900 ppm). Specific growth rates at high CO2 were from 19 to 60% higher than in low CO2 treatments in 4 species and 44% lower in 1 species; there was no significant change in 2 species. Higher CO2 availability also resulted in elevated C:P and N:P molar ratios in Thalassiosira pseudonana (~60 to 90% higher), lower C:P and N:P molar ratios in 3 species (~20 to 50% lower), and no change in 3 species. Carbonate system-driven changes in growth rate did not necessarily result in changes in elemental composition, or vice versa. In a subset of 4 species for which fatty acid composition was examined, elevated CO2 did not affect the contribution of polyunsaturated fatty acids to total fatty acids significantly. These species show relatively little sensitivity between present day CO2 and predicted ocean acidification scenarios (year 2100). The results, however, demonstrate that CO2 availability at environmentally and geologically relevant scales can result in large changes in phytoplankton physiology, with potentially large feedbacks to ocean biogeochemical cycles and ecosystem structure.

Joint Meeting of the Northeast Aquaculture Conference and Exposition and the 35th Milford Aquaculture Seminar, 14-16 January 2015, Portland, Maine

A before-after-control-impact (BACI) experiment was conducted to examine the effects of hydraulic clam dredging on sediment biogeochemistry of a leased shellfish bed of Mercenaria mercenaria, northern quahog, over the course of an entire growing season. Six study plots (0.67 ha each), three dredged and three not dredged, off of Milford, Connecticut, in Long Island Sound, were sampled from May to October 2009 for porewater fluxes of total ammonia, oxygen, and hydrogen. Particulate samples were also analyzed for grain size, total nitrogen, total carbon, total sulfur, and organic carbon. Statistical analysis indicated no significant difference between dredged and not dredged sites. Grain size and oxygen flux explained 22% of the variation in the total benthic species assemblages; grain size and either total carbon or organic nitrogen explained 18% of the variation in molluscan abundance. Our study demonstrates that one-time hydraulic shellfish harvesting had minor effects on the sediment chemistry of a leased clam bed.

The estuaries and continental shelf system of the United States Mid-Atlantic are subject to ocean acidification driven by atmospheric CO2, and coastal acidification caused by nearshore and land-sea interactions that include biological, chemical, and physical processes. These processes include freshwater and nutrient input from rivers and groundwater; tidally-driven outwelling of nutrients, inorganic carbon, alkalinity; high productivity and respiration; and hypoxia. Hence, these complex dynamic systems exhibit substantial daily, seasonal, and interannual variability that is not well captured by current acidification research on Mid-Atlantic organisms and ecosystems. We present recommendations for research priorities that target better understanding of the ecological impacts of acidification in the U. S. Mid-Atlantic region. Suggested priorities are: 1) Determining the impact of multiple stressors on our resource species as well as the magnitude of acidification; 2) Filling information gaps on major taxa and regionally important species in different life stages to improve understanding of their response to variable temporal scales and sources of acidification; 3) Improving experimental approaches to incorporate realistic environmental variability and gradients, include interactions with other environmental stressors, increase transferability to other systems or organisms, and evaluate community and ecosystem response; 4) Determining the capacity of important species to acclimate or adapt to changing ocean conditions; 5) Considering multi-disciplinary, ecosystem-level research that examines acidification impacts on biodiversity and biotic interactions; and 6) Connecting potential acidification-induced ecological impacts to ecosystem services and the economy. These recommendations, while developed for the Mid-Atlantic, can be applicable to other regions will help align research towards knowledge of potential larger-scale ecological and economic impacts.

A before-after-control-impact (BACI)-style experimental design was used to assess the short-term effects of hy drau lic clam dredging on the benthic community of a leased shellfish bed along the Connecticut coast of Long Island Sound, where hard clams Mercenaria mercenaria are cultivated. Three replicate samples were collected from 6 plots (0.67 ha each) on a weekly basis from May through October 2009. Dredging was conducted in early July in 3 of the 6 plots, while 3 control plots were not dredged. Pairwise comparisons and multivariate analyses of main effects and interactions indicated that ecological indices did not differ significantly between dredged and not dredged plots, although sample date and plot both had significant effects. Assemblages of individual species were associated with specific sediment types found within the clam bed. Natural seasonal settlement patterns and sediment grain size had a greater influence on the benthic community than discrete hydraulic clam dredging.

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.

Sediment and porewater samples (1997–1999) were collected in the Northern Reach of the San Francisco Bay and Sacramento–San Joaquin Delta for determinations of sedimentary selenium and its chemical speciation. Total sedimentary selenium increased with depth, with approximately 50% of the sedimentary selenium as elemental selenium and 35% as organic selenide. Porewater total dissolved selenium increased with depth in the estuary and Delta, and fluxes out of the sediments were calculated at 0.01 and 0.06 nmol cm−2 year−1 for the estuary and Delta, respectively. Present-day sediment–water exchange of dissolved selenium and internal transformations cannot explain the observed increase in total sedimentary selenium with depth. However, mass balance calculations demonstrate that the increase in total selenium with depth may be linked to higher dissolved selenium concentrations in the water column in the 1980s, suggesting that the sediments could be used as historical recorders of selenium in the estuary.

The enzyme-labeled fluorescence (ELF-97®) substrate produces an insoluble, fluorescent yellow-green product at the site of alkaline-phosphatase (AP) activity. Fifteen coastal phytoplankton species were tested to determine if AP activity could be detected in phosphate- depleted media. All species tested, except Synechococcus bacillaris, expressed AP activity. Subsequently, threshold concentrations of soluble reactive phosphate (SRP) at which AP activity could be detected by ELF-97® were deter- mined for Chaetoceros neogracile, Chlorella autotrophica, Isochrysis sp., Prorocentrum minimum ,a ndTetraselmis chui. Microalgal species differed significantly in the SRP con- centration at which AP activity was first detectable (10.1- 16.4 µM), well above concentrations normally considered limiting for phytoplankton. P. minimum began to express AP activity at a higher SRP concentration than the other algal species; this may be attributable to a relatively high DNA/cell ratio in P. minimum, compared to the other phytoplankton. Thus, phytoplankton species may respond to phosphorus deficiency at high SRP concentrations.

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.

A biogeochemical model was developed to simulate salinity, total suspended material, phytoplankton biomass, dissolved selenium concentrations (selenite, selenate, and organic selenide), and particulate selenium concentrations (selenite + selenate, elemental selenium, and organic selenide) in the San Francisco Bay estuary. Model-generated estuarine profiles of total dissolved selenium reproduced observed estuarine profiles at a confidence interval of 91–99% for 8 different years under various environmental conditions. The model accurately reproduced the observed dissolved speciation at confidence intervals of 81–98% for selenite, 72–91% for selenate, and 60–96% for organic selenide. For particulate selenium, model-simulated estuarine profiles duplicated the observed behavior of total particulate selenium (76–93%), elemental selenium (80–97%), selenite + selenate (77–82%), and organic selenide (70–83%). Discrepancies between model simulations and the observed data provided insights into the estuarine biogeochemical cycle of selenium that were largely unknown (e.g., adsorption/desorption). Forecasting simulations investigated how an increase in the discharge from the San Joaquin River and varying refinery inputs affect total dissolved and particulate selenium within the estuary. These model runs indicate that during high river flows the refinery signal is undetectable, but when river flow is low (70day residence time) total particle-associated selenium concentrations can increase to .2 m gg 21. Increasing the San Joaquin River discharge could also increase the total particle-associated selenium concentrations to .1 m gg 21. For both forecasting simulations, particle-associated selenium was predicted to be higher than current conditions and reached levels where selenium could accumulate in the estuarine food web.

Increasing amounts of atmospheric carbon dioxide (CO2) from human industrial activities are causing changes in global ocean carbonate chemistry, resulting in a reduction in pH, a process termed “ocean acidification.” It is important to determine which species are sensitive to elevated levels of CO2 because of potential impacts to ecosystems, marine resources, biodiversity, food webs, populations, and effects on economies. Previous studies with marine fish have documented that exposure to elevated levels of CO2 caused increased growth and larger otoliths in some species. This study was conducted to determine whether the elevated partial pressure of CO2 (pCO2) would have an effect on growth, otolith (ear bone) condition, survival, or the skeleton of juvenile scup, Stenotomus chrysops, a species that supports both important commercial and recreational fisheries. Elevated levels of pCO2 (1200–2600 μatm) had no statistically significant effect on growth, survival, or otolith condition after 8 weeks of rearing. Field data show that in Long Island Sound, where scup spawn, in situ levels of pCO2 are already at levels ranging from 689 to 1828 μatm due to primary productivity, microbial activity, and anthropogenic inputs. These results demonstrate that ocean acidification is not likely to cause adverse effects on the growth and survivability of every species of marine fish. X‐ray analysis of the fish revealed a slightly higher incidence of hyperossification in the vertebrae of a few scup from the highest treatments compared to fish from the control treatments. Our results show that juvenile scup are tolerant to increases in seawater pCO2, possibly due to conditions this species encounters in their naturally variable environment and their well‐developed pH control mechanisms.