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1. Experimental ocean acidification and food limitation reveals altered energy budgets and synergistic effects on mortality of larvae of a coastal fish

   https://doi.org/10.3389/fmars.2023.1240404  

   Siegfried, Emma; Johnson, Darren W. (August 2023, Frontiers in Marine Science)

   Ocean acidification (OA) presents a unique challenge to early life stages of marine species. Developing organisms must balance the need to grow rapidly with the energetic demands of maintaining homeostasis. The small sizes of early life stages can make them highly sensitive to changes in environmental CO₂levels, but studies have found wide variation in responses to OA. Thus far most OA studies have manipulated CO₂only, and modifying factors need to be considered in greater detail. We investigated the effects of high pCO₂and food ration on rates of growth and mortality of a coastal fish, the California Grunion (Leuresthes tenuis). We also examined how CO₂and food levels affected feeding success, metabolic rate, and swimming activity – processes reflective of energy acquisition and expenditure. In general, exposure to high CO₂decreased energy intake by reducing feeding success, and increased energy expenditure by increasing metabolic rate and routine swimming speed, though the magnitudes of these effects varied somewhat with age. Despite these changes in energetics, growth of biomass was not affected significantly by pCO₂level but was reduced by low ration level, and we did not detect an interactive effect of food ration and pCO₂on growth. However, under OA conditions, larvae were in poorer condition (as evaluated by the mass to length ratio) by the end of the experiment and our analysis of mortality revealed a significant interaction in which the effects of OA were more lethal when food energy was limited. These results are consistent with the idea that although energy can be reallocated to preserve biomass growth, increased energetic demand under ocean acidification may draw energy away from maintenance, including those processes that foster homeostasis during development. Overall, these results highlight both the need to consider the availability of food energy as a force governing species’ responses to ocean acidification and the need to explicitly consider the energy allocated to both growth and maintenance as climate changes. 

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2. Acidification and hypoxia interactively affect metabolism in embryos, but not larvae, of the coastal forage fish Menidia menidia

   https://doi.org/https://doi.org/10.1242/jeb.228015  

   Schwemmer, T. G. Baumann (November 2020, Journal of experimental biology)

   Ocean acidification is occurring in conjunction with warming and deoxygenation as a result of anthropogenic greenhouse gas emissions. Multistressor experiments are critically needed to better understand the sensitivity of marine organisms to these concurrent changes. Growth and survival responses to acidification have been documented for many marine species, but studies that explore underlying physiological mechanisms of carbon dioxide (CO2) sensitivity are less common. We investigated oxygen consumption rates as proxies for metabolic responses in embryos and newly hatched larvae of an estuarine forage fish (Atlantic silverside, Menidia menidia) to factorial combinations of CO2×temperature or CO2×oxygen. Metabolic rates of embryos and larvae significantly increased with temperature, but partial pressure of CO2 (PCO2) alone did not affect metabolic rates in any experiment. However, there was a significant interaction between PCO2 and partial pressure of oxygen (PO2) in embryos, because metabolic rates were unaffected by PO2 level at ambient PCO2, but decreased with declining PO2 under elevated PCO2. For larvae, however, PCO2 and PO2 had no significant effect on metabolic rates. Our findings suggest high individual variability in metabolic responses to high PCO2, perhaps owing to parental effects and time of spawning. We conclude that early life metabolism is largely resilient to elevated PCO2 in this species, but that acidification likely influences energetic responses and thus vulnerability to hypoxia. 

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3. Temperature and pH Effects on Growth of Four Species of Commercially-Important Bivalves from Tank Experiments

   Thatcher, D.; McMahon, T.; Whitney, N.; Guay, K.; Franklin, H.; Stewart, J.; Williams, B.; Wanamaker, A.; LaVigne, M. (December 2022, American Geophysical Union Fall Meeting)

   The Gulf of Maine is a highly productive and economically important region in the northwestern Atlantic that has undergone rapid warming in recent decades and is susceptible to ocean acidification (OA). These stressors may have substantial impacts on local fisheries. Therefore, understanding the combined effects of warming and OA to commercially important shellfish is vital. To test responses to warming and OA, Mercenaria mercenaria (hard clam), Mya arenaria (soft-shell clam), Plactopectin magellanicus (sea scallop), and both juvenile and adult Arctica islandica (ocean quahog) were grown in flowing seawater tanks for 20.5 weeks in controlled pH (7.4, 7.6, 7.8 or 8.0 (ambient) ± 0.02) and temperature (6, 9 or 12 ± 0.56 °C) conditions at Bowdoin College’s Schiller Coastal Studies Center. The specimens’ diet was supplemented with high-quality food (Shellfish Diet) throughout the experiment. Temperature effects were a significant contributor in all shell growth metrics (maximum height, dry weight and buoyant weight) in all species except the height and dry weight of adult A. islandica. Additionally, pH effects were significant in the height of M. mercenaria and in the dry weight of juvenile A. islandica samples. Overall, mortality rates ranged from 1.5% in juvenile A. islandica to 24% in M. mercenaria, with results varying by species and treatment conditions. Additionally, differences in final shell condition were noted among the various treatments indicating that, although most of the organisms survived and grew, the elevated temperature and/or lower pH conditions might not have been ideal for thriving. Considering all results of growth and survival, the four species showed a differential response to the same warming and acidification conditions. As suggested by prior research, the availability of high-quality food may allow certain species to tolerate the future warming and/or OA conditions modeled in this experiment. Experimental results may reveal the species-specific resiliency of economically valuable shellfish to changing ocean conditions as well as guide future planning to safeguard regional ecosystems and fisheries. 

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4. Growth of Oyster ( Crassostrea virginica ) Larvae in Small‐Scale Systems Using an Algae Concentrate Food Source

   https://doi.org/10.1155/2024/1890826  

   Tarnecki, Andrea M; Cleveland, Alexes; Capps, Meghan; Rikard, F Scott (January 2024, Aquaculture Research)

   Qin, Jianguang (Ed.)

   Replicated studies are advantageous for optimizing larval rearing of the Eastern oyster (Crassostrea virginica) and increasing the availability of high‐quality seed for the continued expansion of the U.S. oyster aquaculture industry. Although small‐scale systems using live algal feeds have been used successfully, rearing larvae on algae concentrate presents additional challenges. To determine the feasibility of rearing oyster larvae in small‐scale systems using algae concentrate, oyster larvae were raised for 2 weeks in replicate control (1,000 L) and microcosm (17 L) tanks. Five aeration strategies were tested in the microcosms in two separate trials. Results of this study indicate similar survival in small systems compared to controls through the appearance of eyed larvae. Accumulated algae and pink biofilm formation in microcosms using polyvinyl chloride (PVC) airlifts suggest that this aeration strategy is undesirable. One‐ and 5‐mL air injectors maintained higher overnight oxygen levels than controls. The recovery of more eyed larvae after 14 dpf in control systems may be the result of significant temperature fluctuations in microcosms. Overall, this study demonstrates that algae concentrate can be used to rear oyster larvae in small‐scale systems, providing a live feed alternative that saves space and labor in replicated studies. 

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5. Effect of High-Density Polyethylene Microplastics on the Survival and Development of Eastern Oyster (Crassostrea virginica) Larvae

   https://doi.org/10.3390/ijerph20126142  

   Bhatt, Sulakshana; Fan, Chunlei; Liu, Ming; Wolfe-Bryant, Brittany (June 2023, International Journal of Environmental Research and Public Health)

   Microplastic (MP) pollution is a growing global concern—especially in estuarine areas that serve as natural habitats and nurseries for many marine organisms. One such marine organism is the Eastern oyster (Crassostrea virginica), which is a reef-forming keystone species in the Chesapeake Bay, the largest estuary in the United States. To understand the potential impacts of MP pollution on the estuary ecosystem, the effects of high-density polyethylene (HDPE) MPs on Eastern oyster larval survival and development were investigated. Three cohorts of larvae were exposed to HDPE MPs with a size of 10–90 µm at a 10 mg/L concentration, after 7 to 11 days of fertilization. After exposure, the number and size of oyster larvae were measured twice a week for approximately 2 weeks until larval settlement. The experiment found that there were no significant differences in the rate of survival between the control and MP-addition treatments. However, we noticed that larval development was significantly delayed with the MP treatment. The percentage of larvae that were ready to settle was 64% with the control treatment compared to 43.5% with the MP treatment. This delay in growth resulted in a delayed larval settlement, which could adversely affect the survival of the Eastern oyster due to the increased risk of predation. The current study demonstrates that MPs could be a risk to the ecology of estuaries, and plastic pollution management is needed for the preservation of these estuaries. 

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