Description: The Atlantic surfclam (Spisula solidissima) supports a $29.2-million fishery on the northeastern coast of the United States. Increasing global carbon dioxide (CO2) in the atmosphere has resulted in a decrease in ocean pH, known as ocean acidification (OA), in Atlantic surfclam habitat. The effects of OA on larval Atlantic surfclam were investigated for 28 d by using 3 different levels of partial pressure of CO2 (ρCO2): low (344 μatm), medium (821 μatm), and high (1243 μatm). Samples were taken to examine growth, shell height, time to metamorphosis, survival, and lipid concentration. Larvae exposed to a medium ρCO2 level had a hormetic response with significantly greater shell height and growth rates and a higher percentage that metamorphosed by day 28 than larvae exposed to the high- and low-level treatments. No significant difference in survival was observed between treatments. Although no significant difference was found in lipid concentration, Atlantic surfclam did have a similar hormetic response for concentrations of phospholipids, sterols, and triacylglycerols and for the ratio of sterols to phospholipids, indicating that larvae may have a homeoviscous adaptation to OA at medium ρCO2 levels. Our results indicate that larval Atlantic surfclam have some tolerance to slightly elevated ρCO2 concentrations but that, at high ρCO2 levels, they may be susceptible to OA.

Description: 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.

Description: After a decade of research on how embryonic fish will respond to the increased dissolved carbon dioxide (ρCO2) levels predicted for the next century, no uniform response to near future acidification has been observed among marine species. We exposed Black Sea Bass Centropristis striata (BSB) embryos to varied levels of ρCO2 (microatmospheres [μatm]) for 48 h during seasonal experiments conducted in 2013–2015 to compare embryonic response among multiple broodstocks. The relationship between ρCO2 concentration and hatching success was inconsistent among years, with a nonlinear, inverse relationship noted in 2014 only, explaining 13% of observed variance. Conversely, ρCO2 was a good predictor of unhatched BSB embryos after 48 h for all years combined (39%) and for 2013 (38%). The ρCO2 concentration was a good predictor of the frequency of vertebral column anomalies for individual years (2013: 40%; 2014: 12%; 2015: 38%) but not when data were pooled for all years. In 2013 and 2015, vertebral column anomalies were relatively consistent below 1,000 μatm and were elevated above that threshold. Preliminary results suggest that BSB embryos may demonstrate resilience to future ρCO2 levels, but the results also highlight the challenges associated with drawing broad conclusions given observed variability in results obtained from different broodstocks and study years.

Description: 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.