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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.

Multi-tiered oyster aquaculture cages may provide habitat for fish assemblages similar to natural structured seafloor. Methods were developed to assess fish assemblages associated with aquaculture gear and boulder habitat using underwater video census combined with environmental DNA (eDNA) metabarcoding. Action cameras were mounted on 3 aquaculture cages at a commercial eastern oyster Crassostrea virginica farm (‘cage’) and among 3 boulders on a natural rock reef (‘boulder’) from June to August 2017 in Long Island Sound, USA. Interval and continuous video recording strategies were tested. During interval recording, cameras collected 8 min video segments hourly from 07:00 to 19:00 h on cages only. Continuous video was also collected for 2-3 h on oyster cages and boulders. Data loggers recorded light intensity and current speed. Seawater was collected for eDNA metabarcoding on the reef and farm. MaxN measurements of fish abundance were calculated in video, and 7 fish species were observed. Black sea bass Centropristis striata, cunner Tautogolabrus adspersus, scup Stenotomus chrysops, and tautog Tautoga onitis were the most abundant species observed in both oyster cage and boulder videos. In continuous video, black sea bass, scup, and tautog were observed more frequently and at higher abundance on the cage farm, while cunner were observed more frequently and at higher abundance on boulders within the rock reef. eDNA metabarcoding detected 42 fish species at the farm and reef. Six species were detected using both methods. Applied in tandem, video recording and eDNA provided a comprehensive approach for describing fish assemblages in difficult to sample structured oyster aquaculture and boulder habitats.

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Juvenile Scup Stenotomus chrysops 0.35–0.95 g were fed two different commercial diets for 9 weeks to determine growth rates. Diets were hand‐distributed to four replicate groups of 45 fish, four times a day. Survival among all treatments was high (90.0–92.5%), and both diets supported good growth. After five weeks, Scup fed diet 1 were significantly greater in length and weight than fish fed diet 2. These differences remained significant throughout the rest of the study. Specific growth rate (SGR) values were 5.8%/d for fish fed diet 1 and 5.5%/d for diet 2, while feed conversion ratios (FCR) were 1.22 for diet 1 and 1.25 for diet 2. Relative growth rate (RGR) values were diet 1 = 3,689% and diet 2 = 3,077%, and daily weight gain (DWG) values were diet 1 = 0.38 g/d and diet 2 = 0.31 g/d. Scup fed diet 1 had significantly greater final live weight, total length, weight gain, SGR, RGR, and DWG measurements than did fish fed diet 2. Juvenile Scup exhibited high growth rates and low feed conversion ratios when fed the two commercial diets, identifying them as a strong candidate species for commercial aquaculture.

Trap sampling was used to survey the relative abundance of juvenile fish and invertebrates near three habitats including an offbottom oyster cage farm (cage farm), a traditional on-bottom oyster culture area (shell bottom), and a natural cobble and boulder reef (rock reef) in a coastal embayment in Long Island Sound near Milford, Connecticut. Ten traps, deployed on two subsites within each habitat (20/habitat), were allowed to soak for~24 hours, two to three times per week, from June through September 2016. The assemblages of juvenile finfish appeared to be similar on the cage farm and rock reef, while the composition of the invertebrate community was more variable among the three habitats. These preliminary observations suggest that oyster cage farms may provide functional habitat that is populated by structure-oriented finfish communities similar to those that are found on natural rock reefs in Long Island Sound.

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.