To date (2017), only a half dozen or so fish species of the Mid-Atlantic have been studied for their response and sensitivity to ocean and coastal acidification. Those studies are based on laboratory experimentation where the earliest, most sensitive life-stages of fish (gametes, embryos, larvae, and young juveniles) are exposed to one of multiple different levels of carbon dioxide (CO2) which is intended to mimic future oceanic and coastal conditions when an ever-greater amount of atmospheric CO2 is expected to be absorbed by and acidify seawater. This is a young yet very active research front with studies becoming ever more realistic and sophisticated. Study advances include 1) using variable CO2 typical of inshore and estuarine waters, 2) estimating the effects of simultaneously acting environmental stressors, e.g., low dissolved oxygen (DO), elevated temperatures, and contaminants typical of inshore waters, and 3) assessing the degree to which young fish can survive and function normally when exposed to these stressors and evaluating whether existing genetic variation exists that might allow adaptation to future high-CO2 conditions. The kinds of complexities revealed in these studies underscore species differences as well as provide evidence that stocks within a species may differ in their responses to acidification.
Several laboratory studies have been conducted on summer flounder. Among other results, summer flounder egg fertilization rate was lower and, among those that were successfully fertilized, fewer survived to hatching when they were exposed to elevated levels of CO2. For larvae, rates of growth and development were accelerated but larval survival was unaffected. In nature, a consequence of accelerated development would be young juvenile summer flounder arriving in bay waters earlier in the season and at smaller sizes than historically normal. These altered features in size and timing of early life events could heighten the risks of death due to consumption by predators or prolonged exposure to the cold inshore waters typical of winter in coastal Mid-Atlantic fish nurseries. Older summer flounder juveniles also showed increased mortality when subjected to highly variable CO2 and DO conditions.
The responses of winter flounder to elevated levels of CO2 differ from that reported for summer flounder. Among other findings, winter flounder fertilization rates increased with increasing CO2 to a point, then they decrease at the highest CO2 levels (most acidic) tested. The fertilization rates decreased with elevated temperatures. Interestingly, the fertilization rate response of New Jersey winter flounder differed from flounder collected in Massachusetts / Southern Gulf of Maine waters in that Massachusetts fish displayed increased fertilization rates at even the most acidic waters but were more sensitive than New Jersey fish to warmer temperatures.
Juvenile weakfish exposed to short-term (30 day) exposures to constant and fluctuating CO2 and DO levels showed negative effects only at the highest level of variability in water chemistry. They appeared to be robust when faced with current-day and projected future CO2 conditions in nursery habitats.
Forage fish, including Atlantic silverside (spearing), inland silverside, and sheepshead minnow are important in the Mid-Atlantic food web. Each of these species has been the subject of acidification studies in university and government labs from Connecticut to Maryland. These forage fish typically spawn during spring and summer in the subtidal zone of estuaries. The adults and offspring experience extreme daily variability in CO2 as well as DO levels, and may experience extremely high summer water temperatures. Researchers have found these fish to be at risk to elevated CO2 when acting alone and in combination with other environmental stressors. Among other responses, these experimental conditions have led to higher mortality of embryos, premature and altered sizes at hatching, and reduced larval growth rates. Adults themselves may be at risk to direct CO2 and DO-induced mortality and to indirect risks such as an increased susceptibility to predators especially when elevated CO2 and low DO occur together. These small-bodied fish lend themselves to studies that evaluate parent-offspring relationships which is important for understanding how spawning season and parentage might influence the sensitivity of offspring to acidification. Results to date for Atlantic silverside show that offspring from parents that spawn in summer – when waters are warmer, more acidic, and have lowest DO concentrations – are themselves more resilient to acidification challenges. Further, offspring from different parents spawned at the same time show significant, inter-family differences in resilience to acidification which suggests that potential exists in this species for adaptation to future CO2 conditions.
Baumann, H., Talmage, S.C., and Gobler, C.J. 2012. Reduced early life growth and survival in a fish as a direct response to elevated CO2 levels. Nature Climate Change 2:38-41.
Chambers, RC, Candelmo, AC, Habeck, EA, Poach, ME, Wieczorek, D, Cooper, KR, Greenfield, CE, and Phelan, BA. 2014. Effects of elevated CO2 in the early life stages of summer flounder, Paralichthys dentatus, and potential consequences of ocean acidification. Biogeosciences, 11, 1613-1626, doi:10.5194/bg-11-1613-2014.
Davidson MI, Targett TE, Grecay PA. 2016. Evaluating the effects of diel-cycling hypoxia and pH on growth and survival of juvenile summer flounder Paralichthys dentatus. Marine Ecology Progress Series 556:223-235. https://doi.org/10.3354/meps11817.
Depasquale, E, Baumann, H, and Gobler, CJ. 2015. Variation in early life stage vulnerability among Northwest Atlantic estuarine forage fish to ocean acidification and low oxygen. Marine Ecology Progress Series 523:145-156.
Lifavi DM, Targett TE, Grecay PA. 2017. Effects of diel-cycling hypoxia and acidification on juvenile weakfish Cynoscion regalis growth, survival, and activity. Marine Ecology Progress Series 564:163-174. https://doi.org/10.3354/meps11966.
Malvezzi, AJ, Murray, CM, Feldheim, KA, Dibattista, JD, Garant, D, Gobler, CJ, Chapman, DD, and Baumann, H. 2015. A quantitative genetic approach to assess the evolutionary potential of a coastal marine fish to ocean acidification. Evolutionary Applications 8:352-362.
Miller, SH, Breitburg, DL, Burrell, RB and Keppel, AG. 2016. Acidification increases sensitivity to hypoxia in important forage fishes. Marine Ecology Progress Series, 549:1-8. http://dx.doi.org/10.3354/meps11695.
Murray, CM, Malvezzi, A, Gobler, CJ, and Baumann, H. 2014. Offspring sensitivity to ocean acidification changes seasonally in a coastal marine fish. Marine Ecology Progress Series 504:1-11.
Winter and summer flounder photos courtesy of NOAA/NEFSC