66 National Marine Fisheries Service Fishery Bulletin First U.S. Commissioner established in 1881 of Fisheries and founder NOAA of Fishery Bulletin Abstract—The Atlantic surfclam (Spi- Effects of ocean acidification on larval Atlantic sula solidissima) supports a $29.2-million fishery on the northeastern coast of the surfclam (Spisula solidissima) from Long Island United States. Increasing global car- Sound in Connecticut bon dioxide (CO2) in the atmosphere has resulted in a decrease in ocean pH, known as ocean acidification (OA), in Shannon L. Meseck (contact author) Atlantic surfclam habitat. The effects Renee Mercaldo-Allen of OA on larval Atlantic surfclam were investigated for 28 d by using 3 different Paul Clark levels of partial pressure of CO2 (ρCO2): Catherine Kuropat low (344 µatm), medium (821 µatm), Dylan Redman and high (1243 µatm). Samples were David Veilleux taken to examine growth, shell height, time to metamorphosis, survival, and Lisa Milke lipid concentration. Larvae exposed to a medium ρCO2 level had a hormetic Email address for contact author: [email protected] response with significantly greater shell height and growth rates and a Milford Laboratory higher percentage that metamorphosed Northeast Fisheries Science Center by day 28 than larvae exposed to the National Marine Fisheries Service, NOAA high- and low- level treatments. No 212 Rogers Avenue significant difference in survival was Milford, Connecticut 06460 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 The process of ocean acidification (OA) 0.1. This ongoing shift in the carbonate sterols to phospholipids, indicating that larvae may have a homeoviscous adap- occurs when increased atmospheric car- system and corresponding decline in bon dioxide (CO ) from anthropogenic pH and Ω may affect the growth and tation to OA at medium ρCO2 levels. 2 Our results indicate that larval Atlantic activities (i.e., burning of fossil fuels survival of marine organisms. surfclam have some tolerance to slightly and deforestation) is absorbed by ocean Representative concentration path- elevated ρCO2 concentrations but that, waters (Caldeira and Wickett, 2003; ways (RCPs) are used to predict future at high ρCO levels, they may be suscep- 1 2 Raven et al. ; Doney et al., 2009). Con- CO2 concentrations. By the year 2100, tible to OA. sequently, concentrations of dissolved under the RCP 8.5 scenario (high emis- − CO2 and bicarbonate ions (HCO3 ) sions) used in climate modeling, CO2 rise, while concentration of carbonate levels will be >1000 µatm, and under 2− ions (CO3 ), pH, and calcium carbon- the RCP 6.0 scenario, CO2 levels will ate saturation level (Ω) decline (Feely be in the range of 720–1000 µatm et al., 2004, 2010; Hönisch et al., 2012; (IPCC, 2014). Projected increases in Duarte et al., 2013). In recent years, CO2 by 2100 are expected to result in the ocean’s natural capacity for buffer- a reduction of 0.2–0.4 in pH and in a ing, a process that normally occurs over 50% decline in aragonite saturation a geologic timescale of 10,000–100,000 level (Ωaragonite), a measure often used years, has been unable to keep pace with in relation to Ω because aragonite is a the rate of acidification (Hönisch et al., common form of calcium carbonate in Manuscript submitted 28 July 2020. 2012; Zeebe, 2012; Zeebe et al., 2016), ocean waters (Feely et al., 2004, 2010; Manuscript accepted 10 May 2020. resulting in a global ocean pH drop of Hartin et al., 2016). It has been pre- Fish. Bull. 119:66–76 (2021). Online publication date: 25 May 2021. dicted that, by the year 2300, CO2 levels doi: 10.7755/FB.119.1.8 will be >2000 µatm and will correspond 1 Raven, J., K. Caldeira, H. Elderfield, to an additional drop of 0.4 in pH (Feely The views and opinions expressed or O. Hoegh-Guldberg, P. Liss, U. Riebesell, et al., 2004, 2010; Hartin et al., 2016). implied in this article are those of the J. Shepherd, C. Turley, and A. Watson. 2005. In a recent climate vulnerability author (or authors) and do not necessarily Ocean acidification due to increasing atmo- reflect the position of the National spheric carbon dioxide. R. Soc. Policy Doc. assessment of fish and invertebrates on Marine Fisheries Service, NOAA. 12/05, 57 p. [Available from website.] the continental shelf of the northeastern Meseck et al.: Effects of ocean acidification on larvalSpisula solidissima from Long Island Sound 67 United States, shellfish species were categorized as highly the coast of New Jersey to measure subsurface pH levels, susceptible to changing climate conditions (Hare et al., which ranged from 7.91 to 8.20, and to measure Ωaragonite, 2016). A conclusion of most of the research on effects of which ranged from 1.5 to 2.2 with higher readings at the OA on marine mollusks has been that larval shellfish are surface (Saba et al., 2019). more sensitive to OA than those in juvenile and adult Although there is evidence of increasing ρCO2 concen- stages (Gledhill et al., 2015; Siedlecki et al., 2021). In lar- trations in waters where larval Atlantic surfclam are val experiments with bay scallop (Argopecten irradians) concentrated during development, data are sparse at (Talmage and Gobler, 2009; White et al., 2013), eastern the thermocline, and the processes and drivers of these oyster (Crassostrea virginica) (Miller et al., 2009; Talmage changes are not understood fully (Boehme et al., 1998; and Gobler, 2009; Gobler and Talmage, 2014), and northern Wang et al., 2017). The limited data that is available, com- quahog (Mercenaria mercenaria) (Green et al., 2004, 2009; bined with model projections for the entire region, indicate Talmage and Gobler, 2009), reduced rates of survival and that some areas in the region where Atlantic surfclam con- growth have been observed when larvae were exposed to centrate will reach global levels of ρCO2 predicted for 2100 acidification levels predicted to occur by 2100. The findings as early as 2030–2050 (Ekstrom et al., 2015; Siedlecki of these studies indicate that an Ωaragonite of ~1.5 results et al., 2021). in physiological responses in marine bivalve species. These Characterizing the effects of OA on Atlantic surfclam studies focused on bivalve species that reside in estuarine is complex in part because of the presence of 2 subspe- water, where changes in temperature, salinity, and partial cies along the coast of the northeastern United States pressure of CO2 (ρCO2) can occur at daily rates (Feely et al., (Hare and Weinberg, 2005). Both subspecies are referred 2010; Dickinson et al., 2013; Duarte et al., 2013), and their to as Atlantic surfclam; however, there are physiologi- results may not be applicable to coastal bivalve species. cal differences between the 2 subspecies. The more A synthesis of available reports on ecological conse- northern subspecies, S. s. solidissima, is larger in size quences of ocean and coastal acidification for species in (length: 150–200 mm) and lives longer (25–30 years) the Northeast U.S. continental shelf large marine eco- than the more southern subspecies, S. s. similis, which system has identified that to date little is known on how ranges in length from 76 to 122 mm and lives for 4.0–5.5 coastal bivalve species will respond to OA (Hare et al., years (Walker and O’Beirn, 1996; Weinberg and Helser, 2016). Recently, juvenile Atlantic surfclam (Spisula solid- 1996). The subspecies differ in geographic range, with issima) were found to have modified physiological pro- the northern subspecies of Atlantic surfclam found from cesses at CO2 levels of RCP 8.5 scenario during a 12-week the Gulf of Saint Lawrence in Canada south to Cape exposure, with them being more sensitive than previously Hatteras in North Carolina and with the southern sub- studied estuarine bivalves (i.e., oyster species and the blue species thought to be distributed primarily in shallow mussel, Mytilus edulis) to increasing ρCO2 levels (Pousse nearshore environments along the coast of Cape Hat- et al., 2020). The results of that study highlight the need teras and in waters of the Gulf of Mexico off the coast of to understand how larval Atlantic surfclam will respond the southeastern United States. to OA conditions. The Connecticut Bureau of Aquaculture identifies Atlantic surfclam are planktonic larvae, transition- Atlantic surfclam in Long Island Sound (LIS) as S. solidis- ing to the pediveliger stage with a foot and “swimming- sima, but results of DNA analysis indicate that S. s. simi- crawling” behavior (Fay et al., 1983; Cargnelli et al., lis, although it is considered the more southern subspecies, 1999). Larval Atlantic surfclam are concentrated near the is located primarily off the coast of Massachusetts; there thermocline and are transported horizontally by currents also is a confirmed population of the southern subspecies (Zhang et al., 2015, 2016; Chen et al., 2019). Along the in waters of New York in LIS (Hare et al., 2010). Results of coast of the northeastern United States, surface waters of a recent survey conducted by the NOAA Northeast Fish- the Atlantic Ocean and Gulf of Maine are characterized eries Science Center indicate that the southern subspecies by high variability, both spatially (with increased acidifi- of Atlantic surfclam may be shifting northward because cation northward) and seasonally (with the lowest values of increased water temperatures (NEFSC, 2017). The during winter and the highest values in summer) (Biao Mid-Atlantic Fishery Management Council in fiscal year et al., 2004; Wang et al., 2013; Xu et al., 2017; Goldsmith 2019 solicited studies to examine whether there has been et al., 2019; Friedland et al., 2020).