National Marine 
Fisheries Service 
NOAA 
TOA A 
TVA 
Abstract—The Atlantic surfclam (Spi- 
sula solidissima) supports a $29.2-million 
fishery on the northeastern coast of the 
United States. Increasing global car- 
bon dioxide (CO,) 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 CO, (pCO,): 
low (344 patm), medium (821 patm), 
and high (1243 patm). Samples were 
taken to examine growth, shell height, 
time to metamorphosis, survival, and 
lipid concentration. Larvae exposed to 
a medium pCO, 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 adap- 
tation to OA at medium pCO, levels. 
Our results indicate that larval Atlantic 
surfclam have some tolerance to slightly 
elevated pCO, concentrations but that, 
at high pCO, levels, they may be suscep- 
tible to OA. 
Manuscript submitted 28 July 2020. 
Manuscript accepted 10 May 2020. 
Fish. Bull. 119:66—76 (2021). 
Online publication date: 25 May 2021. 
doi: 10.7755/FB.119.1.8 
The views and opinions expressed or 
implied in this article are those of the 
author (or authors) and do not necessarily 
reflect the position of the National 
Marine Fisheries Service, NOAA. 
Fishery Bulletin 
é& established in 1881 << 
Spencer F. Baird 
First U.S. Commissioner 
of Fisheries and founder 
of Fishery Bulletin 
Effects of ocean acidification on larval Atlantic 
surfclam (Spisula solidissima) from Long Island 
Sound in Connecticut 
Shannon L. Meseck (contact author) 
Renee Mercaldo-Allen 
Paul Clark 
Catherine Kuropat 
Dylan Redman 
David Veilleux 
Lisa Milke 
Email address for contact author: shannon.meseck@noaa.gov 
Milford Laboratory 
Northeast Fisheries Science Center 
National Marine Fisheries Service, NOAA 
212 Rogers Avenue 
Milford, Connecticut 06460 
The process of ocean acidification (OA) 
occurs when increased atmospheric car- 
bon dioxide (CO,) from anthropogenic 
activities (i.e., burning of fossil fuels 
and deforestation) is absorbed by ocean 
waters (Caldeira and Wickett, 2003; 
Raven et al.'; Doney et al., 2009). Con- 
sequently, concentrations of dissolved 
CO, and bicarbonate ions (HCO; ) 
rise, while concentration of carbonate 
ions (One: pH, and calcium carbon- 
ate saturation level (Q) decline (Feely 
et al., 2004, 2010; Hénisch et al., 2012; 
Duarte et al., 2013). In recent years, 
the ocean’s natural capacity for buffer- 
ing, a process that normally occurs over 
a geologic timescale of 10,000—100,000 
years, has been unable to keep pace with 
the rate of acidification (H6nisch et al., 
2012; Zeebe, 2012; Zeebe et al., 2016), 
resulting in a global ocean pH drop of 
‘Raven, J., K. Caldeira, H. Elderfield, 
O. Hoegh-Guldberg, P. Liss, U. Riebesell, 
J. Shepherd, C. Turley, and A. Watson. 2005. 
Ocean acidification due to increasing atmo- 
spheric carbon dioxide. R. Soc. Policy Doc. 
12/05, 57 p. [Available from website.] 
0.1. This ongoing shift in the carbonate 
system and corresponding decline in 
pH and Q may affect the growth and 
survival of marine organisms. 
Representative concentration path- 
ways (RCPs) are used to predict future 
CO, concentrations. By the year 2100, 
under the RCP 8.5 scenario (high emis- 
sions) used in climate modeling, CO, 
levels will be >1000 patm, and under 
the RCP 6.0 scenario, CO, levels will 
be in the range of 720-1000 patm 
(IPCC, 2014). Projected increases in 
CO, by 2100 are expected to result in 
a reduction of 0.2—0.4 in pH and in a 
50% decline in aragonite saturation 
level (Qaragonite)» 2 Measure often used 
in relation to Q because aragonite is a 
common form of calcium carbonate in 
ocean waters (Feely et al., 2004, 2010; 
Hartin et al., 2016). It has been pre- 
dicted that, by the year 2300, CO, levels 
will be >2000 patm and will correspond 
to an additional drop of 0.4 in pH (Feely 
et al., 2004, 2010; Hartin et al., 2016). 
In a recent climate vulnerability 
assessment of fish and invertebrates on 
the continental shelf of the northeastern 
