Meseck et al.: Effects of ocean acidification on larval Spisula solidissima from Long Island Sound 71 
significant difference in metamorphosis of Atlantic surf- 
clam between the low- and high-pCO, treatments. 
Lipid concentration and percent lipid measured at the 
end of the experiment indicate variable responses to the 
tested OA conditions (Table 2). Phospholipids and tria- 
cylglycerols constituted a large portion of the total lipid 
concentration (58-69%) for all treatments, and there 
were no significant differences in these characteristics 
between treatments (F ratio=1.612, P=0.28). There was 
no significant difference in the sterol-to-phospholipid 
ratio (F ratio=0.77, P=0.77). 
Discussion 
Atlantic surfclam from LIS performed better at pCO, 
levels predicted for the RCP 6.0 scenario than at current 
levels or levels predicted for the RCP 8.5 scenario, result- 
ing in a hormetic (U-shaped) response for growth, larval 
shell height, and percentage of larvae that successfully 
completed metamorphosis. This response is atypical of 
estuarine bivalve larvae in OA experiments of previous 
studies; larvae in those studies had negative responses 
at pCO, levels reported for the RCP 6.0 and RCP 8.5 
Table 2 
Final lipid concentrations (in micrograms per gram of wet weight) and percent lipid (lipid concentra- 
tion divided by total lipid concentration multiplied by 100) for laboratory-reared larval Atlantic surfclam 
(Spisula solidissima) at the end of the experiment (after 28 d) conducted in 2015 with 3 treatments that 
exposed larvae to low (344 patm), medium (821 patm), and high (1243 patm) levels of partial pressure of 
carbon dioxide (pCO,). Values with different superscript letters are significantly different (P<0.05). Stan- 
dard errors of the mean are provided in parentheses. For all analyses, degrees of freedom equaled 6. The 
adult brood stock used to rear individuals for this study were collected in 2014 from waters of Connecticut 
in Long Island Sound. ND=not detected. 
Lipid 
Acetone mobile polar lipids 
Alcohols 
Diacylglycerols 
Ethyl esters 
Ethyl ketones 
Free fatty acids 
Glycerol ethers 
Hydrocarbons 
Methyl esters 
Methyl ketones 
Phospholipids 
Sterols 
Steryl wsters/wax esters 
Triacylglycerols 
Sterol—phospholipid ratio 
Total 
Lipid 
Acetone mobile polar lipids 
Alcohols 
Diacylglycerols 
Ethyl esters 
Ethyl ketones 
Free fatty acids 
Glycerol ethers 
Hydrocarbons 
Methyl esters 
Methyl ketones 
Phospholipids 
Sterols 
Steryl esters/wax esters 
Triacylglycerols 
Lipid concentration (ug/g) by treatment level of pCO, 
Low 
34.20 (18.44) 
ND 
ND 
1.91 (1.10) 
15.07 (4.69)* 
16.49 (4.90) 
ND 
3.42 (0.96)* 
ND 
15.07 (8.16) 
117.43 (52.14) 
13.26 (5.04) 
ND 
105.82 (89.66) 
0.14 (0.02) 
316.12 (173.88) 
Medium 
95.94 (18.44) 
ND 
ND 
ND 
50.43 (4.69)? 
22.86 (4.90) 
ND 
8.23 (1.27)? 
ND 
50.43 (8.16) 
219.68 (52.14) 
32.24 (5.04) 
4.65 (2.68) 
342.17 (89.66) 
0.15 (0.02) 
806.35 (173.88) 
High 
80.23 (18.44) 
4.22 (2.43) 
ND 
ND 
37.63 (4.69)*” 
24.36 (4.98) 
ND 
5.43 (0.54)*” 
ND 
37.63 (8.16) 
199.07 (52.14) 
24.54 (5.04) 
1.36 (2.68) 
220.12 (89.66) 
0.13 (0.02) 
613.01 (173.88) 
Percent lipid by treatment level of pCO, 
Low 
15.68 (2.85) 
ND 
ND 
1.39 (0.80) 
3.59 (0.78) 
7.04 (1.03) 
ND 
1.60 (0.46) 
ND 
4.76 (0.55) 
35.35 (2.38) 
4.81 (0.59) 
ND 
22.79 (6.30) 
Medium 
11.52 (2.85) 
ND 
ND 
ND 
3.96 (0.78) 
2.82 (1.03) 
ND 
1.11 (0.46) 
ND 
6.48 (0.55) 
28.11(2.38) 
4.08 (0.59) 
0.43 (0.26) 
41.50 (6.30) 
High 
14.32 (2.85) 
1.51 (0.87) 
ND 
ND 
2.46 (0.78) 
4.37 (1.03) 
ND 
1.07 (0.46) 
ND 
6.47 (0.55) 
34.17 (2.38) 
4.42 (0.59) 
0.28 (0.26) 
30.95 (6.30) 
F ratio 
F ratio 
0.42 
1.0 
