Biological Response of Spisula Solidissima (Atlantic Surfclams) to Varying Carbonate Chemistry in the Mid-Atlantic Bight

Spisula solidissima (Atlantic surfclams) are bottom dwelling bivalves native to the Mid-Atlantic Bight (MAB). They are sensitive to ongoing climate change-induced ocean warming and ocean acidification. Ocean warming has increased bottom temperatures and ocean and coastal acidification has depressed the aragonite saturation state ( $\Omega_{\text{Arag}}$ ), an essential mineral for shell-forming organisms. Ongoing changes in carbonate chemistry may negatively impact the physiology of surfclams which could in turn impact New Jersey surfclam fisheries. A gap in ocean acidification research is access to co-located biological response monitoring. Most literature on organism response is from single-species laboratory studies and may not capture realistic, natural conditions, or variability. Simultaneous measurements of surfclam biological response indicators need to be co-located with carbonate chemistry observations in the field to observe and predict biological impact in situ. The objective of this project was to conduct co-located sampling to determine the correlation between observed carbonate chemistry and biological data from Atlantic surfclams in their natural habitat. A vessel-based survey was performed to collect oceanographic measurements, including carbonate chemistry, and surfclam samples off New Jersey on the Mid-Atlantic shelf. Mean bottom or subsurface oceanographic measurements were used as inputs to $\Omega_{\text{Arag}}$ . A subsample of surfclams at each station were measured for shell length, thickness, and weight. Shell strength was also determined using a tensile strength machine and was defined as the force (kiloNewtons) applied in the middle of the shell at which the shell begins to break. Shell strength was standardized to shell weight for each shell (kN/g). Results showed no significant correlations between shell strength and carbonate chemistry. This could be due to potential acclimation capacity, potential buffering capacity of seawater, and/or potential energy reallocation. The results indicate that shell strength may not be the best metric to determine the impacts on Atlantic surfclams in a highly variable environment. The exposure to low $\text{pH}/\Omega_{\text{Arag}}$ may need to be much longer to see responses in shell strength. The lack of correlation between shell strength and carbonate chemistry does not mean that Atlantic surfclams were not impacted by pH and $\Omega_{\text{Arag}}$ , but other unmeasured physiological metrics may have instead been affected.