Date of Award

Fall 12-20-2019

Level of Access Assigned by Author

Open-Access Thesis

Degree Name

Doctor of Philosophy (PhD)

Department

Marine Bio-Resources

Advisor

Timothy Bowden

Second Committee Member

Ian Bricknell

Third Committee Member

Paul Rawson

Additional Committee Members

Brian Beal

Aria Amirbahman

Abstract

Sediment acidification has been shown to negatively impact clams of economic importance such as the soft-shell clam, Mya arenaria Linnaeus, 1758, and hard clam, Mercenaria mercenaria (Linnaeus, 1758). Effects of sediment acidification on razor clams, including the Atlantic jackknife clam Ensis leei M. Huber, 2015, are unknown. E. leei has been identified as a species with potential for aquaculture operations on the New England coast. E. leei may be resilient to acidification and thus persist in acidified sediments where other clams cannot. To this end, the impact of acidified surface sediment on the internal immune capacity of adult (mean shell length 17.6 ± 0.9 cm) E. leei at 10°C and 20°C was tested. Surface sediment was acidified from pH ~7.2 to ~6.0 using sediment bacteria. Crushed E. leei shell was used to keep the surface sediment of the ambient pH groups ~6.8. Hemocytes (circulating blood cells) are responsible for carrying out immune functions in bivalves, and thus were the target for internal immune capacity assays. Hemocyte parameters measured included cell viability, total hemocyte counts, differential hemocyte counts, and phagocytic capacity. A condition index was calculated using the wet flesh weight and dry shell weight to assess the physiological condition of the clams. In addition, these health parameters were measured in E. leei collected over the course of a year no more than 30 hours after they were taken from the field site for seasonal trends in baseline immune capacity. The presence or absence of ripe gonads was also noted in these clams. Only total hemocyte count and percent of clams with ripe gonads correlated positively with the temperature of the collection site. A 30-day exposure period to the acidified sediment kept in recirculating aquaria had no significant impact on any of these parameters. In addition, all the clams buried into the sediments of their respective treatments within an hour of being placed there. These results indicate that the internal immune capacity of E. leei adults is not impacted by acidified surface sediments. Additional work will be needed to determine if juvenile E. leei are resilient to acidification as well.

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