Date Awarded

Summer 2021

Document Type

Thesis

Degree Name

Master of Science (M.Sc.)

Department

Virginia Institute of Marine Science

Advisor

Rochelle Seitz

Committee Member

Romuald Lipcius

Committee Member

Carl Friedrichs

Committee Member

Kimberly Reece

Abstract

The soft-shell clam, Mya arenaria, is a benthic, filter-feeding, infaunal clam typically found in intertidal and shallow subtidal waters. Chesapeake Bay stocks of M. arenaria have been depleted since the 1960s due to various factors including predation, temperature, low recruitment, habitat loss, disease mortalities, and commercial harvest. As an important prey item for many commercial species, low abundances of these clams are mostly the result of the voracious appetite of the blue crab, Callinectes sapidus. In addition to predation, summer water temperatures in the Chesapeake Bay are likely driving the low abundances of M. arenaria, as water temperatures commonly surpass the optimal thermal range for this species (2 – 28 C). This study addresses several gaps in our understanding of M. arenaria, and the conditions required for an aquaculture industry for this species to be successful in the Chesapeake Bay. A series of caging experiments and mesh experiments were conducted over two years (2018 and 2019) and at two tidal zones (intertidal and subtidal) in Timberneck Creek and Catlett Islands, VA to examine the recruitment and survival of M. arenaria. In 2018, cages were constructed of ¼” (0.63 cm) VEXAR mesh and cut-off 5-gallon buckets and compared to open plots in two seasons, spring and fall. In 2019, cages were constructed of perforated aquatic plant pots with one of two mesh types, netting or VEXAR, and one of two mesh sizes, ¼” or ½”, cable tied over the top of each cage. One open cage (no mesh covering cage) treatment served as a control at each of the tidal zones at each site. There were two replicates of each caging treatment at each site and tidal zone. Each cage was filled with sediment and 10 marked and measured M. arenaria were planted ~2.5 cm in sediment. One cage of each treatment at each site and tidal zone was collected and examined 6 months from deployment date (and the remaining cages one of each treatment) were collected and examined 12 months from deployment date. At each tidal zone, “iButtons” (temperature loggers) were deployed to collect continuous water temperature measurements. In the lab, clams were identified, counted, measured, and analyzed for organic content using standard ash-free dry-weight (AFDW) measurements. The presence of crabs that had entered into cages made a significant difference in the survival of outplanted clams across all treatments for both tidal zones. Net treatments yielded significantly greater densities of recruits as compared to open and VEXAR treatments in both tidal zones. Overall, the presence of caging and netting increased Mya arenaria survival and recruitment. Netting offered enough protection from predators to allow clams to grow to harvestable sizes within six months. Caging mesh type and size played a role in M. arenaria recruitment and survival, with recruits tending to be more abundant in the ¼” net treatments. This study provides evidence that protection by caging and netting increases survival and recruitment of Mya arenaria – indicating that it is possible to have a successful soft-shell clam aquaculture operation developed in the Chesapeake Bay.

DOI

http://dx.doi.org/10.25773/v5-hnta-5775

Rights

© The Author

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