Date Awarded

2013

Document Type

Dissertation

Degree Name

Doctor of Philosophy (Ph.D.)

Department

Virginia Institute of Marine Science

Advisor

Romuald N. Lipcius

Abstract

The northern diamondback terrapin (Malaclemys terrapin ) is the only estuarine turtle residing along western Atlantic and Gulf of Mexico coasts of North America. Through predation, terrapins may be a key species in coastal marine habitats by exerting top-down control on marsh invertebrates, and thereby help to maintain healthy marshes. Despite the terrapin's ecological importance, there has not been a thorough study of terrapin foraging ecology and movements in lower Chesapeake Bay. In this dissertation, the research focused on the foraging habits of diamondback terrapins and their effects within salt marsh and seagrass habitats of lower Chesapeake Bay. I provided detailed analysis of the diet of diamondback terrapins captured from both salt marsh and seagrass habitats that showed preferred foraging in seagrass beds when present, as well as prey differentiation by terrapin size, i.e., small vs. large terrapins. Three general patterns in dietary overlap based on terrapin size were common for M. terrapin. By habitat, there was substantial overlap in prey choice, though further analyses determined selectivity for barnacles Balanus spp. by small terrapins in seagrass beds. Small terrapins from marsh-mudflat habitats consumed more periwinkles than large terrapins from marshes or all terrapins from marsh-SAV habitats. The size of ingested periwinkles was related to terrapin size with snails ingested by mature females presenting a bimodal distribution. Two mesocosm prey choice experiments showed that terrapins had a preference for juvenile blue crabs (Callinectes sapidus) over periwinkles and mottled dog whelks (Nassarius vibex). A third revealed terrapins were less successful in finding and consuming blue crabs with increasing percent cover of vegetation. An acoustic telemetry study confirmed that small terrapins, which included all males and juvenile females, had better-defined home ranges than adult females and stayed mostly in shallow near-shore water in seagrass beds of lower York River, whereas large females entered these areas on flood and high tides. A logistic regression model predicted that small terrapins were less likely to move out of an area than large females. Males made infrequent, long distances trips within the study area not associated with mating. Both genders and size classes also frequently moved between non-connected Zostera marina beds in the study area. This research provided the first field evidence that terrapins ingested viable eelgrass seeds incidental to consuming Z. marina epifauna. A second logistic regression model revealed that small terrapins were more likely to consume seeds than large terrapins. The diamondback terrapin is considered a "species of concern" in Virginia, but it has minimal protection with little enforcement. This dissertation provides empirical evidence supporting the diamondback terrapin's ecological importance within Chesapeake Bay that can be incorporated into conservation strategies to promote recovery and protection of the species within Virginia.

DOI

https://dx.doi.org/doi:10.25773/v5-tfhj-v826

Rights

© The Author

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