Date Thesis Awarded

5-2023

Access Type

Honors Thesis -- Access Restricted On-Campus Only

Degree Name

Bachelors of Science (BS)

Department

Biology

Advisor

Randolph Chambers

Committee Members

Christopher Patrick

James Skelton

Linda Morse

Abstract

Coastal marine ecosystems are highly dynamic environments that are formed and maintained not only by abiotic processes but are often strongly influenced by their biota as well. Abiotic processes have been a focal point in coastal ecological research and conservation for what drives the development and long-term dynamics of coastal ecosystems’ seascape and function. Yet, marine megafauna, due to their large body mass and mobility, can have powerful influences on ecosystem dynamics through myriad mechanisms including physically modifying their habitat. Without incorporating both environmental and fauna inputs there will remain a gap of knowledge in our understanding on the control and maintenance of coastal ecosystem function. Large-bodied stingrays are marine predators commonly found in tropical and sub- temperate seagrass meadows, yet their ecological role in seagrass ecosystems is currently understudied. We know that rays, as benthic foraging consumers, can modify habitat structure when searching for prey, which may drive seagrass heterogeneity. Here, we investigate the impacts of individual disturbance events by foraging stingrays on the structure and function of eelgrass (Zostera marina), a dominant seagrass species, in Virginia’s Coastal Bays. We conducted transect surveys to quantify whether seagrass heterogeneity i.e., patchiness and proximity to bed edge alter ray pit intensity both separately and interactively. In paired ray pits (i.e.,

canopy height and shoot density, as well as plant biomass to quantify the localized effects on the structure and function of ray foraging pit edges. While seagrass meadow heterogeneity and edge proximity did not alter where rays forage, there was some evidence pointing to foraging preference for bed edge. Prior to peak growing season, ray pit disturbances appear to reduce adjacent seagrass canopy by 10 cm and shoot density by 69% compared to undisturbed seagrass. However, after peak growing season, seagrass canopy at the edge of ray pits was marginally higher compared to undisturbed areas, suggesting seagrass edge recovery after the initial pit. From this recovery, we found no stingray effects on primary production, or the total biomass produced, minus the pit created by the end of the growing season. Our results suggest that stingray foraging creates within meadow microhabitats, and when disturbances are small-scale (i.e., 0.5 – 2.0 m2 ) these impacts are localized without cascading degradation beyond the pit edge. Our study provides evidence that marine megafauna can play a measurable role in structuring coastal ecosystems, while also not compromising the long-term productivity and diversity of the ecological community.

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