Incorporation of Species Interactions in Seagrass Conservation and Restoration

Abstract

Coastal ecosystems and the valuable services they provide have and continue to be degraded by anthropogenic stressors across the globe. Conservation efforts to mitigate deleterious impacts have largely failed at aiding ecosystem recovery such that restoration has become a predominant method of stemming the loss of critical habitats and the communities they support. Globally, it is estimated that 29% of seagrass beds have been lost or converted, and this translates to trillions of dollars lost in ecosystem services as well as commercial and recreational prospects. In this dissertation, I evaluate how ecological interactions can alter restoration trajectories and shift community dynamics. Namely, I focus on facilitative and trophic interactions among seagrasses, bivalves, and the associated nekton and mesograzer communities propagate through seagrass ecosystems. To do this, I use a combination of scientific literature review, surveys, and manipulative field experiments to apply ecological theories of species interactions in seagrass restoration and conservation. Reviews of the coastal restoration research reveal a paucity of studies that consider biological interactions as important factors that may determine restoration success (Chapter 1). Because foundation species, such as seagrasses, can promote the success and survival of numerous other organisms through facilitation, I further tested if and how a facilitation cascade among seagrass beds and pen clams, Atrina rigida, may affect local diversity and ecosystem functions (Chapter 2). Since studies have, in fact, shown that positive interactions can also enhance restoration of coastal foundation species, I investigated in how the inclusion of intra- and interspecific interactions can affect seagrass restoration from seed and adult shoots. Finally, given that top-down influences can also affect bivalve abundances and seagrass productivity, I explored how large predator removals (via exclusion stockades) may shift seagrass community structure and propagate onto primary producers. In these studies, I find that facilitative interactions can promote not only the success and yield of bivalve populations, but that in some instances, bivalves can also, in turn, facilitate the growth of seagrasses. Similarly, alteration to diversity at higher trophic levels can have positive top-down impacts on bivalve abundances despite alterations to mesopredator abundances. Whereas biological interactions have historically been ignored in the restoration literature, my dissertation research makes the argument that consideration and incorporation of species interactions is necessary for understanding the ecology that underlies the stability, recovery, and resilience of coastal ecosystems.