Assessing the impact of terrestrial watershed input on coastal coral reef communitites

Dixson, Danielle L.Anthropogenic impacts on coastal ecosystems can be pervasive as humans alter the natural environment to suit their needs. A common alteration that coastal communities make to the environment is the removal of native vegetation in order to grow crop plants. The use of fertilizers on these crops can also harm coastal ecosystems through the discharge of non-point source pollution via watershed runoff. Rainwater passes through watersheds and carries a variety of chemicals from the terrestrial systems into aquatic coastal ecosystem. Chemical cues produced by crop plants, such as coconut, have been shown to negatively impact coastal coral reef communities through negative behavioral changes in coral reef fish. This thesis assessed the influence that vegetation community composition within a watershed has on the biodiversity of coastal coral reef ecosystems. First, unmanned aerial vehicles were utilized to map an island in Fiji and delineate the watersheds of the island. Next, machine learning algorithms classified the vegetation communities within those watersheds. This allowed the coverage of vegetation types to be quantified within each watershed. Finally, the coral reefs surrounding the island were separated based on the corresponding upland watershed. The biodiversities of those coral reefs were compared to reveal that watersheds containing coconut (which produces a repulsive chemical cue) did not negatively impact the health of adjacent coral reefs, when those watersheds were also dominated by native vegetation. The findings in this thesis provide evidence that, in the case of negative chemical cues produced by coconut, native vegetation has the potential to overpower the coconut and mitigate any harmful effects. This work furthers the idea that the relationship between land and sea is dynamic, and community-scale approaches should be utilized when assessing the impacts of terrestrial ecosystems on coastal coral reef communities.University of Delaware, School of Marine Science and PolicyM.S