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▼a Coastal habitats protect dynamic shorelines, sequester carbon, filter pollutants, and support whole fisheries. Coasts are vulnerable to both global climate change and local human impacts, e.g., nutrient loading, shoreline development, and overharvest, which threaten the provision of these ecosystem services through changes in community structure and functioning. This combination of global and local change affects species both at the top and bottom of food webs simultaneously. Therefore, realistic studies of multi-level interaction networks is the best way to predict the consequences of these changes on ecosystem services and functions. Here, I tested how human activities alter top-down and bottom-up processes within tropical marine food webs. I used a combination of surveys and experiments along Great Abaco Island, The Bahamas to ask the following questions: (1) how does shoreline development affect the relative abundance and distribution of marine megafauna, (2) what are the separate and interactive effects of overfishing and habitat degradation on reef fish community assemblage, (3) what is the relative importance between predation and nutrients shifts in determining seagrass invertebrate community composition, and (4) how does the introduction of artificial reefs alter the trophic ecology of a Critically Endangered predator?(1) To determine how shoreline development affects the abundance and distribution of megafauna, I used a consumer-grade drone to survey sharks, rays, and turtles in developed and non-developed tidal creeks. Importantly, a detection success experiment determined that drones are an effective, non-invasive tool to monitor megafauna in shallow, clear waters. My surveys showed, on average, 35% more megafauna along non-developed shorelines than developed shorelines. (2) To determine the relative importance of overfishing (top down) and habitatdegradation (bottom up) on reef fish communities, I designed a fully factorial experiment manipulating predator presence and reef structural complexity on 16 artificial reefs. Over three months, I found the presence of a predator and increased reef habitat complexity had an additive effect on reef fish total abundance, with increased fish abundance by 250% and 300% compared to reefs without predators and decreased complexity, respectively. (3) To mechanistically test the role of fishes' consumptive and fish-derived nutrients provision effects on seagrass invertebrate communities, I conducted surveys and predator exclusion experiments within an ongoing, seven year factorial manipulative field experiment that manipulated local ambient nutrient dynamics. In low nutrient waters, I found that invertebrate biomass was strongly decreased by fish predation. However, when human-derived nutrients were present, additive effects of top-down (negative) and bottom-up (positive) control on invertebrate biomass and species density were present. (4) Lastly, I examined changes in the diet and movement behavior of juvenile Nassau grouper residing on natural and artificial reefs. Over a seven month study period, I found individuals located on natural reefs were larger on average than individuals on artificial reefs, grouper diet depended on individual fish size and home reef surrounding habitats, and for shifts in grouper movement, reef type altered how often individuals resided away from reef habitat. I found artificial reefs may be a simple management tool to enhance complex habitat within coastal systems, but because there were shifts in the trophic ecology of an important reef predator, wildlife managers should consider the potential cascading consequences for changes in inter- and intraspecific species interactions before artificial are introduced into a system. |