In tropical seascapes, coral reefs often exist in proximity to marine vegetated habitats such as seagrass, mangroves, and macroalgae. This habitat mosaic offers the possibility for connection and exchange of both organisms and nutrition between habitats, mediated by biological and physical processes. This dissertation examines flows of organisms and nutrition between coral reefs and tropical vegetated habitats in the central Red Sea through 3 different mechanisms: 1) Use of multiple habitat types by tropical marine fishes, 2) Transport of algal material to coral reefs via the foraging behavior and movements of herbivorous fishes, and 3) Physical flow of water between coastal habitats. The results of this thesis suggest that coastal tropical habitats maintain a variety of ecological links at different spatial and temporal scales. A large fraction (36%) of fish species found on coral reefs are also found in at least one marine vegetated habitat in the central Red Sea, with many species mainly living in vegetated habitats as juveniles. This demonstrates the value of mangrove, seagrass, and macroalgae habitats to coral reef fishes, and suggests that many species make ontogenetic migrations between reef and non-reef habitats through their lives. Two species of herbivorous reef fishes (Naso elegans and N. unicornis) were found on coral reefs with algae in their guts which likely originated from nearby Sargassum-dominated macroalgae canopies, representing a fish-mediated, cross-habitat flux of nutrition from macroalgae habitats to coral reefs. Finally, we used a combination of remote sensing, a dye tracer study, and in-water measurements to observe water movement from shallow seagrass and mangrove habitats to nearby lagoon and coral reef habitats. Water exiting seagrass and mangrove habitats had altered concentrations of various nutrients (such as increased particulate organic carbon or decreased dissolved nutrients), suggesting that Red Sea mangroves and seagrasses change nutrient concentrations in water and the movement of water from these habitats to coral reefs could supply reefs with an allochthonous source of nutrition. These various linkages, controlled by a range of physical and biological processes, highlight the interconnected nature of tropical coastal ecosystems, and thereby the need to conserve whole habitat mosaics in the pursuit to protect coral reefs and maintain healthy and functioning coastal ecosystems.

Wetlands play a vital role in regional and global biogeochemistry by controlling the movement and cycling of nutrients and carbon. While individual wetlands may provide these ecosystem services, high density wetland landscapes, referred to as wetlandscapes, can have far reaching aggregate effects on elemental cycling and solute transport. Here we use forested Delmarva bays or wetlands as a study ecosystem to explore physical and biological controls on wetland chemistry within forested wetlandscapes. The Delmarva wetlandscape consists of thousands of geographically isolated wetlands on the Delmarva Peninsula, United States, which despite their proximity to each other have highly variable sizes, shapes, hydrology, vegetative cover, and biological communities. This physical and biological variation makes the Delmarva wetlandscape an ideal ecosystem to understand spatio-temporal heterogeneity and drivers of biogeochemistry. In this dissertation, I demonstrate that water chemistry within the Delmarva wetlandscape is heterogeneous both within and between surface water and groundwater systems (Chapter 2). Surface water chemistry was primarily influenced by temporal factors (season and month), followed by local hydrology. In contrast, groundwater chemistry was strongly influenced by water level below ground surface and interaction with organic soil layers. These results are important in understanding both internal wetlandscape water chemistry dynamics and export of solutes such as dissolved organic matter (DOM) to adjacent river ecosystems. Further, these results suggest that local biological and hydrological factors strongly affect surface water chemistry in wetlands. To explore these factors, I used an observational approach to determine the role of larval amphibians on wetland biogeochemistry (Chapter 3) and employed high-resolution chemistry sensors to study the effect of hydrological changes on surface water dissolved organic matter concentrations (Chapter 4). Animal waste can contribute substantially to nutrient cycling and ecosystem productivity, yet little is known of the biogeochemical impact of animal excretion in wetland habitats. A common and abundant amphibian in Delmarva wetlands are wood frog (Lithobates sylvaticus) tadpoles. I found that wood frog tadpole aggregations elevated nutrient recycling, microbial metabolism, and carbon cycling in Delmarva wetlands. These results provide evidence for the functional and biogeochemical role of tadpole aggregations in wetland habitats, with important implications for ecosystem processes, biodiversity conservation, and ecosystem management. To further explore the role of hydrology on DOM concentrations, I utilized high-resolution fluorescent dissolved organic matter sensors (fDOM) and applied river solute transport frameworks and metrics to wetland catchments. I found that there was heterogeneity in wetland response to changing hydrology and that seasonality and potentially bathymetry influences fDOM concentrations. Together, these studies inform our understanding of wetlandscape heterogeneity and DOM export, as well as biological and hydrological drivers of biogeochemistry. / Doctor of Philosophy / Wetlands control the movement of nutrients and carbon at local, regional, and global scales. There is a large body of knowledge demonstrating the importance of wetlands to the transport of dissolved water constituents, such as dissolved organic matter (DOM) and nutrients. However, there is little information on what controls surface water chemistry in these wetland landscapes and less is known about belowground water chemistry. In this study I examined the role of water level, wetland shape, and time (i.e., year, month of the year, and season) on surface and groundwater chemistry in wetlands. I found that water chemistry was different between surface and groundwater and that differences were primarily due to seasons or months in surface water wetlands, while water level and flooding of organic matter-rich soil layers controlled groundwater chemistry. These results indicate that there are differences in water chemistry between surface water and groundwater that are controlled by unique drivers. These results also suggested that biological processes such as animal presence may influence wetland chemistry. To understand the role of animals in wetland chemistry, I studied the effect of wood frog (Lithobates sylvaticus) tadpole waste on nutrient concentrations in wetlands and found large tadpole groups are significant recyclers of nitrogen and phosphorous, which were used by microbes as nutrients, leading to enhanced leaf litter break-down in wetlands. These findings imply that tadpoles have an important role in wetland ecosystems by creating locations of enhanced nutrient and carbon cycling and that conservation of amphibian species may also preserve ecosystem processes in wetlands. Additionally, my initial study suggested that hydrology influences DOM concentrations in wetlands. I used high-frequency chemistry sensors to detect fluorescent dissolved organic matter (fDOM) concentrations, which represents a fraction of DOM. I found that relationships and patterns in fDOM concentration were complex, and that season and wetland shape were important in wetland DOM dynamics. Overall, this dynamic behavior across seasons and between wetlands indicates that wetland response to water levels can drive differences in water chemistry between wetlands and is important in our understanding of wetland response to storm events. The information gained from these studies is important in understanding how large wetland landscapes function and control movement of nutrients and carbon. Further, my research has uncovered the role of animal species in controlling nutrient and carbon cycling in wetland environments as well as the complex response of fDOM to water level changes in individual wetlands.