The effects of submarine groundwater discharge on tropical reef benthic community composition, structure, and primary productivity
The effects of submarine groundwater discharge on tropical reef benthic community composition, structure, and primary productivity
Date
2018-12
Authors
La Valle, Florybeth Flores
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Nelson, Craig E.
Department
Marine Biology
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Abstract
Submarine groundwater discharge (SGD) is recognized as an important source of inorganic nutrients and freshwater to coastal waters worldwide. SGD has been implicated in changing benthic community structure and hypothesized to enhance primary productivity. The goal of this dissertation is to elucidate the role of SGD in structuring benthic macroalgal communities and changing overall reef productivity in a tropical ecosystem (Maunalua Bay, O‘ahu, Hawaiʻi) by measuring a suite of variables in situ and using a variety of modeling techniques to understand when and where SGD structures benthic communities. I used benthic chamber stable isotope incubations to show that SGD increases carbon uptake of a dominant benthic alga by 82% and water column carbon uptake by 32%. The highest uptake rates occur at intermediate salinities (~21−22), indicating that mixing of nutrient-rich groundwater stimulates the productivity of algae and plankton in specific areas of coral reefs. Using surveys of macroalgae and in situ growth experiments, I found that species-specific macroalgal biomass and growth are significantly related to both SGD and long-term integrated indices of wave and wind exposure. I also related multivariate community structure to the temporal and spatial variability in tidally modulated SGD. At SGD seeps I documented low diversity and higher biomass of benthic species that can tolerate the biogeochemistry associated with high concentrations of SGD. Reefs with SGD can be hotspots for algal restoration and for species with large tolerance ranges for temperature, salinity, and nutrients to thrive. The site differences in both the SGD biogeochemistry and community structure underlines the importance of doing these types of studies at the watershed level. Understanding the effects of SGD on coastal communities will help direct and prioritize conservation and management efforts.
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Ecology,
Environmental science,
Biology,
algae,
coastal,
groundwater,
nutrients,
salinity,
SGD
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110 pages
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