Trophic Dynamics on Degraded Coral Reefs: Analyses of Nutrients and Isotope Fractionation in the Biosphere 2 Ocean
Abstract
Due to climatic changes and increased anthropogenic stressors, oceans are experiencing rapid biogeochemical transformations, causing degradation of coral reefs that are crucial to biodiversity, ecotourism, infrastructure, and society. However, it remains difficult to quantify the relative importance of "bottom up" (e.g., algal cover) and "top down" (e.g., herbivorous grazing) controls on nutrients, productivity, and overall health of coral reef ecosystems. As reef systems are sensitive to nitrogen, carbon, and other nutrients, knowledge about these habitats' geochemical makeup as a function of algae cover is key to understanding their overall health. Similar to oceans today, the Biosphere 2 Ocean (B2O) has experienced coral reef degradation, providing an opportunity to assess nutrient and herbivory dynamics during bioremediation. After removing 100 m2 of algae, the geochemistry of the mesocosm was monitored to observe any changes. We hypothesize that as algae coverage decreases, the ocean will become more oligotrophic. Carbon and nitrogen isotopic percentages and fractionation ratios across trophic levels were also measured. These isotopic fingerprints were then applied to a sediment core to determine how the ratio of nitrogen isotopes changed temporally through the sediment profile. We hypothesize that the ratio of 15N:14N (δ15N) should increase up the B2O trophic levels. In times of increased nutrient concentrations, we also expect less 15N to be deposited in the sediment. This study will provide a much fuller understanding of changes in nutrients, trophic dynamics, and productivity throughout the history of the B2O, methods that may be applied to our oceans today. Based in the complexity and scale of the B2O system, these bioremediation methods and geochemical fingerprints may be applied in situ to degraded reefs.
- Publication:
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AGU Fall Meeting Abstracts
- Pub Date:
- December 2019
- Bibcode:
- 2019AGUFMPP42C..20T
- Keywords:
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- 0454 Isotopic composition and chemistry;
- BIOGEOSCIENCES;
- 0473 Paleoclimatology and paleoceanography;
- BIOGEOSCIENCES;
- 0491 Food webs and trophodynamics;
- BIOGEOSCIENCES;
- 4950 Paleoecology;
- PALEOCEANOGRAPHY