Hot moments in spawning aggregations: implications for ecosystem-scale nutrient cycling
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Biogeochemical hot moments occur when a temporary increase in availability of one or more limiting reactants results in elevated rates of biogeochemical reactions. Many marine fish form transient spawning aggregations, temporarily increasing their local abundance and thus nutrients supplied via excretion at the aggregation site. In this way, nutrients released by aggregating fish could create a biogeochemical hot moment. Using a combination of empirical and modeling approaches, we estimate nitrogen and phosphorus supplied by aggregating Nassau grouper (Epinephelus striatus). Data suggest aggregating grouper supply up to an order-of-magnitude more nitrogen and phosphorus than daily consumer-derived nutrient supply on coral reefs without aggregating fish. Comparing current and historic aggregation-level excretion estimates shows that overfishing reduced nutrients supplied by aggregating fish by up to 87 %. Our study illustrates a previously unrecognized ecosystem viewpoint regarding fish spawning aggregations and provides an additional perspective on the repercussions of their overexploitation.
KeywordsSpawning aggregation Nitrogen Phosphorus Nassau grouper Epinephelus striatus Biogeochemical hot moments
We thank the volunteers and businesses that provided logistic support during the collection of data on the grouper aggregation part of the Reef Environmental Education Foundation Grouper Moon Project, and Friends of the Environment for logistical support during creation of the N and P excretion models. We also thank the comments of the anonymous reviewers whose inputs greatly improved this manuscript. This study was funded by Reef Environmental Education Foundation, the Cayman Islands Department of the Environment, Lenfest Ocean Program, the Disney Wildlife Conservation Fund, the National Oceanic and Atmospheric Administration International Coral Reef Conservation Program (Grant NA04-NOS 4630287), J. Edward Mahoney Foundation, Environmental Protection Agency STAR Fellowship (J.E.A), National Science Foundation (NSF) Doctoral Dissertation Improvement Grant (J.E.A), and National Science Foundation (Biological Oceanography 1259306 and 0746164).
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