MEPS 420:27-44 (2010)  -  DOI: https://doi.org/10.3354/meps08846

ABSTRACT: The formal protection of the Hawaiian green turtle Chelonia mydas in the 1970s has led to significant increases in the number of individuals recorded throughout the archipelago. Reduced growth rates and poor body condition of individuals at a number of foraging sites, including Kaloko-Honokoōhau National Historical Park (Kaloko), suggest that some aggregations have reached carrying capacity. To better understand the ecological structure and processes of the reef system at the park, we developed an ecosystem model that synthesized available data on Kaloko for the year 2005 and included 26 groups, spanning the entire trophic web. Model results showed that the combined grazing pressure of the different herbivore functional groups (i.e. reef fish, sea urchins, and green turtles) in Kaloko matched total algal production. Sea urchins exerted the strongest control over algal resources, partly because of their large biomass in park waters. Results confirmed that the Kaloko green turtle aggregation has reached carrying capacity. Green turtles help maintain low algal cover, and thus resilience of reefs in the face of disturbance, and should be explicitly included in studies of ecosystem dynamics on reefs. Our work also provides a ‘current-condition’ baseline for Kaloko, and a valuable tool for the assessment of the future marine ecosystem impacts of projected urban expansion plans around the park.

KEY WORDS: Marine turtles · Ecosystem-based management · Ecopath · Coral reef · Herbivory · Phase shift · Nutrient enrichment · Kona coast · Hawaii