Identifying current reef resource condition to support local management action.
Funding provided by: Western Pacific Coral Reef Institute
The Republic of the Marshall Islands (RMI) comprises a vast extent of the tropical, central Pacific Ocean, encompassing extensive marine resources, but also creating a substantial challenge for developing the insight needed for their sustainable use. This study examined coral-reef ecosystems across and within two atolls that differ with respect to their human presence, Rongelap (nearly pristine) and Majuro (urban center of RMI). Coral, fish, and benthic substrate data aggregated at the site-level highlighted strong inter-atoll differences, but more remarkably, there were consistent differences in data dispersion for all assemblages.
Human influence served to increase multivariate, site-level separation, yet, within each site, decreased the variation among replicate coral quadrats and fish surveys. Both patterns suggest consequences for ecosystem maintenance, inferring enhanced isolation and reduced redundancy, respectively. Beyond examine ecological states, we draw upon inter and intra-atoll gradients to define an ecological cascade, whereby: 1) shark, secondary consumer, large-bodied planktivore, and parrotfish biomass all declined along a gradient of human influence, 2) herbivore and detritivore acanthurids increased in density and biomass, 4) primary producer biomass increased, 6) massive, encrusting, and high-relief coral abundance decreased, despite having stable population densities, and finally, 7) the dominance of opportunistic, tolerant coral assemblages emerged.
In summary, shark presence appears to enhance the biomass and body-size of several major food-fish families in comparison to human presence, and through the outlined cascade, protects against the chain of ecosystem interactions. Certainly the RMI has numerous atolls that reside somewhere along the gradients developed in this study. Continuing to fill in the gaps will afford managers a better ability to translate existing and desirable levels of fishing pressure required for conservation success.