Anthropogenic and Natural Stresses on Selected Coral Reefs in Hawai'i: A Multidecade Synthesis of Impact and Recovery

Abstract

In 2002, quantitative phototransect surveys documenting coral community structure off three coastal resorts in Hawai'i were repeated to produce long-term data sets of 12 to 22 yr duration. At the first site, in Honolua Bay off the Kapalua Resort on Maui, a runoff event from surrounding pineapple fields following a winter storm in early 2002 deposited sediment on the inner reef that remained in the bay for at least 6 months. Between 1992 and 2002 survey data showed that significant declines in coral cover occurred on seven of eight transects, causing an overall reduction in coral cover of about 33% throughout the entire bay. Rainfall records indicate that the 2002 storm was of relatively small magnitude; however subsequent resuspension and flushing by waves did not take place for several months, exacerbating the smothering effects of the sediment. Periodic sedimentation events of various magnitude and duration have resulted in cycles of damage and recovery that have produced a coral community that reflects intermediate disturbance and a coral community structure dominated by sediment-resistant species. The two other long-term surveys, off Mauna Lani Resort on the west coast of the island of Hawai'i (1983-2002), and Princeville Resort on the north shore of Kaua'i (1980-2002), both revealed a pattern of consistent increase in coral cover at all stations. At these open coastal sites, anthropogenic effects are undetectable relative to natural factors that affect coral community structure. A lack of maximum wave events during the interval between surveys may partially explain the increase in coral cover. Activities from shoreline development appeared to have no effect on coral community structure during the study interval. The results of these three studies suggest a framework for coral reef management in Hawai'i by concentrating efforts on embayments and areas with restricted circulation. Because such areas compose less than 10% of the coastal areas, the overall condition of the majority of coral reefs in Hawai'i is relatively good. Nevertheless, embayments are major recreational sites and it is these environments for which we suggest that the major need for management exists and should be focused. On a global scale, concerns of catastrophic loss from anthropogenic impact to coral reefs may be valid in many areas of the world, but they do not accurately depict the condition of coral reefs in Hawai'i.