Comparison of Water Quality and Reef Coral Mortality and Growth in Southeastern Kane'ohe Bay, O'ahu, Hawai'i, 1990 to 1992, with Conditions before Sewage Diversion

摘要

Growth and mortality of the three dominant coral species occurring in Kane'ohe Bay were determined for four periods from November 1991 to January 1993 at four stations in the bay's southeast basin. Twelve water quality parameters were monitored biweekly to monthly at these stations from November 1991 to August 1992. Both water quality measurements and coral survival and growth indicated considerable improvement to conditions that prevailed when treated sewage was discharged into this area of Kane'ohe Bay. Mean concentrations for orthophosphate, nitrite + nitrate, ammonia, and chlorophyll a, and mean values for light extinction and sedimentation were significantly less than those measured during time of sewage discharge in 1976-1977. Means of all of these except orthophosphate were not significantly different from means measured in 1978-1979 during the first year after sewage diversion. Mean orthophosphate concentration was approximately double the mean of the first year after diversion, and this increase may relate to increased abundances of the green macroalgae Dictyosphaeria cavernosa (Forskal) Boer-gesen that have been observed in this section of the bay in recent years. Mon-tipora verrucosa (Lamarck) survived and grew well throughout the study period at all four stations, including stations in areas where rapid mortality and minimal growth occurred for this species in 1969-1971. The other two species, Porites compressa Dana and Pocillopora damicornis (Linnaeus), showed different survival and growth patterns according to station location. Most rapid mortality and lowest growth generally occurred for P. compressa at the station most affected by land runoff in the southernmost section of the bay. However, the major cause of early mortality and poor growth of Porites compressa at that location was the nudibranch Phestilla sibogae (Bergh), which rapidly consumed tissues of corals transplanted to that station, suggesting that predators that control P. sibogae parasitism elsewhere in the bay are absent from that area. Pocillopora damicornis survival and growth declined at all stations throughout the study, and this species may have been affected by fish predation. Growth of M. verrucosa and P. damicornis showed significant positive relationships with water turbidity values within a range of up to ca. 1.0 NTU.