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Sewage diversion and the coral reef community of Kane‘ohe Bay, Hawai‘i: 1970- 1990

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Item Summary

Title: Sewage diversion and the coral reef community of Kane‘ohe Bay, Hawai‘i: 1970- 1990
Authors: Evans, Christopher W.
LC Subject Headings: Coral reef ecology--Hawaii--Kaneohe Bay.
Sewage disposal in the ocean--Hawaii--Kaneohe Bay.
Green algae--Hawaii--Kaneohe Bay.
Issue Date: Dec 1995
Publisher: University of Hawai‘i, Honolulu
Citation: Evans, Christopher W. Sewage diversion and the coral reef community of Kane‘ohe Bay, Hawai‘i: 1970- 1990. Honolulu: University of Hawai‘i, 1995.
Abstract: The coral reefs of Kane'ohe Bay, on the windward coast of O'ahu, Hawai'i, have
changed markedly over the last half century. Some of the most spectacular coral reefs in
Hawai'i were reported from Kane'ohe Bay in the late 1800's and early 1900's, but with the
beginning of extensive military dredge and fill operations during the World War IT era,
conditions in the bay began to change dramatically. After the War, rapid urbanization of
the area began and conditions in the bay continued to decline until pressure from the public
and scientific community led to the diversion of the large sewage discharges in the
southeast lagoon to a newly built deep ocean outfall outside the bay in 1977-1978.
Although conditions temporally improved, recent surveys indicate that current conditions
in the bay are not as favorable as expected.
This study provides a time series analysis of changes in coral and algae cover in
Kane'ohe Bay based upon a series of coral reef surveys conducted throughout the bay in
1970171, 1983, and 1990. Beginning in 1970171, conditions in the bay were highly
degraded and scientists speculated that eutrophication and sedimentation, as a result of
urbanization and construction, were the primary cause of an observed decline in lagoon
corals communities in the southeast lagoon and an explosive growth of the green "bubble
algae", Dictyosphaeria cavemosa, which was smothering corals in the middle lagoon. In .
1983, six years after major sewage discharges were diverted from the bay, surveys
indicated dramatic improvements in water quality and the reefs showed signs of recovery.
D. cavemosa algae levels, associated with earlier nutrient pollution, plummeted to less than
twenty percent of their former abundance levels and coral cover increased by over two
hundred percent. Although it was predicted that the coral reefs of Kane'ohe Bay would
continue to recover, surveys in 1990 indicate that coral recovery slowed or ceased and the
growth of the green "bubble algae", D. cavemosa, more than doubled compared to 1983
levels. In addition to the failure of the t~o dominant coral species Porites compressa and
Montipora capitata to continue to recover, almost all of the less common coral species
including Pocillopora damicomis, Fungia scutaria, Cyphastrea ocellina, and some others,
showed significant declines in reef cover.
Although this study was not able to detennine the exact causes of the observed
changes in Kane'ohe Bay, it is suggested that high nutrient inputs provided favorable
conditions for the changes in coral and algae cover. High nutrient levels are thought to
have been derived from a number of sources including chronic sewage pollution, increased
sedimentation from runoff, and reef kills associated with acute but large episodes of
freshwater runoff. Some of these nutrient inputs may have been the result of non-point
source and point source sewage pollution derived from leaky sewer lines, cesspool and
septic tank discharges, commercial tour and recreational boat waste discharges, and
periodic sewage bypasses from municipal wastewater treatment plants and sewage pump
stations. Other nutrients may have been derived from increased sedimentation following
extensive land clearance, land development, and highway construction. Additional factors
may include a decrease in herbivorous fish species owing to over fishing and the ability of
D. cavemosa algae to concentrate nutrients from underlying substrates and excretion from
infaunal organisms. Other factors such as increased nutrient recycling from the sediments,
possible increased nitrogen fixation from reefs, and natural fluctuations in relative species
abundances may also be responsible for some of the observed changes in coral reef
community structure. Although rare, the largest nutrient fluxes followed the catastrophic
freshwater reef-kill events caused by severe rainstorms in conjunction with low tides and
low wind conditions in 1965 and 1987-1988. Although the cause and effect relationship is
still uncertain, the highest levels of Dictyosphaeria cavemosa algae ever recorded in
Kane'ohe Bay occurred in the years following these storm events.
Results of this study indicate that further research is needed to monitor ongoing
conditions in the bay and determine what is preventing the reef ecosystem from returning to
its former more pristine condition. Because water quality parameters generally remained
the same or improved compared to previous polluted conditions, it is suggested that current
measures of water quality are not reliable in forewarning against coral reef degradation in
Kane'ohe Bay. Although a reduction in all future development in and around the bay
would probably help maintain environmental conditions at the status quo, additional
regulations and enforcement may be needed to help reduce disturbances caused by existing
land and water use. It is suggested that a reduction in nutrient inputs to the bay would be
beneficial to reef corals. Recommendations made by the Kane'ohe Bay Task Force
outlined in the Kane'ohe Bay Master Plan should serve as a model and be implemented as
soon as possible. Continuing assessment of the Kane'ohe Bay coral reef ecosystem and
surrounding watershed will then need to be made on a regular basis to ensure that further
degradation of the reefs is not occurring.
Description: Thesis (M. A.)--University of Hawaii at Manoa, 1995. Includes bibliographical references (leaves 166-175).
Pages/Duration: 192 pages
Rights: Copyright Cristopher W Evans
All UHM dissertations and theses are protected by copyright. They may be viewed from this source for any purpose, but reproduction or distribution in any format is prohibited without written permission from the copyright owner.
Appears in Collections:M.A. - Geography

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