Twenty-seven species of known or suspected coral skeletal
borers were identified from shallow Hawaiian reefs. In
comnarison to inventories of the borer communities collected
from other tropical areas Hawaiian corals had an abundance
of polychaetous annelids, fewer species of sipunculans,and
acrothoracican barnacles, and far fewer boring sponges.
Polychaetes were responsible for the majority of the
bioerosion of dead coral in Kaneohe Bay, Oahu.
Comparisons of living and dead sections of coral colonies
indicated that the borer community was more diverse and
abundant in areas of the skeletons lacking living tissue.
Skeletal densities of three common coral species with branching
growth form were found to influence the abundance of coral
borers. The least dense skeletons had greater population
densities of borers. It is suggested that these three species
of corals can coexist in close proximity due, in part, to the
development of varying abilities to withstand invasion by
skeletal borers.
In order to determine rates, si te preference and seasona.li.ty
of settlement a series of settlement plates were cut from coral
and placed in the field at ten sites in Kaneohe Bay, Oahu.
Extrapolating from the surface area of the settlement plates,
mean recruitment rates of coral borers were found to be
10,000 - 50,000 individuals m-2 month-1. The recruitment
rates and species composition of epibiotic and borer faunas
settling; on the dead coral plates differed dramatically between
areas in Kaneohe Bay due to the effects of differences in
physical and biological factors caused by sewage and slltation.
The larvae of coral borers generally lacked clear
seasonal settlement periods, suggesting that one or more
mechanisms (e.g. continuous reproduction, long pelagic phase,
etc.) functioned to assure the presence of larvae throughout
the year. The ultimate cause for the development of such a
strategy may be that the time and location of the production of
suitable settlement sites on the reef surface is. unpredictable.
Some of the larvae of both epibiotic and borer species exhibited
settlement selectivity with respect to the position of the
settlement surface. This finding indicates that the distribution
of borers in coral skeletons might be due, in part, to active
selection by the laryae for particular conditions.
Development of the epibiotic and borer communities of dead
coral was monitored using sequentially collected blocks cut
from the coral Porites lobata. The abundance and species
composition of these communities were found to differ between
sites in Kaneohe Bay because of several biological and physical
factors. In the south bay increased food supplies (in the
form of plankton and plankton-derived detrital material).
due to sewage enrichment, support extensive populations of
filter and deposit-feeding invertebrates including coral
borers. Sewage diversion did not appear to have had any
dramatic effect on these communities by the end of the study
period. In the north bay, where food availability is lower,
fewer borers and epibiotic organisms were collected.
The effects of fish grazing are considered to be another
important factor determining the species composition and
abundance of the coral borer community. Grazing fish were
rare in south Kaneohe Bay during the study period, which may
help to explain the abundance of sessile epifaunal species.
In the north bay fish grazing is extensive and contributes
to the growth of encrusting coralline algae on the test blocks
and the benthos.
Based on the results of the long term block study it was
found that in Hawaii sessile filter-feeding invertebrates do
not exclude coral borers from the substratum or inhibit their
growth. In south Kaneohe Bay, where conditions caused
increased abundances and growth rates of filter and depositfeeding
invertebrates, bioerosion rates were accelerated.
Encrusting coralline algae, which flourish on reefs exposed to
fish grazing (eg. north Kaneohe Bay), inhibit settlement of
borers and grow over burrow apertures, thus reducing the
population of borers within the dead coral. Bioerosion rates
of exposed, coralline algal covered, dead coral substrata
are very low on pristine shallow Hawaiian reefs. / Bibliography: leaves 181-192.
| Identifer | oai:union.ndltd.org:UHAWAII/oai:scholarspace.manoa.hawaii.edu:10125/18150 |
| Date | 12 1900 |
| Creators | White, Janet K. F. |
| Publisher | University of Hawaii, Honolulu |
| Source Sets | University of Hawaii at Manoa Libraries |
| Language | en-US |
| Detected Language | English |
| Type | Thesis, Text |
| Format | 238 pages |
| Rights | 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. |
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