Coral recruitment on a high-latitude reef at Sodwana Bay, South Africa: research methods and dynamics.
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Date
2011
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Abstract
Coral recruitment is a key process that contributes to the community structure and resilience of coral
reefs. As such, quantification of this process is important to assist with the management of these
threatened ecosystems. While coral recruitment has been the focus of numerous studies over the past
30 years, an understanding of this process on the high-latitude reefs of South Africa is limited. In
addition, variations in methods used in recruitment studies make the results difficult to compare. A
rapid in-situ method for universal application in the detection of early post-settled recruits would
thus be useful.
In this study, scleractinian coral recruitment was investigated at three study sites on Two-mile Reef,
over two six-month sampling periods, covering summer and winter. Two components were
investigated by attaching settlement tiles consisting of ceramic and marble tiles, and ceramic tiles
conditioned with crustose coralline algae (CCA) onto the reef in a spatially structured experimental
design. Firstly, coral recruitment was compared on the three different tile surfaces and fluorescence
photography was investigated as a rapid in situ technique to detect early post-settled recruits.
Fluorescence photography was then used to compare recruitment on tiles with the surrounding
natural substrata. Secondly, the spatial and temporal variation in the abundance, composition and
size of recruits was investigated. Additionally, the percentage cover of biota surrounding each recruit
within three millimeters of its corallum was visually estimated to quantify the microhabitat
surroundings of coral recruits.
Overall recruitment on the three tile types differed, yet spatial variation in coral recruitment,
regardless of tile surface, accounted for most of the variance in recruitment. While the highest
recruitment occurred on CCA tiles, this was not significantly greater than ceramic tiles, indicating
that the conditioning of ceramic tiles with Mesophyllum funafutiense CCA did not enhance coral
settlement in this study. Although many recruits were not detected with fluorescent photography
(73%), it proved useful to reveal recruits as small as 0.75 mm in corallum diameter, and indicated
that recruitment on the tiles and natural substratum differ significantly. Spatially, the abundance and
composition of coral recruits differed between study sites, within sites, and predominantly occurred
on tile edges. Coral recruitment was lowest at shallower sites, and was dominated by pocilloporids
regardless of study site. Additionally, the abundance and composition of recruits differed between
the two sampling periods, with a 6.6-fold decrease in the mean abundance of recruits from summer
to winter, with only pocilloporid settlement occurring in the latter season. The majority of recruits
were <3 mm, and their microhabitat was dominated by bare substrata and crustose coralline algae.
The results suggest that, while the choice of artificial settlement surface used in such studies can
have a profound influence on the results, spatial variation in recruitment can be greater. The recovery
of scleractinian coral taxa on Two-mile Reef in the event of a severe disturbance is expected to
differ, with greatest recovery in areas of high levels of recruitment. The microhabitat surrounding
recruits is described here for the first time, suggesting that further research into coral-crustose
coralline algae interactions is warranted. Finally, while fluorescence photography has its limitations,
it shows promise as a useful tool for rapid qualitative, but not quantitative, assessment of
recruitment.
Description
Thesis (M.Sc.)-University of KwaZulu-Natal, Westville, 2011.
Keywords
Coral reefs and islands--KwaZulu-Natal--Sodwana Bay., Corals--KwaZulu-Natal--Sodwana Bay., Theses--Marine biology.