Sexual reproduction of Pocillopora damicornis (Cnidaria : hexacorallia) at high latitude off Durban, South Africa.
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Date
2009
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Abstract
Pocillopora damicornis is one of the best-studied and most widespread of corals.
Previous studies on its sexual reproduction have yielded a diverse and contradictory view of
its reproductive strategy. This coral has long been considered a typical hermaphroditic
brooder. However, recent studies have demonstrated that its dispersal may also occur through
broadcast spawning of gametes. Since both modes of reproduction have advantages for
dispersal, P. damicornis reproductive traits are probably driven by environmental pressures.
High-latitude habitats are considered marginal for corals since they fall beyond the “normal”
limits of coral development. They provide, therefore, a good opportunity to study
reproductive strategies that have evolved under different environmental pressures. The pattern
and timing of reproduction were studied in P. damicornis on the high-latitude reefs of
Durban, KwaZulu-Natal, South Africa (29°S). Branches were randomly selected from
colonies on a monthly basis from October 2007 to April 2008. After fixation and
decalcification, the coral tissues were processed for histology and cross-sectioned to reveal
the presence and stages of gametes within the polyps. The number and size of gametes were
estimated using image analysis. P. damicornis in Durban is hermaphroditic and all polyps
contained oocytes and spermaries at the end of the breeding season. Since no brooding of
embryos or planulae was found in the 175 polyps analysed during the seven-month study
period, this coral is presumed to be a broadcast spawner in South African waters. P.
damicornis invested seven to eight months in gametogenesis and oogenesis was initiated one
month before spermatogenesis. Gametogenesis was confined to the warmer months of the
year, commencing during the increase in seawater temperature at the onset of summer.
Gamete development was poorly synchronised between colonies during the initial months of
breeding, but mature oocyte stages were dominant in all polyps at the end of the breeding
season. Spawning was inferred from the disappearance of gametes in April 2008, and may
have occurred during full moon in March 2008. This happened before the drop in temperature
at the end of summer. P. damicornis in KwaZulu-Natal exhibited a pattern and timing in its
reproduction similar to that found in south Western Australia at 32°S.
Keywords: coral; Scleractinia; Pocillopora damicornis; high latitude; sexual reproduction;
South Africa.
Description
Thesis (M.Sc.)-University of KwaZulu-Natal, 2009.
Keywords
Zoantharia--Reproduction., Zoantharia--KwaZulu-Natal--Durban., Theses--Zoology.