Zoantharian abundance in coral reef benthic communities at Terengganu Islands, Malaysia

Abstract

Zooxanthellate zoantharians of the genera Zoanthus and Palythoa are increasingly being studied in baseline work such as confirming distributions and long-term monitoring studies in shallow subtropical and tropical waters. There is some evidence that suggests that these genera increase in abundance as an ecological ‘phase shift’ response to ecological degradation. However, such studies have been limited to a few regions, including the Greater Caribbean, Brazil, and Japan, with little work performed in the waters of Southeast Asia and the central Indo-Pacific (CIP). We investigated changes in zoantharian cover within coral reef benthic communities around Terengganu, Malaysia, between July 2013 and September 2014, utilizing the Coral Video Transect method to survey the benthic communities of nine coral reefs. Zoantharian abundance was observed to be inversely proportionate to other major benthic groups (algae, dead corals, hard corals). Overall, zoantharians thrived in reefs with lower biological diversity of reef-building corals. Additionally, at one site (Pasir Akar) we documented a very sudden and large increase of zoantharian cover over two months from March to May 2014. This increase occurred after the reef was heavily damaged during monsoon season. Our results demonstrate that zoantharians are an understudied yet common major component of reefs in Southeast Asia, and that large changes in their abundance can occur very rapidly. Further research investigating longer-term trends of zoantharian abundance in Southeast Asia and the CIP are needed to ascertain if dramatic increases are part of a ‘normal’ recovery process or represent phase shifts in the benthic community structure of coral reefs.