MICHAELMAS

Michaelmas Reef has been surveyed extensively since 1986 when it was initially classified as No Outbreak. Since this time, reef-wide live coral cover dropped from moderate to low levels in the initial years of survey and has remained generally low ever since. In 2003 reef-wide live hard coral cover was low at 1-10%. Residual localised COTS populations have been a common feature in most years on this reef since 1993 with 2003 being the first year since 1999 that COTS have not been recorded from this reef. Although overall COTS numbers have been below outbreaking levels they have had localised impact on coral communities in small areas of what is a very large reef. Michaelmas Reef remains classified as No Outbreak. No bleaching was observed and White Syndrome Disease was restricted to small numbers of individual coral colonies during manta tow surveys in 2003.

Detailed surveys of fixed sites show that hard coral cover increased from approximately 14% in 1993 to 27% in 1999 but then declined slightly, to 22% in the year 2000. This decline in cover is likely to have been caused by COTS feeding activity. Overall trends in cover of hard coral were mainly driven by changes in the cover of the genus Acropora and despite recent declines, this genus remains the most abundant hard coral on this reef. Cover of this genus averaged approximately 10% in the year 2000. Cover of other hard corals has remained low, averaging less than 3% throughout the study. In the year 2000 cover of algae averaged 42%, while cover of soft coral has remained stable during this study and currently averages 30%. The family Acanthuridae has shown a marked decline over the period of surveys with steady declines in the three most abundant species, (Ctenochaetus spp., Acanthurus nigrofuscus and A. lineatus). The family Scaridae also shows significant declines however species level trends are variable. Four of the common species of Scaridae returned the lowest abundance recorded in the 2000 survey. In contrast Chaetodontidae are increasing with C. citrinellus, C. trifasciatus and C. trifascialis all increasing over recent years. Chromis viridus appeared for the first time in the 2000 survey though given the sharp increase in 1999 and subsequent return to prior abundances in 2000 of C. atripectoralis, C. ternatensis and C. weberi the longevity of this increase will have to be watched. Pomacentrus lepidogenys showed the same one year pulse as several of the Chromis, though P.philippinus and P. bankanensis increases have been more stable with steady increases since 1997 and 1996 respectively. Increases of Plectroglyphidodon lacrymatus have peaked after a long period of increase.

Michaelmas (No. 16-060) is a middle shelf crescentic reef with an area of 30 sq.km. Last surveyed November 2002.







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