JOHN BREWER REEF
Intensive Surveys: Trends in fish abundances
The decline in coral cover since 2000 was reflected by changes in some fish taxa but not others. Although inter-annual variation in abundance was often high, the abundances of many taxa had shown few consistent trends over the survey period. The abundance of two often coral-associated taxa, butterflyfishes (Chaetodontidae) and the damselfish genus Chromis, decreased with coral cover to very low levels from 2003 onwards. While the overall abundance of the genus Pomacentrus varied little from 2002 onwards, the drop in abundances from highs in 1996 and 1997 were driven largely by one species, the highly coral-dependent Pomacentrus moluccensis. Conversely, the algal farming species P. wardi increased in abundance once coral cover was low. Presumably this was related to increases in farmable substrate. Abundances of Acanthochromis polyacanthus (from a monospecific genus) also increased in conjunction with a decline in hard coral cover. The explanation for this change is not obvious. It is perhaps noteworthy that when surveyed in 2011 abundances of three damselfish genera (Amblyglyphidodon, Chrysiptera and Neoglyphidodon) were the lowest recorded. The explanation for this pattern is also not obvious but mortality caused by physical or habitat related effects of Cyclone Yasi cannot be discounted.