Reef foraminifera as bioindicators of coral reef health: Low Isles Reef, northern Great Barrier Reef, Australia

Declining water quality associated with changes in land use over the past century is considered a significant environmental threat to the health of coral platforms of the Great Barrier Reef, Australia, in particular for those situated in nearshore areas of the wet tropics. Of these reefs, perhaps the most well known is Low Isles Reef, which has been studied since 1928. Decline in scleractinian coral cover and increased abundances of soft-bodied corals and macroalgae since the 1950's have led researchers to speculate that the reef is being affected by increased nutrient and sediment fluxes from nearby rivers. The Foraminifera in Assessment and Monitoring (FORAM) Index (Hallock and others, 2003) is a numerical indicator of the suitability of water quality to support reef growth based on foraminiferal assemblages. To assess whether nutrification is an issue near Low Isles Reef, FORAM Index (FI) values were calculated from a suite of 50 samples collected from the reef top. Results were compared to FI values from Heron Reef, a mid-shelf platform in the southern Great Barrier Reef Province known for its lush scleractinian coral population. FI values from both reefs indicate that, overall, conditions favor coral growth. A Student's t test indicates the FI values between the two reefs are similar. Principal components analysis shows that the FI values are not being constrained by water depth or depositional environment. Lower FI values, which indicate conditions unsuitable to marginal for coral growth, are restricted to particular locations on Low Isles Reef and can be explained in the context of local processes associated with the long-term geomorphological evolution of the reef. Results (1) do not support the notion that agricultural activities in nearby coastal catchments have adversely affected coral populations on Low Isles Reef and (2) demonstrate the applicability of the FI for regions outside of the western Atlantic and Caribbean, for which the index was originally created.