3.1. Study 1
In the Whitsunday Islands, 33 of the 38 indicator candidates
changed significantly along the water quality gradient (Table 2).
In massive Porites, colony colour became significantly darker, tissue
thickness decreased, while surface rugosity and the density
of macroborer apertures in living surfaces increased strongly
towards the reefs with higher values of the WQI (Fig. 2a). In
P. damicornis, concentrations of chlorophyll a almost doubled and
symbiont density increased 2.5-fold, while skeletal density
declined by 15% towards the higher WQI (Fig. 2b). The FORAM index
also declined along the gradient (Fig. 2c). In contrast, partial
mortality of massive Porites and protein per unit surface area in
P. damicornis were unrelated to the WQI.
The abundance and composition of various benthic groups also
changed along the water quality gradient (Table 2 and Fig. 2d and
e). The cover of hard corals and octocorals declined fivefold and
eightfold from low to high WQI (from 50% to 10% and from
25% to 3%, respectively; Table 2). The taxonomic richness of hard
corals and octocorals also declined, from 11.5 to 4.0 hard coral
taxa, and from 6.5 to 1.5 octocoral taxa per transect. The cover of
crustose coralline algae was low throughout the Whitsunday Islands
but declined to almost zero at sites with the highest WQI. Total
macroalgal cover increased strongly along the gradient from
near-absence in clear water to >50% on turbid reefs, particularly
due to increases in Phaeophyta and Rhodophyta.