This study demonstrated that a large number of physiological,
population and community measures change consistently along
water quality gradients on inshore coral reefs of the GBR. The data
confirm that nutrient enrichment and turbidity fundamentally
alter reef ecosystems at all levels of organisation, akin to the
well-documented effects of soil nutrient loading and shading in
terrestrial ecosystems.
With increasing turbidity and nutrients, reef communities progressively
shift from those dominated by phototrophic animals, to
those consisting of phototrophs and macroalgae, and then to those
dominated by macroalgae and very few phototrophs in very shallow
water, and an absence of phototrophs and an abundance of
abiotic substrata and heterotrophic animals at greater depths
(Birkeland, 1997). Our bioindicator system quantifies the dual
shifts, from corals to macroalgae, and from photo- or mixotrophy
to heterotrophy, by four of the measures: