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Abstract

ASSESSMENT OF CORAL REEFS USING HERBIVORY/NUTRIENT ASSAYS AND INDICATOR GROUPS OF BENTHIC PRIMARY PRODUCERS.

Mark M. Littler and Diane S. Littler
National Museum of Natural History
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Rapid assessment protocols for determining and monitoring the status of any given coral reef are provided and include measuring: (a) standing stocks of functional indicator groups, (b) herbivore populations, (c) water-column nutrient levels, (d) tissue C:N:P ratios, (e) algal physiological-response assays, and (f) herbivory assays. These measurements can reveal quantitative tipping-point levels beyond which resilience to undesirable phase shifts begins to become critically reduced. Universal tipping-point approximations are reviewed for inorganic nutrients, and posited for the first time for herbivory. The relative roles of top-down and bottom-up controls in determining benthic community structure and the health of coral reefs are especially important management concerns. This paper specifically addresses the top-down effects of herbivory and bottom-up effects of nutrient enrichment on critical indicator groups; i.e. reef-building corals, crustose coralline algae, dense turf algae, and frondose macroalgae. A predominance of (a) massive corals and calcareous coralline algae relative to frondose macroalgae and algal turfs indicates a healthy spatially heterogeneous condition reflecting low nutrients and high herbivory. An abundance of (b) frondose macroalgae illustrates the least desirable condition of elevated nutrient levels and reduced herbivory, possibly reflecting pollution in concert with destructive herbivore fishing practices. High coverage of (c) coralline algae suggests healthy high herbivory levels, but problems with elevated nutrients that are inhibitory to some corals. Domination by (d) dense turf algae indicates desirably low nutrient levels, but an inadequate herbivory component. The experimental results demonstrate flaws in some of the previously published manipulative methods and provide insights for the improvement of in-situ nutrient studies on coral reefs. The fast growth and turnover rates of fleshy algae compared to other reef organisms highlight their value as early-warning indicators of reef degradation.