MEPS 258:79-86 (2003)  -  doi:10.3354/meps258079

Contrasting effects of turf algae on corals: massive Porites spp. are unaffected by mixed-species turfs, but killed by the red alga Anotrichium tenue

Jamaluddin Jompa1,2,3, Laurence J. McCook2,4,*

1Department of Marine Biology, James Cook University, Townsville, Queensland 4811, Australia
2Australian Institute of Marine Science and CRC Reef Research, PMB 3, Townsville, MC, Queensland 4810, Australia
3Present address: Faculty of Marine Science and Fisheries, Hasanuddin University, Makassar 90245, Indonesia
4Present address: Great Barrier Reef Marine Park Authority, PO Box 1379, Townsville, Queensland 4810, Australia
*Corresponding author. Email:

ABSTRACT: Competition between corals and algae is an important process on coral reefs, especially during reef degradation, when abundant corals are often overgrown by benthic macroalgae. Despite the widespread assumption that macroalgae are able to out-compete corals for space, there have been very few experimental studies testing the nature of this interaction. This study compared the effects of a filamentous red alga, Anotrichium tenue, with those of mixed-species, filamentous algal turfs on massive Porites spp. corals on inshore reefs of the central Great Barrier Reef, Australia. We compared mortality of coral tissue in plots with A. tenue naturally present on live coral tissue, plots in which A. tenue was naturally present but experimentally removed, and plots where mixed algal turfs were naturally present but A. tenue was not. The results indicate that A. tenue killed coral tissue by active overgrowth. Removing the alga removed the effect. In contrast, general, mixed-species algal turfs did not cause any mortality of coral tissue. We suggest that 2 particular traits of A. tenue may facilitate its effects on the corals. First, unlike most filamentous turf species present, it was able to overgrow live coral tissue, perhaps due to allelochemical effects. Second, individual algal filaments trap relatively large amounts of mucus from the corals and of sediment, apparently increasing the damage to underlying coral tissue. Surveys indicated that A. tenue primarily affected massive Porites spp., that overgrowth effects were not site-specific, but that occurrence of infected corals was not widespread. In particular, distribution patterns were not consistent with an effect of terrestrial runoff. This study provides evidence of an exceptionally lethal effect on corals by a single species of filamentous alga, and emphasizes the species-specific nature of coral-algal competitive outcomes, even within a functional group.

KEY WORDS: Coral-algal competition · Anotrichium tenue · Epilithic algal community · Filamentous algal turfs · Porites spp.

Full text in pdf format