Author: David L. Ballantine, Ph.D.
Institution: University of Puerto Rico Mayaguez
One of the recently recognized threats to coral reef health is overgrowth by macroscopic algae. Algal blooms are becoming increasingly widespread on a worldwide scale with the phenomenon involving both geographical expansion and increased biomass. Virtually all macroalgal blooms appear to be initiated by nutrient enrichment. Degradation of coral reefs often involves a phase shift from abundant coral to dominance by macroalgae and the phase shifts have become increasingly common in tropical coral reefs. Presence of filamentous cyanobacteria on coral reefs has been increasingly reported in recent years. As a result of observations made during benthic algal demographic sampling performed as a function of CRES activities, we have identified cyanobacterial blooms, principally comprised of Schizothrix mexicana at the coral reef at the edge of the insular shelf offshore from La Parguera. The cyanobacteria were observed to have a high percent cover on a variety of living coral substrata. Presently under study is an evaluation of percent cover, biomass and persistence of the cyanobacteria utilizing photographic permanent quadrats. Additional observations will include frequency of contact with other benthic organisms, principally corals, and the outcome of these potentially competitive interactions. Also resulting from CRES benthic algal demographic sampling, we have also recently observed a red algal species, Metapeyssonnelia corallepida, which forms extensive carpets over living Millepora complanata. Coral tissue beneath the Metapeyssonnelia is killed as a result of the algal overgrowth. Presently under study is an evaluation of percent cover and persistence of Metapeyssonnelia on fore-reef habitats utilizing photographic permanent quadrats. Algal spreading rates are being documented by tagging individual corals with Metapeyssonnelia and monthly measuring distance to the algal growth front. Individual coral colonies with Metapeyssonnelia present will be also tagged and any changes in the coral integrity will be recorded over time.
Potential Management Benefits: Presence of large populations of cyanobacteria overgrowing live coral is an easily recognizable indication that there is an abnormality in community balance. By relating cyanobacterial cover on corals with observed deleterious effects on corals would allow these cyanobacteria to be used as indicator organisms.
References & more
- Research reports: August 2006, February 2006, October 2005, June 2005, February 2005
- Ballantine D.L. et al. (2008) Chapter 9: Biology and Ecology of Puerto Rican Coral Reefs. Coral Reefs of the USA, B.M. Riegl and R.E. Dodge (eds.). Springer Science + Business Media B.V.
- McManus J.W., Polsenberg J.F. (2004) Coral-algal phase shifts on coral reefs: ecological and environmental aspects. Progress in Oceanography 60 (2-4): 263-279