Competition between macroalgae and corals: effects of herbivore exclusion and increased algal biomass on coral survivorship and growth
Lirman D. 2001. Competition between macroalgae and corals: effects of herbivore exclusion and increased algal biomass on coral survivorship and growth. Coral Reefs. 19(4):392-399
Recent declines in coral abundance accompanied by increases in macroalgal cover on Florida reefs highlight the importance of competition for space between these groups. This paper documents the frequency of coral-algal interactions on the Northern Florida Reef Tract and evaluates the effect of grazer exclusions and experimental algal addition on growth and tissue mortality of three coral species, Siderastrea siderea, Porites asteroides, and Montastrea faveolata. The frequency of interactions between corals and macroalgae was high as more than 50% of the basal perimeter of colonies was in contact with macroalgae; turf forms, Halimeda spp., and Dictyota spp. were the most common groups in contact with corals. Decreased grazing pressure resulted in significantincreases in algal biomass within cages, and cages corals showed species-specific susceptibility to increased algal biomass. While no effects were detected for S. siderea, significant decreases in growth rates were documented for caged P. astreoides which had growth rates three to four times lower than uncaged colonies. When an algal addition treatment was included to duplicate maximum algal biomass levels documented for reefs in the area, colonies of P. astreoides in the algal addition treatment had growth rates up to ten times lower than uncaged colonies. High susceptibility to algal overgrowth was also found for the reef-building coral M. faveolata, which experiences significant tissue mortality under both uncaged (5.2% decrease in live tissue area per month) and caged (10.2% per month) conditions. The document effects of increased algal biomass on coral growth and tissue mortality suggest a potential threat for the long-term survivorship and growth of corals in the Florida Reef Tract if present rates of algal growth and space utilization are maintained.
- Type
- Journal Article
- Authors
- Lirman, D.
- Units
- BISC
- Keywords
- Algae, Bache Shoal (East) Biscayne National Park FL, brown algae, Competition, Coral, Dictyota, Elkhorn Reef Biscayne National Park FL/, Green algae, Growth, Halimeda, Herbivory, Macroalgae, Montastrea faveolata, Mortality, mustard hill coral, Porites astreoides, Siderastrea, Triumph Reef Biscayne National Park FL