Explanation of Indicator
Coral reefs are important to coastal ecosystems for several reasons. These massive limestone structures provide shelter to mobile aquatic animal species. Unusually high gross primary production is recycled within the reefs. The principal producer organ
isms are microscopic algae that live within the coral tissues. This symbiotic relationship enhances the biological activity of the community in terms of the abundance and the diversity of plants and animals found on the reefs. Reefs are also important a
s natural breakwaters to storm surges and large wave forces. A loss of coral reefs could result in increased erosion of the coast.
The principal causes of reef degradation are direct toxification and increased turbidity. Examples of toxification include oil pollution from boats and marinas, compounds that leach from bottom boat paints, and urban runoff pollution. In addition to nat ural turbidity, if the water clarity is degraded by human-caused turbidity for long periods of time, then coral reef life is inhibited and problems occur.1 Other causes for reef degradation are over-exploiting fish stocks and lobster, exceeding the carry ing capacity of a particular area for snorkeling and diving, and physical destruction caused by ship and boat groundings. Massive storms, winter cold fronts, and disease are also responsible for reef degradation. The decline or loss of coral reefs may b e an indirect indicator of exceedance of the carrying capacity of an area.
This indicator focuses on three different aspects of coral reef community dynamics: number of species, diversity, and evenness. The number of species present is simply the number of different species in the reef community. Diversity is an index that re lates the different number of species to their relative abundance. The evenness index refers to how the diversity of species compare to each other. For example, a system with the same number of individuals from each species would have an evenness of one , whereas in a system where one or more species were predominant over others, the evenness index would be less than one.
Data Characteristics
SOURCE
The source for this information is Walt Jaap, The Florida Marine Research Institute, 100 Eighth Avenue SE, St. Petersburg, Florida 33701-5095, or at (813) 896-8626.
ACQUISITION The data are available in hard copy. There are no costs associated with the acquisition of these data.
COLLECTION There are presently eight stations and they are sampled annually. As the result of a funding increase, a new program will evaluate twelve offshore reefs, ten patch reefs, and eight hard bottom areas between Elliot Key and Key West. Sampling efforts will continue at Dry Tortugas as well.
Data Limitations
These data are limited at the current level of study in that the data only provide a glimpse into the functioning and status of reef communities. The current status and trends monitoring has limitations because of the restricted sample size. These trend
s cannot be inferred to be universal.
Data Analysis
The four study areas discussed in this indicator are Bird Key Reef, Pulaski Shoal, Texas Rock, and Western Sambo. The number of species at the four sites remained relatively stable from 1989 to 1993, with the exception of Pulaski Shoal. The increase in
taxa between 1992 and 1993 was the result of an increase in Octocorallia
Species diversity at the four study areas exhibits a generally increasing trend with the exception of Bird Key Reef, which lost diversity between 1991 and 1992 due to a loss of taxa of stony corals and octocorals.
Most of the study areas maintained their respective evenness index values from 1989 to 1993. The stability of these areas indicates that there has been no significant disturbance during the study period. Bird Key Reef, however, experienced a slight decr ease in evenness. Any change in evenness over time indicates some type of disturbance in the system. The cause of this disturbance at Bird Key Reef is unknown, but the “no name” storm in March of 1993 is a suspected cause.
