Maintenance of fish diversity on disturbed coral reefs - Article Example

Essay The study examined the effects of habitat disturbances on the species richness of fishes in the coral reefs of the Great Barrier Reef (GBR) region. Many fish species like the Teleost fishes constitute an important part of the reef ecosystem and are also major sources of food to those living in the coastal areas. Since many reef fishes are associated with the reef substratum, the natural and anthropogenic disturbances have been found to cause profound damages to the coral reef structure and also influence the species richness of the fish population.

Studies have shown that reduction of coral cover due to such environmental disturbances have caused algal colonization in the vacant coral reef area which has resulted in an abundance of fish species that thrive on algal feeds and this replacement causes a change in the species richness. However, other studies have also shown that certain types of disturbances such as coral disease and bleaching, during which the structural complexity of the coral reefs are maintained, may actually not cause any change in species richness thus stressing the point that the extent of habitat damage and the condition of the reef will determine the fish species richness.

The study analyzed the data collected from surveys carried out for a period of 11 years to determine the effect of various disturbances on the coral cover, structural complexity of the reef and diversity of the fishes. The biological and physical changes in coral reef and its consequent effect on the reef fish community were analyzed. The study encompassed documenting the changes occurring in the coral cover, structural complexity and species richness in 10 reefs along the GBR. The major disturbances that were found to occur during the study period included COTS outbreaks, storms and coral bleaching.

Disturbed reefs collected from 47 areas which were subjected to such disturbances were used for the study. in addition 3 control reefs which were not subjected to any disturbances was analyzed and the results were compared with that of the disturbed reefs. Following the sampling, the coral cover was expressed as a percentage of the substratum and the species richness of 210 fishes from 10 families was recorded using a single observer. The fishes were placed under ecological groups according to their dependency on corals or other EAM- feeders.

A 360° pan view of the reef under study was made using video camera to study the structural complexity of the habitat. Statistical methods such as ANOVA were used to study the changes that occurred in coral cover or species richness during the period of the study. The annual changes in species richness for both the coral dependent group and the EAM feeders were calculated. Using the Principle Component Analysis (PCA) based on correlation matrix, the effect of coral losses on species richness was estimated.

The relation between percentage of live coral cover and structural complexity of the habitat with that of species richness was identified using the mixed-effect modeling. The results found that the hard coral cover had deteriorated in the 10 reefs under study with the rate varying with the type of disturbance. Those affected by storms showed rapid declines. However, the structural complexity declined only in 5 reefs with the live coral cover showing a decline and a positive relation to structural complexity.

The species richness was found to be stable in 7 reefs with variations being observed in the other 3 reefs. Loss of coral dependent species was compensated with an increase in EAM feeders. All the above factors were found to be normal in the control reefs. Hence this study has determined the fact that disturbances which do not affect structural complexity but only cause a significant reduction in the coral cover does not affect the species richness of the fishes associated with the reefs. However, in the present study the limited amount of variations in structural complexity has not lead to a definitive identification of structural complexity as a major cause for species diversity in the reefs.

References Wilson, S.K., Dolman, A.M., Cheal, A.J., Emslie, M.J., Pratchett, M.S., and Sweatman, H.P.A. “Maintenance of fish diversity on disturbed coral reefs.” (2008).