Temporal patterns of diversity, abundance and evenness for invertebrate communities from coastal freshwater and brackish water rock pools

Aquatic invertebrate data were collected from 49 erosional, Jamaican, rock pools between 1989 and 1998 and used to describe temporal patterns of species diversity. This unique series of pools on the north coast of Jamaica, classified as either brackish (31) or freshwater (18), was used to determine how diversity changes over time, whether there was a difference between pool classifications, and the impacts of environmental variables. Mean community metrics (richness, diversity, evenness, abundance) were not significantly different between freshwater and brackish pools. However, there were significant differences among the eight sampling dates and differences over time depended on pool classification. Measures of diversity for freshwater pools were relatively constant over time, implying little change at the community level. Brackish pools showed significant differences over time in species richness, total abundance, and evenness implying that community composition and structure were not static but changed in response to either environmental or biotic changes (possibly initiated by environmental change). Some temporal changes in community metrics could be linked to temporal changes in environmental variables. In brackish water pools, a significant increase in pool salinity between January 1991 and January 1992 corresponded to an increase in species richness, likely due to an increase in marine fauna. Similarly, changes in abundance and evenness corresponded to changes in temperature, dissolved oxygen, and pH. In addition, physicochemical variables used in this study were shown to affect community metrics and those relationships depended on pool classification. Most relationships between community metrics and environmental variables were negative with the exception of Simpson's diversity index for which positive relationships were found. This may indicate that, as pool conditions become less favorable, a few species flourish and dominate the community.