Spatial and temporal dynamics of freshwater wetlands on the eastern shores of St. Lucia, as reflected by their macrofaunal composition and distribution.

Abstract

The wetlands on the Eastern Shores of Lake St Lucia are primarily groundwater fed and exhibit a variety of hydrological regimes that give rise to a high degree of habitat and species diversity. Hydrologically unstable systems experience ecophasal shifts that can disrupt an established steady state within the wetland ecosystem. Communities of both plants and animals can accordingly disintegrate into more or less isolated populations, open to re-invasion by preceding or "new" species when conditions change again. Given the ephemeral and episodic nature of much of the surface water on the Eastern Shores, ecological dynamics of this type are likely. Fish and aquatic invertebrates were sampled from a number of routine and other sites between May 2002 and April 2003. Measurements of various environmental and abiotic factors (including pH, ionic conductivity and dissolved oxygen levels) were taken with each sample in order to establish relationships between environmental changes and the assemblages of aquatic fauna occurring within the Eastern Shores wetlands. Conditions on the Eastern Shores during the study were somewhat anomalous, as the region experienced drought conditions during this period. The Eastern Shores wetlands support a diversity of aquatic fauna, including at least four species of freshwater fish listed as rare or threatened by the IUCN. The aquatic organisms existing within this dynamic system exhibited changes in abundance and distribution that reflected the spatial and temporal changes in their environment. The relationships between aquatic organisms and their environment were complex, with assemblages being affected by combinations of changing environmental and habitat variables as well as other factors such as the environmental stability of habitats and stochastic effects. Given the complex nature of these interactions, aquatic macrofauna on the Eastern Shores are likely to be best conserved through the preservation a heterogeneous mix of wetland habitats, maintaining the diversity of wetland structure and function on the Eastern Shores that can facilitate an element of lottery in the development and structure in biotic assemblages.