Tropical Island Fish Assemblages Are Resilient to Flood Disturbance Mortality

Aquatic communities are structured by a combination of deterministic and stochastic processes.  Periods of stable environmental conditions, favoring the development of communities regulated by deterministic processes, are interrupted by random periods of disturbance that restructure communities and populations.  We quantified fish movement, density, and habitat before and after a major flood disturbance in a Caribbean island river using radiotelemetry, passively monitored PIT tags, removal estimates of fish densities, and habitat surveys.  Native stream fish populations showed evidence of acute mortality, but little evidence of downstream displacement in those fish that remained.  Although the abundance of most fish species was reduced after the disturbance, populations responded with recruitment and migration into upstream habitats.  Rapid recovery processes acting at the population level appeared to dampen effects at the community level, as community parameters (species richness and diversity) demonstrated that the overall structure of the fish assemblage changed minimally.  The native fish assemblage appeared to be resilient to the flood disturbance, rapidly compensating for mortality during the flood with improved recruitment and recolonization of upstream habitats.  On tropical islands, flood disturbances may act as a community filter, removing exotic species while having minimal net effect on natives, thereby maintaining native stream fish assemblages.