Large dams and migratory biota affect tropical stream ecosystems at different scales in Puerto Rico
Greathouse, Effie Armenta
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I studied the ecological roles of diadromous fauna (freshwater shrimps, fishes, and snails) in Puerto Rico in the context of examining consequences of their loss from streams above dams. I combined several approaches: (1) development of a sampling method, (2) description of longitudinal patterns in biomass of macroinvertebrate functional groups in a tropical stream system, (3) sampling of and experimentation within a replicated large-scale perturbation caused by large dam construction, and (4) comparison of small- and large-scale experiments/perturbation. The new sampling method was effective, allowing me to examine relationships between diadromous fauna and non-decapod invertebrates in subsequent studies of longitudinal patterns and effects of dams. Longitudinal sampling in a minimally-impacted tropical stream system with no large dam showed that, despite dominance by a low diversity of diadromous fauna, distributions of functional groups generally followed predictions of the River Continuum Concept developed from temperate river systems. Sampling and experimentation within sites above large dams and in stream systems without large dams revealed that decimation of diadromous populations above large dams has cascading effects on benthic algae, organic and inorganic matter, nutrients, and non-decapod invertebrates. However, differences between dammed and undammed sites varied by habitat and stream gradient. Finally, small-scale experimental manipulations of diadromous fauna predicted the directions and magnitudes of the effects of large-scale losses of diadromous fauna upstream from large dams. This research is an integration of studies on ecological roles of diadromous species and human impacts which cause these species’ loss. This integration showed that large dams impact benthic stream environments by extirpating diadromous species in Puerto Rico and suggests a need for more data sets which simultaneously examine ecological roles and declines of diadromous species within the same region.