Ecological studies of dams and migratory fauna, Puerto Rico related data sets

PROJECT DESCRIPTION: The ecological roles of diadromous fauna (freshwater shrimps, fishes, and snails) in Puerto Rico were studied in the context of examining consequences of their loss from streams above large (height >15 m) dams. Four sub-projects were conducted:
(a) Indirect upstream effects of dams: consequences of migratory consumer extirpation in Puerto Rico. This sub-project examined the effects of decimation of migratory fauna populations on stream ecosystem structure above large dams. We compared streams above large dams to streams without large dams, in terms of relative abundances of migratory fauna and ecosystem components affected by migratory fauna in previous in situ experiments. Previous research indicated that: (1) all native fishes and shrimps in Puerto Rico are extirpated from habitats upstream of large dams without regular spillway discharge because they are diadromous, whereas streams above large dams with regular spillway discharge have greatly reduced abundances of diadromous fauna, and streams without large dams have relatively natural fish and shrimp assemblages (Holmquist et al. 1998); and (2) small-scale experimental exclusion of native shrimps and fishes decreases leaf decay rates and increases epilithic organic and inorganic matter, chlorophyll a, carbon, nitrogen, carbon-to-nitrogen ratio (C:N), and chironomid biomass (Pringle et al. 1999, Crowl et al. 2001, March et al. 2001, March et al. 2002). We examined whether sites above large dams had higher levels of epilithic coarse organic matter, algae, fine organic and inorganic matter, carbon, nitrogen, C:N, and non-decapod invertebrates, consistent with previous findings of small-scale experimental shrimp and fish exclusions.
(b) Do small-scale exclosure/enclosure experiments have relevance for large-scale extirpation of migratory fauna? This sub-project took advantage of large dams to examine effects of experimental scale. Alteration of migratory stream populations due to large dams represents a large-scale (i.e. whole-catchment), long-term (i.e. decades) "extirpation experiment. " We compared this large-scale perturbation to four small-scale experiments (two exclusion experiments in sites with no large dams and two shrimp addition experiments in dammed sites) that we conducted in a subset of the sites sampled in sub-project (a). We examined whether small-scale experiments predicted effects at the large-scale in terms of direction and magnitude.
(c) Conservation and management of migratory fauna and dams in tropical streams of Puerto Rico. This sub-project was a review, in which we: (1) examined Puerto Rico's potential to serve as a window into the future of freshwater migratory fauna in tropical regions, given the island's extent and magnitude of dam development and the available scientific information on ecology and management of the island's migratory fauna, and (2) reviewed ecology, management and conservation of migratory fauna in relation to dams in Puerto Rico. Our review included a synthesis of recent and unpublished observations on upstream effects of large dams on migratory fauna and an analysis of patterns in free crest spillway discharge across Puerto Rican reservoirs.
(d) Ecological effects of non-migratory native and non-native fauna above large dams in tropical streams, Puerto Rico. This sub-project consisted of a set of electric exclusion experiments conducted above two of the dammed sites in sub-project a. Previous research demonstrated higher abundances of exotic fishes above large dams (Holmquist et al. 1998). Thus, these experiments examined whether exotic fishes affect stream ecosystem patterns and confound any interpretations in sub-project a regarding roles of migratory macroconsumers.