PROJECT DESCRIPTION: Three experiments were performed to study the influence of decapods on ecosystem processes. In the first one (catalogued as LTERDBAS #104) the hypothesis that differences in macrobiotic assemblages can lead to differences in the quantity and quality of organic matter in benthic depositional environmentsamong streams in montane Puerto Rico was tested. The experimental results were consistent with findings of an independent survey of six streams in four different drainages. Four streams that had an abundance of omnivorous shrimps but lacked predaceous fishes, had extremely low levels of fine benthic organic and inorganic material. In contrast, two streams that had low densities of shrimps and contained predaceous fishes had significantly higher levels. Results showed a strong linkage between species and ecosystem characteristics: interstream differences in the quantity and quality of fine benthic organic matter resources were determined by the nature of the macrobiotic assemblage. Furthermore, patterns in the distribution of shrimp assemblages reflected landscape patterns in the benthic depositional environment among streams.
In the second experiment (LTERDBAS #105) the role of freshwater shrimp, which dominate the faunal biomass of many tropical headwater streams, was studied. The enclosure/exclosure experiments in a montane Puerto Rican stream the direct and indirect effects of two dominant taxa of atyid (Atyidae) shrimp, Atya lanipes Holthius and Xiphocaris elongata Guerin-Meneville was examined. Both shrimp taxa caused significant reductions in sediment cover on rock substrata, reducing sedimentation and enhancing algal biovolume on clay tiles in cages.We evaluated the mechanism by which A. lanipes influences algae and benthic insects by comparing patterns of algal biomass, taxonomic composition and shrimp-presence treatments both with and without manual sediment removal. The shrimp exclusion treatment without manual sediment removal had significantly lower algal biomass and greater sedimentation than all other treatments. The treatment in which shrimp were excluded but sediment was manually removed, however, accrued almost the same algal biovolume as the shrimp enclosure treatment, supporting the hypothesis that sediment removal enhances the biovolume of understory algal taxa.
The effects of biotic (shrimp) and abiotic (discharge) factors on the depositional environment were quantified in a montane stream in Puerto Rico in a third experiment (LTERDBAS #106). Electricity was used experimentally to exclude large (approximately >1cm in length) biota without artificially increasing sedimentation as in cage enclosure/exclosure experiments in stream systems. Unelectrified control substrata had natural high densities of atyid shrimp. Atyid shrimp can significantly affect the accumulation of organic and inorganic materials on rock substrata in stream pools between high-discharge events.
Created By: Eda C. Melendez-Colom (emelend@lternet.edu
)
Last Modified On: April 9, 2002