DATA SET IDENTIFIER: Effects of biotic (shrimp) and abiotic (discharge) factors on the depositional environment quantified in a montane stream in Puerto Rico. (Shrimp/Algae/Can J. Fish Aquat. Sci. (1994))

PROJECT TITLE: Influence of Decapods on Ecosystem Processes

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.

LTER CORE AREAS: (Annotate all that apply)

Population Dynamics

LEF LTER 1 RESEARCH TOPIC: (Annotate all that apply)

Spatial and Temporal Distribution of Populations

SOURCE OF FUNDING (SPONSOR): NSF BSR-91-07772

DATA SET ABSTRACT: Effects of biotic (shrimp) and abiotic (discharge) factors on the depositional environment were quantified in a montane stream in Puerto Rico. 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. Shrimp (>1cm in length) were excluded from substrata by semicircular fence hooked up to battery-powered fence chargers which emitted continuous pulses of electricity. Unelectrified control substrata had natural high densities of atyid shrimp. Significantly greater masses of total sediment, fine and large organic particles, and algal biovolume occurred in shrimp exclusion treatments relative to controls. Shrimp exclusion treatments experienced slow and steady accumulation of sediments under base flow conditions and a large stepwise increase in sediment following a storm. No measurable sediment accrued in the presence of natural densities of shrimp under base flow conditions. Shrimp rapidly removed sediments that accrued during the storm (440-620 g*m² dry mass^-1), decreasing sediment mass in control treatments to near prestorm levels (5-13 g*m² dry mass^-1) within 30 h. Atyid shrimp can significantly affect the accumulation of organic and inorganic materials on rock substrata in stream pools between high-discharge events.

DATA SET METHODS: Electric exclosure devices were constructed to exclude large (approximately >1 cm) invertebrates from foraging on rock substrata in a shaded pool (approximately 3.5 m length X 2.3 m width) of the Quebrada Toronja. Treatments were designed to either exclude or allow access to shrimp or other relatively large organisms such as crabs and fish. For more detailed methodology see publication.

REFERENCES:

CROSS REFERENCE (other data sets related to this one): LTERDBAS 104  :Shrimp/ Organic Matter/ Ecology (1999); LTERDBAS 105  :Shrimp/ Algae/ Oecologia (1993); LTERDBAS 106: Shrimp/ Algae/ Can. J. Aquat. Sci. (1994)

SAMPLE LOCATION: N/A

STORAGE SITES: DM Cabinet DM003 Drawer 3

INVESTIGATOR'S ASSIGNED KEYWORDS: shrimps, Puerto Rico, electro exclusion, algal biovolume, sediment, Atyid, Xiphocaris, organic particles, algae, montane streams, diatoms, blue-green filamentous

LEF LTER OFFICIAL KEYWORDS (See table): Q TORONJA, RIVER, SEDIMENTATION, DECAPODS, PEER REVIEWED JOURNAL

PUBLICATIONS:
Pringle, C.M., Blake, G.A. (1994) Quantitative effects of atyid shimp (Decapoda: Atyidae) on the depositional environment in a tropical stream: use of electricity for experimental exclusion. Can. J. Fish. Aquat. Sci. 51: 1443-1450

DISSEMINATION: UNRESTRICTED

REASONS TO RESTRICT DATA IN THIS DATA SET BEYOND ITS TWO YEAR POLICY PERIOD*:

*WILL HAVE TO BE APPROVED BY LTER PRINCIPAL INVESTIGATORS: J. ZIMMERMAN, A. LUGO , D.J. LODGE

SITES DESCRIPTIONS: The experiments were carried out in pools of the stream Toronja. 32cm in diameter rings were placed in the stream. The control hoops were not electrified while the exclusion hoops were.

Geographical positional system (GPS) Coordinates for each location:

location	latitude	longitude

NAME OF ON - LINE CATALOG :LTERDBAS
RECORD #: 106
DOCUMENT TYPE:
PRIORITY TO BE ENTERED: N/A