The importance of freshwater shrimps in tropical stream ecosystems

Puerto Rico RiverBugWaterfall

Many tropical stream animals are diadromous, meaning they spend variable portions of their life cycle in both freshwater and saltwater. This life history attribute necessitates some degree of migratory behavior. In Puerto Rico (and many other tropical island systems), fishes and shrimps dominate community biomass, but their relative biomass is highly variable among stream systems. Why is this? Interestingly, landscape topography plays a large role in determining the structure of stream communities. In some streams, large waterfalls prevent the upstream migration of predatory fishes, but pose no problem for upstream movement of shrimps. Consequently, some headwater streams have extremely high biomass of shrimps and very few (often none) predatory fishes. Other streams that lack major waterfalls contain moderate numbers of predatory fishes (e.g., American eels, Mountain Mullet) and very few shrimps because of strong predation pressure. This contrast in foodweb structure among nearby headwater streams provides an ideal situation for examining the role of consumers in ecosystem-scale dynamics.

My research focused on the following topics:

  1. To what degree do shrimps influence whole-ecosytem nutrient (i.e., nitrogen and phosphorus) cycling in tropical streams? How does their importance vary across the landscape?

  2. What is the magnitude of shrimp secondary production in Puerto-Rican streams? How long do freshwater shrimps live? What basal food resources support shrimp production (i.e., trophic basis of production)?

  3. Can ecological stoichiometry theory (specifically Threshold Elemental Ratio models, see Frost et al. 2006) help predict when and where shrimp are limited by the nutrient content of their food? Do patterns of shrimp elemental content and nutrient excretion follow those predicted by stoichiometric theory?

  4. What is the relative importance of direct consumption vs. bioturbation by shrimps in fine sediment removal? Research conducted by Alexandra Santana (undergraduate at Universidad Metropolitana, Puerto Rico)


  • Alan P. Covich, University of Georgia
  • Jonathan P. Benstead, University of Alabama
  • James G. March, Washington Jefferson College
  • Alonso Ramirez, University of Puerto Rico
  • William H. McDowell, University of New Hampshire
  • Todd A. Crowl, Utah State University