Water Resources Research Act Program

Principal Investigators: Frank Camacho

Abstract: Insular streams and rivers are ecologically and culturally valuable resources on tropical high islands. As population growth on Micronesian high islands has increased over the past half century, watersheds are increasingly being threatened by anthropogenic disturbances. On Guam, deforestation in southern watersheds is largely the result of wildfires associated with illegal hunting activities; in these areas, riparian forests have been replaced by fire-adapted savanna vegetation. These savannas are associated with high levels of erosion and sedimentation and may be ineffective at preventing these particles from entering rivers. While considerable attention has been given to the effects of erosion and sedimentation on terrestrial systems and adjacent marine habitats (e.g., coral reefs and estuaries), how sediment load and the floristic composition of the riparian vegetation influence the ecosystem dynamics and biodiversity of the insular streams that transport these particles is poorly known. In order to address these gaps we will examine the diversity, distribution, and abundance of streamfish and macroinvertebrate assemblages in stream reaches under different levels of (1) riparian canopy closure, (2) sediment load, and (3) vegetation type (i.e., savanna versus ravine forest). Furthermore, microhabitat usage, such as focal point substrate and current velocity, will be characterized. We will conduct seasonal field surveys of streamfish and macroinvertebrate abundance in four streams from southern Guam using standard visual census techniques. Within each stream reach, 10 cascades, runs, and pools will be sampled and the focal point substrate of individual fish will be recorded. Additionally, sediment load from sediment traps and percent canopy closure, as measured with a moosehorn densiometer, will also be analyzed. Physicochemical analyses of pH, nutrient concentrations, and water temperature will be recorded for each habitat. Line-intercept transects will be used to characterize the taxonomic composition of the riparian community. The matrix of species x physical and chemical data will be analyzed using general linear models and several distance-based measures of similarity to determine the importance of sediment load, savanna vegetation, and percent canopy closure on the biodiversity and habitat use patterns of instream fish and invertebrates. Several key objectives will be addressed by this study: (1) This project will attempt to expand our current state of knowledge about how sediment load and canopy cover influence biodiversity and habitat use by native streamfish and macroinvertebrates; (2) a relational database will be created of streamfish densities and the various physical and chemical parameters of each habitat and will be provided to local resource agencies; (3) significant training in stream monitoring techniques will be available for an undergraduate student; (4) we will provide a public workshop on streamfish identification and monitoring methods based upon the results of our survey and analyses. This project would dramatically improve our understanding of the ecology of native streamfish and macroinvertebrates in relation to riparian vegetation and sediment load across several watersheds on Guam. Such fundamental information regarding how habitat use by these organisms is altered by high sediment loads and savanna vegetation is critically needed by resource managers in order to make sound decisions regarding restoration of these upland habitats.