Factors Affecting the Distribution of Atyid Shrimps in Two Tropical Insular Rivers

Abstract

We investigated factors affecting distribution of atyid shrimps, common inhabitants of insular freshwater ecosystems. Several abiotic and biotic variables were measured to determine their influence on atyid shrimp densities in two streams on the western Pacific island of Guam. Randomly selected sites, composed of three habitat types (rimes, runs, and pools), were surveyed in the rainy and dry seasons. We made visual counts of instream fauna in 2-m2 quadrats within each site. Various statistical analyses suggested that habitat type is a major factor affecting atyid distribution on Guam. However, results of a transplant experiment, conducted to test the effect of predators on atyid distribution directly, were noteworthy: no atyids remained in pools containing the transplanted jungle perch Kuhlia rupestris in the field. Our data indicate that both environmental factors and faunal interactions may be important influences on atyid distribution.