Life history features of some macroinvertebrates in a French Polynesian stream

The invertebrate fauna of the Opunohu River catchment in Moorea, French Polynesia, studied 1988–1989, was numerically dominated by four species of neritid snails, one species of thiarid snail, two species of atyid shrimp, two species of palaemonid shrimp, and ten species of coenagrionid, chironomid, and simuliid insect larvae. Numbers of egg capsules of neritid snails were higher in riffles (maximum x density > 10,000/m² surface area) than pools, were highest in riffles in September and pools in August, and were lowest in both habitats in March and December. The snail Neritina canalis Lamarck and the shrimp Atyoida pilipes Newport, Caridina weberi DeMan, Macrobrachium lar Fabricius, and Macrobrachium australe Guerin‐Menévílle are diadromous: they enter freshwater as juveniles and migrate upstream; their larval offspring return to the ocean for growth and development. Ovigerous females of A. pilipes and M. lar were mainly found in austral fall; ovigerous females of C. weberi and M. australe were found in both austral fall and spring. Ovigerous females were the largest individuals of each shrimp species collected. Mean size of N. canalis, A. pilipes, C. weberi, and M. lar was generally larger in upstream than downstream reaches; no such difference was found for the non‐diadromous thiarid snail Melanoides tuberculata Müller. Coenagrionid, chironomid, and simuliid insect larvae have multiple cohort populations but at least one simuliid species occurs as a single cohort. Downstream habitat alteration may strongly influence the distribution of diadromous species.