THE EFFECTS OF A FRESHWATER GRADIENT ON ZOOPLANKTON DISTRIBUTION AND COPEPOD RESPONSE TO SALINITY SHOCKS
Abstract.Estuaries are some of the most productive ecosystems in the world; though human development and global warming are threatening them. Zooplankton communities can serve as biological indicators of stresses due to their short lifecycles and sensitivity to environmental shocks, such as salinity changes. Studies have looked at the effects of freshwater shocks in the lab outnumber those that surveyed natural zooplankton distributions change along the freshwater gradient created by outflow from rivers. This study surveys the distribution of various taxa and examines the relationship this has with salinity by sampling zooplankton in Pao Pao River and Opunohu River on the island of Moorea in French Polynesia. In addition, this study tests the ability of copepods native to brackish water in Pao Pao to survive various shocks of increasing or decreasing salinity over time, as well as their response to bright light. Significant differences were found in overall community composition between bays and along the freshwater gradient. Most taxa exhibited strong correlations to salinity levels; some positive, some negative and some parabolic. Sharp rises in salinity appear not to affect copepod survival rates significantly, but abrupt drops do have significant effects. Light seems to repel copepods significantly as well.