The relative importance of introduced fishes, habitat characteristics, and land use for endemic shrimp occurrence in brackish anchialine pool ecosystems

Abstract

Anchialine ecosystems are groundwater- fed brackish coastal habitats that contain high per- centages of endemic fauna and are at risk from anthropogenic stressors, introduced species, and sea level rise. Data on endemic species distribution, habitat condition, and species/habitat interactions in this ecosystem are scarce across large spatial scales. This study offers the most thorough regional perspec- tive on anchialine pool habitat characteristics along the western and southern coastlines of the island of Hawaii since the 1970s. Daytime surveys of 398 anchialine pools documented the widespread distribution of two dominant endemic shrimp Halo- caridina rubra and Metabetaeus lohena in a wide range of habitats. Introduced fishes (tilapia, poeciliids) were present in about 25% of pools. Generalized additive models were used to determine the relation- ship between shrimp occurrence and pool character- istics, invasive species, water properties, and land use. Introduced fishes had a strong negative effect on the occurrence of H. rubra and M. lohena. High benthic silt cover and adjacent development also had sig- nificant negative relationships with shrimp occur- rence. Our results indicate that conservation efforts should include controlling introduced fishes, prevent- ing new introductions, minimizing siltation, and protecting groundwater resources and low-lying coastal areas.