Water Resources Research Act Program

Principal Investigators: Rebecca Ostertag, Richard MacKenzie

Abstract: Stream flow is critical for native Hawaiian fish and shrimp, delivering food resources and providing linkages between streams (adult/juvenile habitat) and the ocean (larval habitat) necessary to complete their amphidromous life cycle. Stream flow is currently threatened by reduced precipitation from climate change, invasion by high-water-use plant species, and water diversions for agricultural or other human uses. What is not known is how native stream fauna will respond to these changes. While decreased stream flow can reduce body condition and reproductive output of native shrimp (Atyoida bisulcata) in streams on Hawaii Island, the underlying mechanisms leading to these changes have yet to be identified. Furthermore, it is unclear if similar effects are happening to other native fauna. One potential mechanism includes shifts in food resources that occur with decreasing stream flow. I propose to examine this mechanism by comparing food web structure across streams that vary in flow. I predict that as flow decreases, the importance of suspended particulate organic matter (POM) as a food resource to native shrimp and gobies (i.e., Lentipes concolor) will decrease, while the importance of benthic algal and insects will increase. This information will not only increase our understanding of how changes in stream flow will impact native stream fauna, but will be used to build a stream classification tool and a decision support tool currently being developed by the USDA Forest Service, Hawaii, and Michigan State Universities to help protect healthy water systems, restore impacted streams and watersheds, and plan for future anthropogenic impacts.