Impacts of aquatic invasive species and land use on stream food webs in Kaua’i, Hawai’i.

Anthropogenic disturbance is restructuring ecosystems and changing interactions within ecological communities. On the Hawaiʼian Islands, habitat degradation is linked to the establishment of invasive species; and together these stressors may lead to declining native populations and changes in food webs. In this study we employed stable isotopes to examine the structure of multiple Hawaiʼian stream food webs with varying levels of these stressors to illustrate interactions between native and non-native organisms that may represent drivers of community change. Limahuli stream contains all five species of native Hawaiʼian gobies, has a small number of introduced species, and minimal human disturbance. ʻOpaekaʼa, Hul¯eʼia and Kapaʼa streams are more heavily invaded than Limahuli and have greater human influence. We found increased species richness, increased trophic diversity, and increased total niche area in the more heavily invaded stream food webs relative to Limahuli. We also found non-native predatory species inhabiting top trophic positions in the three more heavily invaded streams and isotope mixing model estimates suggest that several species of non-natives have overlapping prey sources with native gobies in these sites. Lastly, we found that native stream organisms were nearly absent in ʻOpaekaʼa stream which also had the highest percent urban development of the streams sampled. Our results suggest significant trophic changes have occurred as the result of introduced species and possibly related to increased human disturbance.