Thursday, May 29, 2008 - 2:45 PM
568

Effects of an invasive n-fixing tree on a hawaiian stream food web

Trisha B. Atwood1, Tracy N. Wiegner2, Jason P. Turner2, and Richard A. MacKenzie3. (1) Tropical Conservation Biology and Environmental Science, University of Hawaii at Hilo, 200 W. Kawili St., Hilo, HI 96720, (2) Marine Science Department, University of Hawaii at Hilo, 200 W. Kawili St., Hilo, HI 96720, (3) Institute of Pacific Islands Forestry, USDA Forest Service, 60 Nowelo St., Hilo, HI 96720

Falcataria moluccana is an invasive N-fixing tree that has become increasingly common to riparian zones in Hawaii; however, its impact on streams is unknown. This study examined impacts of F. moluccana leaf litter on the food web of a 1st order stream located on Hawaii Island, using naturally occurring 13C and 15N isotope tracers.  Isotopic signatures of particulate organic matter, macroalgae, invertebrates, and fishes were compared between non-invaded and invaded sites along a stream.  Stable isotope analysis revealed that primary producers and consumers were depleted in 13C and enriched in 15N at the invaded site compared to the non-invaded site.  Food web analysis indicated that F. moluccana leaf litter was a major food source for amphipods and C. analis, and a minor source for P. clarkii and all three fishes at the invaded site.  Mixing models indicated that N derived from F. moluccana contributed 49% of the δ15N signature of the macroalgae in the invaded site.  Results from our study suggest that F. moluccana is directly altering food webs within this stream and contributing biologically available N to primary producers.  Our findings provide evidence of the ability of invasive riparian N-fixing trees to alter the structure of stream food webs.   


Web Page: food webs, invasive species, N-fixing tree

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