Meeting Abstract

P3.118  Monday, Jan. 6 15:30  Algal showdown: invasive Gracilaria vermiculophylla vs. native species in Virginia’s coastal bays NEEDHAM, CN*; SALERNO, CR; BERKE, SK; Siena College; Siena College; Siena College cn09need@siena.edu

Invasive species have the potential to disrupt food webs if they displace resources that native species prefer. In the coastal bays of Virginia, the red alga G. vermiculophyllais a problematic invader that represents more than 90% of all macroalgal biomass in protected intertidal habitats. If G. vermiculophyllais a lower quality resource than native algae, then regional food webs may be affected. We assessed grazer preferences for G. vermiculophyllaversus two native algae – the congeneric red alga G. tikvahiae , and the green alga Ulva lactuca. Grazers included two common amphipod species, Ampithoe rubricata and Gammarus mucronatus, the Eastern mud snail Nassarius obsoletu s, and the onuphid polychaete Diopatra cupre a. All four species preferred the native Ulva to either Gracilaria, and did not substantially feed on either the native or the invasive Gracilaria species in 3-way choice experiments. In feeding assays using freeze-dried algae mixed with agar, D. cuprea readily consumed all three species in equal amounts, suggesting that the preferences are rooted in the red algae’s physical properties rather than chemical defenses. For D. cuprea, we also assessed growth and regeneration over a one-month period in which worms were maintained on a diet of G. vermiculophylla, G. tikvahiae , or Ulva alone, or a mix of all 3 supplemented with shrimp meat. While worms given meat grew and regenerated the most, we found no differences among the algae, suggesting that G. vermiculophyllamay be an acceptable food resource in the absence of preferred species. Future work will assess the relative rates at which grazers consume the invasive vs. native algae, and the extent to which small epifaunal invertebrates use invasive vs. native species as habitat.