Gracilaria vermiculophylla in the Virginia coastal bays: Effects of a non-native macroalga on nitrogen dynamics, trophic cascades, and public health

Gracilaria vermiculophylla is a cryptic, invasive red macroalga that is native to Southeast Asia and has invaded many temperate estuaries in North America and Europe. The high tolerance of this alga to desiccation and temperature stress has allowed it to proliferate on the marsh and mudflat where other macroalgal species cannot. As part of this study we first genetically verified the widespread distribution and diversity of G. vermiculophylla in the Virginia coastal bays. Further work using a ¹⁵N tracer determined that the addition of this macroalga to marsh and mudflat systems could increase nitrogen levels in the sediments, vegetation, and invertebrates. At the same time, G. vermiculophylla presence can increase rates of denitrification on mudflats. In addition, we found that at current densities, G. vermiculophylla may increase food availability to and foraging intensity of migrating shorebirds. As part of the final facet of this study we have found pathogenic bacterial species (Vibrio parahaemolyticus, Vp) associated with G. vermiculophylla tissue. Vp can cause severe gastrointestinal infections when raw or undercooked shellfish are consumed that contain the bacteria and is therefore of concern when monitoring water quality in coastal waters. Future work in fall 2012 will investigate if oysters growing on mudflats with mats of G. vermiculophylla have higher levels of Vp in their tissue than those growing on bare mudflats. Together, these five studies will help to expand on our current understanding of G. vermiculophylla effects on temperate estuaries.