Nitrogen transfers mediated by a perennial, non-native macroalga: a 15N tracer study

Mats of macroalgae can alter nutrient regimes in intertidal communities, such as mudflats, marshes and beaches, by transferring nutrients to the surrounding habitat. Previous work has focused on ephemeral species of macroalgae that decompose in these intertidal environments. However, unlike ephemeral macroalgae, perennial species can be long-lived, resident members of intertidal systems and hence their role in mediating nutrient transfers may therefore be different. In this study, we used a N-15 isotope tracer to determine if nitrogen from a perennial, non-native macroalga (Gracilaria vermiculophylla) could be found in other macrophytes and in higher trophic groups on salt marshes and mudflats in shallow coastal bays in Virginia. We found that sediment on marshes and mudflats, marsh cordgrass (Spartina alterniflora), and mudflat invertebrates all incorporated nitrogen from G. vermiculophylla, indicating that this perennial alga is important in the transfer of nutrients within, and between, trophic levels.