The role of invasive marine plants for macrofauna nutrition in the Wadden Sea

Abstract Wadden Sea macrozoobenthos has access to food sources of different quality. In addition to microphytobenthos (MPB) and macroalgae (e.g. Fucus vesiculosus Linnaeus, 1753), the invasive C 4 grass Spartina anglica C.E. Hubbard has become an abundant primary producer in the Wadden Sea. To elucidate the role of different primary producers for the nutrition of typical Wadden Sea consumers, we conducted a mesocosm experiment with four food treatments ( S. anglica , F. vesiculosus , MPB and all three resources together) under a simulated tidal cycle. We used consumers of different feeding types—the omnivorous polychaete Hediste diversicolor (O.F. Muller, 1776), the interface-feeding bivalve Limecola balthica (Linnaeus, 1758) and the surface deposit-feeding snail Peringia ulvae (Pennant, 1777)—and analyzed their biomass, δ 13 C and δ 15 N stable isotope values and fatty acid (FA) profiles. After 4 weeks, the biomass of H. diversicolor increased in treatments that contained F. vesiculosus , but decreased in the treatment with MPB. δ 13 C values of H. diversicolor reflected those of the food sources provided and FA profiles varied strongly between the treatments, indicating feeding on copepods and bacteria as well as macrophytes. The biomass of P. ulvae significantly increased in treatments with S. anglica and all three resources. However, δ 13 C values of P. ulvae differed significantly between the treatments and were unrelated to the food sources except for MPB. FA profiles confirmed the assimilation of MPB in this species. δ 13 C values and FA composition of L. balthica were similar in each of the treatments and did not resemble the resources provided. Instead, the high proportion of respective marker FAs indicated feeding on plankton. δ 15 N values of the consumer species declined significantly in the order H. diversicolor  >  L. balthica  >  P. ulvae in each of the treatments. These results indicate different strategies in food source use of the three consumer species with the performance of the generalist feeders H. diversicolor and P. ulvae exceeding that of the selective feeder L. balthica .