Trophic Assessment of the Invasive Hydrozoan Gonionemus vertens using Stable Isotope Analysis: You are What You Eat

Gonionemus vertens, commonly known as the clinging jellyfish, is a small hydrozoan known for its conflicts with humans due to its paralysis and neurotoxins. Native to the Pacific Ocean, it has now invaded numerous systems including the Mediterranean, European, and United States coastal waters. In the United States, it has flourishing populations from New Jersey to Maine. However, many questions remain as to how it arrived and spread, but equally important is what impact this species may have in the invaded communities they now reside. Research suggests that G. vertens actively feeds on zooplankton during the evening, but direct evidence is lacking. Field observations of G. vertens have demonstrated a variety of macrofauna in their gastrovascular pouch including fish and peracarid crustaceans. As these organisms are extremely abundant in the vegetation where they live, it is highly probable that they contribute to their diet. We collected specimens and potential food resources to conduct N and C isotope analysis from three locations (RI, CT, and NJ). The NJ and CT populations had similar carbon values at -17 ��13C, while the RI was -13 ��13C. However, with regards to Nitrogen, the populations varied. NJ populations were substantially enriched (12.5 ��15N), compared to CT (10.2 ��15N) and RI (9.2 ��15N). Consequently, three trophic structures may be present among these three regions with NJ having the greatest Nitrogen enrichment suggesting they are feeding potentially 1 trophic level higher than the other populations. With respect to Carbon, RI populations may be gaining greater energy resources from the vascular plant Zostera marina, while CT and NJ may have greater inputs from macroalgal sources. Continued evaluation will help elucidate the trophic status of this invasive species and shed light on its actual diet.