Trophic ecology of a corymorphid hydroid population in the Bahía Blanca Estuary, Southwestern Atlantic

Abstract

Solitary macroscopic polyps are rare, and ecological information about them, such as diet and feeding rates is scarce worldwide. Here we describe the population of the solitary and seasonal polyps of Corymorpha januarii found in the Bahía Blanca Estuary, Argentina, and provide one of the first approaches to define their feeding ecology by gut content analysis. We analyzed the substrate and the accompanying benthic components, and provided in situ observations as well as observations on polyps kept in aquarium. A mean of 4 types of trophic items per polyp and 13.33 consumed prey items per polyp were obtained, representing a daily carbon consumption of 1.8 mg C per polyp per day and 75 mg C per square meter per day when considering polyp densities. The daily mass-specific ingestion rate was 20.5 % of polyp biomass. Polyps of C. januarii showed a variable diet composed mainly of organic matter and zooplanktonic prey, and probably selected copepods, mysids, and other zooplanktonic prey of lower or no swimming capacity (e.g., barnacle larvae and invertebrates, and fish eggs). The diversity of the prey ingested indicates that C. januarii is highly adaptable to changing environmental conditions, and this organism may have a significant role in energy transfer in estuarine waters.