Regional Studies in Marine Science 31 (2019) 100746 Contents lists available at ScienceDirect Regional Studies in Marine Science journal homepage: www.elsevier.com/locate/rsma Trophic ecology of a corymorphid hydroid population in the Bahía Blanca Estuary, Southwestern Atlantic M. Sofía Dutto a,∗ , M. Cecilia Carcedo a,b , Eugenia G. Nahuelhual a , Alberto F. Conte a , Anabela A. Berasategui a , Maximiliano D. Garcia a , F. Alejandro Puente Tapia c , Gabriel N. Genzano c , Mónica S. Hoffmeyer a,d a Instituto Argentino de Oceanografía (IADO, CONICET-UNS), La Carrindanga km 7.5, B8000FWB, Bahía Blanca, Argentina b Departamento de Biología, Bioquímica y Farmacia, Universidad Nacional del Sur (UNS), San Juan 670, Bahía Blanca, Argentina c Instituto de Investigaciones Marinas y Costeras (IIMyC), FCEyN, Estación Costera Nágera. UNMdP-CONICET., CC 1260, 7600, Mar del Plata, Argentina d Facultad Regional Bahía Blanca, Universidad Tecnológica Nacional (UTN), 11 de abril 461, B8000LMI, Bahía Blanca, Argentina article info Article history: Received 6 August 2018 Received in revised form 8 June 2019 Accepted 29 June 2019 Available online 8 July 2019 Keywords: Corymorpha januarii Diet Feeding rates Carbon flux Coastal ecosystem Argentina 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. © 2019 Elsevier B.V. All rights reserved. 1. Introduction The finding of solitary macroscopic hydroids usually repre- sents a valuable and unique discovery. They are rarely seen and, therefore, poorly studied (Schuchert et al., 2016). Corymorphid polyps correspond to this group of large athecate and rare hy- droids whose record in nature comprises an occasional event usually associated with fortuitous findings of few specimens from faunal expeditions (e.g., Watson, 2008; Vervoort, 2009; Genzano et al., 2009). Moreover, like numerous hydroid species in tem- perate waters (Bavestrello et al., 2006), corymorphid polyps show strong seasonality, displaying several cycles of senescence and re- generation that make them disappear from benthos for prolonged periods (Bouillon et al., 2004). These life cycle features result in a reduced likelihood that these polyps will be collected and studied. Consequently, ecological information on corymorphid ∗ Corresponding author. E-mail address: msdutto@criba.edu.ar (M.S. Dutto). polyps, such as population patterns, habitat, and diet, is very scarce. Hydroids play a key role in bentho-pelagic-coupling processes in shallow marine ecosystems because of their great abundances and high predation impact on a wide food spectrum, from detri- tus, diatoms, and benthic microplankton to egg and fish larvae (Coma et al., 1995; Gili and Hughes, 1995; Gili et al., 1996, 2008; Puce et al., 2002; Orejas et al., 2013). However, their ecological significance was particularly well demonstrated in colonial hy- droid polyps with colonial consumption rates of over 10 3 prey items per square meter per day and 5.5 to 225 mg C per square meter per day, and 5.4 to 199.2 captured items per hydrant per day (Gili et al., 1998; Orejas et al., 2000, 2001, 2013; Gen- zano, 2005). Comparatively, trophic knowledge for solitary hy- droid polyps is scarce and, except for Torrey’s observations (1904) on gastral content in Corymorpha palma, there are no studies, to our knowledge, on the natural diet and feeding rates of marine solitary hydroids. One of the largest corymorphid hydroids in the Southwestern Atlantic is Corymopha januarii. It lives in tropical and temperate https://doi.org/10.1016/j.rsma.2019.100746 2352-4855/© 2019 Elsevier B.V. All rights reserved.