Feeding ecology and trophic impact of the hydroid Obelia dichotoma in the Kongsfjorden (Spitsbergen, Arctic)

• Published in: Polar Biology
• Main Authors: Orejas, Covadonga, Rossi, Sergio, Peralba, Áurea, García, Eva, Gili, Josep Maria, Lippert, Heike
• Format: Article in Journal/Newspaper
• Language: English
• Published: Springer 2013
• Subjects: Trophic ecology; Benthic suspension feeders; Hydroids; Obelia dichotoma; Arctic; Lesund; Alfred Wegener Institute; Kongsfjord*; Kongsfjorden; Polar Biology; Zooplankton; Spitsbergen
• Online Access: http://hdl.handle.net/10261/72151; https://doi.org/10.1007/s00300-012-1239-7

12 pages, 4 figures, 4 tables Obelia dichotoma is a thecate hydroid with a worldwide distribution, occurring mainly on shallow water hard substrates. Since the trophic ecology of hydroids in polar waters is badly understood, the aim of the present work was to study qualitatively and quantitatively the diet of these organisms in an Arctic environment and to determine their trophic significance. For this purpose, the density of the hydroid population was documented, and simultaneously, zooplankton was sampled in two different years (1997 and 1998). Prey capture rates were estimated by analysing the gastrovascular content of the polyps in a diurnal cycle. Additionally, the digestion time of O. dichotoma was measured by laboratory feeding experiments using diatoms as food items. The analyses of the gastrovascular cavities of the polyps sampled during the diurnal cycles showed that O. dichotoma fed mainly on faecal pellets, organic matter and microalgae. Zooplankton prey was also observed, but gastrovascular contents and zooplankton abundance did not show any correlation in both years. The consumption rates of the hydroid populations differed between the 2 years. It was almost double (8.9 mg Carbon m−2) in 1998 compared to 1997 (5.5 mg Carbon m−2). The significance of the environmental variability in the feeding ecology and population dynamics of hydroids under Arctic conditions is discussed The support of the scientific and technical staff of the Koldewey-Station, the members of the Alfred Wegener Institute (AWI) diving team and the Ny-A° lesund International Research and Monitoring Facility is gratefully acknowledged. Thanks are due to the AWI for technical and financial support. The first author was financially supported by a Deutscher Akademischer Austausch Dienst (DAAD) fellowship (A/96/13073) and a European Commission fellowship from the programme Training and mobility of researchers (TMR-CT97-2813). S. Rossi was funded by a Ramón y Cajal contract (RYC-2007-01327). Special thanks to Prof. Dr. Wolf E. Arntz ...