Abundance and Composition of Available Zooplankton for Cold-water Coral Nutrition in Comau fjord, Chile

Nur Garcia-Herrera1,2, Astrid Cornils1, Barbara Niehoff1, Jürgen Laudien1, Gertraud Maria Schmidt1, Verena Häussermann3,4, Humberto E Gonzalez3,5 and Claudio Richter1,2, (1)Alfred Wegener Institute Helmholtz-Center for Polar and Marine Research Bremerhaven, Bremerhaven, Germany, (2)University of Bremen, Biology/Chemistry, Bremen, Germany, (3)Austral University of Chile, Institute of Marine and Limnological Sciences, Valdivia, Chile, (4)Huinay Scientific Field Station, Huinay, Chile, (5)Research Center: Dynamics of High Latitude Marine Ecosystems (IDEAL), Punta Arenas, Chile
Abstract:
Cold-water corals (CWC) directly depend on planktonic food as their principal source of energy. However, zooplankton abundance changes considerably with community composition, population dynamics, seasonal and diel migration patterns. The Fjord Comau (Chilean Patagonia) is characterized by seasonal variations inducing changes in the primary production and therefore, triggering corresponding changes in the abundance and composition of zooplankton. CWC live and grow in the acidified waters of this fjord, yet, the link between zooplankton distribution and seasonality and the prey field of CWC is not well understood. In this study, we investigated the seasonal development of a zooplankton community, sampling the whole water column (0-50-100-200-300-400-450 m) with a Nansen net (100 μm) once every season. During each sampling event, one sample was taken during day time and one during night to tackle diel vertical migration. The wet volume and the taxonomical composition of the zooplankton community were determined. Maximum plankton volume was found during the summer season, which was twice as high as during the rest of the year, showing strong seasonal variation. The maximum volume in the water column was found between 100-200 m water depth during day and between 0-50 m during night time throughout the year, indicating diel vertical migration. The taxonomical analysis using a ZooScan digital imaging system identified Copepoda as the most abundant group (ca. 60% of the volume of the total zooplankton community) followed by nauplii 6% in spring and Ostracoda 2% in summer. It is discussed if the high abundance of zooplankton during the warmest and driest season could be used by the sessile CWC to form energy reserves. However, it is not clear yet, if the respective CWC are food limited during the rest of the year. In conclusion, this study improves our understanding on zooplankton migration and seasonality and thus food availability for CWC.
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