Springtime zooplankton size structure over the continental shelf of the Bay of Biscay
- 1IFREMER, Centre Bretagne, Département Dynamique de l'Environnement Côtier, B.P. 70, 29280 Plouzané, France
- 2Centro Oceanográfico de Gijón, Instituto Español de Oceanografía, Gijón 33212, Spain
- 3IFREMER, Centre Bretagne, Unit. Sciences et Techniques Halieutiques, B.P. 70, 29280 Plouzané, France
- 4Centro Oceanográfico de Vigo, Instituto Español de Oceanografía, Vigo 36200, Spain
- 5IFREMER, Centre Nantes, Département Écologie et Modèles pour l'Halieutique, rue de l'Île d'Yeu, 44300 Nantes, France
- 6GEOMAR, Helmholtz-Center for Ocean Science, Düsternbrooker Weg 20, 24105 Kiel, Germany
Abstract. Linking lower and higher trophic levels requires special focus on the essential role played by mid-trophic levels, i.e., the zooplankton. One of the most relevant pieces of information regarding zooplankton in terms of flux of energy lies in its size structure. In this study, an extensive data set of size measurements is presented, covering parts of the western European continental shelf and slope, from the Galician coast to the Ushant front, during the springs from 2005 to 2012. Zooplankton size spectra were estimated using measurements carried out in situ with the Laser Optical Plankton Counter (LOPC) and with an image analysis of WP2 net samples (200 μm mesh size) performed following the ZooScan methodology. The LOPC counts and sizes particles within 100–2000 μm of spherical equivalent diameter (ESD), whereas the WP2/ZooScan allows for counting, sizing and identification of zooplankton from ~ 400 μm ESD. The difference between the LOPC (all particles) and the WP2/ZooScan (zooplankton only) was assumed to provide the size distribution of non-living particles, whose descriptors were related to a set of explanatory variables (including physical, biological and geographic descriptors). A statistical correction based on these explanatory variables was further applied to the LOPC size distribution in order to remove the non-living particles part, and therefore estimate the size distribution of zooplankton. This extensive data set provides relevant information about the zooplankton size distribution variability, productivity and trophic transfer efficiency in the pelagic ecosystem of the Bay of Biscay at a regional and interannual scale.