Copernicus Marine Service Ocean State Report, Issue 5
Karina von Schuckmann, Pierre-Yves Le Traon, Neville Smith, Ananda Pascual, Samuel Djavidnia, Jean‐Pierre Gattuso, Marilaure Grégoire, Signe Aaboe, Victor Alari, Brittany Alexander, Andrés Alonso-Martirena, Ali Aydoğdu, Joel Azzopardi, Marco Bajo, Francesco Barbariol, Mirna Batistić, Arno Behrens, Sana Ben Ismail, Alvise Benetazzo, Isabella Bitetto, Mireno Borghini, Laura Bray, Arthur Capet, Roberto Carlucci, Sourav Chatterjee, Jacopo Chiggiato, Stefania Angela Ciliberti, Giulia Cipriano, Emanuela Clementi, Paul Cochrane, Gianpiero Cossarini, Lorenzo D’Andrea, Silvio Davison, Emily Down, Aldo Drago, Jean‐Noël Druon, Georg H. Engelhard, Iván Federico, Rade Garić, Adam Gauci, Riccardo Gerin, Gerhard Geyer, Rianne Giesen, Simon Good, Richard Graham, Marilaure Grégoire, Eric Greiner, K. Gundersen, Pierre Hélaouët, Stefan Hendricks, Johanna J. Heymans, Jason T. Holt, Marijana Hure, Mélanie Juza, Dimitris Kassis, Paula Kellett, Maaike Knol-Kauffman, Panagiotis Kountouris, Marilii Kõuts, Priidik Lagemaa, Thomas Lavergne, Jean‐François Legeais, Pierre-Yves Le Traon, Simone Libralato, Vidar S. Lien, Leonardo Lima, Sigrid Lind, Ye Liu, Diego Macías, Ilja Maljutenko, Antoine Mangin, Aarne Männik, Veselka Marinova, Riccardo Martellucci, Francesco Masnadi, Elena Mauri, Michael Mayer, Milena Menna, Catherine Meulders, Jane S. Møgster, Maeva Monier, Kjell Arne Mork, Malte Müller, Jan Even Øie Nilsen, Giulio Notarstefano, José L. Oviedo, Cyril Palerme, Andreas Palialexis, Diego Panzeri, Silvia Pardo, Elisaveta Peneva, Paolo Pezzutto, Annunziata Pirro, Trevor Platt, Pierre-Marie Poulain, Laura Prieto, Stefano Querin, Lasse Rabenstein, Roshin P. Raj, Urmas Raudsepp
Abstract
An efficient ocean management for fisheries requires accurate data over large spatial scales. The horizontal gradient of chlorophyll-a (and the derived mesozooplankton habitat index) exemplifies a plankton-to-fish index in support of a sustainable ocean management that targets fisheries and ecosystem productivity. The gradient of chlorophyll-a, as expressing the productivity of fronts, showed to be active long enough to sustain the development of mesozooplankton and to attract predators. In the global ocean, the chlorophyll-a gradient characterizes about 10 to 20% of the phytoplankton productivity that is transferred along marine food chains. Despite the warming of the surface ocean over the period 2003-2019, the global area-averaged trend of frequency of chlorophyll-a gradients, which is associated to the mesozooplankton feeding habitat and fish productivity, appears to be slightly positive with, however, contrasted regional trends.Daily values of chlorophyll-a gradient can be computed at global scale for the last two decades as well as up to near real-time. This is critical to improve our understanding of the plankton-to-fish dynamics, especially under the current effects of climate change, and to build observation-based operational products that will inform the future spatial and dynamic ocean management. The computation of such gradient requires a specific expertise in ocean colour, making them difficult to obtain for non-specialists. Their operational availability could therefore offer a critical benefit to ecosystem modelers and marine biologists and, in turn, to regional fisheries management facing overexploitation and the effects of climate change. Marine policies such as the EU Common Fisheries Policy and the Marine Strategy Framework Directive will ultimately be efficiently supported by the use of chlorophyll-a gradient as a direct, observation-based, biological variable monitoring the marine ecosystem productivity across a wide range of spatial and temporal scales.