Long term mesozooplankton changes in coastal waters of North Spain

At the present situation of climate change in which we are immersed, temporal series arise as a powerful and reliable way of detecting changes and responses of marine ecosystems through time. The key role of the mesozooplankton community in ecosystems together with its particular life-cycle features, makes this group a preferential candidate to be studied in temporal series. Coastal areas are especially sensitive to environmental changes and the Cantabrian Sea, due to its singular geographical conditions, it is an attractive example to perform time series studies. In order to evaluate modifications and responses of mesozooplankton to environmental variations in the central Cantabrian Sea, we conducted a monthly sampling campaign during 17 years along a coastal-oceanic transect. One physical variable, Sea Surface Temperature (SST), and six biological variables (integrated Chl a, mesozoplankton biomass, abundance, and proportions of three different size classes), were analyzed. We could characterize the general annual cycle for the study variables at this location of the Cantabrian Sea and detect differences between more coastal or oceanic conditions. A long-term positive trend for SST (0.023 C yr-1) is confirmed, but surprisingly, the more stratified and oligotrophic conditions to which it should lead, do not produce the expected decreasing trend neither for Chl a nor for mesozooplankton biomass or abundance. Far from this, we report a positive long term trend increase for these biological variables. We also detected an increasing trend for the mesozooplankton size-spectra structure towards a more bimodal distribution, with a higher proportion of large and small size organisms. Finally, we found several year periods of positive and negative anomalies for the different study variables which have to be taken into account when long-term trends are analyzed.

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0511 - Biology