Observatory of climate change of the coasts and pelagic ecosystem of the Bay of Biscay

The global warming of the oceans and the impact of extreme events, exacerbated by accelerating sea levels, are challenges that coastal societies must address urgently to anticipate impacts in the next decades. To address this at regional and local scales, there is a need of implementing an integrated system for monitoring climate change and its effects. This study presents the basis for building the marine observatory of climate change of the Bay of Biscay and Basque coast. We have used an integrated and flexible time-series analysis methodology, based on Generalized Additive Mixed Models (GAMMs), to detect trends on 19 indicators (on marine physics and chemistry, atmosphere, geomorphology, and marine biota and commercial fishes) within the context of climate change. The results 80 historical time series analysed (~512,000 observations) indicate four main groups of climate regime shift in the Bay of Biscay: 1) A gradual shift associated to climate change starting in the 80’s, with a warming of the sea surface to 100 m depth in the last four decades in the coast and the entire bay (0.10-0.25 °C per decade), increase in air temperature and sunshine days, with impacts to benthic community redistribution in the Basque coast, favouring warm-water species relative to cold-water species. Weight at age for anchovy and sardine decreased in the last two decades. 2) Sea level rise (1.5-3.5 cm per decade) with accelerating rates, associated also to global climate change. 3) Increase of extreme wave events (Hs100: 27 cm per decade) in the southeastern bay probably associated to windy conditions and impacts on beach erosion, which might be due to interdecadal climate variability. 4) Changes in the water column vertical structure in the south-eastern bay, probably due to higher marine stormy weather, with increase river flow extremes, nutrient concentration, dissolved oxygen, phytoplankton concentration and zooplankton biomass at the entire bay. Current trends on plankton biomass are contrary to expected climate change scenarios in the region. Estimating accurate rates of sea warming, sea level rise, and disentangling the future pathways of marine productivity is key to define the best adaptation criteria for coastal communities and fisheries sector.