For over 15 years, EuskOOS, the coastal observatory of the southeast Bay of Biscay, has been collecting data on various physical variables in the region. Recent initiatives aim to improve the observatory’s capabilities by developing a multidisciplinary infrastructure better equipped to address critical needs related to the sustainable management of this coastal area and the challenges posed by global change. Among the observation infrastructures available in the region, there are a high-frequency (HF) radar system, a network of buoys, as well as two gliders equipped with hydrographic, biogeochemical and biological sensors. These technologies, sometimes combined with satellite data, enable a detailed study of small-scale coastal variability and its role in modulating transport and fate of biological and biogeochemical quantities.

Lagrangian Coherent Structures (LCS), inferred using HF radar-derived Finite Size Lyapunov Exponents (FSLE), and satellite Chl-a images, showed that (sub)mesoscale structures such as eddies, fronts and along-slope currents within the slope and the Capbreton canyon area, as well as strong and persistent winds, can significantly impact the distribution of anchovy eggs and larvae and act ase effective mechanisms for their physical aggregation over short time scales (20 days). Similarly, LCS were used to study the dynamics of a well-developed river plume and the effects of advection in biogeochemical quantities. In this case, the combination of glider observations in the water column with HF radar, SST and Chl-a images at the surface enabled the characterisation of the plume and its strong extension towards the west (along 85 km). The plume produced strong upper-ocean stratification with marked Chl-a, temperature, salinity and nitrate anomalies within the upper 15 m and exhibited a very rapid evolution. After the event concluded, the glider retraced its original path and these anomalies had rapidly shifted, resulting in a well-mixed upper layer.