Size-fractionated seston abundance and biochemical composition, over the anchovy spawning period in the Basque shelf (Bay of Biscay), during years 2000 and 2001

The nutritional environment for fish larvae is analysed for the Basque continental shelf (Bay of Biscay), during the main anchovy-spawning period (spring) over two years. The quantity and quality of Suspended Particulate Matter (seston) is analysed for total particles, microparticles (20-200 μm) and mesoparticles (200-1000 μm). Separately, the characterisation of the < 20 μm particles is made, by subtracting the values obtained for micro- and mesoparticles, from the values for total seston. During the study period, the interannual variability on the nutritional environment was higher than inter-month, or spatial, variability. Changes in total seston quantity and quality were found to be associated to river discharges and marine circulation; these represented mainly the changes in the < 20 μm particles, which had the lowest nutritional value. In contrast, micro- and macroparticles were constituted mostly by living particles; they were found to have a higher nutritional value. Changes in abundance and quality showed similar trends in micro- and mesoparticles, but differed in the < 20 μm particles. However, the nutritional quality of particles increased with temperature within the three fractions. Biochemical analyses revealed that the nutritional environment, for fish larvae, was rich over the Basque continental shelf during both of the years investigated.