GRADIENTS OF PHYTOPLANKTON ABUNDANCE, COMPOSITION AND PHOTOSYNTHETIC PIGMENTS ACROSS THE ALMERIA-ORAN FRONT (SW MEDITERRANEAN-SEA)

As a part of the interdisciplinary study of the geostrophic front of t he eastern Alboran Sea (''Almofront-1'', April-May 1991), several char acteristics of phytoplankton biomass have been measured at the regiona l scale to evaluate the gradients between the frontal jet and the surr ounding water masses. Microplanktonic diatoms, chlorophyll a and fucox anthin were the most abundant in the front by 1-2 orders of magnitude whereas pico- and nanoplankton, which consist mostly of prymnesiophyte s, and 19'hexanoyloxufucoxanthin tended to be the most abundant in the adjacent waters. Correlations between the various phytoplankton compo nents and tracers are examined. The Almeria-Oran front behaves typical ly as a fertilisation site in an otherwise oligotrophic environment. F rontal fertilisation favored the growth of one or a few opportunistic, autochthonous diatom species, the remainder of the Alboran Sea being occupied by a diversified population of the smallest size-classes of p hytoplankton.