GRADIENTS OF PHYTOPLANKTON ABUNDANCE, COMPOSITION AND PHOTOSYNTHETIC PIGMENTS ACROSS THE ALMERIA-ORAN FRONT (SW MEDITERRANEAN-SEA)
Résumé
As a part of the interdisciplinary study of the geostrophic front of the eastern Alboran Sea (''Almofront-1'', April-May 1991), several characteristics of phytoplankton biomass have been measured at the regional scale to evaluate the gradients between the frontal jet and the surrounding water masses. Microplanktonic diatoms, chlorophyll a and fucoxanthin were the most abundant in the front by 1-2 orders of magnitude whereas pico- and nanoplankton, which consist mostly of prymnesiophytes, and 19'hexanoyloxufucoxanthin tended to be the most abundant in the adjacent waters. Correlations between the various phytoplankton components and tracers are examined. The Almeria-Oran front behaves typically as a fertilisation site in an otherwise oligotrophic environment. Frontal 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 phytoplankton.