MEPS 195:15-27 (2000)  -  doi:10.3354/meps195015

Mesoscale features of phytoplankton and planktonic bacteria in a coastal area as induced by external water masses

Raffaella Casotti1,*, Christophe Brunet1,2, Bianca Aronne3, Maurizio Ribera d¹Alcala1

1Stazione Zoologica ŒA. Dohrn¹, Villa Comunale, 80121 Naples, Italy
2Université du Littoral, LISE, UPRES-A 8013, 62930 Wimereux, France 3Istituto Universitario Navale, viale Acton, 80100 Naples, Italy

ABSTRACT: The effects of different water masses and their physical structures on phytoplankton and bacteria were investigated in a coastal area of the Mediterranean Sea, the Gulf of Naples (Italy) on 9 and 10 November 1995. A small eddy (8 km in diameter), generated from offshore waters, occupied the inner part of the Gulf at surface, while the Modified Atlantic Water (MAW) intruded between 60 and 80 m depth. Phytoplankton communities as identified by HPLC pigment analysis (total) and flow cytometry (ultraphytoplankton) showed peculiarities in the different subsystems. Cryptophytes dominated by pigment biomass were everywhere, while diatoms were more abundant at the coast and nanoflagellates at offshore stations. In the MAW, a peculiar phytoplankton community, different to that in the other water masses, occurred, and 2 populations of prochlorophytes were distinguished based on scatter and red fluorescence observations. Total bacterial numbers were significantly correlated to chlorophyll a (chl a) concentrations. Different populations of heterotrophic bacteria were identified based on apparent DNA content. Percentages of 2 such populations were significantly correlated to total chl a</