Seasonal variation in copepod abundance in relation to other zooplanktonic groups in the northwestern Mediterranean

Abundance of adult copepods and late copepodid stages from the upper 50 m in the Golfe du Lion (N.W. Mediterranean) was studied by the author in 1986, 1987, and 1988 for each season. Altogether 87 stations at 22 fixed locations were sampled in the frame of the multidisciplinary French/Spanish programme Pélagolion/Leopel in the near-coastal region (≤ 25 m bottom depth), the Rhone dilution zone, the neritic region (≤ 200 m bottom depth), and the oceanic region (200—2000 m bottom depth). Abundance of other zooplanktonic groups was estimated and total zooplankton biomass was determined for the upper 50 m. Copepod abundance was highest during September 1986 (all regions) and July 1987 (neritic). Total biomass was highest during July 1987 and May/June 1988, caused by high abundance of many other zooplankters. Most abundant copepod species were: Clausocalanus spp., Paracalanus parvus (Claus, 1863), Oithona spp., Oncaea Corycaeus spp., spp., Centropages typicus Krøyer, 1849, Calanus helgolandicus (Claus, 1863), and Temora stylifera (Dana, 1849). Generally, copepodids slightly outnumbered the adult copepods in the coastal and neritic region, but they were twice to three times more numerous than adults in the oceanic region. Beside copepods, Cladocera formed the most important group at the near-coastal stations near the Rhone mouth; Siphonophora and Salpidae were most abundant at the neritic and oceanic stations.