Appearance of Chelophyes appendiculata and Abylopsis tetragona (Cnidaria, Siphonophora) in the Bay of Villefranche, northwestern Mediterranean

The vertical and temporal distribution of two calycophoran siphonophores, C helophyes appendiculata (Eschscholtz, 1829) and Abylopsis tetragona (Otto, 1823) in the Bay of Villefranche (northwestern Mediterranean) was investiga ted by an analysis of three different planktonic time series. A daily serie s (1993-1995) showed seasonal peaks of the nectophores of C. appendiculata during spring and particularly in late summer, while the abundance of A. te tragona remained similar throughout the year. A weekly series (1994-1995) s howed that C. appendiculata (nectophores and eudoxids) became concentrated above the thermal discontinuity, in the most stratified and warm waters, wh ereas A. tetragona was collected in large numbers below this discontinuity. A 27-year survey (1966-1993) showed long-term fluctuations of these siphon ophore populations, which became abundant in the Bay starting from 1980 and especially after 1984, when the water column grew warm and hypersaline, co rresponding to a less rainy period. Temporal (seasonal and long-term) and b athymetric (between 10 and 60 m depth) successions of these two siphonophor es were noted in this shallow coastal bay. (C) 1999 Elsevier Science B.V. A ll rights reserved.