Small-scale distribution of macroplankton and micronekton in the Ligurian Sea (Mediterranean Sea) as observed from the manned submersible <i>Cyana</i>

Abstract

A series of eight submersible dives (the MIGRAGEL I cruise) was made during late April 1986 using the French submersible Cyana to investigate macrozooptankton in the upper 400–700 m of the water column. Paired day and night dives were made at stations 3, 6, 13 and 23 nautical miles off Cape Ferrat, near Villefranche-sur-Mer, France; the distances represent different areas in the frontal system of the Ligurian Sea. Detailed day/night vertical distribution data are shown for the most abundant species; these include the narcomedusa Solmissus albescens , teleost fish Cyclothone spp., small appendiculanans (primarily Oikopleura albicans ), large appendicularians (an undescribed oikopleurid), diphyid siphonophores (mostly Chelophyes appendiculata ) and an abundant lobate ctenophore. Salps, pyrosomes, amphipods ( Phroniuma sedentaria ), pteropods ( Cavolinia inflexa ), macroscopic ‘star-like’ protozoa and marine snow are also briefly discussed. The coastal zone was dominated by small appendicularians in the upper layers, with other filter feeders including large appendicularians in deeper water—these just above a non-migratory population of carnivorous Cyclothone . The carnivorous medusa Solmissus albescens moved throughout the upper 600 m in the course of its diel vertical migration. Offshore, carnivores were dominant throughout the water column, with numerous diphyid siphonophores in the upper layers, and Cyclothone , lobate ctenophores and macroprotozoa abundant in deeper water. Solmissus was also present, and was more numerous offshore than in the coastal zone.