Spatial variability of the Siphonophora along the radial Calvi-Nice (Corsican side)

The spatial distribution of the Siphonophorae has been examined, in Occidental Mediterranean, along the radial Calvi-Nice, from Calvi up to 30 miles offshore in September 2009. The variation of the abundance of the plankton and of the Siphonophorae was put in relation with the hydrological structures of the Liguro-Provençal front. This structure separates the coastal waters of Atlantic origin from the offshore central Mediterranean waters of deep origin.
Globally, the larger abundances of Siphonophorae were present in inshore waters between the front and the coast. Both nectophores (asexual stage) and gonophores and bracts (reproductive stage) of Lensia subtilis occured only in the inshore waters.
The nectophores of Chelophyes appendiculata occured at all sampling stations with no significative variation. However, the abundance of the bracts and the gonophores increases when we get closer to the coast.
This allows us to hypothesize that the maximum of reproduction is located in waters close to the coast. On the other hand, the larvae abundance of calycophoran siphonophores, in the plankton samples, increase from the coastal waters to the offshore waters with a maximum of abundance at the station located at 25 miles offshore. That contradiction could be explained by plankton net avoidance of small larvae, by current transport or by variable hatching success at the various stations. The larvae of physonect siphonophores are more often found offshore.