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Lagrangian transport of benthic species in the Ligurian sea (Western Mediterranean)
Stefano Aliani, Annalisa Griffa, Carla Micheli, Anne Molcard, Andrea Peirano
Istituto Scienze Marine Sezione di La Spezia CNR
amolcard@rsmas.miami.edu(Abstract received 05/11/2005 for session A)
ABSTRACT
The records of alien species in the Ligurian sea recently increased. Some were directly transported by humans, and others were transported by currents. In this work we aim i) to use a simplified mathematical model to describe the possible time scale that a passive larva requires to travel from the Corsica Channel to the Ligurian sea; ii) to assess whether rafting of organisms on floating objects may affect dispersal processes; iii) to show evidences of long distance dispersal which may supply the local populations. A Lagrangian model has been applied to study dispersion of passive tracers by simulating a high number of particles/larvae. Results of such simulations show that after 30 days only 3% of the larvae can reach the Ligurian coast from the Corsica Channel. Floating debris were estimated from visual sightings during oceanographic cruises in the Ligurian Sea and areas of high concentration were used to assess the potential of floating objects as ways of extending dispersion of settled larvae. After 30 days 11% of larvae reached one of the highest concentration area and after settling on debris the possibility to reach the Ligurian coast increased to 33%. For some species, extension of geographic range can be related to transport of mature individuals on floating objects more efficiently than the active or passive dispersal of reproductive units. The links between offshore presence and coastal settling are under discussion but some clues of connection are from the Mediterranean seagrass Posidonia oceanica. The plant reproduces by floating seeds that are usually found stranded on the beaches. Samples of seeds were collected on the Tuscan and Ligurian beaches to show the possibility of genetic supply despite long distances. A small part of the seeds found stranded in Monterosso (East Liguria) was from offshore. The model suggests that possible sources are from the south.
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2005 LAPCOD Meeting, Lerici, Italy, June 13-17, 2005