Comparative study of the growth of the two co-occurring introduced green algae Caulerpa taxifolia and Caulerpa racemosa along the Tuscan coast (Italy,western Mediterranean)

Caulerpa taxifolia and C. racemosa are tropical green algae now found in the Mediterranean, where the former was accidentally introduced and the latter presumably also introduced; both species have spread rapidly and invaded a variety of habitats. Since 1996, the two algae have co-inhabited a region along the Tuscan coast near Livorno. The present study has been carried out to evaluate the invasive capacity of the two species. After one year, the increase in surface area was 67.5 % for C. taxifolia and 284.8 % for C. racemosa, while the increase in patch number was 11.4 % and 121.4 % respectively. The stolon growth of the two algae followed a similar trend, as is showing the same temporal variations with the maximum growth rate between August and October. At the end of the study period, the increase in stolon length and number was significantly higher in C. racemosa than in C. taxifolia. The results of the present study show a higher invasive potential in C. racemosa than in C. taxifolia, although further studies are necessary to evaluate the competition between the two algae and the effect of their simultaneous presence on the benthic community.