Photosynthetic plasticity of an invasive variety of Caulerpa racemosa in a coastal Mediterranean area: light harvesting capacity and seasonal acclimation

At the beginning of the 1990s a new strain of Caulerpa racemosa began to spread rapidly throughout most of the Mediterranean Sea. Genetic investigations suggested this new variety could be a recent hybrid between the var. turbinata-uvifera, already present in the Mediterranean basin, and an unknown tropical strain. In summer, the season of maximal biomass development, C. racemosa frequently compete with seagrasses. Laboratory experiments based on the construction of P versus E curves and pigment analysis demonstrated the high capacity of this alga to reorgamse its photosynthetic apparatus in relation to the available light under the canopy of a Cymodocea nodosa meadow. Using the same methodological approach, we also investigated the adaptive capacity of the var. occidentalis to winter environmental conditions, certainly the most critical for a tropical seaweed. Although maintenance metabolism was also suggested by a remarkable biomass decrease, C. racemosa var. occidentalis showed acclimation capacities. The ability of the alga to adapt to different light environments may contribute to its colonisation success in Mediterranean coastal biotopes.