On the occurrence, structure and distribution of deep-water Cystoseira (Phaeophyceae) populations in the Port-Cros National Park (north-western Mediterranean)

Three deep-water Mediterranean endemic species of Cystoseira spp. are found in the Port-Cros National Park (France, NW Mediterranean): C. zosteroides, C. spinosa var. compressa and C. funkii. They are abundant between 25 and 47m depth, but abundances are spatially heterogeneous, being greater on the seaward side of the park. Stands are usually dominated by one species and it is suggested that current regimes could be responsible for the observed partitioning patterns. Plant density varies depending on the species composition and location of the populations. Size structure patterns show a log-normal distribution indicating mature populations with low recruitment and/or high recruit mortality. The previously unnoticed existence of these deep-water, mature and vulnerable algal populations in one of the best studied Mediterranean areas, which was declared a National Park in 1963, indicates a need to increase basic research activities in coastal deep waters in order to increase our knowledge of Mediterranean biodiversity and underwater seascapes.