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

Abstract

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.

Keywords:

• Cystoseira
• deep-water algae
• Mediterranean
• population structure
• biodiversity
• conservation

Acknowledgements

Financial support was provided by the Port-Cros National Park. We would like to thank H. Bergère, Chief de Secteur of the Port-Cros National Park, and the rangers who gave us free access to the reserve and provided all the technical, scientific and human support we requested. Special thanks also to all colleagues who assisted us in the field: J.M. Cottalorda, M.L. Susini, C. Linares, D. Diaz, and M. Zabala. We are very grateful to T. Belsher (IFREMER) for giving us access to the recent cartography of Port-Cros National Park, which allowed us to locate precisely the study sites. We are also grateful to M. Foster, A. Szoboszlai, A. Buschmann and M. Graham for their valuable comments and critical evaluation of previous versions of the manuscript. The manuscript has also benefited from a careful review by M. Verlaque and an anonymous referee. We also thank the support and help of A. Meinesz and all the researchers and technical staff of the Laboratoire Marin Littoral of the Université de Nice-Sophia Antipolis.