VARIATIONS IN THE STRUCTURE, MORPHOLOGY AND BIOMASS OF CAULERPA TAXIFOLIA IN THE MEDITERRANEAN-SEA

Year-round morphological variations were investigated in Caulerpa taxi folia collected from the invaded regions of the northern Mediterranean Sea at different depths and from different types of substrates as wel l as from monthly samples in a dense unshaded meadow at a depth of 4 m at Cap Martin, Alpes-Maritimes, France. This tropical Ulvophyceae, re cently introduced into the Mediterranean, shows pseudoperennial growth ; although no single part of the thallus persists for more than a year , the individual persists by means of indefinite vegetative developmen t. The length of the stolons varies from 150 to 352 m m(-2) over the y ear. The rhizoid pillars are regularly spaced, showing no seasonal var iation, with one pillar along the stolen every 1.63+/-4.3 cm in averag e. The density of primary fronds varies from 5100 to 13 920 m(-2), wit h the maximum number of ramifications, 25 000 m(-2), occurring in spri ng. From late summer to autumn, primary fronds were without necrosis a nd with few ramifications. From winter to spring, however, these frond s often displayed numerous ramifications and their distal ends were us ually broken or necrosed. These variations counterbalanced one another so that the vegetation cover at 9 m depth was always 100% with a rela tively constant total biomass (average of 500 g dw m(-2)).