Variations in the structure, morphology and biomass of Caulerpa taxifolia in the Mediterranean Sea

Year-round morphological variations were investigated in Caulerpa taxifolia collected from the invaded regions of the northern Mediterranean Sea at different depths and from different types of substrates as well as from monthly samples in a dense unshaded meadow at a depth of 4 m at Cap Martin, Alpes-Maritimes, France. This tropical Ulvophyceae, recently 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 development. The length of the stolons varies from 150 to 352 m m(-2) over the year. The rhizoid pillars are regularly spaced, showing no seasonal variation, with one pillar along the stolen every 1.63+/-4.3 cm in average. The density of primary fronds varies from 5100 to 13 920 m(-2), with the maximum number of ramifications, 25 000 m(-2), occurring in spring. From late summer to autumn, primary fronds were without necrosis and with few ramifications. From winter to spring, however, these fronds often displayed numerous ramifications and their distal ends were usually broken or necrosed. These variations counterbalanced one another so that the vegetation cover at 9 m depth was always 100% with a relatively constant total biomass (average of 500 g dw m(-2)).