Dispersal of Caulerpa racemosa Fragments in the Mediterranean: Lack of Detachment Time Effect on Establishment

Abstract

The importance of thallus fragmentation in the recruitment of the invasive, introduced alga Caulerpa racemosa (Forsskål) J. Agardh at the margins of Posidonia oceanica (L.) Delile beds was studied. A multifactorial experiment was designed to estimate the importance of detachment time on the seasonality of establishment of vegetative fragments and whether this pattern was consistent at different temporal and spatial scales. The approach consists of dispersing drifting fragments of Caulerpa racemosa, detached from substratum 0, 5 and 10 days before, along the margin of a bed of Posidonia oceanica and recording the number of fragments established after 1 month. The results showed that a large number of fragments became established in this habitat and that the greatest number of fragments were found during summer. Surprisingly, the time of detachment from substrate was not found to influence the probability of success in establishment. The results of this study indicated that dispersal by fragmentation is likely to contribute to the wide spread of this alga in the Mediterranean Sea. The spread of this alga via fragmentation is predicted to be the greatest during summer when the largest proportion of fragments are re-established. Geographical patterns of dispersal can thus be interpreted on the basis of this reproductive strategy, of hydrographic studies and experimental evaluation of resistance of fragments to desiccation and drift. The results obtained in this study, together with those obtained at another site using the same experimental approach for Caulerpa taxifolia (Vahl) C. Agardh, suggest that vegetative fragmentation plays a large role in the dispersal of rhizophytic introduced fast-spreading species in the Mediterranean Sea. This reproductive strategy would be in accordance with invasive and fast-spreading abilities exhibited by members of the Bryopsidales.