The role of vegetative fragmentation in dispersal of the invasive alga Caulerpa taxifolia in the Mediterranean

This study evaluated the importance of fragmentation in the recruitment of the fast-spreading, introduced green alga Caulerpa taxifolia at the margins of beds of the seagrass Posidonia oceanica. A multifactorial experiment wa s designed to test the hypotheses that there are seasonal differences in pa tterns of establishment of vegetative fragments, whether this process chang es with depth and whether these patterns were consistent at different spati al and temporal scales. Our experimental approach consisted of dispersing d rifting fragments of C. taxifolia along the margin of a bed of P. oceanica and recording the number of fragments established after 1 mo. The results s how that a surprisingly large number of fragments become established in thi s habitat and that numbers varied in space and time: the probability of est ablishment of fragments was greatest during summer especially at the shallo w sites, but smaller in spring and smallest in winter. Differences among ar eas were also found: a great variability in establishment of fragments depe nded on the site and time within season. Results indicate that dispersal by fragmentation can greatly contribute to a very wide spread of the alga in the Mediterranean. We predict that spread will be greatest during summer wh en a large proportion of fragments can re-attach to the substratum, even at shallow sites. Such information is important for the understanding of the ecology of this species and, with the help of hydrographic studies, in the prediction of its patterns of geographic dispersal.