Is the vegetative development of the invasive chlorophycean, Caulerpa taxifolia, favored in sediments with a high content of organic matter?

We performed an in situ experiment raising the concentration of organic matter in sediment relative to the natural concentration, and quantified biomass development of the invasive alga, Caulerpa taxifolia, and native C. prolifera. Our objective was to determine whether vegetative development of C. taxifolia is favored in sediments with a high content of organic matter. The number of stolon apices and fronds, and the total dry weight of C. taxifolia at the end of the experiment increased relative to initial values in the ‘‘natural’’ sediment, while those in the ‘‘organic matter-enriched’’ sediment did not change. As a result, the vegetative development of C. taxifolia in the ‘‘organic matter-enriched’’ sediment was marginally lower than that in the sediment with natural concentration of organic matter. The contention that the vegetative development of the invasive C. taxifolia is favored in sediments with a high content of organic matter is not sustained. Additionally, we wanted to evaluate whether the presence of an external source of dissolved organic carbon (DOC) would facilitate the survival of Caulerpa taxifolia and C. prolifera under conditions unfavorable for biomass development. To this end we performed two laboratory experiments (one under light-saturated and another under light-limited conditions) where we maintained fragments of C. taxifolia and C. prolifera in the presence of different low molecular weight DOC compounds and assessed the survival of the two species. Mortality of Caulerpa fragments occurred under light-limited conditions only and showed no relationship to the presence of any of the low molecular weight DOC compounds tested. Our results, therefore, do not provide support for the contention that the presence of low molecular weight DOC compounds could contribute to alleviating negative effects associated with light-limited conditions.