Limited impacts of a marine invader on seagrass after five years.
Caulerpa taxifolia is a marine green macroalga that has invaded many countries and is endemic to tropical locations, including Queensland. Outbreaks of C. taxifolia were first discovered in NSW, Australia, in April 2000. It has now been recorded from 13 estuaries or coastal lakes, growing primarily in soft sediments near or amongst seagrasses. It has often been assumed that C. taxifolia has severe negative impacts on native seagrasses, but there is little published empirical evidence. Here I describe results of a manipulative experiment and two long-term observational studies which tested hypotheses about impacts of C. taxifolia on the areal coverage of two species of seagrass. Considerable temporal variability in the abundance of C. taxifolia has made interpretation of results difficult. But it appears that the algal invader is having little effect on the cover of dense seagrasses, while causing localised, short-term reductions in the cover of sparse Zostera capricorni. There is good evidence that seagrasses can regrow in areas that were or still are colonized by C. taxifolia.