Effects of competition between two introducedCaulerpa

Competitive interactions between 2 introduced algae,Caulerpa taxifoliaandC. racemosa, were studied in 2 experiments. The first separately evaluated the interspecific and intraspecific effects on both species by manipulating their abundance. The second investigated the fate of fragments ofC. taxifoliatransplanted into patches ofC. racemosa, in contrast to those established on algal turfs.C. racemosaandC. taxifoliahad similar temporal trends in growth but reached different sizes. The overall increase in stolon length at higher densities for both species suggested that positive interactions are very important. However, there was a significant interspecific effect onC. taxifoliastolon length but no effect onC. racemosa. Furthermore,C. taxifoliafragments transplanted intoC. racemosapatches showed clear signs of stress with respect to those transplanted into algal turfs: blades became blanched and eroded. Overall, the results of this study suggest that growth increases with density augmentation, therefore suggesting that invasive characteristics of the species may increase with the time of colonisation. Both species tend to spread faster at higher density. Overall, where both species co-occur, we predict thatC. racemosawould be the favoured species as regards the outcome of competition.