[Effects of macroalgae on growth of 2 species of bloom microalgae and interactions between these microalgae in...

We studied the effects of fresh tissue and culture medium filtrate of Ulva pertusa (Chlorophyta) and Gracilaria lemaneiformis (Rhodophyta) on growth of 2 causative bloom species: Prorocentrum donghaiense and Alexandum tamarense, in laboratory conditions. Both U. pertusa and G. lemaneiformis, especially their fresh tissues, significantly interfered with the growth of the co-cultured microalgae. P. donghaiense could be completely killed in the bialgal culture, but growth of A. tamarense in it was little affected. Simultaneous assay on the effects of culture medium filtrates showed that the culture filtrate of A. tamarense had algicidal effect on P. donghaiense, while that of P. donghaiense had little effect on growth of A. tamarense. We simulated the interactions between P. donghaiense and A. tamarense in the bialgal culture by using a mathematical model. Results show that the effect of P. donghaiense inhibited by A. tamarense is about 17 times larger than the inhibitory effect of P. donghaiense exerted on A. tamarense. The joint effects of multialgal cultures on microalga were analyzed. Results present that the multialgal cultures of either U. pertusa or G. lemaneiformis on P. donghaiense are synergism, and the joint effect of U. pertusa and P. donghaiense on A. tamarense is additional. However, it was difficult to determine the joint effects of G. lemaneiformis and P. donghaiense on A. tamarense. Results suggest that allelopathy is the most likely reason responsible for the results obtained in this paper.