Effect of UV-B irradiation on interspecific competition between Ulva pertusa and Grateloupia filicina

We report the effect of UV-B irradiation(9.6 kJ m-2day-1)on interspecific competition between two species of macroalgae,Ulva pertusa(U)and Grateloupia filicina(G),in co-culture.Growth of U.pertusa and G.filicina was inhibited by UV-B irradiation in mono-culture and specific growth rate (μ)declined as a result.Interspecific competition between U.pertusa and G.filicina was closely related to the initial weights when co-cultured.When initial ratios of U.pertusa(U)to G.filicina(G)were U:G=1.2:1 and 1:1,U.pertusa was the dominant algae.When the initial U:G ratio was 1:1.2,G.filicina was competitively dominant in the earlier stage,but U.pertusa grew faster,superseding G.filicina in the later stage.At initial ration U:G=1:1.4,G.filicina was predominant.Under UV-B irradiation,the competitive ability of G.filicina was weakened and the interspecific competitive balance favored U.pertusa,which suggests that G.filicina was more sensitive to UV-B irradiation.We also probed the potential allelopathic effects between the two species,which led to mutual growth inhibition.