Feeding preferences of Paracentrotus lividus exposed to native and non-native macroalgae

The effects of alien macroalgal invasions on ecosystem functioning may depend on the feedingchoice of native herbivores between native and non-native algae. The co-occurrence of twoinvasive Caulerpa species, C. taxifolia var. distichophylla and C. cylindracea in Southern Sicily,offered the possibility to investigate the feeding preferences of a generalist native grazer, thesea urchin Paracentrotus lividus, for native vs non-native food. A multiple choice feeding experimentwas set to assess whether and to which extent P. lividus consumes the exotic macroalgaewhile in presence of the preferred native ones. Multiple choice feeding assays were run withthe following food sources simultaneously offered to P. lividus: C. cylindracea, C. taxifolia vardistichophylla, a mix of C. cylindracea and C. taxifolia var distichophylla, Dictyopteris membranacea,Cystoseira spp. and a mix of D. membranacea and Cystoseira spp.. Paracentrotuslividus exhibited a stronger feeding preference for the mix of the two exotic macroalgae andfor C. cylindracea alone. On the other hand, C. taxifolia var distichophylla resulted barelyconsumed, although the amount ingested was greater when C. taxifolia var. distichophylla wasmixed with the congeneric alga. Our findings confirmed the strong palatability of C. cylindraceaand the potential role of P. lividus in controlling the spread of this exotic species. Given thelow consumption of C. taxifolia var. distichophylla recorded in this study, it is unlikely that P.lividus may contribute to limit the spread of the new exotic Caulerpa species.