We tested the assumption that fouling pressure by the blue mussel Mytilus edulis on a small spatial scale - especially onto a given substratum type - is homogeneous. Artificial substrata were exposed to natural recruitment within and outside different microhabitats. These microhabitats were monospecific patches (diameter in the meter range) in a mixed subtidal community composed of the brown algae Laminaria saccharina, and Chorda tomentosa, the green filamentous alga Cladophora rupestris, and the blue mussel Mytilus edulis. While mussel spat settled in all microhabitats, recruitment was far from homogeneous. Within microhabitats, artificial substrata were preferred over living surfaces. Recruitment also differed between microhabitats exhibiting identical preference gradients on living surfaces and associated artificial substrata: recruitment preference for microhabitats increased in the order Laminaria saccharina < control area (stone or mud) < Chorda tomentosa < Cladophora rupestris < Mytilus edulis. In a second experimental approach on a smaller spatial scale (cm range), we assessed mussel recruitment in the vicinity of identical aliquots of some of the microhabitat-constituting species. Again, Laminaria proved to be of least, Cladophora of highest attractiveness. We conclude that primary settlement of mussel spat is not only influenced by the structure of the substratum (e.g. filamentous forms) but additionally by nearby macroorganisms - presumably by exuded chemical cues as suggested by the second experiment.
ASJC Scopus subject areas