The role of the blue mussel (Mytilus sp.) as a habitat-forming species on subtidal hard and soft substrates in the Baltic Sea

• The role of habitat-modifying species may differ between different environmental settings. Therefore, we compared the effects of aggregating suspension-feeding blue mussels Mytilus sp. on associated species on subtidal hard and soft substrates. We used random quantitative samples collected from hard and soft substrates to assess species richness, composition and community structure of the Mytilus-red algal habitat in the northern Baltic proper. On soft substrate, we found a positive relationship between the biomass of Mytilus sp. and the red alga Furcellaria lumbricalis, while Phyllophora spp. was associated to Mytilus on both substrate types. On soft substrate, Mytilus sp. facilitated F. lumbricalis and other algal species by providing secondary substrate for attachment, e.g. shell and entangling byssus treads. This close Mytilus-red algal association had the same species richness on both hard and soft substrates. However, community structure differed between substrate types, especially when comparing the animal community. Multivariate analyses showed that on hard substrate, F. lumbricalis determined community structure, both individually and even more so in combination with Mytilus sp. In contrast, on soft substrate, Mytilus sp. was found to structure the plant, but not animal, community. Species interactions were found to differ between substrate types. A positive relationship was found between Mytilus sp. and Macoma balthica on hard substrate, while not on soft substrate. In general, the facilitating effects of Mytilus sp. on associated species were stronger on soft compared to hard substrates.

Nyckelord

ecosystem engineering

facilitation

Mytilus sp.

red algae

species interactions

biodiversity

species richness

community structure

Marine Ecology

marin ekologi

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vet (ämneskategori)

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