Selective consumption and facilitation by mesograzers in adult and colonizing macroalgal assemblages |
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Authors: | Samuli Korpinen Veijo Jormalainen Joona Ikonen |
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Institution: | (1) Section of Ecology, Department of Biology, University of Turku, 20014 Turku, Finland;(2) The School of Biological Sciences, University of Portsmouth, Portsmouth, UK |
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Abstract: | Grazing pressure on macroalgae in littoral communities may vary with algal species, the age of an algal individual and grazer
identity. Previous studies on alga–grazer interactions have shown that grazer preference for an algal species may release
another one from interspecific competition. We measured the impacts of four common grazer taxa and the natural grazer guild
on macroalgal communities at both their colonization and adult stages, and compared the impacts to grazer exclosures. The
grazer effects were stronger on colonizing than on adult macroalgae; grazers did not reduce the total density of adult algae.
Grazers both feed on propagules and indirectly facilitate other algae, depending on the grazer or algal species. Hydrobia species increased the settlement of spores of the red alga Ceramium tenuicorne. Similarly, the gastropod Theodoxus fluviatilis tended to facilitate one crustose algal species, but decreased the propagule density of annual filamentous algae, suggesting
a preference for one species to the advantage of another. Effects of crustacean mesograzers on the studied macroalgae were
weak. These results indicate that northern Baltic macroalgae are limited to grazing mainly during their colonization stage. |
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