Balance between biological and physical components in the impact of Mytilus edulis on associated organisms

Abstract

An ecosystem engineer’s influence on associated organisms includes 2 components: physical and biological. The physical component is the spatial environment created by the ecosystem engineer, while the biological component is the physiological activity of the engineering species. However, little is known about the ratio between these components. We evaluated this ratio for Mytilus edulis L. by means of a field experiment in which communities of organisms that developed on bare ceramic plates (controls, C) were compared with those that formed on plates carrying patches of live mussels (L) or artificial patches made of mussel dummies (D). The experiment was performed using 2 different age-size groups of mussels and dummies (small-young and large-old). Live mussels had only a weak positive effect on species richness of the associated organisms, but the structure of the communities that formed on tests plates (L, D and C) differed significantly. The similarity of the communities of associated organisms between C and L was 1.5-3 times less than between C and D. Mussel size-age factor had no significant effect on community structure other than on the algal assemblage. The results of this experiment suggest that the influence of mussels on associated organisms cannot be reduced to only the effect of increasing complexity of the spatial environment. The influence of the biological component is significant and can exceed that of the physical component. Thus, in ecosystem engineering, non-living spatial structures cannot serve as an identical substitute for a population of living organisms.

Mussels and canopy-forming algae as ecosystem engineers: their contribution to community organization in the rocky sublittoral

“…Defining the composition of communities and disentangling the processes that shape their diversity in biologically generated habitats are crucial for ecology and conservation. Still, much uncertainty exists about how the population-level traits of habitat forming species contribute to species diversity and ecosystem processes (Gribben et al, 2017), and how cooccurring habitat-formers together affect the species pool (Yakovis et al, 2008;Bishop et al, 2013;Passarelli et al, 2014;Khalaman et al, 2021;Yakovis and Artemieva, 2021). Multiple habitat providers -that may differ in structure, function, and density -organize most ecosystems across the globe (Bruno and Bertness, 2001).…”

“…Alternatively, studies have contrasted the community in the biogenic habitat with either bare surfaces or annual ephemeral structures (Kraufvelin and Salovius, 2004;Wikström and Kautsky, 2007) or sampled communities at different depths (Westerbom et al, 2019a) complicating comparisons as depth per se has a strong influence on species composition. Therefore, there is currently little comparative data on how different engineering species under similar conditions affect the composition and structure of the associated community (see also Khalaman et al, 2021) and how they together enlarge space occupation for that community.…”

“…Additionally, (3) expanding the work to other benthic habitats would involve a set of uncontrollable variables (e.g. substratum, depth, predator pressure, wave exposure, temperature) that would make comparisons challenging (Khalaman et al, 2021). Understanding the structure and functioning of biologically generated habitats as biodiversity upholding structures is particularly important as they are increasingly being impacted by large-scale changes, prompted by natural and anthropogenic drivers.…”