Abstract
Facilitation by foundation species commonly structures terrestrial and marine communities. Intraspecific variation in individual properties of these strong facilitators can affect the whole suite of the dependent taxa. Marine macroalgae often act as ecosystem engineers, providing shelter and substrate for numerous associated organisms. Epibiosis of foliose red algae, however, remains underexplored, especially in the high latitudes. Here we studied sessile macrobenthic assemblages associated with a foliose red algae Phycodrys rubens in the White Sea (66° N) shallow subtidal, and the effect of individual plant properties on their structure. The blades of P. rubens develop annually, and it is possible to tell the young (usually larger) plant parts from the old ones. We hypothesized that epibenthic community structure depends on plant part age and size. We examined epibiosis on 110 plants at two sites, and the results generally supported our hypotheses. Old plant parts were several times smaller, and had higher total cover than young parts. Sponges strongly dominated the epibiosis on old parts, and young parts were dominated by polychaetes and bryozoans. Plant part surface area negatively correlated with total cover on young parts, while on old parts the relatioship was location-specific. On young parts the relative abundance of a polychaete Circeis armoricana increased with surface area, and the proportion of sponges decreased. The patterns indicate that epibenthic community structure is linked to the demography of an ecosystem engineer.
Highlights
Interspecific biotic interactions are powerful drivers of community structure
To assess the effects of location and individual size variation in the ecosystem engineer on the suite of dependent species, we examined the effects of site, P. rubens surface area and their interaction on total percent cover separately for young and old parts of P. rubens collected in September 2015 with beta-regression
In September 2015, 57% of individual plants had only a young part and no old part compared to 17% in July
Summary
Interspecific biotic interactions are powerful drivers of community structure. Though ecological research has long revolved around competition or predation, in recent decades the interest in positive interactions revealed the crucial role of facilitation [1,2]. Space is one of the most limiting resources in marine benthic communities [4]. Marine macrophytes act as secondary substrate and provide complex habitat architecture, functioning as ecosystem engineers [5]. By hosting numerous epibenthic taxa, they increase abundances and diversity in marine ecosystems (reviewed in reference [6]). Spatial structure and functioning of the epibenthic assemblages associated with brown and green algae have been extensively explored (reviewed in reference [7]), macrobenthic epibiosis of red algae has been largely overlooked. The research has been focused on bacterial colonisation and algal anti-fouling activity (e.g., references [8,9,10])
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