Abstract
Ice can be an important structuring factor physically removing intertidal flora and fauna. At high latitudes in particular, the removal of canopy-forming algae by ice scour may be important as their canopy may serve to modify the extreme environment for marine organisms at low tide. We simulated the effect of ice scouring by manipulating the biomass of the canopy-forming algae Ascophyllum nodosum in a sub-Arctic fjord (‘Full canopy’, ‘Reduced canopy’, ‘Bare (start)’, ‘Bare (annual)’). Over a three-year period, we quantified key physical parameters and the recolonization of flora and fauna to test the hypothesis that A. nodosum and rock rugosity facilitate recolonization of sub-Arctic intertidal fauna and that potential facilitation could rely on an ability of A. nodosum canopy to modify air temperature and ice scour. Finally, we estimated the recovery period of A. nodosum canopy height to pre-disturbance levels based on estimated early growth rates. We found that A. nodosum canopy facilitated higher species richness and recolonization of dominating faunal species (Littorina saxatilis, Littorina obtusata, Mytilus edulis and Semibalanus balanoides), and also significantly reduced the high temperatures in summer and raised the low temperatures in winter. The abundance of M. edulis and A. nodosum recolonization increased significantly with rock rugosity and the recovery of A. nodosum canopy height was estimated to a minimum of 15 years. We conclude that algal canopy and rock rugosity play key roles in structuring sub-Arctic intertidal communities, likely by modifying environmental stress such as extreme temperature, desiccation, and by increasing the settling surface and the habitat complexity. As the distribution of canopy-forming algae is expected to shift northward, they may act as a key habitat facilitating a northward colonization of intertidal fauna in the Arctic. We highlight the importance of considering scales relevant to biological communities when predicting impacts of climate change on distributional patterns and community structure in the Arctic intertidal.
Highlights
In intertidal ecosystems, air temperature, exerting a major control on biological processes, can be modified by a number of factors acting at scales that are relevant to biological communities (Helmuth, 1998; Helmuth et al, 2010)
With a multiple linear regression, we show that both canopy biomass and rock rugosity influenced the total M. edulis density positively [MLR, R2 = 0.726, F(2, 12) = 19.53, p < 0.001]
These findings support the hypothesis that algal canopy has an overall facilitating effect on faunal recolonization in a sub-Arctic intertidal. This is opposed to findings from a temperate intertidal, where an overall neutral response in barnacle recruitment to A. nodosum canopy cover was observed at both mid- and high intertidal levels (Beermann et al, 2013)
Summary
Air temperature, exerting a major control on biological processes, can be modified by a number of factors acting at scales that are relevant to biological communities (Helmuth, 1998; Helmuth et al, 2010). Several studies have shown the impact of canopy-forming algae on the understory community and patterns of recolonization as they alter the physical environment (Dayton, 1971; Hawkins, 1983; Jenkins et al, 1999a, 2004; Cervin et al, 2004). These studies are mostly restricted to the temperate intertidal as we found only one example from the sub-Arctic intertidal, mainly focusing on biotic factors (Ingólfsson and Hawkins, 2008)
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