Environmental stressors shaping rocky intertidal species distribution in Northern Norway

Marta Prieto del Campo¹, Markus Molis¹

¹Arctic University of Norway, Norway

Interspecific interactions significantly shape community structure, like predation by controlling prey abundance. However, environmental stress can influence the magnitude of predator control on prey in contrasting ways. The Environmental Stress Model (ESM) suggests that predation impact decreases with increasing physical stress, while the Menge-Olson Model predicts the opposite. Both models are not mutually exclusive, as predation impact depends on the relative effect of environmental stress on predator and prey. This study addresses how multiple stress gradients shape distributions of interacting species on rocky intertidal shores at high latitude.
In northern Norway, numerous creeks cross the intertidal, creating horizontal salinity gradients superimposed by a vertical tidal stress gradient. We assessed the distribution, shaped by both salinity and thermal stress, of blue mussels (Mytilus spec.), their main predator, dogwhelks (Nucella lapillus), and seaweed canopies (Ascophyllum nodosum) as a stress ameliorator in three large and two small creeks of Storfjorden. We observed at low intertidal of large creeks maximum blue mussel abundances in creeks, while dogwhelk abundance peaked next to creeks, and canopy cover continued to increase further away from the creeks. However, at low intertidal of small creeks, blue mussel abundance declined in creeks, whereas dogwhelk abundance peaked here. Species distribution also varied across tidal height, with canopies dominating at high intertidal. These results support the ESM, suggesting that increasing physical stress reduce predator abundance. Where dogwhelks and seaweeds tolerate physical stress, they may both regulate blue mussel abundance by predation and whiplash, respectively. Therefore, blue mussels dominate inside large creeks as a strategy to avoid disturbances. Upcoming experiments will examine the relative contributions of whiplash effects and predation in shaping these patterns across stress gradients.