Brenton A. Twist1,2, Stefanie D. Zaklan Duff3, Christopher M. Pearce4, Patrick T Martone1,2
1 Department of Botany, University of British Columbia, Vancouver, BC, Canada
2 Hakai Institute, Hyacinthe Bay Road, Quadra Island, Vancouver, BC, Canada
3 Department of Fisheries and Aquaculture, Vancouver Island University, Nanaimo, BC, Canada
4 Fisheries and Oceans Canada, Pacific Biological Station, Nanaimo, BC, Canada
In recent years dramatic shifts from healthy kelp forests to urchin-dominated barrens have become prevalent, severely affecting ecosystems and local economies. While these two ecosystem states are known to differ in coralline community structure, there is a lack of understanding of coralline derived bottom-up controls in these systems. Previous research has demonstrated critical roles of coralline algae in nearshore ecosystems, inducing invertebrate larval settlement and influencing kelp spore settlement and germination, yet coralline algae are incredibly diverse and ecological differences among coralline species are poorly understood. We studied the settlement patterns of red urchins and several common kelp species from the Pacific Northwest on a range of molecularly-identified coralline algal species to better characterize these ecological interactions. Settlement rates of red urchins and juvenile canopy-forming kelp densities did not differ significantly across coralline algal species that were abundant in both kelp forest and urchin barren habitats. This suggests the generality of urchin and canopy-forming kelp recruitment and their ability to recruit into nearshore systems regardless of the coralline composition. However, differences were observed for a sub-canopy kelp species, where settlement was inhibited on crustose species but actively recruited to articulated coralline species, suggesting that articulated corallines typically absent in urchin barrens would need to recover before this sub-canopy species could return. These results contribute to our understanding of kelp forest community assembly and could have important implications for kelp forest recovery following changes in coralline community structure in urchin-dominated barrens.