Signals of resilience and change in tidepool fish communities on the Pacific coast of Vancouver Island, Canada

Abstract

Aim: Ocean warming and marine heatwaves have emerged as strong predictors of biodiversity change in coastal systems. Here, we test for systematic change in tidepool fish communities between recent and historical data sets, which include the North Pacific marine heatwave of 2014–2016. Location: Periodic sampling occurred since 1966 at study site isolated from human activities on the Pacific west coast of Vancouver Island, Canada. Methods: Repeated fish sampling at seven wave-exposed rocky shore tidepools was conducted on 8 (historical: 1966–1993) and 5 (recent: 2012–2016) occasions during low tide using methods that capture all individuals present (including cryptic and rare species). Species were subsequently identified using standard taxonomic approaches and abundances recorded. These data comprised the basis for analyses of both community-level and species-specific responses to test for differences in the historical and recent time periods. Results: We did not detect systematic increases or declines in species density, total abundance of fishes within tidepools and community similarity between historical and recent sampling events in high-intertidal pools. However, fish communities from low-shore pools decreased in the number of species present, overall abundance and community similarity. Those species lost from the lower pools were non-resident rare species typical of subtidal environments. By contrast, a warm-affinity crevice kelpfish was observed only recently. We also found that six species had higher or lower abundances between historical and recent sampling events, and one species occurred at higher vertical heights. Main conclusion: Fish communities in high-intertidal pools were resilient between historical and recent sampling periods, and lacked evidence of invasion. However, some signals of community and species changes were evident in the lower shore. Overall, these communities may reach a threshold with ongoing ocean warming and continued monitoring is required to reveal any major changes as they unfold.