Local environmental conditions predict spatial transitions in seaweed community composition in a rocky intertidal ecosystem
Date
2022
Authors
Spriel, Brittnie
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Abstract
Kelp forests are considered the most vulnerable temperate marine ecosystems to climate change, and recent marine heatwaves have caused considerable kelp losses. Globally, heat stress has induced phase shifts from kelp to more heat-tolerant turf algae ecosystems with less structural complexity, resulting in a loss of food, habitat, and productivity. Currently, the relationships between temperature and intertidal kelp and turf species in the Northeast Pacific is not thoroughly understood, as majority of research has focused on subtidal kelp abundances over temporal scales. Here, I investigated how a spatial temperature gradient of ~6 oC, combined with local variation in wave energy at sites within Barkley Sound, Vancouver Island, B.C., influences the abundance of kelp and turf algal species in the rocky intertidal. High kelp cover was primarily observed at sites with the lowest water temperatures, and at sites with high wave energy relative to other sites with similar local temperatures but low wave energy. Accordingly, I found that the percent of kelp cover, as well as kelp diversity (measured as species richness, Simpson diversity, and Shannon diversity) were all significantly negatively influenced by temperature, and positively influenced by wave energy. No kelp species were found at sites above 15.8°C, and Egregia menziesii was the only species to be found across all sites that contained kelp. These results indicate that kelp is negatively influenced by increasing temperatures, and that high wave energy may act to ameliorate heat stress. In contrast, turf cover was significantly negatively correlated with kelp cover, such that turf cover was significantly greater at sites with higher temperature and lower wave energy. The results indicate that on a spatial scale, an increase in temperature, combined with variation in wave energy, significantly drives the absence of kelp species, and further the dominance of less structurally complex turf algae. These significant effects of local environmental variation could have implications for how climate change may be negatively influencing the structural complexity of seaweed communities in the rocky intertidal.