Diversity of intertidal macroalgae as spatial insurance in the marine intertidalResistance, Resilience and Phase Shifts

Lars Gamfeldt^{1, 2}, Benedikt Schrofner-Brunner¹

¹University of Gothenburg, Sweden - ²Gothenburg Global Biodiversity Centre, Sweden

Biodiversity is changing rapidly over multiple spatial scales. However, our knowledge about the functional consequences of biodiversity change comes mainly from studies focused on small scales. We know less about the role of biodiversity at larger scales, which encompass higher environmental heterogeneity. According to spatial insurance theory, biodiversity is important for sustaining high ecosystem functioning in a heterogeneous landscape if species are favoured under different environmental conditions under which they are also most productive. I will present current work that our research group is doing to test this theory, using marine rocky shores as our model system. On the Swedish west coast, different intertidal fucoid seaweed species occupy relatively distinct depth zones. This suggests that a diversity of macroalgal species is required for providing habitat and sustaining ecosystem functioning across multiple depth zones in the intertidal landscape. However, it is not known if the decline in the abundance of one algal species in one zone can be compensated by increases in other seaweeds that naturally dominate in different zones. A previous study in our study region using adult intertidal seaweed plants suggests that some fucoid species may indeed be able to expand their vertical distributions and compensate for the decline in other species. However, it is very plausible that abiotic stressors, and predatory interactions, are acting mainly on newly settled algae. To determine the role of seaweed diversity in sustaining productive beds of seaweed across the full intertidal vertical gradient, we have initiated a multi-year field experiment. Across multiple shores, we exclude each of four key species of brown macroalgae, and combinations of the same species, and monitor their biomass over time. I will present preliminary results from this experiment.