Population persistence of the perennial kelp Eisenia arborea varies across local spatial scales

Abstract

Perennial stipitate kelps are globally distributed and individual species can inhabit broad latitudinal ranges, expressingnotably longevous persistence. Despite the foundational role kelps provide to their communities, little is knownabout the variability in persistence of the stipitate kelps at local spatial scales. We studied the population persistence ofEisenia arborea, a heat- and wave force-tolerant perennial stipitate kelp with a distributional range extending from BritishColumbia to south of the range limit of all other northeast Pacific kelps, in Baja California Sur, Mexico. Persistencecharacteristics for E. arborea among sites were compared and used to test the hypothesis that stand persistence varied atlocal spatial scales around Isla Natividad, a Pacific island off the Baja California peninsula with documented spatiotemporalenvironmental heterogeneity. Collected individuals around the island were “aged” using the previously validatedage estimation technique of counting annual cortical dark rings. After detecting no significant differences among sitesin the covariation between estimated ages for collected individuals and stipe length, we utilized in-situ population-levelstipe length measurements to more rapidly predict age structures within six stands around the island. Predicted agestructures, and associated stand densities, revealed persistence characteristics and density varied at local scales and astrong positive relationship existed between stand density and stand mean and maximum ages. We speculate that standsresponded differently to deterministic influences (e.g., the 2014–2016 marine heatwave and / or competition with Macrocystis)resulting in heterogenous local persistence of this foundation species.