Rapid population recovery of a foundation species from experimental small-scale harvesting

Abstract

Ecological stability is central to understand how disturbances challenge the persistence of populations and communities through time, particularly when species with strong effects on other species are disturbed. The bull kelp Durvillaea incurvata is a foundation habitat forming species that provides habitat, food, and shelter for various species, and supports the livelihoods of human communities along the southeast Pacific coast of Chile. Harvesting of D. incurvata has raised concerns about the long-term viability of its populations, but the stability responses of bull kelps to anthropogenic disturbances are still unclear. Here, we conducted a manipulative field experiment in which we removed once all individuals of the bull kelp from two sites in southern Chile. We simulated the loss of bull kelps to harvesting in 1-m2-plots interspersed in matrices of dense D. incurvata stands. Fronds cannot regrow from the holdfasts after harvesting. Holdfasts were therefore also removed, a practice not typically carried out by local gatherers. For 25 months we quantified bull kelp recruitment, holdfast densities, percent cover, mean frond size and density, biomass, and population size structure in two rocky intertidal sites. In both sites, all metrics completely recovered within five to seven months. The removal of D. incurvata did not have a significant impact on recruitment, which was constant during the experiment. The relatively small spatial scale of the disturbances, constant recruitment provided by the surrounding bull kelp matrix, and the removal of holdfasts that released settlement substratum may have allowed for the strong stability responses in these populations. Therefore, spatial heterogeneity, which allows for settles to colonize the disturbed plots, should be prioritized in management strategies of natural seaweeds stands.