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

Abstract

Ecological stability is central to understanding how disturbances challenge the persistence of populations and communities through time, especially when key species are impacted. The bull kelp Durvillaea incurvata is a foundation, habitat-forming species that provides food and shelter for various species and supports the livelihoods of human communities along the Chilean coast. Harvesting of Durvillaea has raised concerns about the long-term viability of its populations, but the stability responses of Durvillaea to anthropogenic disturbances remain unclear. Here, we conducted a manipulative experiment in which we removed, once, all Durvillaea individuals from two sites in southern Chile to simulate the spatial scale of harvesting and to describe the population resilience and recovery following disturbance. In 1-m² plots interspersed in matrices of dense Durvillaea stands, we removed fronds and holdfasts, a practice not typically developed by gatherers, testing an alternative harvesting strategy. For 25 months, we quantified Durvillaea recruitment, holdfast densities, percent cover, frond length and density, biomass, and population size structure. All metrics completely recovered within 5-7 months across sites. The removal of Durvillaea did not have a significant impact on recruitment, which was constant during the experiment. The small spatial scale of the disturbances, the constant recruits supplied by the surrounding bull kelp matrix, and the removal of holdfasts that released settlement substratum allowed for the strong stability responses in these populations. Therefore, harvesting strategies that promote spatial heterogeneity, such as the removal of whole individuals at a small spatial scale, should be prioritized in management schemes of natural seaweed stands.