Fica Rojas, E. | Search bioRxiv

bioRxiv2025

Understory low compositional stability enhances functional stability in response to bull kelp removal in southern Chile

Background and Aims.Ecological stability is central to understand the ability of natural systems to respond to disturbances, especially when these occur directly over important species within communities, such as foundational species. The bull kelp Durvillaea incurvata is common in intertidal and shallow subtidal rocky shores, supporting a diverse understory. The direct harvesting of Durvillaea constitute a common practice along the Chilean coast able to disrupts the abundances of the understory community and as well aggregated properties such as overall community biomass. Thus, we investigated the resistance, resilience, and recovery of the understory community of Durvillaea subjected to an experimental kelp removal in two sites from the temperate Chilean coast. Methods.We simulated a pulse removal of Durvillaea cause by direct harvesting, by removing once all the individuals within experimental plots and then we monitored the composition and biomass of the sessile and mobile understory community for 25 months. Key Results.After the disturbance we observed a rapid recovery of Durvillaea cover and varying stability responses of the understory community. Community composition showed a low resistance to the disturbance but returned rapidly within 5 - 7 months to pre disturbance levels (high resilience), however showed an incomplete recovery compared to controls. While community biomass displayed high resistance to the disturbance and then remained constant across time (resilience = 0), showing a complete recovery compared to control communities. Conclusions.Differing from Durvillaea dominated communities from other regions, our analyzed communities showed rapid recovery dynamics in compositional and functional aspects, resulting highly resilient to the type of disturbance applied. In addition, since varying stability responses reported, we encourage the use of multiple dimensions of stability to exhaustively characterize the responses of Durvillaea dominated communities and other kelps, when exposed to disturbances.

ecology↗

bioRxiv2023

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

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.

ecology↗