On the Stability of Kelp and Canopy-forming Algae: A Stability Framework for Canopy-forming Algae, A Review of Research and a Case study on Post-harvest Recovery Absence of Lessonia trabeculata

Jasper Van Vlasselaer

Abstract Chapter One: A Stability Framework for Canopy-forming Algae, A Review of Research

Scientists use the same terminology in order to compare, recreate, and proceed on findings of others. For ecologists, this often entails describing stability in time or space of a population, species, or community. However, the terminology used in the field of canopy-forming algae is fluid and inconsistent. Here, a revivification of the Stability framework developed by Grimm & Wissel in 1997 was integrated with a review on the research on stability of canopy-forming algae and the effect of drivers thereon. All publications were linked together on the basis of three main aspects of stability: resistance, recovery, and resilience. To do so, search queries were performed on “kelp” with the drivers: “climate change”, “herbivory”, and “harvesting”. This resulted in 146 online publications, of which the review on research was performed, as well as categorizing the research itself into the aspects of stability. Disregarding the original terminology used, all publications investigated the effect of one or more drivers, on one or multiple aspects of stability. This review illuminated some geographical gaps where little research on stability is performed. It also showed that most of the currently used terminology regarding stability can be reduced to the three terms proposed by the Stability framework.

Abstract Chapter Two: A Case study on Post-harvest Recovery Absence of Lessonia trabeculata

Kelp forests are highly biodiverse temperate reefs with important economic value. However, due to a variety of negative drivers including climate change, harvesting, and overgrazing, kelp forests worldwide are declining. At Quintay, Central Chile, a harvesting experiment was performed on the kelp Lessonia trabeculata in 2016. Barrens where created to visualize the resilience and subsequent recovery of L. trabeculata. Four years later, the barrens did not show signs of recovery. This study investigates the absence of recovery of L. trabeculata at Quintay. Four important kelp forest characteristics: fecundity, growth, recruitment, and herbivory, were compared between two non-harvested and two harvested patches. By SCUBA diving, data on growth, recruitment and invertebrate herbivory were gathered. Additionally, stipes and blades were taken to analyze adult sporophyte growth and fecundity. Growth and fecundity were not impaired. No recruits were found in the non-harvested patches, and although some small areas with recruits were found in the harvested patches, most was barren seabed. Invertebrate density was greatly increased in the harvested patches compared to the non-harvested patches and pre-harvest conditions of the 2016 experiment. These results indicate that sea urchin and gastropod herbivory stabilizes the barrens and inhibit recovery by grazing on recruits.