Integrative management of sea urchin fisheries: the safe-operating zone between sustainable fishing and marine forests conservation

Simone Farina¹, Romagnoni Giovanni², Boada Jordi³, Tamburello Laura¹, Marzloff Martin⁴, Vargiu Riccardo¹, Di Franco Antonio¹, Calò Antonio¹, Minguito-Frutos Mario⁴, Sinerchia Matteo⁵, Ceccherelli Giulia⁶, Guala Ivan⁷, Hereu Bernat⁸, Alcoverro Teresa³

¹Stazione Zoologica Anton Dohrn (SZN), Italy - ²Christian Albrechts-Universitaet zu Kiel (CAU), Germany - ³Centre D’Estudis Avançats de Blanes (CEAB-CSIC), Spain - ⁴Institut Francais de Recherche pour l’Exploitation de la Mer (IFREMER), France - ⁵Consiglio Nazionale delle Ricerche (CNR), Italy - ⁶University of Sassari (UNISS), Italy - ⁷International Marine Centre (IMC Foundation), Italy - ⁸University of Barcelona (UB), Spain

Sea urchins can drive macroalgal forests regime shifts towards unproductive bare rock states when populations are released from predatory control. Some fishing communities harvest sea urchins intensely, locally depleting sea urchin populations and ultimately allowing erect macroalgae to recover, provided that environmental conditions are suitable and the community structure (i.e. grazers, competitors, and predators of both) does not prevent the recovery. The collapse of marcoalgal forests and the depletion of sea urchin populations due to overfishing are thus two extremes of the same continuum. To avoid these extremes, that is, to conserve marine forests while maintaining the population viable, sea urchin populations should be kept within two thresholds, i.e., avoiding too high or too low abundance. However, quantification of these thresholds is rare, highly case-specific, and seldom applied to manage the ecosystem in a holistic manner. In addition, the socioeconomic context may influence harvesting of sea urchins. The threshold of economic sustainability may be influenced not only by direct costs and profits associated with sea urchins, but also by the availability of alternative species for fishers, trophic interactions, market dynamics, and cultural perspectives. Here, we propose a conceptual framework to identify the safe operating space between sustainable fisheries and marine forest conservation. Our framework consists of a three-threshold approach to manage sea urchin dynamics including an upper and a lower density threshold, alongside an economic threshold. These thresholds are identified using locally relevant metrics and indicators that consider environmental conditions, predator and competitor effects, and socioeconomic factors. Identifying these thresholds and systematizing the proposed framework is essential to achieve a holistic management that prevents abrupt changes and fluctuations between extremes caused by natural and/or anthropogenic factors which may lead to irreversible regime shifts. Our proposed approach aligns with the principles of ecosystem approach to fisheries and adaptive management, making it highly relevant and applicable across coastal systems worldwide.