Sustainable management of economically valuable seaweed stocks at the limits of their range of distribution: Ascophyllum nodosum (Phaeophyceae) and its southernmost population in Europe

Abstract

Seaweeds such as Ascophyllum nodosum are essential components of coastal ecosystems, being frequently relevant both ecologically and economically. The current increasing demand for seaweed biomass must be compatible with sustainable management practices of these resources. This study aims to provide supporting evidence for the establishment of management plans for “edge populations” (at their distributional limits) with commercial interest using, as a model, the southernmost population of A. nodosum in Europe (which occurs on the northern coast of Portugal). In this study, standing stock, biomass renewal and seasonal and spatial patterns of occurrence of this Ascophyllum unexploited population were assessed in order to evaluate harvesting potential. A total of 16 patchily distributed and variable sized beds, covering an area of 112,126 m2, were delimited during late summer/autumn of 2016, providing a standing stock of 30,952.12 kgdw. The abundance of these populations was stable over time (2005–2010), although small-scale spatial variations and changes in individual biomass due to seasonal loss could be identified. However, the potential biomass renewal as estimated for this whole population was 290.3 kgdw year−1, representing only 0.94% of the calculated standing stock. Based on these results, the importance of considering the population’s renewal potential is highlighted in addition to individual phenotypic traits when managing harvesting. Specifically, given the vulnerability and ecological relevance of the studied population, the recommendation herein is to avoid harvesting of this species at its southernmost location in Europe.