Assessment of the ecological status of the Gongolaria abies-marina forests (Sargassaceae, Phaeophyceae) in the Canary Islands, Northeast Atlantic ocean

Gongolaria abies-marina is a threatened habitat-forming species. It was once widespread across the shallow subtidal zones of the Canary Islands, but most of these forests have now disappeared. In this study, we present the first assessment of the status of G. abies-marina forests at multiple spatial scales. We evaluated canopy cover and thallus length, along with key forest traits such as community structure, and community descriptors (richness and Shannon‒Wiener diversity). Additionally, we examined the relationships of these ecological descriptors within a range of environmental and anthropogenic variables. The results revealed marked spatial variability in the condition of G. abies-marina forests. In the southern parts of the islands, only small patches or isolated individuals were observed, characterized by low G. abies-marina cover and limited thallus development. In contrast, better forest conditions were recorded along the northern coasts, where populations were larger and, in some sites, formed continuous belts. Both cover and thallus length were higher in these sites and were positively linked to the forest size. Among the environmental variables, wave exposure and cloud cover showed the strongest relationship with G . abies-marina cover and thallus length. No clear relationships were found between the abundance of G. abies-marina and human impacts; however, associations with certain community species were detected. • Cover and thallus length of Gongolaria abies-marina are indicators of the forests condition. • Currently most algae communities in these forests are primarily formed by caespitose algae. • Wave action influences positively the forest condition. • Only in a few places is it possible to find forests in good condition