Marine foundation species support to biodiversity: a systematic review and guidance for new standards

Thomas Benoit¹, Aurélien Boyé¹, Bastien Mourguiart¹, Mathieu Chevalier¹, Cédric Bacher¹, Victor L. Jardim², Anaëlle Bizien¹, Martin P. Marzloff¹

¹Ifremer, France - ²LEMAR, France

Marine foundation species, through their structure and biological activity, can shape environmental gradients and create unique species-rich ecosystems. However, the function and integrity of these ecosystems are highly threatened by global changes that can alter the physical structure of foundation species and ultimately lead to their decline. Thus, it is crucial to understand how individual foundation species uniquely contribute to seascape features and support biodiversity. To address this, we conducted a systematic review of 296 articles examining how foundation species affect biodiversity, either by reporting relative comparisons of biodiversity metrics associated with foundation species or assessing their relationship with foundation species traits (measured at the individual or habitat scale). Our study shows that presence and extent of foundation species generally facilitate community diversity, although these relationships vary across studies. Community composition also varies within and across foundation species, however, the quantitative synthesis of foundation species effects remains challenging. To better understand these variations, a wide range of foundation species traits have been measured and related to diversity metrics. Yet, this approach has so far been restricted to a few foundation species, with a strong bias toward easily measurable traits that are difficult to interpret due to their involvement in multiple processes. Dedicated efforts to assess more detailed species traits often provides valuable insights into faunal responses but hamper comparisons across foundation species. To reconcile this diversity of traits, we have classified foundation species traits into 26 standardised categories, which constitutes a valuable framework to consolidate the interoperability of future research on foundation species support to biodiversity. This classification and the associated database on foundation species-biodiversity relationships will foster a comprehensive assessment of how multiple foundation species shape heterogeneous seascapes, which is crucial for predicting the effects of habitat alteration on coastal biodiversity.