Anaëlle Bizien 1, Jacques Grall1,2, Michel Le Duff2, Sandrine Derrien-Courtel3, Thomas Burel1
1Univ Brest, CNRS, IRD, Ifremer, LEMAR, 29280 Plouzané, France - 2Université de Brest, France - 3Muséum National d’Histoire Naturelle, Station Marine, France
Rocky reefs are increasingly impacted by global change, resulting in significant alterations in ecosystem functioning and the services they provide. Macroalgae are experiencing regressions in temperate zones, making them valuable bio-indicators for assessing the health of coastal areas. Interpreting natural variations in alpha and beta diversity remains a challenge, particularly when seeking a critical view of ecological health across biogeographical regions or even within diversity hotspots at a regional scale. In the North-East Atlantic, the macroalgal communities of Breton coasts have been regularly sampled since 2004, as part of monitoring efforts under regional initiatives and European environmental directives. This unique dataset provides a rare opportunity to test a new taxonomy-based statistical index, the Ecological Quality Assessment (EQA), to macroalgal communities. By comparing previously published Water Framework Directive macroalgal indicators—often based on taxonomic richness or functional traits approaches —with these innovative statistical methods, we propose a new framework for monitoring the health of seaweed-dominated habitats that can be applied globally. A key strength of this study lies in its ability to yield reliable results in both rocky bottoms and rocky shores. As a result, midshore fucoids exhibit seemingly irreversible declines over both the short and medium term. In subtidal zones, kelp forest regressions also appear substantial; however, their trajectory shows a slightly more optimistic outlook regarding long-term survival. By tracking changes from a reference state, this method has the potential to detect community shifts regardless of the geographical area considered. Additionally, this tool offers insights into the probability of communities to return to their initial states, making it a powerful resource for assessing ecological resilience and recovery potential.
Biography
Anaëlle Bizien is a PhD student at the Laboratory of Environmental Marine Sciences (Plouzané, France) working on long-term dynamics of macroalgal communities of rocky shores. She focuses on understanding their drivers, role as bioindicators and distribution models. She has developed expertise in taxonomy, community responses and numerical ecology, while studying a wide range of coastal habitats.