The collapse of marine forests: drastic reduction in populations of the family Sargassaceae in Madeira Island (NE Atlantic)

Abstract Species of the genera Cystoseira , Ericaria Gongolaria and Sargassum (family Sargassaceae) are key components Mediterranean-Atlantic marine forests, essential for biodiversity ecosystem functioning. Populations these foundational species particularly vulnerable to anthropogenic impacts, likely be intensified under future scenarios climate change. The decline even disappearance have been reported in different areas world. At Madeira Island (NE Atlantic), populations abies-marina selaginoides vulgare filipendula most ecologically relevant Macaronesian suffering a drastic during last decades, especially on southern coast island, where pressure is higher than north coast. lack sufficient temporal coverage qualitative quantitative studies Sargassaceae communities poses challenge establish specific period this decline. Consulting historical records, we set first time timeline that shows an evident decrease 20 years Island. Following timeline, pinpoint start decade 2000s. This can confirmed places like Funchal Reis Magos, with significantly records. Currently, benthic shallow subtidal rocky reefs along south dominated by sea urchins crustose coralline algae, so-called urchin barrens. However, some cases, they entirely covered layer sediment. We discuss possible factors contributing changes, bringing Madeira’s forests dramatic As many animal rely represents invaluable ecological loss coastal island.