Common Maërl

<em>Phymatolithon calcareum</em>, the common maerl, is a free-living, non-geniculate coralline red alga in the family Hapalidiaceae. It is found along the coasts of Brazil, Norway, and Sweden, typically forming extensive maerl beds in shallow subtidal marine environments. These beds consist of accumulations of living and dead maerl thalli, creating complex three-dimensional habitats that support high biodiversity. The common maerl is classified as Data Deficient on the IUCN Red List, meaning insufficient information exists to accurately assess its conservation status. Maerl beds are among the most biodiverse shallow marine habitats in European and South American coastal waters, providing nursery grounds for commercially important fish and invertebrates. The species grows extremely slowly, making maerl bed recovery from physical disturbance very prolonged. Threats include bottom trawling, dredging, and changes in water quality. Maerl has historically been harvested as a soil conditioner in agriculture, leading to significant reductions in some European populations.