Marine Wildlife Encyclopedia
Maerl Phymatolithon calcareum
The term “maerl” describes various species of unattached coralline seaweeds that live on sea beds. Phymatolithon calcareum forms brittle, purple-pink, branched structures that look more like small corals than seaweed. It grows as spherical nodules at sheltered sites, or as twigs or flattened medallions at more exposed sites. In places with some water movement from waves and tides, but not enough to break the maerl nodules, extensive beds can develop. Maerl is as much a habitat as a species, and both the living maerl and the maerl-derived gravel beneath it harbor many small animals. Maerl grows slowly and the beds are vulnerable to damage from bottom trawlers.