Maerl

Overview

Lithothamnion corallioides is a species of calcified red seaweed that forms the structural foundation of maerl beds, which are unique, slow-growing marine ecosystems. It typically exists as a free-living, unattached plant, creating complex, three-dimensional lattices of branched nodules on the seafloor.

Appearance

This alga is characterized by its rigid, arborescent (tree-like) structure, consisting of fragile, cylindrical branches that are typically less than 1 mm in diameter. When alive, the thalli display a vibrant pink to violet hue, but they turn a stark greyish-white upon death. Individual plants often form nodules that can reach up to 5 cm in diameter, though their overall shape is highly variable.

Distribution & Habitat

Lithothamnion corallioides is found in the Mediterranean Sea and the northeastern Atlantic, ranging from the British Isles south to the Canary Islands. It thrives in sheltered, stable environments with moderate to high water flow, typically on sand, mud, or gravel substrates. While it is most common in the sublittoral zone, it can occasionally be found in the lower littoral zone, often coexisting with other coralline algae like Phymatolithon calcareum.

Biology & Behavior

As a slow-growing organism, maerl can form deposits that are thousands of years old, with living thalli accumulating on top of dead layers. The species exhibits significant physiological plasticity, allowing it to adapt to varying environmental conditions. Reproduction occurs through both fragmentation—where broken pieces continue to grow—and the production of spores that settle on sediment particles or shells to form new nodules.