Maerl

thumb|Maerl off the coast of the Isle of Arran thumb|Calcified remains of maerl, on the "coral beach" in the Isle of Skye thumb|Maerl in Lanildut. thumb|Pieces of popcorn-like maerl from Fuerteventura island. Maerl (also rhodolith) is a collective name for non-geniculate coralline red algae with a certain growth habit. Maerl grows at a rate of c. 1 mm per year. It accumulates as unattached particles and forms extensive beds in suitable sublittoral sites. The term maerl originally refers to the branched growth form of Lemoine (1910) and rhodolith is a sedimentological or genetic term for both the nodular and branched growth forms (Basso et al., 2015). The terms rhodolith and maerl are used in very similar ways. A study in 2023 clarifies that maerl refers to only living, branched coralline thalli, while rhodolith includes unattached coralline red algae, both dead and alive.

==Description== In Europe maerl beds occur throughout the Mediterranean, along most of the Atlantic coast from Portugal to Norway, and in the English Channel, Irish Sea and North Sea. The distribution of maerl is dependent on water movement, light and salinity concentration. Maerl beds occur in the photic zone, and can be found to around 30 m depth in the British Isles and up to 120 m deep in the Mediterranean. Maerl deposits can reach up to 10 m thick, but are usually much thinner; carbon dating has shown that they can be more than 5500 years old.