Lithothamnion spp.

crustose coralline algae

Worldwide oceans (intertidal to deep subtidal)

Native to North America

Overview

Lithothamnion spp. is a genus of crustose coralline red algae in the family Hapalidiaceae, found in marine waters worldwide from the intertidal zone to depths of 200 m (660 ft) or more. The algae deposit calcium carbonate in their cell walls, forming hard, stony, pink to purple-red crusts and nodules over rock, shells, and other surfaces. Crusts range from a thin coating less than 0.04 inch (1 mm) thick to layered mounds several inches across, with a chalky texture and a surface marked by small wart-like bumps or low ridges. Some species form free-living rounded nodules called rhodoliths or maerl that accumulate into beds on the seabed. Growth is slow, often less than 0.04 inch (1 mm) per year, and individual crusts can persist for decades. The pink colour comes from the pigment phycoerythrin, which masks the green of chlorophyll. Lithothamnion spp. beds build reef-like structures that shelter many marine animals, and the algae help cement coral reefs. Bleaching to white occurs when the alga dies and only the calcified skeleton remains. The genus is sensitive to ocean acidification, which dissolves its calcite skeleton.

Native Range

Lithothamnion spp. occurs in oceans worldwide, from polar to tropical seas, on rocky reefs, in tide pools, and on the seabed down to the limit of light penetration. Maerl beds formed by the genus are widespread on the cool-water continental shelves of the North Atlantic and elsewhere.

Suggested Uses

Maerl, the loose nodules formed by Lithothamnion spp. and related algae, has been harvested as a soil conditioner and animal feed additive, and as a source of calcium and trace minerals. Coralline crusts are valued in reef aquariums for their colour and for stabilising live rock. Maerl beds are protected habitats in many regions because of their slow growth and ecological role.

How to Identify

Identify by the hard, stony, pink to purple-red crust or nodule firmly attached to or resting on a marine surface, with a chalky calcified texture and a bumpy or ridged surface. The calcite skeleton and lack of a fleshy body separate coralline algae from other seaweeds. Lithothamnion spp. differs from related genera by microscopic details of its reproductive chambers.

Appearance

Colors

Foliage Colors

pink

red

Bloom Information

Lithothamnion spp. does not flower. It reproduces by spores formed in small calcified chambers called conceptacles, which appear as raised pores or bumps on the crust surface. Reproduction can occur year-round in stable conditions, with some species releasing spores seasonally in response to temperature and light.

Growing Conditions

Water & Climate

Water Needs

High

Care & Maintenance

Care Guide

Lithothamnion spp. grows only in clean, fully marine seawater with stable salinity and adequate light, attached to hard surfaces or lying free on the seabed. It cannot tolerate fresh water, drying, or burial by sediment. Growth is very slow and depends on dissolved calcium carbonate, which makes the genus vulnerable to ocean acidification. In aquariums, coralline crusts establish on rock under strong light, stable calcium and alkalinity, and good water movement. Maerl beds take decades to centuries to form and recover slowly from disturbance such as dredging.