Sea Mat

Overview

Mesophyllum expansum, commonly known as the Sea Mat or "Grand mésophylle," is a calcified red alga that plays a significant role as a structural component of Mediterranean coralligenous habitats. This species is recognized for its complex, layered growth form and its ability to thrive in shaded marine environments.

Appearance

This alga typically grows as a calcified, encrusting plate or a series of overlapping, thin, leaf-like lobes. Its coloration is highly variable, ranging from light pink or orange to deep red, often featuring distinct white margins. Mature specimens can form extensive, fragile structures reaching up to 30 cm in diameter and 20 cm in height. Because of its delicate nature, it adheres only partially to the substrate and can be easily damaged by physical contact.

Distribution & habitat

Mesophyllum expansum is primarily found in the Mediterranean Sea and parts of the nearby Atlantic, including the Canary Islands, the Azores, and the coast of Morocco. It is a sciaphilic (shade-loving) species, commonly inhabiting shaded areas from shallow waters down to depths of approximately 90 meters. It is frequently observed growing on the rhizomes of Posidonia seagrass and within coralligenous reef communities. Research suggests that the species may adapt to rising sea surface temperatures by shifting its distribution toward deeper, cooler waters.