Grande Flustre

Overview

Flustra foliacea, commonly known as hornwrack, is a colonial marine animal often mistaken for seaweed due to its bushy, leaf-like appearance. Despite this resemblance, it is a bryozoan—a colony of tiny, interconnected organisms called zooids that work together to survive.

Appearance

This species forms stiff yet flexible, light grey to brown fronds that typically reach 6 to 20 cm in height. The fronds are composed of two layers of tongue-shaped zooids arranged back-to-back. When fresh, the colony emits a distinct, lemon-like scent. Under close inspection, the surface of the fronds reveals a rectangular, pore-like structure, and the edges of individual zooids may feature small, club-like spines.

Distribution & habitat

Found throughout the temperate North Atlantic, this bryozoan prefers stable, hard substrates such as stones, shells, or bedrock. It thrives in circalittoral zones, particularly in areas with moderately strong to strong tidal currents, and is typically found at depths ranging from 10 to 100 meters. While it lives subtidally, colonies are frequently washed ashore following storms.

Biology & behavior

As a suspension feeder, the colony captures nutrients from the water column using the tentacles of its zooids. These colonies act as vital microhabitats, providing a stable surface for various epizoobionts, including other bryozoans, sponges, and hydroids. The species is a hermaphrodite and can live for several years, with growth occurring primarily from spring through autumn, often pausing during the winter months.