ウチワサボテングサ

Overview

Halimeda discoidea is a species of calcified green macroalgae widely distributed across tropical and subtropical oceans. It is a key reef-building organism that plays an important role in marine ecosystems by contributing to the structural complexity of reef environments.

Distribution & habitat

This species is found globally in warm waters, including the Atlantic, Indian, and Pacific Oceans. It typically attaches to hard substrates such as rocky surfaces and reef flats, though it can sometimes be found with its base partially buried in sandy areas. It thrives in a range of depths, from shallow intertidal zones to deeper reef environments.

Appearance

Recognized by its distinct, flat, and coin-like segments, this alga features the largest individual segments of any species within the genus Halimeda. The thallus is typically erect, reaching heights of up to 15 cm, and ranges in color from bright green to grayish-green. Because it is heavily calcified, it possesses a firm, rigid structure that distinguishes it from many soft-bodied seaweeds.

Biology & behavior

As a calcified alga, it actively stores calcium within its tissues. It is known for its morphological plasticity, meaning its growth form can vary depending on environmental conditions like light intensity and water depth. While it is generally hardy, it may appear pale or white if moved to low-light conditions, as its chloroplasts retract into the tissue; it typically regains its green color once exposed to sufficient light. Reproduction occurs through both fragmentation and the production of gametes.