Chlorophyta, Green Algae
Bryopsis plumosa (Hudson) C. Agardh
Chlorophyta, Order: Caulerpales; Family: Bryopsidaceae.
Bryopsis, means ‘moss’. And, indeed, when the Bryopsis plumosa is well developed, the delicate thallus adopts the shape of moss. The species name describes the feather-like shape of the thallus.
The algal branches are green and very soft, and they gently sway with the water current. When the thallus unfurls in the water, the algal structure is revealed: individuals are constructed around a central bipinnate axis, from which even thinner filaments spread sideways. The filaments’ direction is horizontal (feather-like), and they get shorter towards the top. The holdfast is connected to the substrate through a rhizoid.
The alga grows up to 10 cm in length, and its width (when unfurled) can reach 1 or 2 centimetres.
Dark green tending to olive-green. Mature individuals sometimes become transparent.
The Bryopsis plumosa is easy to identify thanks to its feather-like shape and the softness of the thallus. However, when the thallus grows old and withers, identification of the species may become somewhat difficult.
This algae is especially common in tidal pools in the intertidal zone and can also be found in deeper water, up to 15 m in depth.
Biology and reproduction
The alga undergoes two unique stages of development: the tall phase and the short phase. The two-stages seem to be diploid. A zygote that is generated by the short phase develops a rigid, gametophytic phase. The gametes differ in form (heteromorphic), are colored various shades of brown and develop along the central branch. Male plants are usually distinguished from female plants, but some individuals are monoecious. Vegetative reproduction occurs both as regeneration of a central branch and as budding. The entire thallus, including its extensive branching, is actually a single, multi-nuclear cell (coenocyte). The alga is preferred and eaten by a large variety of marine invertebrates.
Seasonality and distribution
The Bryopsis plumosa is the most common species of the genus, both in the Eastern Mediterranean and around the world. The species is common in warm seas and may be found throughout the year.
Bryopsis plumosa - the illustration shows the structure of the wall-less coenocytic and reproductive cells at various stages of development.
About sixty species of Bryopsis have been reported in the Mediterranean and, if sub-species are taken into account, this number exceeds 100. Among them, the Bryopsis hypnoides may be found along our coast, but it is rare and similar to the Bryopsis plumosa. Species differ from one another in their side-branch arrangement along the central ‘stalk’. In Bryopsis hypnoides, they are arranged in a spiral or else irregularly. In Bryopsis plumosa, they are arranged in parallel, like a feather. Additional species reported in the area include: Bryopsis adriatica (J. Agardh) Meneghini
Bryopsis balbisiana Lamouroux
Bryopsis corymbosa J. Agardh
Bryopsis cupresina Lamouroux
Bryopsis cupressoides Kutzing
Bryopsis disticha (J. Agardh) Kutzing
Bryopsis muscosa Lamouroux
Bryopsis pennata Lamouroux.