E-Flora BC: Electronic Atlas of the Flora of British Columbia

Family Description:
Members of this family are small uniaxial forms that occur in the mid to high intertidal zone on our shores.

Species description:
Sea Moss is a pinkish to almost black (especially when dry) alga that grows in small, bushy tufts on rocks or, at least in California, on the valves of the California Mussel (Mytilus californianus). By late April the individual tufts are about 3 cm (1.25 in) high. Each tuft consists of a highly branched, wiry stem attached to a small, discoidal holdfast. The branching pattern is somewhat dichotomous; that is, at each fork, both branches are about the same size (about 0.5 mm in diameter). The branches can have swollen tips. When the tide goes out, the tuft stands erect on the rock and can dry to a brittle hardness, only to rehydrate when the tide returns. Stepping on the tufts when they are brittle smashes them, so take care to step around them.

If you examine a small piece of Sea Moss with a 10X field lens, you will see prominent conical "spines" along the main axes. These spines are really just very short (but soft) branches and are very characteristic of this species of alga.

Sea Moss has an isomorphic life history, so gametophytic individuals are indistinguishable from tetrasporophytes. Experiments performed in central California showed that both phases had similar rates of both respiration and photosynthesis whether in or out of the water but these rates decreased with increasing loss of water from the tissues.

Sea Moss prefers to grow in exposed locations.

Individuals collected from southern British Columbia/northern Washington State were able to withstand a week of immersion in water at a temperature of 28°C (82°F), making this one of the most thermally tolerant of our local algae.

Larvae of the Pacific Blue Mussel (Mytilus trossulus) settle preferentially on Sea Moss.

Sea Moss is sometimes grazed by limpets, which benefit from its high caloric value (4.10 Calories per gram of dry weight).