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

Family Description:
Members of this family have bodies that are either tubular and one cell thick or bladelike and two cell layers thick. Most cells contain a single nucleus and a single chloroplast. The chloroplast is flattened to cuplike in shape, and has one to several pyrenoids.
Typically, the alternation of generations shown by members of this family is isomorphic, with sporophytic generations similar to gametophytic generations. When asexual spores are formed, they are motile and bear four flagella. Gametes are biflagellate.

Species description:
Sea Hair grows on rocks or is free-floating, especially in tidepools. It likes protected waterways and is often found growing luxuriantly where freshwater seeps across the upper or mid intertidal zones.

Sea Hair is usually bright green, but becomes yellowish when reproductive and often bleaches whitish in the sun. The hollow tubes have walls formed of a single layer of cells. These tubes arise from a small holdfast, and can reach 20 cm (8 in) or more in length and up to 5 mm (0.2 in) in width. The tubes are usually widest at their tips and can be constricted at irregular intervals. You often find many individuals growing in a clump.

This is the favorite food of the Sea Slater (Ligia pallasii), an isopod often found in the high intertidal zone.

In Scotland, researchers found that the natural chemical B-dimethylsulphoniopropionate (mercifully shortened to DMSP) is the principal molecule by which Sea Hair regulates its solute balance with the water in which it is growing. Sucrose and proline are also used. When Sea Hair was exposed to water of increased salinity, in the short term (48 hr.) the concentrations of proline and sucrose increased but that of DMSP remained unchanged. Over the long term (35 days), however, while proline concentrations remained high, sucrose levels fell and DMSP concentrations increased. What this means is that simpler organic compounds, which are more easily made, are used for short-term osmotic balance, while DMSP, which is much more difficult and energetically expensive to make, is used for most long-term adjustments.