Green blades of Ulva sp. in the high intertidal zone of Asilomar Beach, CA.
Green Seaweeds | 61
Identifying Pacific Seaweeds
Prasiola (short sea lettuce) p. 61
Ulva (sea lettuce) p. 62
Ulvaria / Kornmannia / Monostroma (dark sea lettuce) p. 64
Prasiola Short sea lettuce
Class Trebouxiophyceae Order Prasiolales Family Prasiolaceae
Number of Species
More than 30 species of Prasiola (Greek=green) are found worldwide, 5 locally: P. linearis, P. crispa, P. borealis, P. delicata and P. meridionalis.
Description
Prasiola is a very small bladed seaweed, at most a few centimetres in length and usually one cell thick. Tufts of these blades resemble little cabbages.
Prasiola can tolerate and exploit high-nitrogen conditions that most plants would find toxic. Mike Guiry (University College, Galway, Ireland) described the distribution of this group in Galway as being associated with telephone poles
Prasiola sp. and a convenient source of nitrogen, in Santa Cruz, CA.
62 | Blades
Pacific Seaweeds
employed by the local canine population, and in one case with a pole behind a pub. Check your neighbourhood watering holes for this telltale species.
Habitat & Distribution
Species of Prasiola in our area are found growing on wood or rock above the high tide level or along freshwater streams. A unique aspect of their distribu-tion is their association with guano of marine birds. Locally, these plants are distributed from Alaska to central California.
Ulva Sea lettuce
Class Ulvophyceae Order Ulvales Family Ulvaceae
Number of Species
Ulva (Latin=marsh plant) contains a stunning 128 species and forms world-wide. Locally, it is represented by about 15 species, of which at least 8 develop into flat blades. Common species in our area include U. californica, U. “lactuca,” U. lobata, U. rigida, U. stenophylla and U. taeniata.
Description
In 2003, molecular studies collapsed Ulva and Enteromorpha into one genus: Ulva. We retain two entries for the genus here; see p. 66 for discussion of cylindrical forms.
Bladed species are two cells thick, and the blade may be long and narrow
Ulva sp.
Green Seaweeds | 63
Identifying Pacific Seaweeds
or fan-shaped, variously lacerated or perforated and reach a length of 1 m (3 ft) but is usually less than 30 cm (12 in). The colour may vary from very pale to emerald green. Often the margins of these plants are white in contrast to their otherwise rich green. The white portions are cells that have discharged their contents as spores or gametes, leav-ing only the cellulose cell walls. In our area, large blades with holes, formerly classified as U. fenestrata (Latin= window), are now known to belong to either U. “lactuca” or U. rigida.
Ulva flourishes where there are rich nutrient conditions. Sometimes, growth gets out of hand, resulting in what is called green tide. An extreme example of this phenom-enon occurs in Venice Lagoon, Italy, where nutrients from Venice sewage and surrounding farmlands support an extraordinary wild monoculture of Ulva. When the waters warm up, the Ulva population depletes all available oxygen and begins to rot, resulting in a nauseating rotten-egg smell. Up to 200 metric tonnes (220 tons) of Ulva are harvested daily, eight months of the year, to combat this situation.
Habitat & Distribution
Plants exist throughout the intertidal and subtidal regions and in tide pools. This genus is perhaps the most cosmopolitan of all seaweeds, being found on all of the world’s coasts. In our region, bladed species of Ulva are distrib-uted from Alaska to Mexico.
Ulva sp. washed ashore at Monterey Harbor.
Ulva sp. and cross-sec-tion (right) showing two cell layers.
64 | Blades
Pacific Seaweeds
Ulvaria / Kornmannia / Monostroma Dark sea lettuce
Class Ulvophyceae Order Ulvales Family Ulvaceae
Number of Species
Only three species of Ulvaria are known worldwide, and two of these, U. obscura and U. splendens, are found locally.
Description
Ulvaria blades are fan-shaped, usually less than 30 cm (12 in) long and are one cell layer thick. Upon dry-ing, Ulvaria turns dark, because of the presence of polyphenol oxidase, an enzyme that is also found in apples and turns them dark upon exposure to air and is considered a strong antioxidant. This feature distin-guishes Ulvaria from other bladed green seaweeds.
Kornmannia and Monostroma are other one-cell-thick green blades found in our area. A microscope is required to determine the number of cell layers. Together with Ulvaria, these plants occur lower on the beach than most Ulva but otherwise are difficult to distinguish in