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
Ulvaria sp.
Ulvaria obscura and cross-section (right) showing one cell layer.
Green Seaweeds | 65
Identifying Pacific Seaweeds
the field. Kornmannia blades remain small (to 5 cm/2 in) and are typically found growing on seagrasses and other seaweeds, with K. leptoderma smaller than Ulvaria and Monostroma, and not turning dark upon drying. A definitive field identification of Monostroma is beyond the reach of mere mortals.
Dopamine, an adrenaline-like compound, is another exotic chemical found in Ulvaria. Could this sea lettuce give a person an adrenaline rush?
Our understanding of the relationships among these local bladed forms is largely the result of the efforts of Maurice Dube (Western Washington University). Dube had a green (seaweed) thumb and cultured these plants through their young, informative stages. He died suddenly when accident-ally struck by a cyclist. The following poem was read at the Fourth North-west Algal Symposium, March 1989, in his memory.
Maurice Dube you accidentally died in your sixtieth year,
While walking a darkened street near your home.
In that very special early morning light,
With a tea-quickened pulse and a little stiff,
You and your students greeted many a low tide,
Heralded by the forceful slap of waves.
A multitude of seaweed forms lie exposed,
Accessible to you and your students.
And a glimpse assures the essential presence of your
Rich green undulant Monostroma.
Maurice, when the pale, cold, waxing moon
Draws back the watery curtain of tide,
We will join you on those compelling shores,
And once again share the marine wonderment.
—Louis Druehl
Habitat & Distribution
Ulvaria is distributed from Alaska to northern California, and various Monos-troma species are distributed from Alaska to southern California. Kornman-nia grows attached to seagrasses and other seaweeds from Alaska to central California.
66 | Cylinders
