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Pacific Seaweeds
Cylinders
Ulva (cylindrical form) Green string 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 7 develop a cylindrical morphology and were formerly contained in the genus Entero-morpha (Greek=intestine form). Common species in our area include: U. compressa, U. linza and U. intestinalis.
Description
Tubular species of Ulva (see p. 62 for discussion of bladed forms) have two cell layers that are separated to form a tube, like a cylindrical balloon. Ulva intestinalis is usually unbranched and cylindrical throughout, whereas U. compressa is often sparsely branched and imperfectly compressed away from the base. The tubes may reach 50 cm (20 in) in length but are usually less than 20 cm (8 in) long, and their width varies from a few millimetres to 4–5 cm (1.6–2 in). Ulva linza is tubular only at the base and looks similar to a bladed Ulva (or a deflated balloon), except that it is long, up to 45 cm (18 in), narrow, 1–4 cm (0.4–1.6 in), and distinctly ruffled.
A shaggy wig of cylindrical Ulva sp. adorns an intertidal rock.
Green Seaweeds | 67
Identifying Pacific Seaweeds
Several studies by Japanese and Italian researchers have shown that a seaweed’s morphology may be dependent on certain epiphytic marine bacteria. When grown in aseptic (free from bacteria) cultures, Ulva and other green seaweeds lose their natural leafy morphology and grow instead into a loose collection of cells. If grown with bac-teria, or even just a certain chemical isolated from bac-teria, the seaweeds develop as normal. These fascinating studies give a glimpse into the chemical communica-tion between seaweeds and micro-organisms in their environment that we have yet to fully understand.
Habitat & Distribution
Tubular Ulva are distributed throughout the intertidal zone, from Alaska to Mexico. Ulva intestinalis is the most common species and is cosmopolitan, being found growing on rock on all continents. It is often associated with freshwater seepages above the high tide level and in high tide pools, which through evaporation become salty to the point of producing crystalline salt. Ulva compressa often grows on other seaweeds and is not associated with fresh water. Ulva linza grows on rock or cobble in the mid- to low intertidal region.
A collection of short, individual Ulva sp. cylinders creates a carpet atop a rock.
Ulva intestinalis and cross-section (left) showing tubular nature of the plant.
68 | Spongy texture
Pacific Seaweeds
Spongy texture
Codium Sea staghorn, green spongy cushion
Class Bryopsidophyceae Order Bryopsidales Family Codiaceae
Number of Species
Of the whopping 143 known species and forms of Codium (Greek=animal skin), 3 are found locally: C. fragile, C. setchellii and C. ritteri.
Description
Codium is a conspicuous seaweed, spongy in texture and very dark green. Two basic morphol-ogies exist: branched forms and cushion forms. The branched forms are typified by C. fragile (sea staghorn). This species is dichotomously branched (each branch produces two more or less identical branches, forming a “Y” shape), giving rise to plants up to 40 cm (16 in) long. The branches are cylindrical, about 0.5 cm (0.2 in) in diameter. Codium setchellii and C. ritteri (green spongy cushion) typify the cushion form. The low-lying cushion may be up to 2 cm (0.75 in) thick and 25 cm (10 in) in diameter.
Codium species consist of long cells (some cells are up to 30 cm/12 in long)
Codium fragile.
Codium fragile and detail (right) of surface cells with gamete-bearing cells (g) as observed in cross-section.
Green Seaweeds | 69
Identifying Pacific Seaweeds
that branch near the plant surface. There they differentiate into a beautiful scale-like “skin,” which can be viewed with the aid of a magnifying glass. These long cells, lacking regular cross-walls, are packed with chloroplast and other cellular components. The sea slug Alesia sucks the chloroplasts from Codium and houses them in a special gland. Here the chloroplasts photosynthesize and produce a slime the animal uses to lubricate its path.
Codium fragile had a unique introduction to the Mediterranean. According to Professor Jean Feldmann (University of Paris), this species was imported from California to the Banyuls-sur-Mer marine station for research purposes prior to World War II. Care was taken to secure these plants in the laboratory, but all for naught. Allied bombers liberated Codium and it has persisted as a noxious weed on local swimming beaches ever since.
Habitat
