The members of this family and order are among the most primitive of the red algae and lack the complex structures that appear in most other reds. The conspicuous individual is the haploid gametophyte, and the alternate phase is a microscopic filamentous "conchocelis" phase that grows within the shells of marine mollusks and barnacles. Egg cells form on the macroscopic gametophyte, and they are fertilized by spermatia from the same or a different plant. Following fertilization, the zygote divides directly into a packet of spores called zygotospores (to differentiate them from carpospores formed in higher red algae). These diploid spores germinate into the diploid filamentous (and presumably perennial) conchocelis. In some species, gametophytic and conchocelis phases produce asexual spores that germinate to give rise to another individual of the same phase. Therefore, despite being structurally simple, many species of Porphyra rival other reds in the complexity of their life cycles. Botanists have suggested that the boring conchocelis phase is an adaptation to resist grazing by such herbivores as limpets. However, fossils of boring conchocelis have been dated to more than 500 million years ago, long before the first limpet appeared.
Porphyra is a difficult genus of red algae, and you cannot expect to identify every specimen you find. Species in addition to those listed below are also found in our area.
Purple Laver grows on rocks or epiphytically on other algae throughout our area, and, at least in California, on the valves of the California Mussel (Mytilus californianus). It forms a broad blade to 30 cm (1 foot) wide and about the same length (occasionally much larger), anchored directly by a tiny discoidal holdfast, although local specimens are much smaller, especially early in the season. The blade margins can be deeply lobed and conspicuously ruffled, and can bear numerous small holes. Growth is diffuse throughout the blade rather than limited to a defined meristem. The blade is purple (or sometimes greenish) in color and, whether wet or dry, has a satiny sheen that can iridesce in sunlight, as can all the species in this genus of algae. The blade is thin (just one cell layer thick) and easily torn, but as the individual dries out during low tide, it first turns rather rubbery and then brittle.
Purple Laver is abundant in spring and summer when it opportunistically colonizes rocks or other algae. Unlike some closely related species, it is not very tasty (to humans, but it is grazed by limpets). Other species of Porphyra are the basis of a billion dollar marine aquaculture industry in the Far East, where they are raised on nets suspended from poles in shallow areas or from rafts anchored over deeper water. When dried, these algae are up to 30% complete protein, and contain abundant minerals such as calcium, iron and iodine as well as impressive amounts of vitamins A and C. They are exceptionally digestible and reported to be effective in lowering blood cholesterol levels. At 4.31 Calories per gram of dry weight, Purple Laver has one of the highest caloric values of any seaweed tested.
In Washington State, researchers compared the gametophytes of the intertidal P. perforata to subtidal ones of P. nereocystis with respect to their light requirements. They found that the intertidal species is sun-adapted because it can withstand strong light, while the subtidal species is more shade-adapted because high light levels inhibit photosynthesis. Probably most if not all intertidal algae are sun-adapted while subtidal species are shade-adapted.
Source: North Pacific Seaweeds
Source: North Pacific Seaweeds
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