Pacific Seaweeds. Louis Druehl

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Pacific Seaweeds - Louis Druehl

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      Both forms of Codium are found in the low intertidal zone from Alaska to Mexico.

      Close-up of Codium fragile branchlet.

      70 | Unicellular forms

      Pacific Seaweeds

      Unicellular forms

      Unicellular green algae are found in two settings on our coasts: those capable of swimming, or motile, and non-motile forms found inside seaweeds and invertebrates. Motile forms are found in tide pools high in the splash zone above the normal high tide level.

      Tetraselmis p. 71

      Elliptochloris p. 71

      ‘Codiolum’ / ‘Chlorochytrium’ p. 72

      A shell stained green by the presence of many ‘Codiolum’ or ‘Chlorochytrium’ unicells.

      Green Seaweeds | 71

      Identifying Pacific Seaweeds

      Tetraselmis

      Class Prasinophyceae Order Chlorodendrales Family Chlorodendraceae

      Number of Species

      Tetraselmis (Greek=four branches; refers to presence of four flagella, cellu-lar swimming appendages) consists of six species locally, the most common and easily distinguished being T. ascus and T. marina.

      Description

      Tetraselmis shifts between two unicellular life stages: a swim-ming form and a sedentary form attached to rock by a long clear filament. Both stages are microscopic. In the filamentous stage, Tetraselmis ascus may form colonies of short profuse branches with pigmented cells at the tips, whereas T. marina colonies are typically of long and sparse branches.

      Habitat & Distribution

      Swimming unicells of Tetraselmis normally inhabit tide pools above the direct influence of the tides. These pools accumu-late salt from ocean spray and are subjected to rain and severe evaporation, resulting in drastic ranges in temperature and salinity—to the point of being a totally dry salt cake! An inhabited pool will resemble pea soup. Tetraselmis is found from BC to central California.

      Elliptochloris

      Class Trebouxiophyceae Order Prasiolales Family status uncertain

      Number of Species

      There are six species in the symbiotic green algal genus Elliptochloris, of which only the species E. marina is found as a symbiont within the tissues of sea anemones.

      Description

      The common Pacific intertidal sea anemones Anthopleura elegantissima and Anthopleura xanthogrammica house microscopic unicellular algae of two types: dinoflagellates and green algae. In this symbiotic relationship, the anemone gains extra nourishment from algal photosynthesis, while the algae gain protection from herbivores and a place to live.

      Tetraselmis.

      72 | Unicellular forms

      Pacific Seaweeds

      Molly Letsch (Le Moyne College) used genetic analysis during her doc-toral studies to determine that the green algal symbionts, formerly referred to as “Chlorella-like” (Greek=green and small), were a new species, which she named Elliptochloris marina.

      Habitat & Distribution

      Species of anemones in the genus Anthopleura are abundant on rocks, in tide pools or crevices and on pier pilings. They are characteristic of the mid-dle intertidal zones of semi-protected rocky shores of both bays and outer coasts. Distribution is from Alaska to Mexico.

      ‘Codiolum’ / ‘Chlorochytrium’

      Class Chlorophyta Order variable Family variable

      Number of Species

      ‘Codiolum’ (Greek=little ball) and ‘Chlorochytrium’ (Greek=little green fungus) are two unicellular forms once considered to be distinct from other green algae (hence their former names Codiolum and Chlorochytrium). We now know them to be the spore-producing phase of several filamentous and bladed green seaweeds (examples are Urospora, p. 53, and Acrosiphonia, p. 55).

      The giant green anemone (Anthopleura xanthogrammica) in which the unicellular Elliptochloris sp. resides.

      Green Seaweeds | 73

      Identifying Pacific Seaweeds

      Description

      These plants are microscopic but can be dense enough in number to appear as a green stain on shells and rocks. The most eagle-eyed of read-ers may detect these minute plants as green dots within bladed red seaweeds such as Mazzaella (p. 127) and Mastocarpus (p. 112).

      Habitat & Distribution

      ‘Codiolum’ and ‘Chlorochytrium’ inhabit bladed and crusty red seaweeds, as well as calcareous structures such as rocks and

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