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Ecological study of Laminaria sinclairii and L. longipes Markham, James W.

Abstract

Laminaria sinclairii (Harvey) Farlow, Anderson and Eaton, found from Southern California to Central British Columbia, and L. longipes Bory, found from Southeast Alaska to the Kurile Islands, differ in several ways from most other kelp plants. Their most distinctive feature is the rhizome-like holdfast, composed of many haptera, from which arise multiple stipes, each bearing a single blade. The two species are very similar to each other and have been distinguished in the past primarily by the presence of mucilage ducts in the stipe of L. sinclairii and the absence of these in the stipe of L. longipes. In order to determine whether the two species are indeed distinct, their distribution, ecology, growth, and reproduction were studied in the laboratory and on beaches in Alaska, British Columbia, and Oregon. The gross distribution of both species appears to be controlled by temperature. Transplants and laboratory cultures indicate that L. longipes is adapted to lower temperatures than L. sinclairii. Salinity apparently has little influence on distribution, as both species tolerate wide ranges of salinity. L. sinclairii was studied in situ on three beaches in Northern Oregon, where the plants are subjected to heavy surf. The sand level on the beaches rises through the summer so that the plants are partly or wholly buried under sand by late summer. The first heavy storms in the fall remove most of the sand. Maximum growth occurs in early summer, prior to burial. The blades are lost in December and new ones are regenerated in January. Ripe sori are produced on the old blades just before they are lost and on the new blades just after they appear. There is little evidence from either field or laboratory studies to indicate that the gametophytes which develop from the spores in these sori normally produce sporophytes. Sexual reproduction of this type is difficult because of the scouring action of the sand. In March and April there is considerable production of new stipes and blades from the haptera at the margins of the holdfast. This vegetative proliferation is apparently the normal method of reproduction. L. longipes was observed in situ in Alaska on only five occasions. Growth is greatest in summer and sori are produced in December. Laboratory cultures indicate that sexual reproduction is very rare in this species. L. longipes is rarely associated with sand. Transplants and laboratory cultures indicate that production of mucilage ducts in the stipes of the two species is not affected by changes in environmental conditions. Comparison of the two species shows they differ in several other points besides mucilage ducts, including length of stipes, width of blades, winter loss of blades, morphology of gametophytes, and habitat. The evidence confirms that they should be retained as two separate species.

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