Growth of Subtidal Laminaria groenlandica in Southeastern Alaska Related to Season and Depth

Abstract

L. groenlandica showed distinct seasonal cycles of growth in length and width, and in increase in weight per unit area of the blades. The 2 cycles differ in timing. Blades of both shallow and deep plants increased in length and width between Jan.-June, with a peak rate of increase in late March and early April. In contrast, blades increased in weight per unit area between June and Sept., with significantly greater increases in plants at 3 m than in plants at 10 m. There are also clear morphological differences between plants in the upper and in the extreme lower depth range. In the upper depth range, the plants have long, flattened stipes with clearly defined mucilage ducts, and wide, thick, bullate blades. In the extreme lower depth range, the plants have short, terete stipes with mucilage ducts seldom discernible, and narrow, thin non bullate blades. Spores first appeared on shallow plants in early May. Most larger plants at all depths were fertile by Sept.