Spatial and Seasonal Distributions of Marine Algal Communities at Amchitka Island, Alaska

Studies on the benthic marine algae at Amchitka Island since July 1967 entailed considerable systematic effort since there have been no major phycological studies of the Bering Sea area since Kjellman (1889). A series of papers on various groups of benthic marine algae at Amchitka has been initiated (Wynne, 1970). Weinmann's (1969) study of the zonation of littoral algae provided a starting point for our ecological studies. More recently we investigated timedependent changes in the littoral biospace since a knowledge of these changes (or lack of them) will allow us to predict and differentiate to some extent natural and possibly man-induced changes. The major environmental factors affecting the distributions of littoral vegetation are terrestrial climate, sea temperatures, and wave action. The climate is maritime. Air temperature varies little, and sky cover and relative humidity are high throughout the year. These conditions are favorable for the development of littoral vegetation. Sea-surface temperatures range from 1 to 2 C in winter to 8 to 10 C in summer. Wave action can be consistently heavy, particularly in the winter. Dredging data indicate that waves of well over 100 m in wavelength are frequent.l Figure 1 shows the heavy wave action encountered at the Island. This condition would lead one to expect an extensive vertical range of littoral algae and an "exposed" configuration of vegetation. This was not the case. In general, even on outer exposed points, the vertical range of macroscopic algae was less than 2 m above mean lower low water. This small vertical range is explained by the presence of extensive benches in the littoral. One of these benches is shown in O'Clair and Chew's Figure 1 (this symposium). Providing an unusually uniform habitat, these benches also act as buffers against the long-period waves approaching Amchitka. The outer edges of the benches generally rise abruptly in depth from 2 to 10 m. At these outer edges, most of the energy dissipates as the waves break (Fig. 2), and water piles on the benches, then flows landward and laterally, and eventually seaward via channels between the benches. The process is shown schematically in Figure 3. The buffering action at the benches must be the underlying cause of the absence of an "exposed" configuration of littoral vegetation. Our first objective was to characterize the distribution of marine algae over This paper is based on work performed under AEC Contract AT(26-1)-171 for Battelle Memorial Institute, Columbus Laboratories. Contribution No. 330, College of Fisheries, University of Washington.