The ice-worn granite shore at Palmer Station appears, at first glance, to be barren at low tide, although the tidal range is about five feet. The tides are of the mixed semdaily and daily types; the lowest intertidal level may at times be exposed for several hours. During the summer months, a well-defined band of filamentous green algae, inclulding such genera as Enteromorpha, Ulothrix, and Cladophora, gives a green tint to the lower foot of the intertidal regions. . . . . .
Judging from the aggregations of limpet shells at feeding stations on rocky eminences well above the sea, Patinigera polaris is obviously a significant item of diet for some bird, probably the Dominican Gull, ahtough feeding was not directly observed. These middens consist of several hundred shells. Some of the shells are surprisingly large, being nearly three inches long and two inches high. If, as observed elsewhere (fide B. Stonehouse, in litteris), the gulls do not feed on the bare rock surface but at the water's edge or slightly below it, there must be a constant upward movement of limpets during the ice-free periods of the year. It is possible that they feed on the seasonal algal growth.
The complete absence of barnacles of any kind is noteworthy, and the apparent sparseness of intertidal life is approached elsewhere on the bare sunbaked rocks of the Galapagos, where there are a few small small snals, no upper zone barnacles, and no limpets whatever (Hedgpeth, 1969). The conspicuous growth and well defined upper limit of the crustose alga Hildenbrandia, in the Palmer region, below approximately tide zero, supports the suggestion by Gauld and Buchanan (1959) that the "Lithothamnia zone" is one of the most universal and charaterisic phenomena of the seashore in all parts of the world. At the Equator, the most significant factor limiting distribution in upper intertidal regions may be the heating of the sun, whereas, in the Antarctic, the action of ice may be the most significant controlling factor.