Ecology of Duck Pond, Wellfleet, Massachusetts with special reference to the vertical distribution of the zooplankton

Abstract

During the summers of 1956 and 1957 an investigation was made of certain ecological relations involving light in Duck Pond, Wellfleet, Massachusetts, because of the unusually high clarity of the water. The maximum transparency observed (extinction coefficient, k = 0.11) was far greater than most ponds and about equal to that in the slope water beyond the continental shelf off the Atlantic coast. The illumination reaching the bottom of the pond at 18 m was 11% of the surface light and made possible a thick growth of Sphagnum at that depth. Phytoplankton was scarce and consisted mostly of minute forms. The zooplankton, which ranged in abundance up to 78 organisms per liter, consisted almost entirely of one species of copepod, Diaptomus minutus Lillj. Quantitative sampling of this population by means of a pump at a series of depths and at various hours of the day revealed a partial migration of this species from near the bottom to the surface at sunset on one occasion, but no large fraction of the population carried out a vertical migration on 4 other sunset periods or 2 sunrise periods subsequently studied. On certain of these occasions, however, there was a slight but detectib1e movement of the animals toward the surface at sunset followed by a redistribution to deeper levels. At sunrise the animals showed a tendency to move at first toward the surface and then away from it, although on one occasion the population remained quite evenly distributed at all levels. It is pointed out that because of the high transparency those zooplankters living in the pond are able to withstand high illumination at all depths. Relations between the extreme water clarity and the activities of the zooplankton, as well as other unusual features of the pond are discussed.