BENTHIC STUDIES IN BUZZARDS BAY III. THE STRUCTURE OF THE SOFT‐BOTTOM COMMUNITY1

Abstract

A series of 24 samples was taken at periodic intervals at a single locality in Buzzards Bay from February 1956 to January 1958. With the exception of 4 samples which departed markedly from the others in regard to sediment composition, very high indices of faunal affinity were obtained within the series. The silt‐clay fraction of the sediment in the 20 samples with high faunal indices varied from 78–91%, and when the contained species were ranked by abundance, the commoner species achieved approximately the same rank from sample to sample. Thus, 8 or 9 species are a constant part of the biological environment of this association, and there is an approximately constant numerical proportionality among them. Seventy‐nine species were obtained from the 20 samples of typical sediment composition. However, 11 species comprised almost 95% of the total fauna by number while the lamellibranch Nucula proxima (58.86%) and the polychaete Nephthys incisa (17.21%) were commonest, Ten species make up 95% of the total biomass. Thus the community, both numerically and by biomass, is characterized by pronounced dominance of few species. The niches of the 9 most common species, representing 93.5% of the community by number, were categorized by method of feeding, kind of food and spatial distribution. Considering only these few factors, it was possible to demonstrate certain differences in niche preference. The relationship of animal numbers to animal weight revealed the expected pyramid of numbers with very few organisms in the largest weight categories and numerous individuals in the smaller weight groups. However, when the biomass within each weight category was determined, the expected inverted pyramid did not result. Numbers are considered more valid than biomass in quantitative benthic studies, since only 0.15% of the fauna constitute 55.17% of the entire weight. The presence or absence of a rare, randomly distributed large animal may alter the biomass of an individual sample by two orders of magnitude.