The relationship of foraminifera and submarine topography on the New Jersey–Delaware continental shelf

Abstract

This study relates the distribution and abundance of foraminifera to the system of ridges and swales (L = several kilometres; ht = 10 to 20 m) off the New Jersey coast. Foraminiferal communities were sampled, and environmental variables (grain size, organic carbon, sediment temperature, depth, percentage of silt-clay, and bacterial populations) were measured at eight stations located in ridge and swale areas during eight quarterly cruises in 1976 and 1977. From 125 core samples (depth = 3 cm; diam = 5 cm), 118 species of living foraminifera were identified, and populations ranging to nearly 1,200 per 20 cm 3 were recorded. Foraminiferal populations differ in response to mesoscale topography, with significantly greater densities of living foraminifera in the swales (x = 305 ± 52) than on the ridges (x = 78 ± 12). Species compositions of faunas on ridges are not obviously different from those in swales. Three hypotheses to explain differences in foraminiferal densities between swales and ridges were tested. (1) Autochthonous environmental conditions: foraminiferal densities are correlated with finer grain size and amount of organic carbon when ridges and swales are compared together; within swales, foraminiferal densities vary inversely with temperature, perhaps as the result of increased predation at elevated temperatures. (2) Differential transportation of foraminifera: size-frequency distributions of Reophax atlantica suggest that transportation of living foraminifera from ridges to swales is not important. (3) Removal by mechanical destruction or predation: laboratory experiments demonstrate that breakage may be significant on ridges where turbulence is greatest.