Sediment community response to a temporally varying food supply at an abyssal station in the NE pacific

Abstract

Long time-series measurements were made to examine the effect of episodic inputs of organic matter to the benthic boundary layer on the sediment community at a site in the eastern North Pacific (Sta. M). Chlorophyll a and pheopigments were used to assess sediment enrichment, and the response of the sediment community was examined with seasonal measurements of sediment community oxygen consumption (SCOC) and sediment ATP from February 1992 to July 1996. In addition, macrofaunal density and biomass were examined in 26 sediment grab samples taken over a 2-year period. In order to determine whether the presence or absence of detrital aggregates correlated with macrofaunal density and biomass, 54 tube core samples were collected with the submersible Alvin at times when detrital aggregates were present on (August/September of 1994) and absent (April 1995) from the sea floor. Large, seasonal inputs of particulate organic carbon (POC) generally resulted in sediment enrichment and significantly correlated with increases in SCOC. Summer maxima in SCOC occurred consistently over our study period, indicating that this trend is a regular seasonal occurrence at Sta. M. Protozoans, primarily agglutinating foraminiferans, and five of the six dominant metazoan taxa exhibited seasonal increases in density during winter months after detrital aggregates had disappeared from the sea floor and approximately eight months after peak SCOC and POC measurements, over a 2-year period. Alvin tube core samples showed that relative protozoan density and biomass increased significantly over a 4-week period following an input of phytodetritus, indicating that these organisms may respond to organic matter inputs on time scales as short as weeks.