The role of eopepod fecal pellets in the deposition of diatoms in Lake Tanganyika1

Abstract

Fecal pellets from a 16,000‐year sediment core from southern Lake Tanganyika account for over 40% of all diatom deposition and about 30% of total bulk sedimentation. Comparison of diatoms inside pellets with those in the surrounding sediment indicates that small, blunt species like Fragilaria brevistriata and Gomphonema clevei are preferentially ingested by grazing copepods. Long, fragile species like Nitzschia spiculum are strongly avoided. Filamentous Melosira spp. seem to be an important food of copepods. This grazing selectivity, coupled with the enhanced sinking rates and preservation of fecal pellets, could distort the fossil diatom record. Relative diatom abundances in pelletized, nonpelletized, and pooled stratigraphies indicate that pellets actually cause shifts of <4% of total diatom abundance in Lake Tanganyika. Even with selective grazing, F. brevistriata and G. clevei are rare in sediments (<2% of all diatoms).