Microbial Food Resources of the Macrofaunal-Deposit Feeder Ptychodera bahamensis (Hemichordata: Enteropneusta)

Biochemcal and traditional analyses were used to characterize the microbial food resources and digestive efficiency of Ptychodera baharnenas an enteropneust hemlchordate Sediment was collected from freshly extruded fecal casts and adjacent feedlng depressions There were no sigmficant differences between casts and depressions in medlan gram size percent silt-clay, denslty of total meiofauna and of nematodes and concentrations of chlorophyll a and phaeophytin Nematodes in casts had a median diameter greater than those in depress~ons Measures of total vlable microbial biomass were 30 '10 (total phospholipid, ester-linked fatty acids) and 49 % (extractible phospholipid phosphate) lower m casts Concentrahons of 33 fatty acids were lower in casts, indicahng that the hemchordate dlgests a w d e variety of microorganisms Only 18 lw7c (as-vaccenic acid) was not lower in casts than in depressions Thls fatty a c ~ d 1s characteristic of eubactena havlng the anaerobicdesaturase pathway, many of which are Gram-negative organisms P baharnensis either cannot digest this funchonal group of bactena or contnbutes gut m~crobes containing 18 l o 7 c to sedlrnent passing through its alimentary canal