COPEPOD GRAZING AND THE BIOGEOCHEMICAL FATE OF DIATOM IRON

We investigated the effects of copepod grazing on fractionation of dia tom cellular Fe into assimilated, dissolved, and fecal pellet pools. G razer assimilation was only weakly dependent on prey N:Fe ratios, with assimilation efficiencies approximately tripling over a 100-fold incr ease in diatom N:Fe ratios. Assimilation efficiencies strongly correla ted with prey subcellular partitioning, however, exhibiting a 1:1 rela tionship to cell cytoplasmic content and a 1:3 relationship with diato m intracellular content. Release of Fe from copepod fecal pellets conf ormed with a two-compartment loss model, with roughly 80% of associate d Fe in a slowly released pool (tb(1/2) = 113 d). Partitioning into di ssolved, assimilated, and fecal pellet pools indicated that all three are important fates for ingested cellular Fe.