The assimilation of detritus-bound metals by the marine copepod Acartia spinicauda
Limnol. Oceanogr., 47(2), 2002, 604-610 | DOI: 10.4319/lo.2002.47.2.0604
ABSTRACT: The bioavailability of Cd, Se, and Zn associated with detritus of different biological origins to the marine copepod Acartia spinicauda was examined under laboratory conditions using the radiotracer approach. Three types of detritus, from the macroalga Ulva lactuca, cell debris of the diatoms Thalassiosira weissflogii and Thalassiosira rotula derived after natural decomposition or extraction, and copepod fecal pellets, were examined. The assimilation of metals from the ingested natural phytoplankton assemblage was also experimentally quantified. The assimilation efficiencies (AEs) of metals in copepods fed with different types of detritus were 47-83% for Cd, 30-59% for Se, and 41-75% for Zn. These values were comparable to the AEs measured previously for copepods fed on living algal cells, indicating that metals associated with biogenic particles were directly available to marine copepods. Labeling time had no effect on the metal AEs in copepods fed on detritus derived from U. lactuca. The metal AEs were higher in copepods fed on the freshly prepared diatom debris than on naturally decomposing debris. Zn associated with fecal pellets was assimilated at comparable efficiencies to those associated with macroalgal and microalgal debris, but Cd and Se were assimilated at a lower efficiency when associated with fecal pellets. The AEs of Cd (84-94%) in copepods fed on the natural phytoplankton assemblage were the highest among all the experiments. There was no obvious effect of the metal distribution in the cytosol of the natural phytoplankton assemblage on the metal AE. The calculated elimination rates of the metals were independent of detritus type and were similar to previous studies. Our study indicated that detritus is a potential food source for marine copepods and the metals associated with the detritus can be efficiently used with a relatively high AE. Detritus may thus play an important role in the overall biogeochemical cycling of metals in the ocean.