Comparison of three techniques for administering radiolabeled substrates to sediments for trophic studies: uptake of label by harpacticoid copepods

Microbial grazing by two species of meiofaunal harpacticoid copepods (Heteropsyllus nunni and Thompsonula hyaenae) was determined by uptake of radioactive labels following their introduction into natural sediments from a low-energy intertidal site in Florida (29°54′40″N; 84°31′30″W) in May 1986. Grazing was related to three methods of radioactive-label introduction: injection, porewater replacement, and slurry. Uptake of label by harpacticoids was examined using two dual-label combinations, 3H-thymidine/14C-bicarbonate and 3H-thymidine/14C-acetate. The injection and porewater-replacement methods yielded statistically indistinguishable results. Results obtained by the slurry method differed significantly from the other two methods. We suggest that the unique results obtained in the slurry method were a consequence of the disruption of microbial-meiofaunal spatial relationships.