Measurement of zooplankton grazing using particles labeled in light and dark with [methyl-3H] methylamine hydrochloride

Abstract

Zooplankton grazing rates were estimated by measuring ingestion of [methyl-3~]methylamine hydrochloride ( 3 ~ ~ e ~ ) lab lled particles. Experiments were carried out in laboratory culture and in diverse natural plankton assemblages (Chesapeake Bay and Sargasso Sea). Uptake of MeA by particulate matter was linear in both Light and dark conditions over the first hour of incubation and was highest In bacteria-sized particles compared to phytoplankton. In situ grazing rates estimated for zooplankton > 200 pm using particles labelled during daylight with both 3 ~ ~ e ~ and NaI4CO3 were similar. The technique was used to measure zooplankton grazing above and below the euphotic zone, day and night in the Chesapeake Bay during May 3 to 5, 1989. Filtration rates showed no die1 pattern but were 2to 10-fold higher in the deep chlorophyllmaximum compared with surface waters. From these data, we conclude that the 3 ~ ~ e ~ technique is useful for measuring grazing on natural particles at night and at depth where NaI4CO3 incorporation by phytoplankton is not sufficient for in situ grazing experiments.