Bioaccumulation and elimination of trace metals in marine copepods

Thesis (M.Phil.)--Hong Kong University of Science and Technology, 2001

Marine copepods are the most abundant and best-known zooplankton in pelagic systems, and they are the direct link between the primary producer and higher trophic levels. Thus, copepods play an important role in the biogeochemical cycling of trace metals in marine ecosystems. Once metals associated with the phytoplankton are ingested by the zooplankton, they can either be retained in the animals, egested as packed fecal pellets, or excreted into the dissolved phase; all of which can considerably affect the fate and distribution of metals in marine systems.In this study, a series of radiotracer experiments were conducted to examine the influence of metal concentration (Cd, Se, and Zn) in ingested phytoplankton and in ambient seawater, and the effect of food concentration on metal assimilation efficiency (AE) and elimination in copepods from Hong Kong coastal waters. The assimilation of detritus-bound metals in marine copepods was also determined.Results from my study indicated that the metal AEs in copepods decreased with an increase in metal concentration. Differences in metal distribution in algal cytoplasm at different ambient metal concentrations may be partially responsible for the observed variation in AEs. In addition, individual response of metal accumulation by Calanus sincus under different food quantity showed that metal AEs decreased significantly with an increase in food concentration, and were positively related to the gut passage time of food material and metals. My study also demonstrated that the detritus-bound metals were also bioavailable to marine copepods, and the metal AEs were comparable to the AEs measured previously for copepods fed on living algal cells. However, the physiological turnover rate was rather consistent and was independent of the metal concentration, food type and concentration, and the species of copepods, although the partitioning of metals between egestion and excretion was metal-specific. Information presented in this study is important to understand the trace metal accumulation in marine copepods and the biogeochemical fate of trace metals in the ocean.