Transport of cadmium and zinc to rocky reef communities in feces of the blacksmith ( Chromis punctipinnis), a planktivorous fish

Abstract

The blacksmith ( Chromis punctipinnis), an abundant planktivorous reef fish off southern California, releases fecal material as it forages in the water column during the day and shelters in reefs at night. This behavior results in direct transportation of cadmium and zinc to reef communities. Cadmium and zinc concentrations, measured in fish feces after digestion in weak hydrochloric acid to better assess metal levels potentially available to detritivores, averaged 24·2 μg cadmium and 368 μg zinc g −1 dry weight of feces. Concentrations of both metals varied significantly among the five sampling dates. Fresh feces spiked with 109Cd and 65Zn adsorbed additional metals for 9 and 6 h, respectively, but the increase was negligible (<0·1%). The total amount of weak-acid-leachable cadmium and zinc egested by sheltering blacksmiths is approximately 4·4 μg and 66·8 μg m −2 night −1, respectively, and may represent more cadmium and almost as much zinc as is transported by the passive settlement of particulate material from the water column. This transport mechanism between planktonic and benthic communities via feces of reef fishes is probably widespread in temperate and tropical seas.