MEPS 204:159-168 (2000)  -  doi:10.3354/meps204159

ABSTRACT: Concentrations of several metals (e.g., Cu and Zn) in barnacles are probably the highest recorded among any marine animals. Physiological processes responsible for such high metal concentrations remain less well quantified. In this study we measured the assimilation efficiency (AE) of Cd, Cr, and Zn in a subtidal barnacle Balanus trigonus, an important fouling organism in the Indo-Pacific region. The bioavailabilities of metals from different phytoplankton diets and zooplankton diet (the copepod Paracalanus aculeatus) were compared. The AEs in B. trigonus feeding on different phytoplankton (diatoms, a dinoflagellate, and a prasinophyte) were in the range 41 to 62% for Cd, 3 to 10% for Cr, and 54 to 85% for Zn. The AEs of Cd and Zn were relatively higher in barnacles feeding on zooplankton diets, ranging from 77 to 78% for Cd and 86 to 88% for Zn. For different phytoplankton diets, we showed that the AEs of Cd and Zn were related to metal distribution in the phytoplankton cytoplasm and the metal gut-passage time. For Cr, no relationship between its AE and its distribution in algal cytoplasm was found, but its AE was significantly dependent on the time of Cr passage through the barnacle¹s gut. The distribution of metals in the copepod¹s soft tissue did not affect the assimilation of metals in the barnacles. Barnacles appeared to assimilate a significant fraction of metals associated with the cell wall/membrane of phytoplankton cells or the exoskeleton of copepods. A significant relationship was also found between the AEs of Cd and Zn, suggesting that their digestion and transport were coupled in the gut. Consistently, comparable fractions of Cd and Zn were distributed in the body gut after 2 d depuration. The high AE of metals found in this study may contribute substantially to the significance of trophic transfer in accounting for the high concentrations of Cd and Zn in barnacles.

KEY WORDS: Barnacles · Dietary uptake · Assimilation · Cadmium · Chromium · Zinc