ASSIMILATION OF TRACE-ELEMENTS AND CARBON BY THE MUSSEL MYTILUS-EDULIS - EFFECTS OF FOOD COMPOSITION

Assimilation efficiency (AE) is an important physiological parameter i n determining trace element influx from food sources into aquatic anim als. We used radiotracer techniques to examine the influence of diet [ seven species of algae (two diatoms, two chlorophytes, a prasinophyte, and two dinoflagellates) and glass beads] on the assimilation of seve n trace elements (Ag, Am, Cd, Co, Cr, Se, Zn) and C in the mussel Myti lus edulis. Trace element assimilation was related to C assimilation a nd cytoplasmic distribution in the algae and to gut passage time in th e mussels. Mussels displayed different C AEs for the different algal d iets; the chlorophytes, which had highly refractory cell walls, were t he least digestible food. Assimilation of Cd, Se, and Zn was directly correlated with C assimilation; for Am, Ag, and Cr, no relationship wi th C assimilation was apparent. For each species except the chlorophyt es, AEs of all elements significantly correlated with their cytoplasmi c distribution within each algal cell. Among all species, AEs of Am, C o, and Se also increased with elemental penetration into the cytoplasm ; however, this relationship was not statistically significant for Ag, Cd, or Zn. With the exception of Cr, AEs of elements increased with g ut passage time, implying more efficient digestion-absorption when the element was retained longer in the digestive tract. In waters contain ing large mussel populations, unassimilated particle-reactive elements should be removed from suspension and enriched in biodeposits in sedi ments, whereas assimilated metals should be enriched in mussel tissues .