Molluscs diatoms

Biogenic A. Calcareous B. Siliceous >30 >30 48 Foraminifera, coccoliths, calcareous algae, molluscs, bryozoa, and corals 14 Diatoms and radiolaria... 

The bioavailability of selenium to a benthic deposit-feeding bivalve, Macoma balthica from particulate and dissolved phases was determined from AE data. The selenium concentration in the animals collected from San Francisco Bay was very close to that predicted by a model based on the laboratory AE studies of radiolabelled selenium from both particulate and solute sources. Uptake was found to be largely derived from particulate material [93]. The selenium occurs as selenite in the dissolved phase, and is taken up linearly with concentration. However, the particle-associated selenium as organoselenium and even elemental selenium is accumulated at much higher levels. The efficiency of uptake from the sediment of particulate radiolabelled selenium was 22%. This contrasts with an absorption efficiency of ca. 86% of organoselenium when this was fed as diatoms - the major food source of the clam. The experiments demonstrated the importance of particles in the uptake of pollutants and their transfer through the food web to molluscs, but the mode of assimilation was not discussed. 

The isotopic composition of strontium of mollusc shells in the early Miocene section of the CRP-1 core (46-62 mbsf) indicated dates of 16.6 0.4 and 18.7 0.3 Ma in agreement with the diatom biostratigraphy of Harwood et al. (1998). The Ar/ Ar date of a volcanic clast (18.4 1.1 Ma) measured by McIntosh (1998) confirms the early Miocene (Burdigalian) age of the sediment. 

---