Assimilation of trace elements ingested by the mussel Mytilus edulis:effects of algal food abundance

Abstract

Pulse-chase feeding and multi-labeled radiotracer techniques were employed to measure the assimilation of 6 trace elements ( l l O m~g , 2 4 1~m , '09Cd, 5 7~o , '$Se and "~n ) from ingested diatoms in the mussel Mytilus e d u l~s feeding at different rates (0.1, 0.49 and 1.5 mg dry wt h-'). Uniformly radiolabeled diatoms Thalassiosira pseudonana were fed to mussels for 0.5 h, and the behavior of the radiotracers in individual mussels was followed for 96 h in a depuration seawater system. Assimilation efficiency (AE) of each element declined with increasing ingestion rate and increased with gut passage time. The importance of extracellular digestion relative to intracellular digestion increased with ingestion activity, which, when coupled with a decline in AE, suggested that extracellular digestion is less efficient in metal absorption. Zn assimilation was most affected by ingestion rate, suggesting that AE may play a role in the physiological regulation of this metal in M. edulis. In an experiment to simulate the effects of an acidic gut, lowered pH (5.5) enhanced the release of elements from intact diatom cells, especially at low particle concentration. These results indicate that both feeding components of the mussel (i.e. gut passage time, digestive partitioning) and metal chemistry (i.e. metal release at lowered pH within the bivalve gut) are responsible for the difference in the assimilation of trace metals at different food quantities observed in mussels.

Cadmium sources and exchange rates for Chaoborus larvae in nature

“…In other studies, inverse relationships have also been reported between IR and the AE of phosphorus by Chaoborus trivittatus (Giguère 1981) and of Cd by marine mussels (Wang et al 1995).…”

“…This increase could be explained if a greater food consumption led to either a higher metabolic rate, and thus a higher loss rate of Cd, or to differences in digestive processes, as has been observed in mussels (Wang et al 1995). The biological half-life (t 1/2 ) of Cd decreased from 117 to 22 d with increasing food density ( Table 2).…”

“…Given the reported influence of factors such as ingestion rate (this study; Munger and Hare unpubl. data), food quality (Reinfelder and Fisher 1991;Wang and Fisher 1996), and temperature (M.-N. Croteau, INRS-Eau, unpubl. data) on metal assimilation efficiency, such differences among studies are to be expected.…”

Influence of a selective feeding behaviour by the blue mussel Mytilus trossulus on the assimilation of 109Cd from environmentally relevant seston matrices

“…'OgCd-AE is defined as the proportion of ingested '09Cd retained after digestion of selected seston and gut evacuation. Wang et al (1995) noted that less than 10% of 2 4 1~m was retained in soft tissue after a 24 h depuration period, and most unassimilated Io9Cd was egested within the first 17 h, after which very little Io9Cd appeared in the FE or was lost from tissues. Based on this, 'OgCd-AE was determined after a 24 h depuration period.…”

“…Given the now recognized importance of incorporating AE into predictive models of metal accumulation, over the last 5 yr a number of studies have reported AEs for several metals, most notably cadmium, silver, cobalt and chromium, by invertebrates, from a variety of substrates, including algae (Borchardt 1983, Harvey & Luoma 1985. Zang et al 1990, Absil et al 1994, Wang et al 1995 organically coated silica beads (Decho & Luoma 1994), and natural sediment (Gagnon & Fisher 1997). …”