WANG, WEN-XIONG, AND NICHOLAS S. FISHER ... - ASLO

206 Wang and Fisher
ilability of 241Am and 65Zn. The main source of Am influx
into mussels is probably the dissolved phase (adsorption)
(Bjerregaard et al. 1985) because AEs for this element are
typically low and food type may have little influence on
bioaccumulation of this element. Mussels are able to reg-
ulate Zn uptake and show a less pronounced response to
a change in environmental Zn concentrations (Amiard-
Triquet et al. 1986). One of the possible physiological
mechanisms underlying Zn regulation is the change in Zn
AE (Wang et al. 1995). Zn influx from the particulate
phase (controlled by a combination of Zn concentration
in food particles, Zn AE, and mussel feeding activity) can
be regulated when mussels are feeding on different types
of food particles. Therefore, the difference in Zn influx
from different food sources could be insignificant, as shown
by Fisher and Teyssie (1986). The influx rate of Zn from
the dissolved phase increases directly with ambient Zn
concentration, suggesting that dissolved Zn uptake is pri-
marily a passive process and does not significantly affect
the regulation of Zn uptake in mussels (Wang and Fisher
unpubl.).
Conclusions
Trace element assimilation in marine mussels seems
to be determined by cytological distributions in ingested
algal cells and GPT in the mussels. Differences in C and
trace element assimilation in mussels ingesting diverse
algal diets suggest a food sorting mechanism in the di-
gestive system of the mussels. In addition to the different
AEs noted for different algal species, the effects of food
composition on metal influx rate from the particulate
phase also depend on the feeding activity of the mussels
on the specific food item and the metal concentration in
the ingested particles. Because mussels selectively ingest
organic-rich particles (Ward and Targett 1989), the higher
AE of some trace elements (e.g. Cd, Se, Zn) associated
with these particles may further increase their overall
influx into mussels. AEs from different food sources must
be considered in quantitative modeling of metal accu-
mulation in mussels.
Additionally, the assimilation of trace elements and
biodeposition of unassimilated elements (in feces and
pseudofeces) may have a pronounced impact on sus-
pended particle loads and the cycling of trace elements
in coastal waters, particularly in waters containing large
bivalve populations (Kelly et al. 1985; Dame 1993). El-
ements that are not efficiently assimilated should be readi-
ly packaged into feces and deposited in sediments, thereby
enriching surficial sediments, as observed by Brown
(1986). Thus, the transfer of trace elements from particles
suspended in the water column to sediments should be
aided by the production of feces (or pseudofeces) by bi-
valves. The retention of trace elements in bivalve fecal
material, which has been relatively little studied (Bjer-
regaard et al. 1985), should influence the fate of these
biodepositcd elements; elements with long retention times
may be buried in the sediments or reingested by benthic
fauna, whereas metals that desorb from fecal deposits
may be remineralizcd back into the dissolved phase. Those
elements that are efficiently assimilated should be con-
centrated in mussel tissues.
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