Hemocyte functions and bacterial clearance affected in vivo by TBT and DBT in the blue mussel Mytilus edulis
Marine Ecology Progress Series
The effects of tributyltin (TBT) and dibutyltin (DBT) on the hemocyte functions of the blue mussel Mytilus edulis were investigated in 2 separate experiments at 2 different cold periods of the year. In Expt 1, we exposed mature mussels to waterborne TBT or DBT (from 5 to 80 ng Sn l -1 ) under flow-through conditions. The mussel hemocytes were monitored for membrane injury (MI), phagocytic activity (PA), lysosome retention (LR) and hemocyte count (HC) over 32 d. Both TBT and DBT significantly
... BT significantly affected all cellular functions measured. MI was present as early as Day 1 for TBT doses >10 ng Sn l -1 and DBT > 20 ng Sn l -1 in Expt 1, and by Day 32 all doses of TBT and all DBT doses >5 ng Sn l -1 had produced significant MI increases. PA was reduced by all doses of TBT and DBT in a time-and dose-responsive manner from Day 1 for TBT >10 ng Sn l -1 and by Days 18 to 32 for all doses of both chemicals. LR was significantly elevated by DBT dose of 80 ng Sn l -1 between Days 1 and 4 but not thereafter. Significant elevations and depressions in HC were observed in mussels exposed to both butyltins, although effects were highly variable and not clearly related to either dose or time of exposure. To confirm our first observations, Expt 2 was carried out using mussels exposed to 40 and 80 ng Sn l -1 TBT or DBT over 13 d under the same experimental design. The hemocytes were monitored for: (1) PA using both microscopic and spectrophotometric observations; (2) LR using 2 incubation times; and (3) HC in hemolymph from individual and pooled mussel samples. The general trends of Expt 1 results were confirmed. In addition to hemocyte assays, mature mussels from Expt 1 as well as mature and juvenile mussels from Expt 2 were injected with the common bacterium Listonella (= Vibrio) anguillarum after 32 and 13 d of exposure, respectively, to TBT or DBT concentrations described above. For both butyltins, a significant dose-related impairment in clearing Vibrio from the hemolymph was observed for all doses in both experiments. Clearance of bacteria was slower for the juveniles than for the adults suggesting that the early life stages of mussels may be more affected by butyltin exposure than adults. This study established strong and sustained responses of hemocyte functions of blue mussels exposed to environmentally relevant, waterborne concentrations of TBT and DBT (0.04 to 0.67 nM as Sn) which is interpreted as an increase of their vulnerability to other environmental stressors and pathogens, even at low seawater temperatures, (< 5°C) often present in high latitude coastal waters.