A new type of effect of potentially hazardous substances: uncouplers of pelagial-benthal coupling.

Abstract

Hydrobionts are mediators of “biogenic migrationof atoms in the biosphere” [1]. This migration is partlyimplemented in the framework of pelagial–benthalcoupling. Trophic activity of bottom filter feedersresults in consumption of the organic matter of plank-ton synthesized in pelagic zones (see, e.g., [2]). Eventhe organic matter that is not assimilated by fulter feed-ers is involved in pelagial–benthal coupling. Suspendedmatter of aquatic ecosystems (including pellets ofinvertebrates) is subjected to gravitational sedimenta-tion [2, 3]. The pellets of invertebrates are formed as aresult of excretion of unassimilated and undigestedfood of phytophagous invertebrates. The degree of foodassimilation in different taxa of invertebrates rangesfrom 1 to 98% [4, 5]. The mean percentage of foodassimilability averaged over many groups of organismsis 16.2–89.6% (Table 1). Therefore, the rest of the foodmatter (10.4–83.8%) remains unassimilated and settlesto the bottom with pellets. Thus, pellets of invertebratesare able to transport a fraction of organic matter synthe-sized in the pelagic zone by photosynthetic organismsfrom this zone to the bottom layers of aquatic ecosys-tems, i.e., to the habitat of benthic organisms (thebenthal).The goal of this work was to determine whetherthere is a potential hazard of disturbance of the pela-gial–benthal coupling induced by water pollution. Itshould be noted that such a hazard of the pollution-induced disturbance of ecosystems has been almostentirely ignored thus far.Bivalve mollusks were objects of this study.Because bivalve mollusks are involved in eliminationand sedimentation of particles suspended in bulk water,these organisms are components of the pelagial–benthal coupling [6–11].The effect of potassium bichromate, a xenobiotic,on the rate of elimination of suspended particles by theBlack Sea mussel Mytilus galloprovincialis was stud-ied. Experimental methods were described elsewhere[10, 11]. Mussels (kindly provided by of A.V. Pirkovaand A.Ya. Stolbov) were grown in water headers in theoutskirts of the city of Sevastopol. The mean bodyweights (raw weights with shell) of experimental(treated with potassium bichromate) and control mol-lusks were 6.53 and 6.59 g, respectively. Both controland experimental tanks contained 13 specimens ofmussel each. Each tank contained 500 ml of sea water(18ppt). The initial concentration of the yeast Saccha-romyces cerevisiae (SAF-Moment, S.I. Lesaffre, 59703Marcq-France) suspension in tanks was 40 mg dryweight per liter. The water temperature was 23.4 ° C.The optical density was measured spectrophotometrri-cally using a SF-26 LOMO spectrophotometer andcuvettes with an optical path length of 10 mm. Similarexperiments were performed with the oyster Crassos-trea gigas , which was also grown under maricultureconditions.The results of our experiments showed that potas-sium bichromate is capable of inhibiting the filtrationactivity of mollusks (Table 2). This reduces the amountof food available for the digestive system of the mol-lusks. The decrease in the amount of food removedfrom water (i.e., the ration decrease) was accompaniedby a visually observed decrease in the rate of formationof pellets. The amount of pellets in the end of the exper-iment in tanks containing potassium bichromate solu-tion in water (0.05 mg/l) was significantly less than incontrol tanks. It was found in our experiments that oys-ters ( C. gigas ) were significantly less sensitive to potas-sium bichromate than mussels ( M. galloprovincialis ).A similar decrease in the amount of suspended par-ticles (plankton cells) eliminated from water wasobserved in our experiments with other xenobiotics,including surfactants, synthetic washing mixtures(SWMs), and liquid washing mixtures (LWMs) (Table 3).In all cases studied, we found that inhibitors of filtra-tion activity caused a decrease in the rate of formationof pellets. Only a few examples of such effects areshown in Table 3. Inhibition of filtration processes wasalso reported by J. Widdows, P. Donkin, D. Page,A.V. Mitin, and some other researchers [9, 10].In addition to experimental studies on planktonelimination from water by marine and freshwater