SECTION 15 



ASPECTS OF THE INTERACTION BETWEEN BENTHOS AND SEDIMENTS IN THE 

 NORTH AMERICAN GREAT LAKES AND EFFECTS OF TOXICANT EXPOSURES 



John A. Robbins^ 



The sediments of the North American Great Lakes are mostly overlain by 

 well -oxygenated waters and support a diverse and abundant population of ben- 

 thic (bottom-dwelling) organisms. Principal species include the freshwater 

 shrimp, Mysis relicta ; the amphipod, Pontoporeia hoyi ; many species of Oli- 

 gochaete worms such as Tubifex tubifex and Limnodrilus hoffmeisteri ; the 

 midge larvae Chironomus anthracinus and a variety of freshwater clams such 

 as Sphaerium and Pisidium spp. Many of these organisms occur in great abun- 

 dance throughout the Great Lakes. The deposit feeding Oligochaete worms 

 occur in polluted harbors in numbers exceeding 1,000,000 m-2 (P. McCall, 

 pers. comm.), and even in the profundal sediments of Lake Erie in densities 

 approaching 50,000 m-2. Characteristically, Pontoporeia hoyi occurs in 

 densities on the order of 1,000 m-2 throughout much of the Great Lakes. In 

 Lake Erie, as well as in the inshore areas of the other Great Lakes, 

 Chironomid larvae densities are roughly 500 m-2 (P. McCall and D. White, 

 pers. comm.). These organism densities represent an enormous biomass 

 dwelling in or interacting with the sediments. 



Not only are certain benthos an important link in the food chain, but 

 many of them significantly affect the stratigraphy of sediments (Robbins et 

 al . 1977) and the exchange of nutrients between sediments and water through 

 such activities as burrowing, feeding, respiration, and excretion. As the 

 fine-grained sediments are both the ultimate sink and a partial source (cf 

 Remmert et^ aj_. 1977) of nutrients in the Great Lakes, the life activities of 

 the benthos are likely to be an important factor in the nutrient cycle. If, 

 in turn, the behavior, physiology, or mortality of benthos are affected by 

 aquatic pollutants, there can be potentially novel and important effects on 

 major nutrient cycles. While there has been considerable work done on the 

 role of benthos in sediment mixing and exchange of substances across the 

 mud-water interface in other lakes (see Petr, 1976 for a review), \/ery 

 little has been done in the Great Lakes. The aim of this paper is to illu- 

 strate the effects of selected benthos on particle and solute transport and 



^Great Lakes Research Division, University of Michigan, Ann Arbor. 

 Michigan 48109. 



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