Zebra mussel dC and dN as a proxy for depth-specific pelagic isotope profiles and lake temperature

Zebra mussels (Dreissena polymorpha) can be used to provide a baseline stable isotope signature, time-integrated with primary production. However, since zebra mussels are uncommon in pelagic zones, their potential as reference species in pelagic water columns has not been fully explored. By investigating mussels growing suspended on a single vertical cable in Lake Constance, we were able to document seasonal (April, May, and August) and depth-dependent (0 22 m) variation in mussel dM and dC. We found a strong correlation between temperature and mussel dN from differing depths; and a strong relationship between temperature and D 15 M (estimated as d15Mmussel d 15 MPOM) and D C (d13Cmussel d 13CPOM). In a pattern that remained consistent over all months, DM decreased with temperature, to the extent that negative values were recorded at temperatures [13°C. Utilizing cabledwelling pelagic mussels as indicators of variation in isotope and temperature for pelagic water could be used as a novel field approach, comparable to in situ experimentation. We suggest that the pelagic mussel approach can be employed in tandem with benthic or littoral mussel isotope values, to develop musselbased lake isoscapes. Such isoscapes may be pertinent to the study of seasonal trophic limnoecology and in tracking the movements of animals.