Zebra mussel δ¹³C and δ¹⁵N as a proxy for depth-specific pelagic isotope profiles and lake temperature

Abstract

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 δ 15Ν and δ 13C. We found a strong correlation between temperature and mussel δ 15N from differing depths; and a strong relationship between temperature and Δ15Ν (estimated as δ 15Νmussel − δ 15ΝPOM) and Δ13C (δ 13Cmussel − δ 13CPOM). In a pattern that remained consistent over all months, Δ15Ν decreased with temperature, to the extent that negative values were recorded at temperatures >13°C. Utilizing cable-dwelling 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 mussel-based lake isoscapes. Such isoscapes may be pertinent to the study of seasonal trophic limnoecology and in tracking the movements of animals.