THE EFFECTS OF LOWER PH ON FRESHWATER MUSSEL SHELL GROWTH IN THE RAQUETTE RIVER IN NORTHERN NEW YORK STATE

Freshwater mussels or unionids are a large and diverse group p of bivalves that can be found on all continents with the expectation of Antarctica. An estimated 71% of unionid species in the U.S. are endangered species in particular due to habitat degradation. Anthropocene alterations of streams and decreasing pH due to acid rain precipitation are amongst the environmental factors imperiling the habitats of these organisms.

In this study, we examine Elliptio complanata a unionid species that frequently occurs in the lakes and rivers of northern New York State. The Raquette River runs through the highlands of the Adirondack Mountains to the lowlands of the St. Lawrence River and, due to the difference in buffering capacity of the bedrock it is flowing over, the pH of the water increases northwards. This offers the opportunity to compare shell growth in different pH regimes. We hypothesize that growth rates of highland mussels will be lower than the growth rate in lowland populations reflecting better growing conditions for shell-building organisms in more alkaline water.

We sampled eight locations, four in the highlands and four in the lowlands. Over 80 valves were cleaned, embedded in epoxy, and cut along the axis of maximum growth with a precision saw. The resulting 1 mm thick sections were glued on microscope slides. The slides were scanned with a high-resolution scanner and the scans were processed in ImageJ, counting and measuring growth rings of each individual. Bertalanffy growth curves were generated and growth rate data has been analyzed using Excel and PAST.

Overall we see a decrease in growth throughout the life span of all individuals. Early in their ontogeny highland individuals are on average larger than lowland clams; later in life, we find fewer differences in length. Growth expressed as a percentage of length increase per year corroborates that highland populations seem to grow faster early in their life than the lowland individuals and later on their growth rate declines more rapidly.

This preliminary data suggests that the organisms that inhabit more acidic environments of the highlands seem to increase size faster at the beginning of their development to be less vulnerable to the negative effects of the water chemistry and then slow down their shell growth due to the more difficult growing conditions.