Leptodora Kindtii (Focke): Seasonal Population Abundance and Food Web Interactions in Lake Ontario; 1984, 1986, and 1987

Abstract

In 1984, 1986, and 1987 five stations in Lake Ontario off Sandy Creek were sampled biweekly to determine the abundance and biomass of the zooplankton Leptodora kindtii (Focke) and its links in the food web. The seasonal abundance and distribution of Leptodora kindtii in Lake Ontario were governed by temperature and productivity of habitat. The minimum temperature which Leptodora kindtii occurred in Lake Ontario was 6.0o C. The highest abundance occurred proportionally with the highest temperatures in the months of late July and August. The population is mostly comprised of the female Leptodora during this period. The first appearance of male Leptodora in Lake Ontario occurred in mid-August and their numbers gradually increased with time. Leptodora kindtii is a multivoltine organism which does not have a clearly separable cohort. Average abundance of Leptodora at the nearshore station ranged from 26.5 Leptodora/m3 in 1984, 2.8 and31.7 Leptodora/m3 (inside and outside the Brockport Water Intake Plant, respectively) in 1986, and zero in 1987. The average abundance for the offshore station ranged from 9.8 Leptodora/m3 in 1984 to 28.7 Leptodora/m3 in 1987. There was a positive correlation between alewife abundance and Leptodora abundance over several years of varying forage fish abundance. This suggests that alewife do not affect Leptodora abundance in Lake Ontario, which is contrary to the results of previous studies in other lakes.