Zooplankton community responses to varying environmental conditions and disturbances

Abstract

The concentration of human development at the southern end of the lake has caused it to operate in a fashion more similar to two interconnected systems, with a less impacted North Basin and a more impacted South Basin, rather than one homogenous waterbody. The differences between the basins are subtle, but this unique characteristic of Lake George allows for the examination of how aquatic environments differ along a gradient of human impact. Different zooplankton communities were present in each of the two deep basins that reflected the conditions present in the basin. Higher rotifer abundances, along with the presence of the indicator taxa Trichocerca sp. and Conochiloides dossuarius in the South Basin demonstrate the effect development has on the increased productivity of the southern end of the lake.

The loss of preferred food sources for B. longimanus could have been enough to cause its disappearance from sampling efforts. However, the prevalence of B. longimanus in other systems with unfavorable zooplankton communities raises the question of what is its diet in lakes that sustain long term invasions. In order to answer this question, a metabarcoding study was conducted examining the gut content of B. longimanus in two lakes with established populations. B. longimanus avoided preying upon the dominant zooplankton species in one of the lakes, and we observed a new predator-prey relationship between this invader and Chaoborus.

In Lake George, Bythotrephes longimanus was first observed in 2011. B. longimanus is an aggressive predator of zooplankton that can completely reshape the communities of invaded lakes. By the end of 2015 Daphnia pulicaria, the most common Daphniid, was no longer observed. In 2017, adult B. longimanus were no longer collected by monitoring efforts. While the invasion was short-lived, it had a persistent impact on the zooplankton community.

The effect that lake conditions have on diel vertical migration, a biologically and ecologically important behavior was examined using high-frequency sensor platforms. In this study, we examined the applicability of high-frequency sensors to the study of the vertical position of the zooplankton in an aquatic system.

Over the last two decades, water temperatures have been rising in Lake George. In 2016, there was an unusually warm winter that allowed for an examination of potential future scenarios under current trends. In 2016, disruption to the normal timing of the onset of the growing season altered the crustacean zooplankton community throughout the entire summer. Calanoid copepods were dominant for the only time in the four years studied, and Daphnia populations declined in favor of Bosmina and Sida. This highlights the threat of a complete restructuring of food web interactions in aquatic systems that is posed by the current climatic trends.

Spatial and temporal changes in the zooplankton community of Lake George, NY were examined over a four-year period from 2014-2017. Lake George is an oligotrophic lake that is affected by the threats posed by nutrient pollution, climate change and the impact of invasive species. The oligotrophic nature of this system coupled with the multitude of threats affecting it makes this an ideal system to study how zooplankton communities respond to environmental change.