Why Are Half of New York Finger Lakes Invaded by Cercopagis pengoi, While the Other Half Have Remained Non-invaded for Over a Decade?

The fish-hook flea, Cercopagis pengoi, is an abundant invasive zooplankton that invaded six of the eleven New York Finger Lakes in 1999, one year after invading Lake Ontario. Cercopagis is predatory, which could alter trophic dynamics of invaded lakes since their food webs are dominated by herbivorous zooplankton. Additionally, Cercopagis is consumed by the region’s planktivorous fish (Alosa pseudoharengus), and may impact their trophic position if they shift from consuming the native herbivorous zooplankton to a diet including the invasive predatory zooplankton. The partial New York Finger Lakes invasion creates a natural experiment ideal for studying the impacts of Cercopagis in invaded lakes and the factors preventing establishment in the non-invaded lakes. This study compares ecosystem characteristics of invaded and non-invaded lakes, including physical parameters, productivity, zooplankton assemblages, and alewife characteristics. High predation from alewife likely prevents the establishment of Cercopagis in non-invaded lakes; these lakes have many characteristics indicative of high alewife densities including poorer alewife condition, and a larger proportion of small bodied to large bodied zooplankton. Other differences include invaded lakes containing significantly more predatory zooplankton and fewer Bosmina, a small herbivorous zooplankton that is likely a key prey item for Cercopagis. Despite the presence of more predatory invertebrates, analysis of alewife gut contents indicated that alewife from invaded and non-invaded lakes are likely feeding at a similar trophic position

Zooplankton-phytoplankton biomass and diversity relationships in the Great Lakes.

Quantifying the relationship between phytoplankton and zooplankton may offer insight into zooplankton sensitivity to shifting phytoplankton assemblages and the potential impacts of producer-consumer decoupling on the rest of the food web. We analyzed 18 years (2001-2018) of paired phytoplankton and zooplankton samples collected as part of the United States Environmental Protection Agency (U.S. EPA) Great Lakes Biology Monitoring Program to examine both the long-term and seasonal relationships between zooplankton and phytoplankton across all five Laurentian Great Lakes. We also analyzed effects of phytoplankton diversity on zooplankton biomass, diversity, and predator-prey (zooplanktivore/grazer) ratios. Across the Great Lakes, there was a weak positive correlation between total algal biovolume and zooplankton biomass in both spring and summer. The relationship was weaker and not consistently positive within individual lakes. These trends were consistent over time, providing no evidence of increasing decoupling over the study period. Zooplankton biomass was weakly negatively correlated with algal diversity across lakes, whereas zooplankton diversity was unaffected. These relationships did not change when we considered only the edible phytoplankton fraction, possibly due to the high correlation between total and edible phytoplankton biovolume in most of these lakes. Lack of strong coupling between these producer and consumer assemblages may be related to lagging responses by the consumers, top-down effects from higher-level consumers, or other confounding factors. These results underscore the difficulty in predicting higher trophic level responses, including zooplankton, from changes in phytoplankton assemblages

Can space-for-time-substitution surveys represent zooplankton biodiversity patterns and their relationship to environmental drivers?

Space-for-Time-Substitution surveys (SFTS) are commonly used to describe zooplankton community dynamics and to determine lake ecosystem health. SFTS surveys typically combine single point observations from many lakes to evaluate the response of zooplankton community structure and dynamics (e.g., species abundance and biomass, diversity, demographics and modeled rate processes) to spatial gradients in hypothesized environmental drivers (e.g., temperature, nutrients, predation), in lieu of tracking such responses over long time scales. However, the reliability and reproducibility of SFTS zooplankton surveys have not yet been comprehensively tested against empirically-based community dynamics from longterm monitoring efforts distributed worldwide. We use a recently compiled global data set of more than 100 lake zooplankton time series to test whether SFTS surveys can accurately capture zooplankton diversity, and the hypothesized relationship with temperature, using simulated SFTS surveys of the time series data. Specifically, we asked: (1) to what degree can SFTS surveys capture observed biodiversity dynamics; (2) how does timing and duration of sampling affect detected biodiversity patterns; (3) does biodiversity ubiquitously increase with temperature across lakes, or vary by climate zone or lake type; and (4) do results from SFTS surveys produce comparable biodiversity-temperature relationship(s) to empirical data within and among lakes? Testing biodiversity-ecosystem function (BEF) relationships, and the drivers of such relationships, requires a solid data basis. Our work provides a global perspective on the design and usefulness of (long-term) zooplankton monitoring programs and how much confidence we can place in the zooplankton biodiversity patterns observed from SFTS surveys.info:eu-repo/semantics/publishedVersio