The Role of Biotic and Abiotic Interactions in Summer Diapause in Cyclopoids: Conceptual Model and Field Validation in Southern Quebec Boreal Lakes

Abstract

Cyclopoid copepods are a dominant component of freshwater zooplankton and the Cyclopidae is the most diverse family. Dormancy is a fundamental process of cyclopoid life history in permanent lakes and temporary ponds. In boreal lakes, cyclopoid diapause has been documented mainly in Northern Europe but more rarely in Northern America. We present the first assessment on summer diapausing cyclopoids (SDC) in 22 boreal lakes in southern Quebec, which vary in their morphometry, tropic status, and predation pressure by fish or invertebrates. We developed a conceptual model to test the hypothesis that diapausing patterns of SDC in boreal lakes are a complex response depending primarily on morphometric and trophic features and secondly on the intensity of hypolimnetic anoxia and predation by fish or invertebrates. Using morphometric indices, lakes were classified in groups varying by the importance of wind-mixing, the strength of thermal stratification during summer, the potential of meromixis, and the risk of predation by fish or chaoborids. Three cyclopoid species (Diacyclops thomasi, Cyclops scutifer, Mesocyclops edax) dominated in all groups of lakes, while Diacyclops nanus and Acanthocyclops vernalis were found in small abundance and only in few lakes. The highest abundances of SDC (density and biomass) were found in sediments of thermally stratified mesotrophic lakes with intermediate wind-mixing index (Ko) and low potential for meromixis (Pm). Strong positive correlations were found between SDC and meiobenthos abundances in all groups of lakes. High biomass of Chaoborus larvae or presence of large populations of fish negatively affected SDC abundances in meiobenthos. Morphometric features, wind-mixing and thermal stratification, as well as the abundance of Chaoborus and fish predators are the key factors governing species diversity and abundance of summer diapausing cyclopoids in boreal lakes.