Salinity shapes zooplankton communities and functional diversity and has complex effects on size structure in lakes

Invasive species are considered the greatest threat to aquatic ecosystem biodiversity. Bythotrephes longimanus, an exotic zooplankton species introduced to North America in the 1980s, is threatening the structure of indigenous aquatic ecosystems as it continues to invade inland Ontario lakes. As a predacious zooplankton species, B. longimanus has been shown to decrease zooplankton abundance, species richness and shift zooplankton community size structure in invaded lakes. However, much of the previous research concerning the predatory effects of B. longimanus has been on surveys of a small number of lakes or has been in controlled mesocosm or lab-based experiments. This study examines the effects of B. longimanus on the zooplankton community using size-structure characterizations (grouping individuals from the community based on size) as community measures for 311 lakes in the Muskoka Region, a highly invaded watershed in Southern Ontario. More specifically, the study explores the size-spectra of invaded versus uninvaded lakes, with reference to an array of environmental lake characteristics (water chemistry, lake morphometry,etc.), and the relevance of B. longimanus activity on the regional scale. By using such a large-scale survey we will be able to appreciate regional-scale effects, as well as encompass the multiple and more indirect trophic interactions that B. longimanus is likely having with the entire aquatic community. (Funding: NSERC & CAISN.)

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Could increased cyanobacterial biomass following forest harvesting cause a reduction in zooplankton body size structure?

Canadian Journal of Fisheries and Aquatic Sciences ◽

10.1139/f06-117 ◽

2006 ◽

Vol 63 (10) ◽

pp. 2308-2317 ◽

Cited By ~ 24

Author(s):

Anas Ghadouani ◽

Bernadette Pinel-Alloul ◽

Ellie E Prepas

Keyword(s):

Large Scale ◽

Size Structure ◽

Forest Harvesting ◽

Profound Change ◽

Order Of Magnitude ◽

Scale Experiment ◽

Zooplankton Communities ◽

Lake Systems ◽

Possible Cause ◽

Cyanobacterial Biomass

Changes in phytoplankton and zooplankton communities were studied in 16 lake-years during a large-scale experimental before–after study as part of the Terrestrial Riparian Organisms Lakes and Streams (TROLS) project. After forest harvesting, phytoplankton biomass and especially cyanobacterial biomass increased in some of the experimental lakes, up to an order of magnitude. Although the response of phytoplankton was not directly related to the intensity of forest harvesting, this large-scale experiment provided a unique opportunity for studying the effects of an increasing gradient in cyanobacterial biomass on zooplankton communities. Cladoceran size structure and biomass were negatively correlated with cyanobacterial biomass, suggesting that large cladocerans and especially daphnids were inhibited by the increase in cyanobacterial biomass. The increase in cyanobacterial biomass seems to have caused a significant reduction in the size structure of zooplankton communities. As no correlation was found between cladocerans and cyanotoxins, our results point more towards feeding inhibition by filamentous and colonial cyanobacteria as a possible cause for the decline in the size structure and biomass of zooplankton communities. These results suggest that the increase in cyanobacterial biomass is likely to cause a shift in the size of zooplankton communities, which will lead to a profound change in functioning of lake systems.

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