Biological effects of planktonic Microcystis and benthic Oscillatoria on macro-benthic animals.

The concurrent presence of cyanobacterial blooms and cyanobacterial derivative pollution in natural freshwater poses serious threats to aquatic biota and human beings. To date, cyanobacteria, especially ignored benthic toxic cyanobacteria, may cause potential harmful impacts on benthic animals. Understanding benthic animals' possible responses to these toxic cyanobacteria is important for assessing cyanobacterial bloom-induced ecological risks. This study investigated the harmful impacts of planktonic Microcystis aeruginosa (generating microcystin) and benthic Oscillatoria sp. (generating cylindrospermopsin) on the feeding behavior, tissue structure, neurotoxicity, oxidative stress, and immunotoxicity of the freshwater macrobenthos clams Lamprotula leai and snails Bellamya aeruginosa under 14-d exposure. Firstly, two cyanobacteria can reduce the clearance rates of clams and snails, causing tissue damage in their digestive glands. Secondly, two cyanobacteria can induce neurotoxicity in clams and snails by altering acetylcholinesterase activities and acetylcholine levels in their digestive glands. Thirdly, two cyanobacteria can lead to oxidative stress in clams and snails by changing the antioxidant enzyme activities, glutathione levels, malondialdehyde levels, and reactive oxygen species levels in their digestive glands. Finally, two cyanobacteria can cause immunotoxicity in clams and snails by altering lysozyme activities in their digestive glands, while two cyanobacteria can also induce inflammatory responses in clams by increasing levels of interleukin-1β and tumor necrosis factor-α in their digestive glands. These data indicated that toxic cyanobacteria can threaten the health of macrobenthos, and the benthic cyanobacteria-induced adverse ecological impacts should not be ignored.