Benthic cyanobacteria and filamentous chlorophytes affect macroinvertebrate assemblages in a large fluvial lake

Benthic cyanobacterial mats serve as a refuge and food for the amphipod Gammarus fasciatus

“…Amphipods captured in mats of L. wollei indeed showed some sign of physiological stress, as evidenced by the higher activities of acetylcholinesterase and glutathione-S-transferase when compared to amphipods from sites devoid of the cyanobacterium (Gelinas et al, 2013). Despite consistent presence of the saxitoxin analog LWTX-1 in all samples collected from St. Lawrence River (range 0.3-153 lg LWTX-1 g -1 DM, Hudon, unpublished data), our laboratory results as well as field observations (Tourville Poirier et al, 2010) showed that amphipods were not deterred by L. wollei. Similarly, three out of four gastropods, when offered a choice between L. wollei and filamentous chlorophytes, were either indifferent or attracted to the cyanobacterium (Visconti et al, 2014).…”

“…In situ, however, amphipods that hide in benthic mats of cyanobacteria would receive less than 1% of incident light (Levesque et al, 2015) and would likely be better sheltered from fish predators than within mats of chlorophytes that generally float at the surface. Biomass of G. fasciatus was indeed threefold higher in mats of L. wollei than in metaphytic chlorophytes in the St. Lawrence River (Tourville Poirier et al, 2010). Acrylic wool (Experiment III) was the favored substratum by G. fasciatus likely because its large fibrous filaments (1,911 lm) trapped a mix of epiphytes, detritus, and sediments that blocked nearly all the light.…”

“…Similarly, the gammarid amphipod Gammarus fasciatus (Say) was consistently more abundant (25 mg g -1 vegetation dry mass) in L. wollei mats than in filamentous green algae and macrophytes (B8 mg g -1 vegetation dry mass) in the St. Lawrence River (Tourville Poirier et al, 2010).…”

“…Additionally, we measured the isotopic signature (d 13 C and d 15 N) of the ribbon-forming macrophyte Vallisneria americana Michx (N = 5), the most commonly observed submerged macrophyte in the St. Lawrence River, and its epiphytes (N = 4), as potential in situ food sources. V. americana was not used in choice experiments since amphipods were found on this macrophyte in densities *10 times less than those found in mat of L. wollei (Tourville Poirier et al, 2010). Prior to analyses, amphipods were starved for 24 h to allow gut clearing and ten whole individuals were pooled per sample.…”

Biotic interactions in freshwater benthic habitats

“…Rejmánková et al (1996) observed a greater abundance of Anopheles albimanus mosquito larvae among mats of Leptolyngbya than at sites lacking this cyanobacterium and demonstrated that female mosquitoes oviposited preferentially in those mats. In surveys of macroinvertebrate assemblages on various primary producers in a Canadian lake, Poirier et al (2010) speculated that the higher densities of mobile invertebrates, particularly amphipods, occupying L. wollei mats may have been a result of lower predation rates by fish among those mats. Our study provides evidence that such a mechanism is plausible.…”