ASSESSMENT OF INFLUENCE OF THE AUTOACCLIMATIZERS ON AUTOCHTHONOUS BIVALVE MOLLUSKS

Anthropogenic transformation of the Caspian Sea biocenoses results in the loss of their uniqueness and decrease of their biodiversity. In recent years the main role in the formation of biomass has played the autoacclimatizant mollusks Abra ovata , Mytilaster lineatus and Cerastoderma glaucum which dominate the biocenoses of the Caspian sea and are the main food components of valuable commercial benthivorous fishes. In 2018 live specimens of Corbicula fluminalis (O. F. Muller, 1774), a new species of bivalve mollusks for the Russian sector of the Caspian sea and the entire European part of Russia, were first discovered on the Daghestan coast.

Plenty of room at the bottom: niche variation and segregation in large-bodied benthivores of boreal lakes

Realized trophic niches of aquatic consumers are expected to reflect the particular abiotic and biotic conditions of the ecosystems they occupy. We examined patterns in the position, size, and shape of trophic niches of two common benthivorous fishes, white sucker (Catostomus commersonii) and lake whitefish (Coregonus clupeaformis), across boreal lakes using a stable isotope approach. In sympatry, white sucker niche positions reflected greater benthic reliance (higher δ13C) and lower trophic elevation (lower δ15N) compared with lake whitefish, and white sucker niche sizes (dispersion in δ13C–δ15N space) were also larger. Niche sizes of both species increased with maximum depth of lakes. Separation of trophic niche positions of the two species increased with increasing water clarity, but their niche sizes did not increase with increasing separation in their niche positions. White sucker occupied a niche position with slightly greater pelagic reliance and trophic elevation and had smaller trophic niches in the absence than in the presence of lake whitefish. Trophic niches of these benthivores appear to be shaped by both environmental factors and interspecific interactions.

Microplastic pollution in St. Lawrence River sediments

Although widely detected in marine ecosystems, microplastic pollution has only recently been documented in freshwater environments, almost exclusively in surface waters. Here, we report microplastics (polyethylene microbeads, 0.40–2.16 mm diameter) in the sediments of the St. Lawrence River. We sampled 10 freshwater sites along a 320 km section from Lake St. Francis to Québec City by passing sediment collected from a benthic grab through a 500 μm sieve. Microbeads were discovered throughout this section, and their abundances varied by four orders of magnitude across sites. Median and mean (±1 SE) densities across sites were 52 microbeads·m−2 and 13 832 (±13 677) microbeads·m−2, respectively. The highest site density was 1.4 × 105 microbeads·m−2 (or 103 microbeads·L−1), which is similar in magnitude to microplastic concentrations found in the world’s most contaminated marine sediments. Mean diameter of microbeads was smaller at sites receiving municipal or industrial effluent (0.70 ± 0.01 mm) than at non-effluent sites (0.98 ± 0.01 mm), perhaps suggesting differential origins. Given the prevalence and locally high densities of microplastics in St. Lawrence River sediments, their ingestion by benthivorous fishes and macroinvertebrates warrants investigation.