Lake browning impacts community structure and essential fatty acid content of littoral invertebrates in boreal lakes

Many lakes in the northern hemisphere are browning due to increasing concentrations of terrestrial dissolved organic carbon (DOC). The consequences of lake browning to littoral invertebrates, however, are not fully understood. We analyzed community structure and fatty acid (FA) profiles of littoral invertebrates in humic (DOC-rich) and clear-water lakes in Eastern Finland. We found higher abundance of chironomids (Diptera: Chironomidae) in humic compared to clear-water lakes, whereas stoneflies (Plecoptera) and mayflies (Ephemeroptera: Baetidae) were more abundant in clear-water lakes. Taxon explained 65% of the differences in the FA composition of littoral invertebrates. However, the proportion and content of polyunsaturated FAs of several taxa were significantly higher in clear-water lakes compared to humic lakes. Our results reveal differences in both community structure and nutritional quality of littoral invertebrates for fish between humic and clear-water lakes.

Littoral invertebrates in waders’ nutrition at migratory stopover sites in the Azov and Black Sea region

Seasonal migration for birds – distant migrants are the most energy intensive. Fat reserves accumulated in the bird’s body before migration and during migratory stopovers determine success of the long-distance flight. Lipids play a vital role both as a source of energy and as structural components of cell membranes. For most migrants to the speed and quality processes fat accumulation affects the feed ration in the field of migration stops. Fodder saturation with essential polyunsaturated fatty acids (PUFAs) is of great importance. Being paramount for physiological processes, these acids cannot be synthesized in the bird’s body. The proposed article is dedicated to the study of waders’ trophic relationships with their prey items, and the use of PUFAs as biochemical markers. This approach is based on the specificity of the fatty acids contained in the lipids of invertebrate to be used as food bird species studied. Significant amount NPZHK waders obtained from forage that can be considered PUFAs as biochemical markers to determine the range and diversity of food producing birds PUFAs ways, and also to study the food chain in ecosystems. A fatty acid spectrum (FAS) of the lipids common for nine littoral invertebrate species (Gammarus aequicauda, Idotea balthica, Artemia salina, Nerеis sp., Nerеis zonata, Theodoxces astrachanicus, Hydrobia acuta, Chironomus salinarius, Chironomus plumosus), which constitute the main component of waders’ diet at the migratory stopover sites in the Azov and Black Sea region, has been studied. Found that the largest amount of total lipids contained in Nereis zonata (4,6 %) and Artemia salina (4,4 %), the lowest amount of total lipids was observed in Chironomus (1,5–1,8 %), which implies that polychaete worms and Artemia salina, as a source of fat, are the most productive for waders. Our research has found that mollusks, polychaete worms, and Artemia salina are the most effective waders’ fodder in the PUFAs content. Mollusks contain the largest amount of PUFAs, their spectrum is ω3 and ω6 PUFAs, especially arаchidonic acid C20:4. Polychate worms are also characterized by a high PUFAs level; they serve for birds as a source of linolenic and linoleic acid groups. Artemia salina contains a large amount of eicosapentaenoic С20:5ω3 and docosahexaenoic С22:6ω3 acids, which getting to an organism of birds, participating in the formation of cell membranes, act as thermal stabilizer lipid bilayers, enhance stamina during long-distance flight. A high abundance of Artemia salina in the feeding areas permit tundra waders to use them as a prey item, which can fulfill the bird’s body with a required amount of fatty acids in a short time. We have established an influence of some environmental factors, as water temperature and salinity, on the lipids FAS of littoral invertebrates. Spectrum analysis of polyene fatty acids in the lipids closely related species of invertebrates living in different salinity water showed that the content of PUFAs in the lipid depend on their food spectrum, and the environmental conditions. Therefore, anthropogenic pressure and changes of water hydrological regime may affect PUFAs content in the lipids of littoral invertebrates. In its turn, this factor may change alimentary behavior and migratory strategy of the birds, which use migratory stopover sites in the region in question. Shallow waters of the Azov-Black Sea region are characterized by different climatic characteristics and a large reserve of phytoplankton. This explains the mass character species studied of invertebrates to feeding areas and their use as basic prey items, many species of waders.

Some ascidians from the southern coast of Madagascar collected during the “AtimoVatae” survey

Surveys of littoral invertebrates along the southern coast of Madagascar have produced the first study of ascidians in this part of the Indian Ocean. Collections were made by SCUBA divers in May and June 2010 down to 25m depth. This region is considered the southern limit for coral reefs but remains diverse biologically. Upwellings and an abundant plankton community particularly favour the abundance of ascidians in this area. Of the 39 species of non-didemnid species described here, eight are new. Ten species are common to South Africa. Other species were for the most part already known from the Mozambique Channel and a few have also been recorded in the western Pacific (either cosmopolitan or introduced).

Limited effects of stocked trout on littoral invertebrates in boreal foothills lakes

Stocking lakes with trout for the purposes of recreational angling is a management strategy that introduces a new predator into these systems and thus deserves careful scrutiny. To assess the impact of non-native trout on littoral invertebrates in naturally fish-bearing lakes in the boreal foothills of Alberta, Canada, we compared their community composition, abundance, and size structure in stocked (n = 5) and unstocked (n = 6) lakes over a 2-year period. We detected no clear negative effects of introduced trout on invertebrate community composition and only few taxa-specific examples of decreased or increased invertebrate abundance. Furthermore, predation by trout had inconsistent direct effects on the size structure of invertebrate populations. Indirect effects were suggested by increased abundances and sizes of some invertebrate taxa in stocked lakes and might also contribute to the limited overall differences that we observed. We propose that net effects of stocked trout on littoral invertebrates are influenced by key characteristics of receiving ecosystems. In our boreal foothills lakes, dense macrophyte cover in warm littoral zones, high productivity, abundant forage fish, and limited densities of trout all likely combine to allow littoral invertebrate communities to withstand the impact of introduced trout with minimal effects.

Assimilation of freshwater salmonid aquaculture waste by native aquatic biotaThis paper is part of the series “Forty Years of Aquatic Research at the Experimental Lakes Area”.

An experimental finfish aquaculture farm was operated in a small lake at the Experimental Lakes Area in northwestern Ontario, Canada. In this study, we used the distinct and enriched carbon and nitrogen isotope ratios (δ13C and δ15N) of rainbow trout ( Oncorhynchus mykiss ) feed and waste to determine whether the operation provided a novel source of energy for native biota. For 1 year prior to and for 3 years during the cage culture, we collected littoral, pelagic, and profundal invertebrates and minnows from the experimental and reference lakes. In both the second and third years of aquaculture, there was a significant increase in δ15N of all organisms sampled in the experimental lake; mean δ15N values of littoral, pelagic, and profundal invertebrates and minnows shifted towards the signature of the fish feed by up to 4.2‰. Significant increases in δ13C of up to 2.6‰ were observed in Mysis , profundal chironomids, and minnows but not in littoral invertebrates or zooplankton. Aquaculture waste became a progressively more important component of minnow diets over the course of this study. The dissolved and (or) particulate wastes of the cage operation became a novel source of energy for the native biota in this experimental lake.

Spatio-temporal dynamics of fish feeding in the lower Mulgrave River, north-eastern Queensland: the influence of seasonal flooding, instream productivity and invertebrate abundance

Wet-season flooding causes dietary shifts in tropical freshwater fish by regulating instream productivity, habitat structure and food availability. These dynamics have been comprehensively documented worldwide, but data are limited for Australia’s Wet Tropics rivers. The aim of the present study was to extend our earlier fish–habitat model for these systems by examining the role of trophic dynamics in determining fish assemblage composition. Chlorophyll a and phaeophytin concentrations, benthic and littoral invertebrates and fish were collected at four sites in the lower Mulgrave River under a range of flow conditions. Wet-season flooding caused significant reductions in instream productivity, whereas habitat disturbance reduced densities and abundances of littoral and benthic invertebrates. However, volumetric gut contents of 1360 fish, from 36 species, revealed seasonal shifts in guild membership by only two species, with fish moving between sites to target their preferred prey items – largely irrespective of differences in habitat structure. As a result, the food consumed by the fish community present at each site closely reflected the seasonal availability of food resources. The present paper questions whether fish community composition in small tropical rivers can be accurately predicted from habitat surrogates alone and encourages consideration of constraints imposed by the trophic dynamics and reproductive ecology of fish.

Response of littoral macroinvertebrate communities on rocks and sediments to lake residential development

Previously pristine lakes of the Laurentian region of Quebec, Canada, have faced increasing residential development of their watershed since the 1970s. We tested whether littoral invertebrates respond to this perturbation, even though open-water nutrients and chlorophyll are not yet altered. We examined changes in biomass, size structure, and taxonomic composition of macroinvertebrates living on rocks and sediments in 13 lakes representing a gradient of lakeshore residential development and watershed clearing. Littoral invertebrates provided early indication of lake perturbation, but their response varied according to the substratum. On rocks, total invertebrate biomass increased along the perturbation gradient and size structure shifted towards large organisms. These changes were likely mediated by a concomitant increase in epilithon biomass, suggesting a bottom-up control. No significant change in total biomass and size structure was observed for invertebrates in sediments. In contrast, taxonomic composition changed with lake development in sediments, but not on rocks. Taxonomic shifts were likely related to changes in sediment heterogeneity due to a decline of woody litter and increased fine particle deposition. Oligochaetes were positively associated to perturbation, whereas mayflies were negatively associated; these taxa could be used as indicators. Sediments were a better sentinel substratum than rocks for biomonitoring the impact of lake residential development.