On the diurnal rhythm and feeding electivity in kilka (<Emphasis Type="Italic">Clupeonella cultriventris</Emphasis>) in Rybinsk Reservoir

Diurnal rhythms, feeding electivity, and feeding resources were studied for the new for Rybinsk Reservoir fish species, kilka (Clupeonella cultriventris). It is revealed that, in Rybinsk Reservoir, kilka actively feeds during day time. Selective feeding is a characteristic of this fish. Yearlings prefer small Cyclopoida and their young specimens dominating in zooplankton. Two-year-old fish actively select innumerous but large crustaceans of genera Heterocope, Bythotrephes, Leptodora, and Cyclops. Possible factors determining selection of food items by kilka are discussed. These factors are as follows: zooplankters’ biomasses, the extent of plankters’ aggregations, body size, and visibility of some prey species for kilka (as determined by movement pattern, transparency and cuticle color, presence of eggs, or large eye).     

Determination of food sources of marine invertebrates from a subtidal sand community using analyses of fatty acids and stable isotopes

The fatty acid compositions and stable isotope ratios of carbon, nitrogen, and sulfur were analyzed in the bivalve mollusks Mactra chinensis, Pandora pulchella, Felaniella usta, and Megangulus zyonoensis, the polychaete Chaetopterus cautus, and the main sources of organic matter in a subtidal sand bottom community in Vostok Bay (Sea of Japan). The fatty acid composition and stable isotope ratios of some bivalves is likely to be indicative of substantial inputs from benthic microalgae and an important role of microbial food chains. Only the filter-feeding polychaete C. cautus showed similarity in these characteristics to suspended particulate organic matter synthesized by phytoplankton. It is suggested that the contribution of benthic microalgae to the diet of a consumer organism, inferred solely from the carbon stable isotope analysis, can be significantly overestimated.     

Circadian rhythmic changes in the lipid composition of muscles in kilka <Emphasis Type="Italic">Clupeonella cultriventris</Emphasis> (Clupeidae,clupeiformes) during natural periodicity of feeding in the feeding and spawning periods in the Rybinsk Reservoir

According to data of observations in 2002–2004, differences in the pattern of diurnal fluctuations in the total content and fractional composition of lipids in muscles of mature specimens of kilka Clupeonella cultriventris from the Rybinsk Reservoir in the feeding and spawning periods were revealed. It was established that the feeding intensity in kilka considerably changes throughout 24 h in both periods of the annual cycle, while diurnal fluctuations in the fatness of muscles are distinctly manifested only in the reproductive period and have a dissimilar pattern in specimens of different sexes. In females and males, they are determined mainly by the change in the content of the fraction of reserve lipids-triacylglycerols, as a rule, by its increase in the light hours of the day, several hours after an increase in the feeding activity of fish. The pattern of diurnal fluctuations of the level of lipid fractions (phospholipids, triacylglycerols, cholesterol, and its ethers) in kilka’s muscles differs from that in the feeding period. Possible causes of the change of diurnal variations of the considered indices of lipid metabolism in kilka at an increase in the endocrine activity of its body in the reproductive period is discussed.     

δ<Superscript>13</Superscript>C and δ<Superscript>15</Superscript>N in tissue of coral polyps and epilithic algae inhabiting damaged coral colonies under the influence of different light intensities

Studies were performed of the carbon and nitrogen stable isotope (δ¹³C and δ¹⁵N) composition (δ¹³C and δ¹⁵N) of the corals Porites cylindrica and P. lutea (5 years after damaging the colonies by the bleaching events) and of epilithic algae settled onto damaged areas of coral colonies. Coral polyps and three epilithic algal communities (‘red algal turf, green algal turf and red calcified crusts’) were sampled along the boundary between communities of coral polyps and algal colonizers from differently illuminated habitats from 2 to 90% of incident surface photosynthetically active radiation (PAR₀). It was found that communities with a predominance of red algae significantly differed from communities with a predominance of green algae in δ¹³C but not in δ¹⁵N values. An influence of habitat irradiance was found only for communities of coral polyps for δ¹³C and δ¹⁵N values: under bright light (70–90% PAR₀) polyp tissues of both coral species were significantly enriched in heavy carbon isotopes and insignificantly in nitrogen isotopes (δ¹³C values difference ~4‰) relative to tissues of corals under lower light 15–50% PAR₀. On the basis of these results we assumed that differences in light intensities in the habitat ranging from 15 to 90% PAR₀ do not influence on accessibility of the main carbon and nitrogen sources for corals and algae, and exchange by these elements between organisms. We also assumed that the relative enrichment in the heavy carbon isotopes of coral tissues in high light is a result of decreased isotope fractionation (or the absence of fractionation in photosynthesis of their zooxanthellae).     

Trophic relationships between macroinvertebrates and fish in St. Petersburg methane seep community in abyssal zone of Lake Baikal

Trophic relationships were examined for macroinvertebrates and fish inhabiting the St. Petersburg methane seep (central part of Lake Baikal, ~1400 m depth). The analyses of the values of carbon and nitrogen stable isotopes showed that all animals associated with the seep were heterotrophs with different feeding strategies; symbiotrophes were absent. Seep animals consumed combined food with different portion of methanederived carbon ranged from 2.7 to 89%. The average δ¹³С values varied in the range of–26.2‰ (in benthopelagic amphipods) to–64.5‰ (in gastropods). The trophic food web in the methane seep consists of filter feeders (pelagic amphipods, trophic position (TP) is 1.9), detritophages (gastropods, TP of 2.2, and burrowing amphipods, TP of 2.1), polyphages and necrophages (nectobenthic and benthopelagic amphipods of TP 2.8–3.2), and predators (planarians of TP 3.6–4.2 and cottoid fish of TP 3.0–3.8). Animals occupying similar trophic positions significantly differed in the δ¹³С values and have partially overlapping components of food.     

Resource partitioning in endemic species of Baikal gastropods indicated by gut contents, stable isotopes and radular morphology

We used multiple analytical methods to demonstrate resource partitioning in five species of coexisting endemic gastropods in the family Baicaliidae and the genus Megalovalvata (Valvatidae) in rocky walls of the underwater canyons in Lake Baikal. We tested whether filter-feeding baicaliids and valvatids consume and assimilate different food using data from gut contents, stable δ¹³C and δ¹⁵N isotopes and radular morphology, with subsequent combined analyses. Our results showed that the four baicaliid species assimilate microalgae, diatoms and bacteria, whereas the single Megalovalvata species mostly assimilates plant detritus. The δ¹⁵N variations in the baicaliids reflect differences in their digestion of seston components, whereas the δ¹³C similarity illustrates consumption of food particles derived from similar primary producers. Gut contents in the baicaliids were dominated by a single species of planktonic diatom, although more than 30 species of microalgae were recorded in all seasons. However, the composition and quantity of additional food particles varied by species. Our results showed that baicaliids have significant fine scale differences in radular tooth morphology, which may allow partitioning of food resources.     

Sulfur,carbon, and nitrogen stable isotope ratios in soft tissues and trophic relationships of fish from the near-shore waters of the peter the great bay in the Sea of Japan

Stable isotope ratios of sulfur (³⁴S/³²S), carbon (¹³C/¹²C), and nitrogen (¹⁵N/¹⁴N) were analyzed in the soft tissues of 12 common species of fish from the near-shore waters of the Peter the Great Bay in the Sea of Japan. The average δ¹³C values of individual species varied from −20.7‰ for planktivorous fish to −16.8‰ for benthivorous fish, reflecting the growing relative contribution of benthic primary producers to fish nutrition. The majority of the various species representatives studied can be assigned to one trophic level, as indicated by their narrow range of δ¹⁵N values (9.9 to 12.6‰). Large interspecific variations were found in the sulfur stable isotope ratios of fish (the mean δ³⁴S values ranged from 11.2 to 19.5‰). This is the result of the different contributions to fish nutrition of infaunal invertebrates that are depleted in ³⁴S due to the microbial food chain of the bottom sediments.     

Sluggish methane discharge and biological traits of benthic invertebrates in Lake Baikal

Hydrobiologia - The biological traits of invertebrates inhabiting freshwater methane seeps are poorly understood. We analysed the relationship between invertebrate abundance and environmental...     

Formation and development of the Black Sea-Caspian kilka Clupeonella cultriventris (Clupeidae) in the Rybinsk reservoir

We studied the state and development of the population of the Black Sea-Caspian kilka Clupeonella cultriventris in the Rybinsk reservoir from 1994 to 2010. The population dynamics, the rate of growth of the kilka, as well as its food relationships with other fish species of the pelagial community, were analyzed. It was found that the period of exponential increase in the numbers was replaced by the period of interannual fluctuations. With the development of the population, tendencies for a decrease in the rate of growth of the kilka and aggravation of its food relationships with other species are revealed, which is determined by changes in the structure of pelagic aggregations of fish. One of the most significant environmental factors determining dynamics of the numbers and state of the kilka population in the northernmost part of its modern range is water temperature.     

The composition of fatty acids and stable isotopes in the detritophage <Emphasis Type="Italic">Acila insignis</Emphasis> (Gould, 1861) (Bivalvia: Nuculidae): Searching for markers of a microbial food web

The fatty acid composition and stable isotope ratios of carbon, nitrogen, and sulfur were analyzed in the protobranch bivalve Acila insignis, a selective detritophage inhabiting subtidal sand sediments of Vostok Bay (Sea of Japan). Soft tissues of A. insignis contained abnormally high concentrations of the polyunsaturated arachidonic acid, 20: 4(n-6), and a rare monounsaturated fatty acid 20: 1(n-13), which distinguishes this species from other bivalves. The high concentrations of these fatty acids in A. insignis, together with the low values of σ³⁴S and the high values of σ¹³C and σ¹⁵N, are probably a result of feeding on the microbial food web.