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Artemia spp. play a key role in hypersaline ecosystems. Artemia can live in a salinity range from 10 to 300-340 g/L, but in water bodies where salinity is between 10 and 100 g/L, it may be absent. Is the absence of Artemia in some Crimean lakes determined by the presence of predators or by salinity? To answer this question field long-term and experimental data collected in the Crimean lakes were used. With the least probability, the populations of Artemia existed in the lakes with a salinity of up to 50 g/L or above 300 g/L. Self-reproducing Artemia populations (all age stages) were most likely (≥80% of occurrence) noted in the salinity range of 150-200 g/L. Longterm monitoring in two lakes showed that in different years, a significant negative correlation of Artemia abundance with the numbers of amphipod Gammarus aequicauda and ostracod Eucypris mareotica was found in both lakes. This correlation can be explained by ostracod and amphipod predation on Artemia. In years without predator populations, the number of Artemia was higher by several times.Experiments showed that these amphipods and ostracods consume brine shrimps of different developmental stages. There are at least 12 crustacean species, 5 insect species, and 2 fish species, all listed in this paper, which inhabit Crimean hypersaline waters and can eat Artemia. Their predation on Artemia often is a main cause of its absence in the salinity range from 10 to 150 g/L.

Chironomidae larvae may represent more than 70% of total Arthropoda numbers in hypersaline waters. Crimea, the largest peninsula of the Black Sea, has more than 50 hypersaline water bodies of marine and continental origin. Chironomidae larvae are common components of their ecosystems, but they still are poorly understood. This paper summarizes the results of a long-term study (2007-2016) of chironomids in Crimean hypersaline waters. More than 400 samples from 38 water bodies were used for analysis. The maximum salinity of water bodies containing Сhironomidae larvae was between 320 and 340 g/L. At first it was shown that Baeotendipes noctivagus (Kieffer, 1911) is the most halotolerant chironomid species in the world. Frequency of larvae occurrence varied and was negatively dependent on salinity. Four chironomid species were found: B. noctivagus, Cricotopus gr. cylindraceus (Kieffer, 1908), Tanytarsus gr. mendax Kieffer, 1925 and Paratanytarsus sp. Ceratopogonidae larvae were also found twice, at salinities of 150 and 270 g/L. B. noctivagus was the most common species, which occurred in 81% of samples with chironomids. Abundance of larvae fluctuated widely and reached high numbers: in planktonto 8 thousand/m 3 , in floating green algae matsup to 3 thousand/m 2 , and in benthosup to 9 thousand/m 2. Nonlinear dependence of chironomid abundance from salinity was observed; maximum abundance was at salinity levels of between 150 and 170 g/L. The average weight of larvae of 0.05-1.50 mm in length varied little in the samples; however, larvae of greater length had a significantly different average weight. Larvae of 8 mm in the samples had the average actual weight, which ranged from 0.750 to 2.203 mg.

Gammarus aequicauda and Artemia spp. are abundant crustacean species in Crimean hypersaline lakes. G. aequicauda preys on Artemia but there was no quantitative data on this before the current study. Predation of G. aequicauda on adult Artemia was studied in experiments with two different approaches evaluating (a) the time balance of the feeding process and (b) the grazing intensity. The threshold prey concentration, when consumption began to increase with increasing concentration, was approximately 15 ind./L in 200-ml vessels and about 5 ind./L in 500-ml vessels. When the Artemia abundance reached 20-25 ind./L, there was no further influence on the gammarid consumption rate. There was a significant negative correlation between the consumption rate of gammarids and Artemia abundance. According to study results, an individual G. aequicauda may eat up to 20-24 Artemia/day. Our study suggests that (a) G. aequicauda is an omnivorous species and can significantly suppress populations of its prey. (b) The two experimental approaches used to study the feeding of gammarids on Artemia produced similar results, and both may be used to quantitatively assess relations in a "prey-predator" system. (c) The abundance of predators and prey, as well as the experimental vessel volume, may influence the feeding rate. (d) The presence of plant food resources such as the leaves of Ruppia does not influence on the predatory feeding rate of G. aequicauda. (e) The rate of prey consumption by G. aequicauda is not constant and depends nonlinearly on prey and predator abundance. (f) Cannibalism occurs in the presence of plant resources only, but not in the presence of Artemia. (g) Other gammarids react to the capture of Artemia by one of them. They swim up to the successful individual and try to take some part of the prey.

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The ecosystems of hypersaline waters are characterized by the simplified trophic webs with the ‘loss’ of predators. In the absence of predators, their role can be effectively performed by omnivorous as Gammaridae species. In Lake Moynaki, a small hypersaline lake, Gammarus aequicauda is one of the most abundant animal species along with chironomid larvae Baeotendipes noctivagus. Both these species are promising objects to use in polyaquaculture, and this adds an importance to know their trophic relations. To analyse G. aequicauda feeding on B. noctivagus, the field and experimental studies were conducted in 2018 and 2019. In two habitats (Ruppia thickets and free water), the abundance of both species significantly differed, and in the thickets of Ruppia, the Gammarus abundance was higher, and of chironomid larvae was less. Taking into account our experimental results and chironomid larvae abundance in the lake during the study period (from 460 to 3,200 ind./m2), the authors conclude that larvae abundance did not limit the rate of their consumption in the lake by G. aequicauda, and one can consume up to 4 larvae per day. Thus, G. aequicauda could receive a diet of about 45% of their weight consuming about 2% of the available larvae daily in areas without the marine grass Ruppia thickets. In Ruppia thickets, chironomid larvae are not important food of G. aequicauda because the Ruppia leaves play a more important role in gammarid diet. With sufficient plant food resources, G. aequicauda can be successfully cultivated together with chironomid larvae.

-Biotic changes and a salinity increase (from 13 to 40 g.L −1 ) occurred in Lake Qarun (Egypt) since 1901. Was salinity increasing a cause of observed biotic changes? To answer this question we used benthos as a model group. Benthos and water sampling was conducted in different seasons (2008−2013). Comparing our and literature data, we discuss the long-term trends and possible causes of benthos changes. Salinity reached 3 g.L −1 in middle of 19th century; and biotic changes caused by this were started. From middle 19th century to 1928 a biotic transformation was driven by the salinity increase; after 1928 a regular alien species introduction caused that a marine community formed. In 1970−2000 eutrophication played a main role in species composition changes. In 2014 ctenophore Mnemiopsis leidyi introduced in the lake; eutrophication, chemical pollution, and a population dynamics of this ctenophore may be main drivers of the ecosystem change now. Benthos biomass gradually decreased during interval 1975−2013 without any correlation with salinity change. A variety of other factors than salinity may be significant in determining the structure and dynamics of communities, and we conclude that we have a small chance to make a correct forecast of possible future ecosystem changes in Lake Qarun.