International Review of Hydrobiology最新文献

The feeding ecology of the two gobiid species monkey goby Neogobius fluviatilis and western tubenose goby Proterorhinus semilunaris was studied in four natural lakes of the Marmara Region (NW Turkey), with special emphasis on seasonal and ontogenetic shifts in diet. Both species had similar food composition consisting of zooplankton and detritus. However, diet composition of both species significantly varied amongst lakes, and particularly so for P. semilunaris with seasonal and ontogenetic differences. Diet composition and seasonal/ontogenetic differences were overall similar to other populations of these gobiid species from both their native and nonnative ranges. The present findings suggest high plasticity in the diet of these two gobies, which can opportunistically utilize available food resources.

We studied two populations of Boeckella gracilipes and two populations of Boeckella gibbosa that inhabit mountain lakes from North-Patagonian Andes with different optical properties. We combined field and laboratory experiments to determine the effects of ultraviolet radiation (UVR) on clearance rate among these taxa that had different UVR defences. The copepod populations differed in photoprotective compounds (carotenoids and mycosporine-like amino acids [MAAs]) and antioxidant enzymes (glutathione S-transferase [GST]). These variations were related to elevation, dissolved organic carbon content and the optical features of the inhabited lakes. Laboratory experiments showed a decrease in the clearance rate (CR) in all populations exposed to UVR. Consistently, the long-term field experiment showed a negative impact of UVR on CR. We conclude that UVR exposure affects feeding, however, the magnitude of this negative effect depends on the exposure intensity and the photoprotective mechanisms used by zooplankton.

Many zooplankton organisms produce resting eggs before harsh environmental conditions. After aquatic systems are recovered, animals hatch from resting eggs and help re-establish active communities. However, although the ability of resting eggs to survive desiccation is largely known, it is unclear to what extent the duration of desiccation affects the viability and hatching patterns of resting eggs. In this study, we assessed the viability of resting egg banks in naturally wet and dry sediments through ex-situ hatching experiments. In addition, we simulated dry out episodes of different durations (2 and 8 months) in wet sediments originating from temporary systems. We observed hatchlings of rotifers, cladocerans, copepods, ostracods, and anostracans in wet and dry sediments. Drying the sediments for different durations did not change the species richness and composition of hatchlings, possibly because temporary systems select for species and genotypes that are more prone to producing resting eggs, which survive desiccation. However, some species were stimulated to hatch after desiccation, suggesting that desiccation might help break the dormancy of resting eggs from temporary systems. Desiccation intervals up to 8 months likely do not affect the viability of resting eggs from temporary systems. Since many lakes are about to experience unpredictable droughts owing to human activities and ongoing global changes, the ability of resting eggs to tolerate desiccation will play a key role in zooplankton community recovery.

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. Long-term 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.