Overwinter Changes in the Lipid Profile of Young-of-the-Year Striped Bass (Morone saxatilis) in Freshwater Ponds

Young-of-the-year (YOY) striped bass (Morone saxatilis) suffer significant mortality during their first winter. While causes of this mortality are unclear, lipids may play role in adapting to winter stresses, including thermal change and food scarcity. To address this, YOY striped bass were placed in mesh cages in freshwater ponds in the fall (November) and were held until the end of winter, in March. Liver and white muscle tissue were sampled at the beginning and end of the study to compare concentrations of specific lipid classes and fatty acid composition. Muscle-tissue total lipid and triacylglycerol (TAG) was higher in March (late winter) samples. Additionally, concentrations of phosphatidylethanolamine (PE) were higher in the white muscle of striped bass sampled in March; this was accompanied by a decrease in proportions of 18:0 and 22:6n-3 in PE (from ~11 to 7% and 36 to 28%, respectively) and 18:1n-9 and 22:6n-3 in phosphatidylcholine (from ~15 to 10% and 24 to 18%, respectively). This suggests that these fish were not utilizing energy reserves in previously described ways and appear to rely more on other lipid classes or body tissues for overwinter survival than those analyzed in this study.

Culture Possibilities of Certain Brackishwater Species at Freshwater: A Climate Change Adaptation Strategy for Salinity Intrusion Prone Areas of Indian Sundarban Delta

Salinity intrusion into coastal mainland or freshwater habitat because of recent climatic changes is exacerbating production risks and challenging the coping capacity of freshwater fish farmers of Sundarban coastal delta in India. Hence, an experiment was conducted to evaluate the survival and growth performance of certain commercially important brackish water species in freshwater, and subsequent low salinities (5 g l−1 and 10 g l−1). Species like Scatophagus argus, Chelon parsia, Terapon jarbua, Etroplus suratensis, and Penaeus monodon showed the highest specific growth rate (SGR) at 10 g l-1 salinity. However, the growth rates were not differed significantly (P>0.05) compared to freshwater. Chelon planiceps and Mystus gulio exhibited the highest SGR at 5 g l-1 salinity, although growth rates of the fish were not differed significantly (P>0.05) with freshwater treatments. Comparable survival and growth of all species in the freshwater condition indicated their ability of healthy acclimation at freshwater ponds. Therefore, these euryhaline fish species can be promoted in the Indian Sundarban for culture in freshwater ponds as climate-resilient adaptation strategies. This study could be useful in decision making during species and farm site selection which eventually will minimize the risks from total crop loss during saltwater inundation.

Bacterial composition reflects fine-scale salinity changes while phylogenetic diversity exhibits a strong salt divide

Climate change induced salinization events are predicted to intensify and lead to increased salt stress in freshwater aquatic ecosystems. As a consequence, formerly distinct abiotic conditions and associated biotic communities merge, and the emergence, loss, and persistence of microbial taxa modify the types and rates of ecosystem processes. This study examined how bacterial taxonomic and phylogenetic diversity and ecosystem function respond to acute salinization events where freshwater and estuarine communities and environments coalesce. We hypothesize that if the salinity change outpaces microbial adaptation or saline microbial populations are not yet established in formerly freshwater conditions, then we predict diminished carbon cycling rates, decreased microbial diversity, and altered the composition of microbial communities compared to historically freshwater communities. We used an experimental mesocosm approach to determine how salinity and the merging of distinct communities influenced resultant bacterial community structure and function. Each mesocosm represented different salinities (0, 5, 9, 13 psu). Two dispersal treatments, representing aquatic communities sourced from brackish 13 psu ponds and a mix of 13 psu and freshwater ponds, were added to all salinity levels and replicated four times. Results revealed that salinity, but not dispersal, decreased bacterial taxonomic and phylogenetic diversity. Carbon mineralization rates were highest in freshwater conditions and associated with low relative abundance indicator taxa. Acute salinity changes, such as localized flooding due to storm surge, will more negatively affect freshwater aquatic communities compared to chronic exposure to salinization where the communities have had time to adapt or turnover resulting in recovered biogeochemical functions.

Density-Dependent Cannibalism in Dragonfly Nymphs (Odonata: Anisoptera) Overwintering in Temperate Freshwater Ponds

Density-dependent mortality by predation and cannibalism has been observed in aquatic insects such as dragonflies in response to shrinking habitat caused by summer drought. Winter conditions might also reduce the amount of livable habitat in temperate ponds and could augment rates of cannibalism. We hypothesized that cannibalism in dragonfly nymphs would increase in winter due to a seasonal decrease in available habitat caused by stratified lower oxygen levels leading to increased nymph density around pond edges. To determine whether cannibalism in nymphs is density-dependent and size-dependent (i.e., with smaller nymphs consumed) we experimentally manipulated nymph density in aquaria. To evaluate whether these patterns are observed in nature during the winter, we conducted field surveys for nymphs in two ponds across the fall and winter seasons. When nymphs were housed at different densities for 24 h, cannibalism was density-dependent, and only smaller nymphs were preyed upon. Our field surveys found that fewer nymphs were caught in the late winter sampling period (mixed-effects model, P < 0.001), and that these were larger than nymphs caught in the fall, although both patterns were restricted to the deeper pond (P < 0.05). Our results were consistent with the process we hypothesized, and the observed reduction in dissolved oxygen at the bottom of the deeper pond. The lack of significant changes to the relative abundance and size of nymphs in the shallower pond reveals that differences in pond characteristics can influence the degree to which winter conditions induce density-dependent cannibalism among dragonfly nymphs.

DESMIDS BIODIVERSITY IN FRESHWATER PONDS OF DISTRICT NAGAUR, WESTERN RAJASTHAN INDIA: A PRELIMINARY INVESTIGATION

The present study was carried out to investigate the desmids biodiversity in traditional freshwater reservoirs of Nagaur district, Western Rajasthan, India. The samples were collected in January 2021 from the freshwater small ponds which harvests rainwater located in and around Nagaur city. These samples were analyzed by following the standard method prescribed by A.P.H.A for assessing the various physicochemical parameters such as pH, TDS, Fluoride, Nitrate, Chloride, total alkalinity, and total hardness to check drinking water quality and for ecological assessment. Furthermore desmids species-level identification and description have been done with the help of standard literatures and monographs. Results of physicochemical parameters indicate the deteriorating drinking water quality of all four sampling sites. In the present study total of 16 species belong to 5 genera i.e. Netrium, Closterium, Cosmerium, Staurastrum, and Eustrum of desmids have been recorded for the first time from the freshwater ponds located in or around the Nagaur city. The higher biodiversity of Closterium and Cosmarium species at Jhada talab confirm its significant relationship with high calcium and nutrient-rich water quality. While low biodiversity of desmids at remaining all village ponds indicates that high pH and oligotrophic quality decreases the desmids biodiversity. Results of this study might be helpful to assess the geographic distribution of desmids flora of Nagaur district and establish water quality of protected freshwater habitats as well as in updating the list of current species of desmids in this sub-region.

Desert fish populations tolerate extreme salinity change to overcome hydrological constraints

The unstable nature of freshwater ponds in arid landscapes represent a sizable challenge for strictly aquatic organisms, such as fishes. Yet the Arabian Desert, bordering the coastline of the Red Sea, plays host to a species very well adapted to such extreme environments: the Arabian pupfish, Aphanius dispar. In this study, we estimated patterns of hydrological connectivity; population structure and stable isotope for samples of A. dispar living in small, isolated ponds of nearly-freshwater in the Arabian desert and highly saline coastal lagoons along the Red Sea. The genomic and hydrological analyses indicate that populations are largely separated by drainage origin, as fish from desert ponds appear to be transported to coastal lagoons of the Red Sea along ephemeral river systems arising from flash flood events. Further, our study indicates there is an ecological change when being washed from pond environments to coastal waters, due to a significant shift in muscle stable isotopes ratios between both groups. Considering that the genetic breaks are mostly observed between drainage origin, this study suggests that A. dispar can survive large changes in salinity and ecological regimes over small time-scales.

Freshwater under the MOSAiC floe: implications of under-ice melt ponds for mass balance

<p>During the melt season in the Arctic, freshwater ponds can accumulate under ice floes as a result of local snow and sea ice melt, far from terrestrial freshwater inputs. Under-ice freshwater ponds have been suggested to play a role in the summer sea ice mass balance both by isolating the sea ice from salty, warmer water below, and by driving formation of ice ‘false bottoms’ at the interface of the under-ice pond and the underlying ocean. </p><p>The MOSAiC drift expedition in the Central Arctic observed the presence of under-ice ponds and false bottoms beginning early in the melt season (June - July) at primarily first-year ice locations on the floe. We examine the prevalence and drivers of these ponds and resulting false bottoms during this period. Additionally, we explore the impact for mass balance using observations from ablation stakes and a 1D model, where freshwater ponds can not only delay summer melt but also result in growth. We speculate that the unique history of the MOSAiC floe likely led to a relatively high occurrence of these features, but the results also suggest that freshwater under-ice ponds and false bottoms may be more common and more persistent in early summer in the Arctic than previously thought. Both have implications for the broader ice-ocean system, for example by reducing fluxes between the ice and the ocean, isolating the primary producers in ice from pelagic nutrient sources, and altering the optical properties.</p>