Impacts of Warming on Reciprocal Subsidies Between Aquatic and Terrestrial Ecosystems

Cross-ecosystem subsidies are important as their recipients often rely on them to supplement in situ resource availability. Global warming has the potential to alter the quality and quantity of these subsidies, but our knowledge of these effects is currently limited. Here, we quantified the biomass and diversity of the invertebrates exchanged between freshwater streams and terrestrial grasslands in a natural warming experiment in Iceland. We sampled invertebrates emerging from the streams, those landing on the water surface, ground-dwelling invertebrates falling into the streams, and those drifting through the streams. Emerging invertebrate biomass or diversity did not change with increasing temperature, suggesting no effect of warming on aquatic subsidies to the terrestrial environment over the 1-month duration of the study. The biomass and diversity of aerial invertebrates of terrestrial origin landing on the streams increased with temperature, underpinned by increasing abundance and species richness, indicating that the greater productivity of the warmer streams may attract more foraging insects. The biomass of ground-dwelling invertebrates falling into the streams also increased with temperature, underpinned by increasing body mass and species evenness, suggesting that soil warming leads to terrestrial communities dominated by larger, more mobile organisms, and thus more in-fall to the streams. The biomass and diversity of terrestrial invertebrates in the drift decreased with temperature, however, underpinned by decreasing abundance and species richness, reflecting upstream consumption due to the higher energetic demands of aquatic consumers in warmer environments. These results highlight the potential for asynchronous responses to warming for reciprocal subsidies between aquatic and terrestrial environments and the importance of further research on warming impacts at the interface of these interdependent ecosystems.

A freshwater crab (Barytelphusa sp.) feeding on a catfish (Pterocryptis sp.)

The freshwater crab, Barytelphusa cunicularis (Westwood, 1836), is a common and widespread crustacean species inhabiting freshwater streams throughout India except the northeast. It is an omnivore that feeds on small crustaceans, gastropods, insects and aquatic vegetation. This species is commonly collected as a food commodity and is also often reared in captivity for the same purpose. In captivity, these crabs seem to prefer animal-based food and are generally fed about 10% of their total biomass in prawn and rice flakes daily. Observations of B. cunicularis feeding in nature are scant in the literature, and to the best of my knowledge there have not been any reports of the species feeding on fish. Herein I report the first observation of B. cunicularis feeding on a Malabar silurus, Pterocryptis wynaadensis, a type of catfish.

Wintering shorebird in sandy coasts of Catania’s gulf (Sicily, Italy): 2011-2020

Sandy coasts are specific habitats of high ecological significance for many species of shorebirds. The Gulf of Catania, in the Eastern coast of Sicily, is considered one of the most important sandy coastal areas of the region for the wintering of different species of Charadriidae and Scolopacidae, also due to the presence of River Simeto’s mouth and other freshwater streams. Since the area has been subject to many changes in the last few decades and recent data were not available, a ten-year monitoring of the wintering shorebird community has been carried out, from January 2011 to January 2020, to understand its current ecological role and to update the knowledge about numbers and trends of Sicilian wintering shorebirds along the coast. A total of 3,171 individuals and 16 different species were observed, including a considerable amount of individuals of Calidris alba and Charadrius alexandrinus, despite the latter showed an 80% decrease in number in the last 20 years in the area. For each species, maximum numbers observed per winter and related five-year averages, estimates, IKA (Index of Abundance per Kilometre) and percentages in relation to the national wintering population have been reported. Furthermore, data about species associations were collected and analysed. This survey shows how the ecological value of River Simeto’s mouth has decreased considerably in the last decades in favour of other locations, such as the mouth of Canale Arci, where almost 50% of the birds were observed.

Hydrological, geochemical and land use drivers of greenhouse gas dynamics in eleven sub-tropical streams

Greenhouse gas (GHG) emissions from freshwater streams are poorly quantified in sub-tropical climates, especially in the southern hemisphere where land use is rapidly changing. Here, we examined the distribution, potential drivers, and emissions of carbon dioxide (CO2), nitrous oxide (N2O) and methane (CH4) from eleven Australian freshwater streams with varying catchment land uses yet similar hydrology, geomorphology, and climate. These sub-tropical streams were a source of CO2 (74 ± 39 mmol m−2 day−1), CH4 (0.04 ± 0.06 mmol m−2 day−1), and N2O (4.01 ± 5.98 µmol m−2 day−1) to the atmosphere. CO2 accounted for ~ 97% of all CO2-equivalent emissions with CH4 (~ 1.5%) and N2O (~ 1.5%) playing a minor role. Episodic rainfall events drove changes in stream GHG due to the release of soil NOx (nitrate + nitrite) and dissolved organic carbon (DOC). Groundwater discharge as traced by radon (222Rn, a natural groundwater tracer) was not an apparent source of CO2 and CH4, but was a source of N2O in both agricultural and forest catchments. Land use played a subtle role on greenhouse gas dynamics. CO2 and CH4 increased with catchment forest cover during the wet period, while N2O and CH4 increased with agricultural catchment area during the dry period. Overall, this study showed how DOC and NOx, land use, and rainfall events interact to drive spatial and temporal dynamics of GHG emissions in sub-tropical streams using multiple linear regression modelling. Increasing intensive agricultural land use will likely decrease regional CO2 and CH4 emissions, but increase N2O.

The potential of sediment and fauna microbiomes in water quality assessment

The Water Framework Directive dictates that all European surface waters must have an ecological quality of good or better. The need for regular and comparable ecological quality assessments drives the development of DNA-based approaches for biomonitoring in freshwater systems. Water quality assessments are traditionally based on biological quality elements (BQE) such as fish, plants and other fauna. Previous studies have shown the potential of metabarcoding as a potential supplement to traditional morphology-based approaches to determine water quality indices. Metabarcoding of the macroinvertebrate community on unsorted bulk samples has the ability to profile freshwater streams into at least 7 water quality categories Kuntke et al. (2020). A follow-up study using the same locations shows that a broad range barcode targeting the ribosomal 16S/18S RNA genes simultaneously demonstrated that ecological quality is reflected in all environmental DNA; the eukaryotic communities, and perhaps even more so, in the microbiome of the sampled streams (unpublished). The relationship between water quality and microbial communities is well-known, but not well-described. Healthy compositions of microbiota are vital for the functioning of many organisms, and this principle extends to the ecosystem level as well. The microbiome of freshwater streams therefore represents a great untapped potential in the development of DNA-based monitoring methods. The aim of this work was to explore links between water quality, environmental DNA collected from bulk and sediment samples, as well as individual macroinvertebrates with relevance for freshwater streams. Previous work on invertebrate communities Kuntke et al. (2020), and bulk sample analysis (total 53 streams) (unpublished) was combined with metabarcoding data of microbial communities from an additional 31 Danish stream sediments, as well as 140 macroinvertebrate indicator species. Metabarcoding of freshwater stream bulk and sediment samples has revealed strong parallels to conventional fauna observations in relation to estimations of water quality. Both the invertebrate and microbial community diversity followed the general trend of increasing to a plateau with higher water quality (data not shown). Macroinvertebrate composition (Fig. 1a) and sediment microbiome composition (Fig. 1b) were observed to be present on a gradient in relation to water quality, with individual taxa being either more, equally or less abundant with changing water quality, and only few solely related to a single category. Microbial populations associated to poor oxygenation (Methylomonadaceae, Rhodocyclaceae), as well as faecal contaminations (Anaerolineaceae, Lentimicrobiaceae) were abundantly observed in sediments of lower ecological quality. This equates to presence of macroinvertebrates able to survive in polluted environments with poor oxygen conditions. Part of the sediment microbiome was also found to be associated to the analysed macroinvertebrate species (Fig. 1c). However, the invertebrates also had their own unique and diverse microbiota, including known endosymbionts (Wolbachia, Rickettsia) and other insect associated microbiota (Acinetobacter, Chryseobacterium). Current sequencing platforms and high quality databases combined with advanced statistical analyses have made it possible to begin the development of modified assessment protocols based on DNA analyses, and could potentially lead to entirely new ecological quality indices for the prediction of water quality. Microbes can be very sensitive to environmental changes, and harbour potential indicator organisms for e.g. pollution, and by extension, water quality in a given stream. Microbiome data is abundant, and easy to obtain from all types of environmental samples, including those collected for metabarcoding of existing BQE such as macroinvertebrates. Exploring the use of sediment and fauna microbiomes has the potential to yield a wealth of new information relating to how ecosystems reflect water quality, and may provide additional indicators for use in DNA-based water quality assessment methods.

A taxonomic revision of Stanjehughesia (Chaetosphaeriaceae, Sordariomycetes), with a novel species S. kaohsiungensis from Taiwan

Stanjehughesia kaohsiungensis sp. nov. is described from decaying wood submerged in freshwater streams from Taoyuan District, Kaohsiung City, Taiwan. The phylogenetic relationship between Stanjehughesia species was sought among representative taxa from related fungal lineages within Sordariomycetes using LSU sequence data. Molecular data revealed the phylogenetic placement of S. kaohsiungensis is within Chaetosphaeriaceae and distinct from Sporidesmiaceae. While the genus is polyphyletic, a synopsis of morphological characters and a taxonomic key for Stanjehughesia species are provided to ease identification.

Difference of ecological half-life and transfer coefficient in aquatic invertebrates between high and low radiocesium contaminated streams

The Fukushima accident emitted radioactive substances into the environment, contaminating litter, algae, sand substrate, aquatic invertebrates, and fish in freshwater streams. Because these substances have substantial effects on stream ecology over many years, it is necessary to clarify the diffusion and decay mechanisms of radiocesium. The transfer coefficient differed among aquatic invertebrate groups, likely due to the differences in habitat. The ecological half-life of cesium was longer where the air dose rate was lower. The transfer coefficient was also higher in areas with lower air dose rate. The radiocesium concentration in algae was inversely related to stream current velocity in the radiocesium-contaminated area. However, this relationship was not observed in the lower air dose rate area: the radiocesium concentration in algae in the rapid-velocity areas tended to be higher than that in the slow-velocity areas. This reverse trend would lead to a longer period of freshwater contamination. The radiocesium concentration would continue to decrease in highly contaminated areas, but it would be difficult to reduce the radiocesium concentration in less-contaminated areas because different contamination mechanisms are at work. Controlling the water flow is key to regulating radiocesium concentration in freshwater ecosystems.