Summer Abundance Research Articles

Dynamics of small metazooplankton in relation with environmental factors: A 12-year study in the coastal zone of the Southwestern Crimea (the Black Sea)

Based on continuous 12-year (2010–2021) monitoring of the average summer abundance of small metazooplankton (SMZ) in the coastal zone of the Southwestern Crimea, the patterns of its interannual fluctuations were investigated. The total SMZ abundance during the study period varied from 37.8 to 176.0 thousand·m−3 in the open coastal area (on average, 104.0 ± 49.2 thousand·m−3) and from 90.3 to 556.8 thousand·m−3 at the bay mouth (on average, 264.5 ± 121.0 thousand·m−3). The crustacean fraction accounted for 85–91% of the total SMZ abundance. Principal component analysis (PCA) showed a noticeable contribution of 48 % of total temperatures and wind speed and different direction repeatability to the SMZ abundance variability. For native data, significant relationships were revealed between the abundance of individual SMZ fractions and hydrometeorological parameters: total temperatures of the warm period of the year (May–October), periodicity of the southern and southwestern, northern winds, calm conditions (events of the absence of wind), and the summer index of the North Atlantic Oscillation (NAO) with a 1-year lag. The application of fast Fourier transform (FFT) with a Hamming filter to the original series and periodograms analysis allowed revealing typical periods of variability in SMZ abundance and hydrometeorological parameters of the environment: 2–4-year and 5–6-year ones. At these scales, a higher number of significant relationships was established with the indicated hydrometeorological parameters, inter alia winter and summer NAO indices, than during the analysis of the original series. The total contribution of hydrometeorological and climatic factors to the variation in the abundance of SMZ increased to 78–79 %. This confirms the assumption that the relationship between SMZ and environmental parameters is characterized by its own features at different scales. Analysis of long-term SMZ different fractions tendencies for Summer 2010–2021, according to the Mann-Kendall criterion, did not show significant results.

Study of the gonadotrophic cycle of Rhipicephalus (Boophilus) annulatus (Say, 1821) (Acari: Ixodidae) in laboratory conditions

The purpose of the research is to determine the physiological characteristics of the single-host tick Rhipicephalus (Boophilus) annulatus depending on environmental factors, including the season of the year.Materials and methods. The study of the gonadotrophic cycle and fertility of B. annulatus was carried out during their seasonal activity from March 2022 to November 2023. The work consisted of two stages: field and laboratory. Ticks were collected manually from cattle in different settlements. Material was collected in natural biotopes according to the generally accepted method using a standard flag and drag. Nourished females were selected for oviposition and kept in laboratory conditions while maintaining optimal temperature and humidity. A total of 1,743 specimens were collected and identified. The sex ratio was 1: 7 with a predominance of females.Results and discussion. The gonadotrophic cycle and reproductive potential of B. annulatus vary by season. In autumn, the oviposition period, taking into account the incubation period, extends to an average of 28 days. The reproductive potential of females varied from 23 to 2194 eggs/ind. In spring, the cycle duration is comparatively shorter and, on average, does not exceed 25 days. Tick fertility can range from 19 to 5503 eggs/ind. which determines their abundance in summer and autumn months. The data obtained confirm the need for acaricidal treatment of animal grazing areas in the foothill zone in late autumn in order to reduce the number of B. annulatus both after winter diapause and throughout the year.

Intra-annual compositions and diversity variations of waterbird communities in China

Waterbirds are often used as indicators of wetland biodiversity and ecosystem health due to their sensitivity to environmental changes. However, most studies have focused on long-term variations of waterbird communities, while the intra-annual changes have rarely been investigated. Here, we analyzed the seasonal dynamics of compositions and the intra-annual variations of species richness and abundance of waterbird communities among the nine major river basins of China, and focused on the effects of different residential types and taxonomic groups on the diversity variations. In most of the nine basins, the waterbird communities in spring and autumn showed high similarity, while those in summer and winter were quite different. Such a seasonal cycle of species composition was caused by the seasonal migration of waterbirds. The season with higher species richness shifted from summer to winter as the latitude of the basin decreased within China, but almost all basins had the lowest community abundance in summer. This was because the variation of richness was directly influenced by the variation in species composition, but the variation of abundance was more influenced by the population size of different waterbird assemblages. Our results emphasized the importance of seasonal dynamics of waterbird communities to the understanding of their migration patterns, and highlighted the impact of different waterbird assemblages on intra-annual community variations. Additionally, we also noted the potential effects of population size and behaviors at different parts of the waterbird life circle on the observations of them. The information gathered in this study will provide guidance for the conservation of waterbird species and their habitats.

Colony‐forming and single‐cell picocyanobacteria nitrogen acquisition strategies and carbon fixation in the brackish Baltic Sea

AbstractPicocyanobacteria are widespread and globally significant primary producers. In brackish waters, picocyanobacterial populations are composed of diverse species with both single‐cell and colony‐forming lifestyles. Compared to their marine counterparts, brackish picocyanobacteria are less well characterized and the focus of research has been weighted toward single‐cell picocyanobacteria. Here, we investigate the uptake dynamics of single and colony‐forming picocyanobacteria using incubations with dual carbon‐13 and inorganic (ammonium and nitrate) or organic (urea and amino acids) nitrogen‐15 sources during August and September 2020 in the central Baltic Sea. Phytoplankton community and group‐specific uptake rates were obtained using an elemental analyzer isotope ratio mass spectrometer (EA‐IRMS) and nano secondary‐ion mass spectrometry (NanoSIMS). Picocyanobacteria contributed greater than one third of the ammonium, urea, amino acids, and inorganic carbon community uptake/fixation in September but < 10% in August when phytoplankton biomass was higher. Overall, single‐cell ammonium and urea uptake rates were significantly higher for single‐celled compared to colonial picocyanobacteria. In a 6‐yr offshore central Baltic Sea time series (2015–2020), summer abundances of colonial picocyanobacteria reached up to 105 cells mL−1 and represented > 5% of the average phytoplankton biomass, suggesting that they are periodically important for the ecosystem. Colonial strain identification was not distinguishable using 16S rRNA gene amplicon data, highlighting a need for refined tools for identification of colonial forms. This study shows the significance of single‐celled brackish picocyanobacteria to nutrient cycling and the importance of considering uptake and lifestyle strategies when assessing the role of picocyanobacteria in aquatic ecosystems.

Ecological assessment of water quality in freshwater wetlands based on the effect of environmental heterogeneity on phytoplankton communities in Northeast China.

Phytoplankton community characterized by strong vitality response to environmental change in freshwater ecosystems. This study aims to evaluate the effectiveness of using phytoplankton diversity as a water quality indicator in wetlands, and find out the main environmental variables affecting the distribution of phytoplankton. From 2020 to 2021, we examined phytoplankton assemblages and water environmental variables in spring, summer, and autumn at eight sampling sites from Hulanhe Wetland, Northeast (NE) China. The results showed that Bacillariophyta was the dominant species. Phytoplankton composition and abundance differed among sampling sites in each season; the abundance in summer (613.71 × 104 ind. L-1) was higher than that in autumn and spring. The water quality assessment of the trophic state index (TSI) based on the four physicochemical indicators was compared with phytoplankton diversity indices, which indicated that the phytoplankton community was stable, and these two indices were significantly lower in summer than in spring and autumn. According to redundancy analysis (RDA), total phosphorus (TP) and nitrogen (TN) were the main environmental variables affecting the distribution of phytoplankton. Temperature and dissolved oxygen (DO) changes also played a role, and their impact on the community was discussed. This work can provide relevant scientific references on the usefulness of phytoplankton diversity structure in assessing water quality in cold regions, in which the succession can be significantly affected by nutrients and temperatures.

Indoor/Outdoor airborne microbiome characteristics in residential areas across four seasons and its indoor purification

Bioaerosols are more likely to accumulate in the residential environment, and long-term inhalation may lead to a variety of diseases and allergies. Here, we studied the distribution, influencing factors and diffusion characteristics of indoor and outdoor microbiota pollution in six residential buildings in Guangzhou, southern China over a period of one year. The results showed that the particle sizes of bioaerosol were mainly in the range of inhalable particle size (<4.7 μm) with a small difference among four seasons (74.61 % ± 2.17 %). The microbial communities showed obvious seasonal differences with high abundance in summer, but no obvious geographical differences. Among them, the bacteria were more abundant than the fungi. The dominant microbes in indoor and outdoor environments were similar, with Anoxybacillu, Brevibacillus and Acinetobacter as the dominant bacteria, and Cladosporium, Penicillium and Alternaria as the dominant fungi. The airborne microbiomes were more sensitive to temperature and particulate matter (PM2.5, PM10) concentrations. Based on the Sloan neutral model, bacteria were more prone to random diffusion than fungi, and the airborne microbiome can be randomly distributed in indoor and outdoor environments and between the two environments in each season. Bioaerosol in indoor was mainly from outdoor. The health risk evaluation showed that the indoor inhalation risks were higher than those outdoor. The air purifier had a better removal efficiency on 1.1–4.7 μm microorganisms, and the removal efficiency on Gram-negative bacteria was better than that on Gram-positive bacteria. This study is of great significance for the risk assessment and control of residential indoor bioaerosol exposure.

Seasonal abundance, lipid storage, and energy density of Calanus finmarchicus and other copepod preyfields along the Northwest Atlantic continental shelf

Abstract Calanus finmarchicus is an abundant calanoid copepod in the New York Bight (NYB) that has energy-dense lipid stores. This study measured C. finmarchicus abundance, lipid storage and energy density and compared it to two other abundant calanoid species in the region. We compared the NYB C. finmarchicus preyfield characteristics with data from two other NW Atlantic coastal ecosystems, the Gulf of Maine (GoM) and Cape Cod Bay (CCB). Copepods from net tows were identified, enumerated, photographed and measured. These data were used to calculate animal biovolume and lipid content as well as the volumetric energy density of the copepod preyfield. C. finmarchicus were most abundant in spring and summer and the mean lipid storage of C. finmarchicus remained largely constant regardless of season and location within the NYB. Centropages typicus were abundant enough in the winter to be more energy-rich than C. finmarchicus. Temora longicornis, while also abundant, never surpassed the energy density of C. finmarchicus. C. finmarchicus in the NYB were comparably lipid-rich to those from the GoM and CCB. C. finmarchicus in the NYB can be a reliable energy source for local predators due to their high spring and summer abundances and year-round storage of high-energy wax esters.

The fate of antibiotic resistance genes and their correlation with microbial communities and wastewater quality/parameters in a wastewater treatment plant under different seasons

Wastewater treatment plants (WWTPs) are the hardest hit areas of antibiotic resistance genes (ARGs) pollution. As an emerging contaminant, ARGs seriously threaten ecological, human, and livestock safety. It is research interest to understand the potential relationship between ARGs, wastewater quality/parameters, and microbial communities. Herein, we compared that the variation of ARGs, wastewater quality/parameters, and microbial communities along the whole treatment processes in the WWTP in summer and winter. Results showed that ARGs abundance in summer is higher than that in winter, and the removal efficiency of ARGs varies with season. In summer, ARGs abundance had a significant correlation with phosphorus concentration, but in winter changed to the content of heavy metals (HM). Meanwhile, the dominant bacteria genera and their abundance were distinct in different seasons. The network analysis illustrated that ARGs are correlated with bacterial genera. Throughout this study, we found that wastewater quality/parameters and microbial community play a key role in the formation of ARGs, and the relationship among them is driven by seasonal variation. This work will help to provide a direction for optimizing wastewater treatment processes and controlling the spread of ARGs from the WWTPs to aquatic environment.

Use of satellite imagery to estimate distribution and abundance of Cumberland Sound beluga whales reveals frequent use of a glacial river estuary

Limiting disturbance in critical habitats is an important part of ensuring the well-being and sustainability of populations at risk, such as Cumberland Sound beluga whales (Delphinapterus leucas). Using non-disruptive Very High Resolution (VHR) satellite imagery, an emerging tool in cetacean monitoring, we aimed to estimate summer abundance and identify critical habitat for Cumberland Sound beluga whales. Specifically we looked in fiords that comprise their summer distribution, such as Clearwater Fiord where there is a large estuary, an important habitat to many beluga populations. Satellite images of the area were collected in 2020 and 2021, at 30 cm resolution, and in 2022 at 50 cm resolution. We evaluated beluga whale distribution using Kernel density, and identified critical habitats as areas consistently part of the beluga whale core distribution across years. Clearwater Fiord abundance estimates were corrected for whales that were too deep to be identified in the images. The estimates were significantly lower in 2021 (197 whales, 95%CI: 180-216) and 2022 (194 whales, 95%CI: 172-218) compared to 2020 (393 whales, 95%CI: 366-422). Other fiords were only imaged in 2021 and 2022, resulting in average corrected abundance estimates for all fiords of 462 (95% CI: 425-502) and 252 (95%CI: 226-280) beluga whales, respectively. Downsampling of 30 cm images to 50 cm resulted in up to 45% fewer whales detected. The only critical habitat identified within the summer distribution was in Clearwater Fiord, in or near the estuary freshwater plume and in a bay to the west of the plume. The identified critical habitats should be areas of consideration in the continued discussion on the protection and sustainability of the Cumberland Sound beluga whale population.

Seasonal dynamics of the jellyfish Rhizostoma pulmo between the two estuaries of Oued Ghis and Oued Nekkour, Al Hoceima Bay (Moroccan Mediterranean coast)

In recent decades, the global environmental balance has been disrupted due to new environmental conditions and increasing anthropogenic pressure. In this context, the increase in frequency and magnitude of jellyfish proliferation in the Mediterranean Sea can be examined as an indicator closely associated with potential impacts of global changes. Despite their importance in ecosystem function and services, current knowledge of jellyfish diversity and phenology is largely lacking in the southern Mediterranean Sea, particularly along the Moroccan Mediterranean coast. Rhizostoma pulmo is a large scyphozoan jellyfish endemic to the Mediterranean. It is the second dominant scyphozoan species in the jellyfish community of Al Hoceima Bay. In this article, we explore the seasonal dynamics of the jellyfish R. pulmo between the estuaries of Oued Ghis and Nekkour at Souani Beach. Due to the disparity between the visual abundance of jellyfish and their rare beaching along the shores of Al Hoceima Bay, we implemented a specific method for collecting R. pulmo. This approach involves the use of a coastal trawl, a fishing net 200 meters long with a mesh size of 5 cm, deployed 80 meters from the shore and pulled from both sides by fishermen. Sampling missions conducted throughout the year 2022 revealed that R. pulmo reaches its maximum abundance in summer. The results indicate a maximum abundance of 0.28 ind/m2 in July 2022, with a maximum umbrella diameter reaching 26 cm in August 2022. Under the jellyfish umbrellas, fry of two fish species and one crustacean species were observed, adding an ecological dimension to this study.

Water Level Fluctuations Modulate the Microbiomes Involved in Biogeochemical Cycling in Floodplains.

Drastic changes in hydrological conditions within floodplain ecosystems create distinct microbial habitats. However, there remains a lack of exploration regarding the variations in microbial function potentials across the flooding and drought seasons. In this study, metagenomics and environmental analyses were employed in floodplains that experience hydrological variations across four seasons. Analysis of functional gene composition, encompassing nitrogen, carbon, and sulfur metabolisms, revealed apparent differences between the flooding and drought seasons. The primary environmental drivers identified were water level, overlying water depth, submergence time, and temperature. Specific modules, e.g., the hydrolysis of β-1,4-glucosidic bond, denitrification, and dissimilatory/assimilatory nitrate reduction to ammonium, exhibited higher relative abundance in summer compared to winter. It is suggested that cellulose degradation was potentially coupled with nitrate reduction during the flooding season. Phylogenomic analysis of metagenome-assembled genomes (MAGs) unveiled that the Desulfobacterota lineage possessed abundant nitrogen metabolism genes supported by pathway reconstruction. Variation of relative abundance implied its environmental adaptability to both the wet and dry seasons. Furthermore, a novel order was found within Methylomirabilota, containing nitrogen reduction genes in the MAG. Overall, this study highlights the crucial role of hydrological factors in modulating microbial functional diversity and generating genomes with abundant nitrogen metabolism potentials.

Estructura y dinámica de población de Tigriopus californicus (Copé´´poda, harpacticoida)

From January 1976 to July 1979, samples of a population of the copepod Tigrlopus californicus were collected at monthly intervals on lower supralittoral level tide pools at Península Foca, ría Deseado (Santa Cruz).&#x0D; Density and samples composition in males, ovigerous and nonovigerous females, coupled individuals and juveniles were determined. Females usually were significantly more abundant than males. The seasonal density changes are considered with respect to the physical environment. Copepods were present throughout the year but abundance in summer is several orders of magnitude greater than in winter, through a rapid autumn decline. A large density increase in spring complete the annual cycle. The frequency of this maxima and mínima appeared to be periodic in time during the sampling years, in annualy cycles. Natural mortality and instantaneous rates of population increase were estimated,and the last compared with the species reproductive potential (computed "in vitro", previously published). The periodic density fluctuation is considered with respect to the seasonal changes in poblational structure through cyclical modifications of the instantaneous rates of population increase.

Spatiotemporal distribution of phytoplankton community structure and its relationship with environmental factors in Hongze Lake, China

Hongze Lake, which ranks as the fourth-largest freshwater lake in China, has considerable importance as a water transfer reservoir under the South-to-North Water Transfer Project. The evaluation of the lake's health and nutritional status could be achieved by the analysis of the phytoplankton community. Nevertheless, the understanding of the long-term phytoplankton dynamics in Hongze Lake after the implementation of the South-to-North Water Diversion remains insufficient. In this study, an investigation was conducted to analyze the community structure, distribution patterns, and environmental factors influencing the abundance of phytoplankton in Hongze Lake. The results of the study revealed that Hongze Lake showed seasonal variations in both the structure and biomass of its phytoplankton population. In fall, winter, and spring, Chlorophyta dominates, while Cryptophyta dominates in summer. Algae predominantly inhabit Chengzi Lake and Lihewa during the summer season. According to the redundancy analysis, temperature is positively correlated with algal abundance in summer but negatively correlated in spring and winter. Furthermore, the mantel analysis indicated that the abundance of different algal species was significantly correlated with dissolved oxygen and nutrient levels. The generalized linear model further clarified the contribution of environmental factors to algal abundance: total nitrogen (weights = 30.67%) ranked second in importance after temperature (weights = 34.52%). The results of this study provide insight into the alterations in the phytoplankton community within Hongze Lake following the implementation of the water transfer project. In addition, these findings offer valuable guidance for the regulation of lake water resources and water quality.

Major shift in the copepod functional community of the southern North Sea and potential environmental drivers

Abstract Copepods form the bulk of secondary production in marine ecosystems and are a major resource for higher trophic levels. Copepods are highly sensitive to environmental changes as they are ectotherms with a short life span whose metabolism and development depend on abiotic conditions. In turn, changes in their functional structure (i.e. functional trait composition) can have impacts on ecosystems. We examined changes in the copepod functional community in the North Sea over the past five decades, using a trait-based approach. We observed a shift around 1986–1988: the copepod community was initially dominated by larger herbivores, with a long development time, diapause ability, and highest abundances in summer. This community changed abruptly after 1986–1988, to a dominance of smaller carnivore taxa, with shorter development times, less ability to enter diapause, and that display higher abundances in autumn. This rapid reorganization could be driven by higher water temperatures, lower dinoflagellate abundances, and lower nutrient concentrations. These changes could impact adjacent trophic levels, such as phytoplankton on which several species graze or fish larvae, leading to a mismatch situation with consequences for fish recruitment. Our results emphasize the impact that global and regional changes could have on coastal ecosystems through the role played by copepods.

Seasonal variability of lotic macroinvertebrate communities at the habitat scale demonstrates the value of discriminating fine sediment fractions in ecological assessments.

Despite lotic systems demonstrating high levels of seasonal and spatial variability, most research and biomonitoring practices do not consider seasonality when interpreting results and are typically focused at the meso-scale (combined pool/riffle samples) rather than considering habitat patch dynamics. We therefore sought to determine if the sampling season (spring, summer and autumn) influenced observed macroinvertebrate biodiversity, structure and function at the habitat unit scale (determined by substrate composition), and if this in turn influenced the assessment of fine sediment (sand and silt) pressures. We found that biodiversity supported at the habitat level was not seasonally consistent with the contribution of nestedness and turnover in structuring communities varying seasonally. Habitat differences in community composition were evident for taxonomic communities regardless of the season but were not seasonally consistent for functional communities, and, notably, season explained a greater amount of variance in functional community composition than the habitat unit. Macroinvertebrate biodiversity supported by silt habitats demonstrated strong seasonal differences and communities were functionally comparable to sand habitats in spring and to gravel habitats in autumn. Sand communities were impoverished compared to other habitats regardless of the season. Silt habitats demonstrated a strong increase in Ephemeroptera, Plecoptera and Trichoptera (EPT) taxa and functional richness from spring into autumn, while vegetation habitats displayed a peak in EPT abundance in summer. Only silt and sand habitats demonstrated temporal variability in functional evenness suggesting that these habitats are different in terms of their resource partitioning and productivity over time compared to other habitats. Gravel and vegetation habitats appeared to be more stable over time with functional richness and evenness remaining consistent. To accurately evaluate the influence of fine sediment on lotic ecosystems, it is imperative that routine biomonitoring and scientific research discriminate between sand and silt fractions, given they support different biodiversity, particularly during summer and autumn months.

Variations in the dairy wastewater properties and bacterial diversity of each unit in membrane-enclosed anaerobic lagoon treatment process in Heilongjiang Province

In order to meet the land use requirements of the treated wastewater from high density polyethylene (HDPE) membrane-enclosed anaerobic lagoons, the physical and chemical properties of the wastewater in an HDPE membrane-enclosed anaerobic lagoon were measured. The total nitrogen content (TN) in wastewater treated in membrane-enclosed anaerobic lagoons is 3165 and 1510 mg/L in winter and summer respectively. The wastewater can be used as liquid organic fertilizer, partly replacing chemical fertilizer. The safety dosage of the wastewater was 21.48 t/ha for rice and 9.54 t/ha for corn, respectively. Meanwhile, the wastewater has the characteristics of high salt (conductivity>16.0 mS/cm) and high organic matter content (COD>16,900 mg/kg). Therefore, the potential negative effects of the wastewater on soil salinity and pH should be assessed. 16S rRNA was used to investigate the bacterial population structure and assess potential biological risks of land use of the wastewater. The wastewater from lagoon has the least and the most bacterial abundance in summer and winter, respectively. The bacterial diversity of wastewater samples from lagoon is the most. 21 and 24 phyla were detected in winter and summer samples respectively. Clostridium is the absolute dominant bacteria in the summer water samples and the absolute dominant bacteria is Trichococcus in winter water samples. Several animal and plant bacterial pathogens such as Campylobacter, Corynebacterium, Facklamia and Erysipelothrix can be detected in the wastewater samples. More than 70% of pathogenic bacteria such as Campylobacter, Facklamia, Erysipelothrix and Acholeplasma can be removed by lagoon in summer, but only about 99% of Corynebacterium is still in the lagoon (XYH). While more than 60% of Corynebacterium, Facklamia and Erysipelothrix are not removed in winter. So the biological risk of land use of anaerobic pond wastewater needs to be considered.

Spatiotemporal distributions of sulfonamide and tetracycline resistance genes and microbial communities in the coastal areas of the Yangtze River Estuary

In this paper, water and sediments were sampled at eight monitoring stations in the coastal areas of the Yangtze River Estuary in summer and autumn 2021. Two sulfonamide resistance genes (sul1 and sul2), six tetracycline resistance genes (tetM, tetC, tetX, tetA, tetO, and tetQ), one integrase gene (intI1), 16 S rRNA genes, and microbial communities were examined and analyzed. Most resistance genes showed relatively higher abundance in summer and lower abundance in autumn. One-way analysis of variance (ANOVA) showed significant seasonal variation of some ARGs (7 ARGs in water and 6 ARGs in sediment). River runoff and WWTPs are proven to be the major sources of resistance genes along the Yangtze River Estuary. Significant and positive correlations between intI1 and other ARGs were found in water samples (P < 0.05), implying that intI1 may influence the spread and propagation of resistance genes in aquatic environments. Proteobacteria was the dominant phylum along the Yangtze River Estuary, with an average proportion of 41.7%. Redundancy analysis indicated that the ARGs were greatly affected by temperature, dissolved oxygen, and pH in estuarine environments. Network analysis showed that Proteobacteria and Cyanobacteria were the potential host phyla for ARGs in the coastal areas of the Yangtze River Estuary.

Phytoplankton Size Structure and Diversity in the Transitional System of the Aquatina Lagoon (Southern Adriatic Sea, Mediterranean).

The Aquatina Lagoon (Southern Adriatic Sea, Mediterranean Ecoregion) is a transitional water ecosystem with great ecological and socio-economic interest. Anthropogenic activities around the lagoon (e.g., agriculture and tourism) and hydrology can affect the environmental quality and biodiversity of the lagoon. Herein, the dynamics and diversity of phytoplankton communities were studied before and after the opening of a new canal connecting the lagoon with the sea, by using different approaches based on an evaluation of the size and structure of the phytoplankton as well as the taxonomic analyses. The lagoon depicted time-related fluctuations in chemical-physical parameters. The phytoplankton trend was characterized by an increase in abundance and biomass in summer, when pico-sized autotrophs dominated. Generally, nano-sized phytoflagellates dominated the community, while micro-sized dinoflagellates and diatoms were less abundant. An increase in the phytoplankton taxa number was observed throughout the years. All the analyzed parameters were generally relatively homogeneous before the opening of the channel, while some quantitative differences among stations were observed in the second sampling period. Considering the statistical evidence, both environmental and biological parameters were affected by the "dilution" effect exerted by marine water inputs. This research supports the evidence that phytoplankton is a good indicator of the environmental status, and the obtained results contribute to the implementation of management strategies for the conservation of transitional water ecosystems.

Including environmental covariates clarifies the relationship between endangered Atlantic salmon (Salmo salar) abundance and environmental DNA

AbstractCollecting environmental DNA (eDNA) as a nonlethal sampling approach has been valuable in detecting the presence/absence of many imperiled taxa; however, its application to indicate species abundance poses many challenges. A deeper understanding of eDNA dynamics in aquatic systems is required to better interpret the substantial variability often associated with eDNA samples. Our sampling design took advantage of natural variation in juvenile Atlantic salmon (Salmo salar) distribution and abundance along 9 km of a single river in the Province of New Brunswick (Canada), covering different spatial and temporal scales to address the unknown seasonal impacts of environmental variables on the quantitative relationship between eDNA concentration and species abundance. First, we asked whether accounting for environmental variables strengthened the relationship between eDNA and salmon abundance by sampling eDNA during their spring seaward migration. Second, we asked how environmental variables affected eDNA dynamics during the summer as the parr abundance remained relatively constant. Spring eDNA samples were collected over a 6‐week period (12 times) near a rotary screw trap that captured approximately 18.6% of migrating smolts, whereas summer sampling occurred (i) at three distinct salmon habitats (9 times) and (ii) along the full 9 km (3 times). We modeled eDNA concentration as a product of fish abundance and environmental variables, demonstrating that (1) with inclusion of abundance and environmental covariates, eDNA was highly correlated with spring smolt abundance and (2) the relationships among environmental covariates and eDNA were affected by seasonal variation with relatively constant parr abundance in summer. Our findings underscore that with appropriate study design that accounts for seasonal environmental variation and life history phenology, eDNA salmon population assessments may have the potential to evaluate abundance fluctuations in spring and summer.

Effects of Biotic and Abiotic Factors on the Spatiotemporal Distribution of Round Scad (Decapterus maruadsi) in the Hainan Island Offshore Area

Fishery resource and environmental data from four surveys conducted in the Hainan Island offshore area from March 2021 to June 2022 were used to investigate the spatiotemporal distribution of round scad (Decapterus maruadsi). A generalized additive model was applied to explore the relationships among abundance and distribution, also biotic and abiotic factors (i.e., temperature, salinity, chlorophyll-a concentration, water depth, phytoplankton abundance, zooplankton abundance, and jack mackerel (Trachurus japonicas) abundance). Round scad abundance (average 67.17 kg/km2) showed distinct spatial and seasonal differences around Hainan Island, with highest abundance in summer (171.72 kg/km2) and lowest abundance in spring (3.06 kg/km2). The optimal model revealed that jack mackerel abundance, sea bottom temperature, sea surface temperature, and latitude very significantly (p &lt; 0.01) affected round scad distribution. Jack mackerel abundance (mainly in the range 0–50 kg/km2) was positively correlated with round scad distribution. The distribution showed a dome-shaped relationship with bottom water temperature in the range 18–30 °C, with maximum abundance at 24 °C. The distribution was negatively correlated with surface water temperature in the range 22–30 °C. Sea surface chlorophyll-a concentration and longitude were significantly correlated (p &lt; 0.05) with round scad distribution. The results provide theoretical support to further investigate the formation mechanism of round scad fishing grounds and to enrich knowledge of pelagic fish abundance in the continental-shelf waters of the northern South China Sea.