Oligohaline Waters Research Articles

Effect of salinity stress and nitrogen depletion on growth, morphology and toxin production of freshwater cyanobacterium Microcoleus anatoxicus Stancheva & Conklin

AbstractCyanobacterium Microcoleus anatoxicus, isolated from a coastal stream in northern California, produces both anatoxin-a (ATX) and dihydroanatoxin-a (dhATX), responsible for dog deaths, but its environmental preferences are unknown. We tested the effect of environmentally relevant stressors, e.g., salinity enrichment and nitrogen (N) depletion, on mat formation and toxicity of M. anatoxicus during the stationary growth phase in culture. Microcoleus anatoxicus showed broad salinity tolerance and the potential to enter estuaries and produce toxins in mesohaline conditions. Maximum growth was observed in oligohaline waters with salinity of 4.6 ppt. Moderate salinity stress (up to 7.8 ppt) did not affect dhATX production significantly. In contrast, higher salinity above 9.3 ppt had a detrimental effect on cell growth and significantly suppressed dhATX production. Formation of a common polysaccharide sheath covering multiple filaments was characteristic with increased salinity and may provide protection against osmotic stress. Microcoleus anatoxicus grown for 40 days in N-depleted medium formed mats with significantly elevated dhATX and increased ATX concentrations. Phycobilisome degradation was a possible acclimation response to N-limitation, as indicated by distinctly keritomized and pale cells in these cultures. In both experiments, most of the anatoxins were extracellular, probably due to toxin leaking during the stationary growth phase.

Monitoring the Extraordinary Ephemeral Emergence of Myriophyllum spicatum L. in the Coastal Lagoon Albufera of Valencia (Spain) and Assessing the Impact of Environmental Variables Using a Remote Sensing Approach

The Albufera of Valencia, a Mediterranean coastal lagoon, has been in a turbid state since 1974, with only four episodes of temporary water transparency in spring. Despite its average depth of 1 m and oligohaline waters, excessive turbidity, fish grazing, and toxic compounds have inhibited submerged macrophyte growth. In spring 2018, a significant area of Myriophyllum spicatum emerged and exhibited significant density until its complete disappearance in August 2018. Using Sentinel-2 and Landsat-8 imagery, we monitored water quality variables and vegetation density during these months. Our study revealed the first unique occurrence of M. spicatum in more than 40 years. A period of increased transparency from summer 2017 compared to previous years seems to be the cause of this appearance, while high summer temperatures caused its disappearance. While improving water quality may help restore submerged macrophyte meadows, our results suggest that summer maximum temperatures may inhibit recovery. Remote sensing, particularly the NDVI index, proved successful in monitoring aquatic vegetation and understanding species-environment relationships. This methodology can enhance future monitoring efforts for macrophyte colonization and expand knowledge of their occurrence and causes of disappearance in this and other similar areas.

Molecular and biological studies of nonindigenous and extremely rare fish species from the western Baltic reported from the Pomeranian Bay (southwest Baltic Proper)

W ięcaszek B., P anicz R., E ljasik P., Tański A., B ushra A. 2023. Molecular and biological studies of nonindigenous and extremely rare fish species from the western Baltic reported from the Pomeranian Bay (southwest Baltic Proper). Folia Biologica (Kraków) 71: 181-194. Water inflows from the North Sea to the Baltic Sea are recognized as a significant factor influencing the diversity of fish species in the region. In this report, we present findings on three newly discovered fish species (Solea solea, Merluccius merluccius, and Limanda limanda) and the presence of species that were previously seldom observed in the Pomeranian Bay and the associated oligohaline waters of Szczecin Lagoon. These fishes were incidentally captured during monitoring surveys of commercially important fish species. Species identification relied on partial sequences of cytochrome c oxidase subunit I (COI), cytochrome b (cytb), and rhodopsin (rho) genes, as well as morphometric diagnostic characteristics. Upon comparing the obtained sequences with GenBank records, it was revealed that the sequences for Merluccius merluccius (rho, GenBank acc. no. OM737733) and Chelidonichthys lucerna (cytb, GenBank acc. no. OM737734) constitute new DNA barcodes. The majority of sequences obtained in our study matched those available in GenBank for fishes inhabiting the North Sea, suggesting spatial and temporal linkages between the two seas. The remaining sequences exhibited similarity to data from the Cantabrian Sea, the coasts of France, and the Norwegian Sea. The study results, in conjunction with information on the inflows of saline waters and data from previous studies on reported fish occurrences, indicate that the bycatch species could serve as potential bioindicators of environmental changes in the study area.

Empirical Formula to Calculate Ionic Strength of Limnetic and Oligohaline Water on the Basis of Electric Conductivity: Implications for Limnological Monitoring

Ionic strength (I; mol·L−1) acts as one of the most important parameters of natural waters. It is indispensable for obtaining ion activities and thus is crucial for describing chemical processes in water solutions. Limnology, I, has many applications, but calculating the partial pressure of CO2 (pCO2) and the carbonate saturation index (SI) are among the most important examples. The determination of I requires the full ion composition of water to be recognized, and when the concentration of some major ion(s) is/are missing altogether, the I value remains unknown. Because historical and monitoring data are often incomplete, it seems useful to provide a method for the indirect assessment of I. In this paper, we developed and tested an empirical model to estimate I on the basis of electric conductivity at 25 °C (EC). Our model consists of two linear equations: (i) Imod = 15.231 × 10−6·EC − 79.191 × 10−6 and (ii) Imod = 10.647 × 10−6·EC + 26.373 × 10−4 for EC < 592.6 μS·cm−1 and for EC > 592.6 μS·cm−1, respectively. We showed that model performance was better than the hitherto used EC–I relationships. We also demonstrated that the model provided an effective tool for limnological monitoring with special emphasis on the assessment of CO2 emissions from lakes.

Effects of Estuarine Environmental Heterogeneity on the Habitat of Gobiidea Species Larvae

AbstractIn aquatic ecosystems around the world, gobies comprise one of the most diverse groups of fishes in estuaries. The Yangtze River estuary, the biggest estuary in the western Pacific, is a major habitat for larval gobies, with the peak spawning and breeding season occurring during late spring and summer. To investigate the adaptation mechanism of larval gobies to environmental factors, three models (a global generalized linear model, a generalized additive model, and a geographically weighted Poisson regression) were used to simulate and forecast the major habitat distributions of larval gobies based on the survey data from 2018 to 2020. Six species of gobies were studied:Rhinogobius giurinu,Odontamblyopus rubicundus,Tridentiger barbatus,Parachaeturichthys polynema,Tridentiger trigonocephalus,andTrypauchen vagina. The habitats for brackish speciesT. barbatuswere mainly in freshwater (where, using the practical salinity scale, salinity is 0–1) of the south branch, whereas the marine speciesP. polynemawas mainly caught in oligohaline waters (where salinity is 1–5) of the north branch. The other euryhaline species were near the exit of the north branch or dispersed throughout the surveyed region. Year, season, salinity, and sample location had significant effects (P < 0.001) on determining the habitat distributions of larval gobies. The geographically weighted Poisson regression identified that the temperature, depth, distance from the coast, and chlorophyllahad a significant effect (P < 0.001) on the local distribution of habitats. This work supplements information about the distribution of major habitats and their interactions with the environment for the ecologically important species of goby in the Yangtze estuary during the larval stage, and the conclusions provide a basis for the management of aquatic ecosystems and biological habitats.

Influence of environmental factors on the formation of zooplankton communities in a large lake system in Uzbekistan

Currently, the Aidar-Arnasai Lake System (AALS) is of great environmental and commercial importance for Uzbekistan. The article discusses the influence of mineralisation, temperature and diversity of biotopes on the change in the species composition in the lakes. The largest number of species is recorded in oligohaline water in the lakes’ littoral zones. They are dominated by the Rotifera and Cladocera and show a greater number of species in the spring. Areas with mesohaline water are dominated by Copepoda, showing the largest number of species in the winter in both littoral and pelagic zones. Biomass of zooplankton poorly correlates with salinity. Depth impacts reliably the distribution of zooplankton biomass, while the spatial accumulation of zooplankton biomass depends on temperature.

Distribution of crustaceans (Malacostraca, Arthropoda) in rivers of the semi-desert zone (with the example of the Volgograd reservoir tributes)

As a result of our studies of the macro- and nectozoobenthos of the rivers of the semidesert zone (the Volgograd reservoir basin), 16 Malacostraca species were recorded, most of which are representatives of the Ponto-Caspian complex. Compared to the Volgograd reservoir, there is an increase in the quantitative indicators of mysids and isopods and a decrease in the number of species, abundance and biomass of amphipods and cumaceans in the semi-desert zone rivers. The average abundance and biomass of crustaceans in the surveyed rivers are approximately 2.5 times lower than in the Volgograd Reservoir. Crustaceans of the Ponto-Caspian and PontoAzov complexes, as well as the isopods Asellus aquaticus (Linné, 1758) inhabit fresh and oligohaline waters, while the gammarids Gammarus lacustris (Sars, 1863) live in oligohaline and polyhaline waters. Amphipods are characterized by the largest number of species, which, taking into account their morphology and the type of substrate which they live on, are assigned to three ecomorphs, namely: clingers, crawlers, and diggers. No symbionts in the Yeruslan basin rivers were found. The noted amphipod ecomorphs are distributed relatively evenly with a slight dominance of crawlers (45%). It has been revealed that two types of crustacean cenoses are formed in the surveyed rivers. The first type is formed mainly by consortium interactions of the edificatory mollusks Dreissena with amphipods Chelicorophium curvispinum Sars, 1895, Dikerogammarus haemobaphes (Eichwald, 1841), mysids Paramysis ullskyi Czerniavsky, 1882, P. lacustris (Czerniavsky, 1882), and associated species. The second cenosis in the rivers is represented by a complex of small coastal mysid species Katamysis warpachowskyi Czerniavsky, 1882, Limnomysis benedeni Sars, 1893, and amphipods Chaetogammarus warpachowsky (Sars, 1894), the relationships within which are based on common biotopic conditions and feeding patterns.

Macrobenthos in the estuary of a typical «salmon» river of Sakhalin Island (on example of the Manuy River)

Species composition, structure, density and biomass of macrobenthos in the estuary of the Manuy River are described, its main communities are defined and their trophic characteristics, production, and distribution along the river channel are determined on the materials collected in July 2021. Three main biotopic zones of the estuary are identified by their hydrological features and parameters of macrobenthos: the river mouth, the lower estuary, and the upper estuary. Bilateral structure of salinity with 0.8–5.0 psu in the upper layer and > 27 psu near the bottom was observed in the lower estuary, whereas the upper estuarine zone was filled mostly by oligohaline water (0.8–1.6 psu), with only a thin refugial layer of the seawater (23.1 psu) at the depth of 0.9 m. In total, 24 species of benthic invertebrates and cyclostomes were presented in the macrobenthos. The species richness varied insignificantly across the estuary, from 4 species/section in its upper part to 9 species/section in the lower part, with lowered richness at the border between the lower and the upper estuarine zones, that corresponded to the theory of critical salinity. The density of macrobenthos distribution decreased from the river mouth to the boundary between the lower and upper zones (from 808.0 ± 162.0 ind./m2 to 16.0±2.8 ind./m2), then increased sharply in the upper estuary (up to 1384 ± 160 ind./m2). The total biomass had two peaks: in the lower estuary (4.381 ± 0.589 g/m2) and in the upper estuary (up to 28.950 g/m2), with the minimum of 0.076 ± 0.015 g/m2 between. The boundary between the meso-, polyhaline lower estuary and the oligohaline upper estuary had the width of several hundred meters. Four benthic communities were identified by various methods of cluster and ordination analysis, regardless of the method: two communities in the upper estuary (communities of Eogammarus kygi and Neomysis awatschensis), one community in the lower estuary (community of Hediste japonica) and the community of Haustorioides at the river mouth. Gathering detritivores formed the basis of biomass and macrobenthic production at the river mouth; collecting detritophages — sestonophages were the most significant in the lower estuary; while three key trophic groups were presented in the upper estuary: 1) collecting detritivores — macrogrinders — scavengers, 2) collecting detritivores, and 3) ground feeders — collecting detritivores. Daily production of macrobenthos was low at the river mouth and in the lower part of the lower estuary but increased in its upper part and in the upper estuary.

Water parameters correlated with the zootechnical performance of shrimp Litopenaeus vannamei grown in oligohaline waters

The present study aimed to correlate the influence of water quality, cultivation time, area, and density of ponds on the zootechnical performance of shrimp Litopenaeus vannamei in oligohaline waters. It was demonstrated that, under the conditions of this research, better control of temperature, pH and water alkalinity can be employed. Ammonia levels were within the normal range and correlated positively with the growth rate (ρ = 0.69859) and production (ρ = 0.66362) of the ponds. There was also a positive correlation between cultivation time and pond density with shrimp weight (ρ = 0.75305 and 0.68933) and pond productivity (ρ = 0.74763 and 0.79367, respectively). Negative correlations were observed between: I) pH with shrimp survival (ρ = -0.73238) and pond production (ρ = -0.68696); II) alkalinity and pond production (ρ = -0.66162). The results show that the cultivation of shrimp L. vannamei in oligohaline waters is viable and there is potential for increased productivity associated with better hydrological monitoring and use of higher density and cultivation time by some producers.

Quantifying euryhaline histories in red drum Sciaenops ocellatus: otolith chemistry and muscle isotope ratios.

The combined use of otolith chemistry and tissue isotopes has the potential to reveal movements, habitat associations and food web interactions at a variety of spatial and temporal scales. Here, we used a combination of otolith Ba:Ca life history transects with muscle tissue δ13 C and δ15 N values to assess habitat use and oligohaline residence in red drum Sciaenops ocellatus in subtropical estuaries in the northwestern Gulf of Mexico. Tissue isotopes were distinct among capture locations, particularly between bays with differing proximity to freshwater inflow sources. Otolith edge Ba:Ca values and tissue δ13 C values were not correlated. These results indicated that fish were not residing in nor feeding in oligohaline waters for significant periods of time within the tissue turnover window of several months prior to capture. However, spatial differences in tissue isotope values indicated limited mixing among bays and relatively high site fidelity during estuarine occupancy. Lifetime otolith Ba:Ca transects revealed individual variability in the magnitude of residence in oligohaline waters. Using a medium oligohaline occupancy threshold, an estimated 82% of individuals used oligohaline waters at some point in their life. However, 66% of individuals spent less than 20% of their life histories in oligohaline waters, suggesting intermittent and infrequent excursions into low salinity waters. Finally, a literature survey identified 56 peer-reviewed publications using combinations of otolith chemistry and tissue stable isotope ratios with a wide range of marker pairings and study aims. The diversity of ecological questions that can be asked with the combined use of these two approaches will provide valuable insight into fish ecology. This article is protected by copyright. All rights reserved.

Intertidal foraminifera from the Mar Chiquita Coastal Lagoon, Buenos Aires Province, Argentina

The present study aims to analyze the composition and distribution of the intertidal foraminiferal assemblages of the Mar Chiquita Coastal Lagoon (southeast coast of Buenos Aires Province). For this purpose, the abundance and diversity of the living and dead fauna were determined; the taphonomic features of the tests were analyzed; and physico-chemical measurements were taken at 10 sites of the lagoon. The assemblages were constituted mainly by autochthonous fauna. The sediment grain size and salinity are the main variables that determine the distribution of species and discerned three assemblages, associated with three sub-environments. The first sub-environment of coarse sediment and mesohaline waters corresponds to non-vegetated plains in the mouth of the lagoon. It contains Buccella peruviana, Elphidium discoidale, and Quinqueloculina patagonica. The second sub-environment of fine sediment and mesohaline waters corresponds to non-vegetated plains in the inlet of the lagoon. It includes Elphidium gunteri, B. peruviana, Ammonia parkinsoniana, Ammonia tepida, Miliolinella subrotunda, Rosalina williamsoni, Pyrgo ringens, Discorbis peruvianus, and Q. patagonica. The third sub-environment of coarse sediment - waters ranging from polyhaline to mixoeuhaline and fine sediment - oligohaline waters corresponds to vegetated and non-vegetated plains and floodplains far from the mouth of the lagoon. It contains Ammonia spp, and E. gunteri.

Life history of spinyhead croaker Collichthys lucidus (Sciaenidae) differentiated among populations from Chinese coastal waters

Otolith microchemistry provides valuable information about the environmental history of individual fish, but few studies have considered the influence of population or stock on life history traits. This study used the Sr/Ca ratio as an index of habitat use of spinyhead croakerCollichthys lucidusfrom 2 different populations (northern and southern China populations), including lifetime otolith microchemistry profiles (n = 63 fish) and determinations of natal habitat selection (n = 352 fish). The otolith data revealed 3 life history patterns inC. lucidus: Pattern 1 individuals spent most of their lifetime (>95%) in mesohaline waters (Sr/Ca range: 3-7 mmol mol-1), particularly during early growth; Pattern 2 individuals migrated from hyperhaline waters (Sr/Ca ≥ 7 mmol mol-1) to mesohaline waters; and Pattern 3 individuals migrated from oligohaline waters (Sr/Ca < 3 mmol mol-1) to mesohaline waters. Pattern 2 and Pattern 3 were specific to the northern and southern China populations, respectively, and Pattern 1 was shared by the 2 populations. The otolith core Sr/Ca ratios showed that mostC. lucidusselected mesohaline waters as their natal habitat (i.e. 90.6% of 352 total individuals); 12.5% (19 of 152) selected hyperhaline waters and fell within the northern China population, and 7% (14 of 200) selected oligohaline waters and fell within the southern China population. These results indicate that life history diversity exists in this species, as the pattern of habitat use largely differed between the northern and southern China populations. The overall findings highlight that the behavior of different populations should be considered when determining fish migration histories.

Assessment of different ionic adjustment strategies in low‐salinity water on the growth of Litopenaeus vannamei and microbial community stoichiometry in a synbiotic nursery system

The aim of this study was to evaluate different ionic adjustment strategies in oligohaline water on the growth of Litopenaeus vannamei and C:N:P stoichiometric ratios of the floc microbial community (MC) in synbiotic nursery system. A 35-day culture (2000 PL's/m3) was carried out in 60 L units in a completely randomized experimental design, with three treatments: T1—seawater diluted to a salinity of 2.5 g/L (control), T2—water with a salinity of 2.5 g/L with potassium (K⁺) adjusted and T3—water at a salinity of 2.5 g/L with its Ca:Mg:K ratio adjusted to 1:3:1, each treatment in triplicates. The MC of flocs and the dissolved fraction (DF) was separated by filtration, where MC >1.6 µm and DF <1.6 µm. The juveniles reached a final weight of 0.40 ± 0.09–0.49 ± 0.04 g, survival above 80% and an average yield of 0.69 ± 0.18–0.81 ± 0.02 kg/m3, without significant differences among the treatments. A stabilizing trend of C:P, C:N and N:P ratios of MC was observed considering the variations of C:N:P in the DF, indicating a homeostatic behaviour of the floc MC, as occurs in systems with high nutrient availability. Our results indicate that the major ions initial concentrations (Ca2+: 25.07 mg/L, Mg2+: 89.75 mg/L and K⁺: 25.00 mg/L), total alkalinity 100.00 mg/L and total hardness 433.30 mg/L provide conditions that do not limit shrimp growth in oligohaline water synbiotic nursery system.

A new species of Bestiolina (Copepoda, Calanoida, Paracalanidae) and complementary description of B. similis (Sewell, 1914) from the Nansei Islands, Japan.

Two species of the calanoid copepod genus Bestiolina occurred in estuarine/coastal waters of the Nansei Islands, southernmost Japan. One of them is described herein as Bestiolina okinawae sp. nov., which is distinguished from known congeners by a combination of the following characteristics: 1) fifth pedigerous somite bearing groups of tiny spinules on the posterior end, 2) female mandible bearing a rod-shaped first gnathal tooth, 3) male left leg 5 with short apical spine on long terminal segment, and 4) legs 23 with endopodal segment 2 lacking spinules. The new species was the dominant zooplankter in oligohaline waters. The other species is morphologically identifiable to Bestiolina similis (Sewell, 1914). Genetic analysis using COI revealed that the two species differed by 9.910.0%, in contrast to small intra-specific genetic variation (0.01.5%). The two species were spatially segregated in low-salinity (230) estuaries and high-salinity (2536) coastal waters, respectively, but co-occurred in some samples. Their body length decreased from the winter (around 20°C) to the summer (around 30°C) by 9.518.1%, depending on the species and sex. In both species, adult males, which lack mandibular gnathobase, were larger than the adult females.

Measurement of salinity in slurry based on modified electrical conductivity method

Salinity is an important factor in the management of inland and oceanic water resources. Currently, the electrical conductivity (EC) method is widely used for the measurement of salinity in different components of the environment. However, this method is not reliable for the measurement of salinity in slurry, as the conversion formula from the EC value to salinity does not consider fine particle size and its content. In this study, the salinity of slurry based on EC measurements was extensively investigated. In total, 1148 laboratory tests and 40 field tests were performed. The results indicate that the EC value is mainly influenced by the salinity, temperature, fine particle size, fine particle content, and sediment concentration of slurry. The fine particle size and its content play an important role in the measurement of salinity in slurry. The surface coefficient of the fine particles was herein considered as the parameter to indicate the effects of fine particle size and its content on the EC value. The results show that the effects of salinity and temperature on the EC measurement are more significant than that of the surface coefficient of fine particles and sediment concentration. Although the EC of slurry is positively and linearly related to salinity and temperature, it has negative relationships with the surface coefficient of fine particles and sediment concentration. Based on dimensional analysis and experimental data, a new formula was proposed for the calculation of salinity which considers the EC, sediment concentration, surface coefficient of fine particles, and temperature of the slurry. This modified conversion formula for the EC method was successfully tested with laboratory, field and other scholars’ data, which assures a reliable salinity measurement of slurry in shallow oligohaline water areas.

Patterns and consequences of life history diversity in salinity exposure of an estuarine dependent fish

While it is common knowledge that Red Drum (Sciaenops ocellatus) inhabit oligohaline waters (salinity <5), lifetime reconstructions of salinity histories have been lacking, and this study provides unique insight into interannual and ontogenetic patterns of oligohaline occupancy by this economically valuable sportfish. Growth consequences of oligohaline exposure and the relationship of oligohaline residency with river discharge were also investigated. Oligohaline exposure varied most during years 2 and 3 of life. During this time, 22% (n = 26/120 individuals) of Red Drum were oligohaline residents (≥ 90% of these years spent in oligohaline salinities), 34% (n = 41) were meso-polyhaline residents (< 10% of years 2 and 3 spent in oligohaline waters), and 44% (n = 53) spent time in both oligohaline and meso-polyhaline salinities. Trends in oligohaline residency match putative Red Drum life history. Oligohaline residents were present during years 1–6 of life; however, oligohaline residency peaked during the second year of life (n = 37, 31%) and by year 7 no oligohaline residents remained. Growth of oligohaline resident Red Drum during years 2–3 of life was lower than non-resident fish. However, long-term growth consequences of oligohaline residency were not apparent. The proportion of oligohaline residents during years 2 or 3 of life was positively related to river discharge. This divergence in salinity residency by juvenile Red Drum demonstrates that life history diversity was present in this population and that oligohaline waters provided important nursery habitat for fish that successfully recruited to the adult population.

Low-level saltwater intrusion alters soil diazotrophic community structure in a subtropical estuarine wetland

Although diazotrophs play a critical role in the nitrogen (N) cycle by supplying new N, the response and mechanism of nifH gene diversity and community structure to minor changes in salinity remain unclear. Here, we investigated the diazotrophic communities in both rhizospheric and non-rhizospheric soils along a low-level salinity gradient across one freshwater (0.08 ± 0.02‰) and two oligohaline (1.27 ± 0.09 and 3.31 ± 0.14‰) wetlands by sequencing the nifH gene. The nifH gene alpha diversity was similar along the salinity gradient, but community structure differed markedly. The most abundant genera across the samples were within the Deltaproteobacteria class, including Geobacter, Desulfuromonas, Pelobacter, and Desulfovibrio. The nifH gene diversity (both alpha and beta diversity) and community structure did not differ significantly between rhizospheric and non-rhizospheric soils. Furthermore, soil salinity, pH, and nutrient availability (i.e., NH4+-N, NO3−-N, and C:N ratio) had synergistic effects on the diazotrophic community structure. In conclusion, the transition from freshwater to oligohaline water significantly altered the diazotrophic community structures but not diazotrophic diversity. Our study shows that saltwater intrusion may affect estuarine N fixation capacity and N cycling processes by reshaping these diazotrophic communities.

Phosphorus mobilization and availability across the freshwater to oligohaline water transition in subtropical estuarine marshes

Internal phosphorus (P) released from sediments, which has been verified to be affected by iron (Fe) and sulfur (S) reactions, strongly influences P cycling and water eutrophication. However, minimal research has been performed to determine how increased low-level salinity in estuarine tidal marshes affects P mobility and its coupled processes. Herein, in situ high-resolution distributions of labile P, Fe, and S in sediment-overlying water profiles were simultaneously measured along an estuarine freshwater-oligohaline gradient (Min River Estuary, China) utilizing newly developed diffusive gradients in thin films technique. Significant variations in the P, Fe, and S concentrations were observed with significantly higher sediment labile P concentrations in the freshwater-oligohaline transition. The observed labile P and Fe coupling confirmed the Fe redox-driven P release mechanism in the sediment, although this coupling was weakened in the freshwater-oligohaline transition. The diffusion flux results revealed that the sediments shifted from P “sink” to “source” with the transition from a freshwater to an oligohaline environment, probably caused by the release of Fe-bonded P stimulated by sulfate reduction. This study determined that increased salinity and the associated environmental responses alter the P remobilization capacity and internal P cycling by changing the sediment P pool and the P-Fe-S couplings across the sediment–water interface. Furthermore, saltwater intrusion into tidal freshwater wetlands caused by strong typhoons or sea-level rise may increase internal P release from sediments, which could have future implications.

Blue crab (Callinectes sapidus) population structure in southern New England tidal rivers: Patterns of shallow-water, unvegetated habitat use and quality.

The blue crab, Callinectes sapidus, has a broad geographic distribution encompassing coastal waters of the eastern United States and Gulf of Mexico, but intraspecific patterns of habitat use and quality are lacking at northern latitudes. This study examined the population structure of blue crabs in the Seekonk and Taunton Rivers (Rhode Island and Massachusetts, USA): two tidally influenced rivers contiguous with the Narragansett Bay Estuary and dominated by shallow-water, unvegetated habitats. Crabs were collected fortnightly from May through August (2012-2016), and abundance- and growth-based metrics were used to assess riverine habitat use and quality. These metrics were also analyzed with respect to crab life history traits and in situ abiotic conditions to elucidate patterns of habitat selection throughout ontogeny. Crabs measuring 8 to 185 mm carapace width (CW; n = 2,577) were collected, and two distinct age-classes occupied the rivers during the spring and summer (maximum abundance ~ 5 crabs/10 m2). The younger age-0+ cohort was numerically dominant (~ 88% of total catch) and comprised of male and juvenile female crabs (mean ± SD abundance = 0.28 ± 0.26 males/10 m2 and 0.14 ± 0.12 juvenile females/10 m2). Males accounted for the majority of age-1+ crabs (~ 83% of cohort), yet sexually mature females were also observed (9% of cohort; mean ± SD abundance = 0.04 ± 0.06 adult females/100 m2; size at 50% maturity ± 95 CI = 129.0 ± 0.2 mm CW). Crabs were spatially segregated along a salinity gradient with males and juvenile females prevalent in oligohaline waters (upper river salinity ~ 5 ppt) and adult females mainly concentrating in higher salinity areas (mid- and lower river salinity ~ 11-21 ppt). Seasonal and interannual patterns in crab abundance also differed by sex and ontogeny. Peak catches of males and juvenile females occurred during the spring and mid-summer, and annual abundances were positively related to dissolved oxygen (DO) concentrations. In contrast, mature females were most abundant during August and years with elevated water temperatures. The absolute and relative growth rates of juvenile crabs equaled 0.9 ± 0.3 mm CW/day and 1.5 ± 0.6 % CW/day, respectively, and were directly related to DO levels. A synoptic examination of crab abundance and growth across a broad geographic range indicated that shallow-water, unvegetated habitats presently serve as functional nurseries in southern New England tidal rivers.

Partial seawater inclusion to improve Litopenaeus vannamei performance in low salinity biofloc systems

Litopenaeus vannamei production in oligohaline waters (0.5–5 g L−1) is a potential alternative for the continuous expansion of shrimp farming. However, ionic imbalance may affect physiological processes and productivity. In this work, natural seawater inoculation was used as strategy for correction of ionic composition in a biofloc-dominated oligohaline system and its effects on the water quality and nursery performance were evaluated. A 27-day trial was conducted using an experimental biofloc-dominated oligohaline water, salt formulation was based on the mean concentrations of the major ions present in natural oligohaline waters found in Northeastern Brazil. The trial was composed of four treatments of natural seawater inoculation (3, 6, 10 and 13%) and a control, without inoculation (0%); all with four replicates. Post-larvae (PL) of 22 days (0.057 ± 0.002 g) were stocked at 1000 PL m−3 in 20,150 L indoor circular tanks. Shrimp were fed 40% crude protein commercial diets twice a day at rations adjusted weekly. Water temperature, oxygen saturation, pH, total ammonia nitrogen, nitrite, nitrate, phosphate, alkalinity, hardness, salinity, conductivity, total suspended solids and settleable solids were monitored. Concentrations of the major ions were measured at the Days 0, 14 and 27. Shrimp sampling was performed weekly and the final zootechnical performance was evaluated by final weight, survival, specific growth rate (SGR), weekly growth rate (WGR), yield and food conversion ratio. Salinity, conductivity and hardness significantly increased according to the increase of seawater inoculation, whereas the other parameters did not differ; all of them were within the range recommended for shrimp culture at low salinity, except nitrate for 0%. Concentrations of Cl−, Na+, Mg2+ and K+ and Na+:K+ ratio significantly increased according to the increase of seawater inoculation. Final weight, survival, SGR, WGR and yield were significantly lower in the 0%, but no differences were found among the treatments (from 3% to 13%). The results found in this work indicate that a seawater inoculation at 3% was an efficient strategy to mitigate negative effects of the ionic imbalance on growth performance of PL reared in biofloc-dominated oligohaline systems.