Assessment of microplastic contamination in some commercial fishes of the southern Caspian Sea and its potential risks.

This study examined the occurrence of microplastics (MPs) in the gastrointestinal tract (GIT) of 384 fishes classified into four species from 11 sites in 2022 from the southern part of the Caspian Sea. GITs of fishes were collected and digested in H2O2 and KOH at 45 °C for 72 h. After filtration, extracted MPs were observed under a stereomicroscope, and selected MP particles were identified using FTIR. Presence of MPs was 68.98% in the GIT of the investigated fish. The mean abundance of MPs was 5.9 ± 0.9 MPs/GIT in Rutilus kutum, 9.2 ± 1.2 MPs/GIT in Chelon auratus, 3.6 ± 0.7 MPs/GIT in Alosa braschnikowi, and 2.7 ± 0.5 MPs/GIT in Vimba vimba. The predominant form of MPs was fiber (58.21%), followed by fragment (34.77%). Black (34.4%), white (19.07%), and blue (14.58%) were the most frequently detected colors of MPs. Overall, 6 MP polymers were identified, dominantly polypropylene (42.86%), polystyrene (17.86%), and cellophane (14.28%). The western part of the Caspian Sea (mostly tourist spots and urban areas) showed more MP pollution in fish compared to the eastern part. Polymer hazard index (PHI) revealed alarming microplastic contamination in the southern Caspian Sea. The PHI value of the present study showed that PES (PHI = 8403.78) and PS (PHI = 535.80) were "Extreme danger" and "Danger" risk categories, respectively.

Aliphatic hydrocarbons in fin spines of adult sturgeon (Acipenser stellatus) and their relationship with potentially toxic elements in the northern and southern regions of the Caspian Sea.

Currently, the pollution of the Caspian Sea by the oil industry is one of the highest problems in this area. Critically endangered species inhabit this sea, such as sturgeons, whose ecological value is incalculable. Thus, we aimed to evaluate the level of contamination of aliphatic hydrocarbons of petroleum and its relation with several toxic elements directly on sturgeons spines. A total of 40 adult starry sturgeons (Acipenser stellatus) were obtained within a repopulation programme in the northern and southern coastal waters of the Caspian Sea. The marginal pectoral fin was extracted from each fish to determine aliphatic hydrocarbons, arsenic, cadmium, mercury, nickel, lead, and vanadium. Subsequently, the sturgeons were released. Clearly, the presence of hydrocarbons was evidenced in all the sampled areas finding higher concentrations in the northern areas (N1 = 1.35 ± 0.4; N2 = 1.65 ± 0.46; N3 = 1.27 ± 0.40; S1 = 0.61 ± 0.22; S2 = 0.85 ± 0.43 mg/kg). Furthermore, to a greater or lesser extent, some toxic elements, mainly Hg and As, have been linked to aliphatic hydrocarbons.

Spatial and temporal distribution of physicochemical parameters of water in Gorgan Bay (the southeast of the Caspian Sea - Iran): Fundamentals for the monitoring of the Caspian Sea coastal areas.

Gorgan Bay as a main part of the Miankaleh (a natural biosphere reserve registered by UNESCO) is one of the richest ecological area in the West Asia and very important internationally recognized refuge for the wildlife. To date, multi physicochemical parameters have not been examined on a large scale. To fill this knowledge gap, the present study aimed to explore the seasonal and spatial variability of water quality parameters of the bay. The results showed that except for depth and transparency, there are significant variations in most parameters across the four seasons. The patterns of these changes in the bay vary, as evidenced by a comparison of the distribution maps of the various factors throughout the year. Notably, alkalinity declined from east to west, reaching its highest levels at important entry points such as the Qarasu River, Bandar-Gaz, and the pier. TDS, on the other hand, increased westward, reaching its highest concentration in the shallow western regions. Maximum depth (310 cm) and transparency (250 cm) were observed in the central bay. While the pH was higher in deeper areas, the distribution of PO4 was more uniform. With lower levels in the east (salinity = 0.40 ‰) and higher levels in the west (salinity = 28.9 ‰), the salinity showed a coherent gradient. Agricultural land use in the basin of the bay and fluxes of nutrients and sediments of the rivers entering the bay has significant contribution to the bay pollution situation. These results will serve as a guide for improving our understanding of the Gorgan Bay ecosystem. They also have implications for informed conservation and management plans adapted to the specifics of this special region within the Caspian Sea.

The decline of kilkas, sturgeons and seals in the Caspian Sea: The potential of qualitative loop analysis for the cumulative assessment of multiple drivers of stress.

Multiple stressors often act concomitantly on ecosystems but detection of species responses follows the "single species-single driver" strategy, and cumulative impacts are seldom considered. During 1990-2010, multiple perturbations in the Caspian Sea, led to the decline of kilka, sturgeon and Caspian seal populations. Specific causes for their collapse were identified but a cumulative assessment has never been carried out. Using loop analysis, a qualitative modelling technique suitable in poor-data contexts, we show how multiple drivers can be combined to assess their cumulative impact. We confirm that the decline of kilka, sturgeon and Caspian seal populations is compatible with a net effect of the concomitant perturbations. Kilkas collapse was certainly due to the outburst of M. leidyi and overfishing. In addition, the excess nutrient might have conspired to reduce these populations. The interplay between concurrent drivers produces trade-offs between opposite effects and ecosystem management must face this challenge.

Highly Pathogenic Avian Influenza A(H5N1) Virus-Induced Mass Death of Wild Birds, Caspian Sea, Russia, 2022.

In May 2022, we observed a substantial die-off of wild migratory waterbirds on Maliy Zhemchuzhniy Island in the Caspian Sea, Russia. The deaths were caused by highly pathogenic avian influenza A(H5N1) clade 2.3.4.4.b virus. Continued surveillance of influenza viruses in wild bird populations is needed to predict virus spread over long distances.

The elevation of a unique population of Corynosoma strumosum (Acanthocephala: Polymorphidae) from the Caspian seal, Pusa caspica, in the Caspian Sea to Corynosoma neostrumosum n. sp.

An isolated population of 700 specimens initially described as Corynosoma strumosum (Rudolphi, 1802) Lühe, 1904 and currently reassigned to Corynosoma neostrumosum n. sp. was collected from one young male Caspian seal, Pusa caspica (Gmelin) in the southern land-locked Caspian Sea in April 2009. Collected worms were morphologically unique compared with those reported by other observers in open waters, especially in shape and distribution of proboscis hooks and trunk spines, dorso-ventral differences in proboscis hooks and their organization, the baldness of anterior proboscis, consistently smaller size of trunk and testes, larger eggs, the rough egg topography, epidermal micropores, and variations in the female gonopore. Molecular data from the internal transcribed spacer region of rDNA and the mitochondrial cox1 gene was also provided to supplement the morphological study of the new species.

Microplastic Pollution in the Gastrointestinal Tract and Gills of Some Teleost and Sturgeon Fish from the Caspian Sea, Northern Iran.

The increasing microplastic pollution in the marine environment has raised global concern. The main risk of microplastics in aquatic ecosystem is their bioaccumulation in aquatic organisms. A few studies have reported microplastic pollution in the digestive system of Caspian Sea fish species, but there is no research on sturgeon species, nor on fish gills. We investigated the occurrence of microplastics in the gastrointestinal tract (GIT) and gills of 62 specimens belonging to four species including three teleosts (Cyprinus carpio, Rutilus kutum, and Chelon aurata) and one sturgeon (Acipenser persicus, a valuable endangered species) from the Caspian Sea between January and March 2022. Fish tissues were removed, exposed for 24 h to 10% KOH, and then dried on filter paper. Particles were observed under a stereomicroscope and analyzed by Raman microspectrometry, scanning electron microscopy, and energy-dispersive spectroscopy. A total of 91 microplastics were detected in the GIT (average of 1.46 ± 1.17 items/individual) and 63 microplastics in the gills (average of 1.01 ± 0.62 items/individual). A significant correlation was not found between the number of microplastics found in both tissues and fish body length, body weight, GIT weight, and gill weight (p > 0.05), except between microplastics isolated from gills and gill weight in C. carpio (rs = 0.707, p = 0.022). The abundance of microplastics in fish followed the order of A. persicus > C. aurata > R. kutum > C. carpio. The microplastics were in the size range of 45 to 5000 µm, with particles of 300 to 1000 µm being the most prevalent; 74.68% of the particles were shaped like fibers, 30.53% were red, and 70.6% were composed of nylon polymer. Environ Toxicol Chem 2023;42:2453-2465. © 2023 SETAC.

Alternative reproductive tactics in goby fishes of the Caspian Sea.

Here we report on the reproductive morphology and histology of three Gobiidae species (the Caspian monkey goby, Neogobius pallasi; the Caspian goby, Neogobius caspius; and the round goby, Neogobius melanostomus) from the Iranian coastline of the Caspian Sea. Based on ageing, reproductive histology, and internal and external morphological measures, it appears that all three of these goby species have two types of reproductive males, a large courting, territorial, male type and a small cuckolding parasitic male type, a phenomenon known as alternative reproductive tactics (ART). Although ARTs have been reported previously for one of these species, the round goby, all reports stem from its invasive range; ARTs have never been reported before in any fish species in the Caspian Sea. In all three goby species there was a large, older male type, with a wide head, dark body colouration, and a large investment in accessory glands (AG), an organ important for female attraction and parental care. But there was also a small, light, younger male type, with a narrow head, longer urogenital papilla, and little investment in AGs. The Caspian goby were the largest of the three species, and in this species the smaller, lighter, presumably cuckolding male morph was quite rare (only about 5% of the reproductive male population). In contrast, many of the round goby and monkey goby males were the small, lighter parasitic type, making up nearly half the population of reproductive males (48% and 40%, respectively). Round goby and Caspian goby males had a prominent mesorchial gland, a fibrous sheath of pheromone-releasing connective tissue that attaches the testes to the dorsal body wall, but all the monkey goby specimens examined lacked this structure. Although ARTs are well documented across fish species and appear to be particularly common in gobies, our study provides the first evidence for ARTs in goby fishes from the Caspian Sea.

Population parameters of the non-indigenous invasive shrimp Palaemon macrodactylus Rathbun, 1902 (Caridea: Palaemonidae) from the southeastern Caspian Sea, with implications for range expansions, threats and conservation.

Knowledge on invasive species is critical for the conservation. This study is the first documentation on population parameters of oriental shrimp (Palaemon macrodactylus) in the southern Caspian Sea, where the occurrence of invasive species is of great importance. The samples were collected using a small beach seine (35 m long and 2.5 m height) monthly from April 2019 to March 2020, and a total of 1643 specimens of P. macrodactylus were sampled. The growth form of the males was negative and that of females positive allometric nature. From the size-frequency distributions, the shrimp's lifespan was estimated to be about 2 years for both sexes. High recruitment can take place over nearly all months of late summer and autumn. The VBGF parameters were L∞ = 65.00 mm, K = 0.82 y-1, and t0 = -0.80 for males, and TL∞ = 71.00 mm, K = 0.51 y-1 and t0 = -0.59 for females. The estimated Z was 3.65 and 3.10 year-1 for males and females, respectively. The total sex ratio was significantly biased toward females in the population. Length group analysis showed a clear pattern of female dominance in lengths larger than 29 mm. Based on the occurrence of ovigerous females, the reproductive period lasts for seven months (April-October). Fecundity, as the number of both eyed and non-eyed eggs per clutch of females, varied from 71 to 2308 eggs shrimp-1 with a mean of 1074 ± 553.8 (±SD) eggs shrimp-1. The estimated relative number of eggs in a clutch of ovigerous females varies between 1208.8 and 1714, with a mean value of 889.1 eggs. female-1. The egg diameter averaged 0.675 ± 0.063 mm (±SD), ranging from 0.512 to 0.812 mm. The relationships of the total and relative number of eggs in a clutch of ovigerous females with their size were statistically significant, while the egg diameter in ovigerous females was independent of shrimp size (length and weight). P. macrodactylus underwent a life-history strategy including high abundance, short life span, high mortality rate, long reproductive season, and female dominance that showed characteristics of r-strategist species, promoting the invasion of this shrimp in the Caspian Sea as a new area of introduction. We are convinced that P. macrodactylus established in the Caspian Sea it is in the last stage of invasion (impact on the ecosystem).

Multivariate analysis of trace elements in starry sturgeon (Acipenser stellatus) spine in different areas of the Caspian Sea.

Sturgeons are one of the most valuable species in the Caspian Sea. There, habitation of the seabed and feeding on benthic organisms makes this species a good indicator of trace element status. Thus, we aimed to determine the concentrations of 31 trace elements in the pectoral fin spine of starry sturgeons, and to evaluate the relationships between the different chemical elements. For this, a total of 40 starry sturgeons were obtained in a repopulation programme from the coastal waters north and south of the Caspian Sea. First, we used a multivariate analysis of variance to establish the differences between zones. Later, to assess relationships between trace elements, we used principal component analysis and cluster analysis. In general, the concentration of many trace elements did not vary between zones. However, some elements, including mercury or arsenic, were found in the north areas at higher concentrations.

Distribution of microplastics in upstream and downstream surface waters of the Iranian rivers discharging to the southern Caspian Sea.

Microplastic pollution in the riverine ecosystems has caught many attentions in the scientific literatures. However, little information is available about the abundance and distribution of microplastics of the rivers discharging to the Caspian Sea. The aim of this study was to assess the spatial and seasonal distribution of microplastics in the surface waters of thirteen rivers discharging to the southern Caspian Sea. Microplastics were found in all stations with uneven distributions. The average concentrations of microplastics in the stations during snowmelt and dry seasons were 1.406 ± 0.1380 microplastics/m3 and 0.4070 ± 0.01500 microplastics/m3, respectively. Positive gradients of the rivers microplastics concentration from upstream to downstream were found. White/transparent polyethylene (PE) particles with the shape of fragment/film and the length (L) of ≤ 1 mm were the most common microplastics in the surface waters of the rivers discharging to the southern Caspian Sea. Also, the mean concentration of microplastics in spring snowmelt and runoff period was 3.45 times higher than in dry period. Factors such as sewage and household wastes; landfills; and recreational-tourism, fishing and agricultural activities along the rivers may contribute to microplastic contamination in downstream stations. Our data provide baseline information of microplastics in surface waters of rivers discharging to the southern Caspian Sea.

Genome-wide data suggest a revision in management of the Caspian Sea trout Salmo caspius.

Salmo caspius Kessler, 1877 is one of the most commercially important species of Salmonidae in the southern basin of the Caspian Sea. The occurrence of its wild populations has undergone sever reduction during the last years. In spite of the yearly restocking activity, still no progress on the recovery of its wild population has been observed. Hence, the present study was done in order to assess the efficiency of the current restocking activity in the southern Caspian basin in term of genetic diversity. DNA extracts of 32 S. caspius from four different groups were screened using 62621 genome-wide single nucleotide polymorphisms (SNP). The overal genetic diversity and Fst values were 0.18 and 0.08, respectively. Considering the observed admixture pattern and the positive values for inbreeding coeficient it seems that S. caspius suffers from its small effective population size. In order to obtain the maximum performance, alonside with expanding the size of brood stocks, rehabilitation of the habitats and spawning rivers of this nationally endangered species is of great importance.

Bioaccumulation of rare earth elements and trace elements in different tissues of the golden grey mullet (Chelon auratus) in the southern Caspian Sea.

Rare earth elements are essential for modern life, although they are also classified as emerging pollutants. Currently, fish studies on these elements are very limited in general, but, with regard to the Caspian Sea, there is no reference to them at all. For this reason, our objective was to determine the concentrations of these elements in the golden grey mullet (Chelon auratus) and to contrast its bioaccumulation patterns with those of arsenic, cadmium, mercury and lead. For that purpose, 20 fish were caught in the southern part of the Caspian Sea. Heavy rare earth element concentrations were higher than light ones and the terbium levels were very high, probably due to anthropogenic contamination. The intestine tissue gave the highest concentrations, which could be indicative of a very low gastrointestinal absorption. For both rare earth and trace elements, muscle was the tissue that accumulated the least, despite which, cadmium and lead levels in muscle were of concern.

An applicability test of the conventional and neural network methods to map the overall water quality of the Caspian Sea.

This study investigates the water quality of the Caspian Sea by examining the presence of nutrients and heavy metals in the water. Water samples were collected from 22 stations and analyzed for nutrient and heavy metal levels. The study used the fuzzy method to prepare water quality maps and employed ANNs methods to predict microbial contamination for future years. The results revealed that the western and northwestern parts of the region had higher nutrient levels (about 40.2 % of the region), while the eastern and northeastern shores were highly polluted due to increased urbanization (about 70.1 % of the region). The long short-term memory (LSTM) method was found to have the highest accuracy compared to other ANNs methods and indicated a recent increase in pollution (RWater quality2=0.940, ROECD2=0.950, RTRIX2=0.840). The study recommends targeted research to identify the causes and means of controlling pollution in light of the predicted increase in pollution in the Caspian Sea.

An impact of non-native species invasions on the Caspian Sea biota.

The Caspian Sea is a large inland brackish basin, vulnerable to invaders due to its long isolation and considerable endemism among its native biota. A brief description of Caspian biota evolution until its modern state is given. The pathways and vectors of invasion and the ways of establishment of non-native species since the early 20th century are summarized. The newly established species are euryphilic, with high ecological plasticity, able to adapt to new environments and to affect their biodiversity. This review is based on unpublished field data, collected in 1999-2019 in the Northern, Middle and Southern Caspian, and on relevant published information. The arrival of non-native species occurred in three periods: (1) in the 1930s, deliberate introductions aimed at enriching commercial stocks and edible resources, (2) since 1952, the construction of the Volga-Don Canal led to the arrival of benthic foulers and macrophytes from ships; (3) since the early 1980s to present, ballast water tanks were mounted on ships, favoring the arrival of phyto- and zooplankton species. Most established non-native species reached the Caspian Sea via the Black Sea. They include both Black Sea native species and non-native species from the North Atlantic areas, which first arrived and established in the Black Sea. Few established non-native species came from brackish water; fresh water fishes were deliberately introduced to develop aquaculture. Though not numerous, these species became dominant in both benthos and plankton communities, where they replaced native Caspian species. Among them, the invading ctenophore Mnemiopsis leidyi, which had no predators, continues to thrive in the Caspian ecosystem, impoverishing its biodiversity and bio-resources. However, lately its natural predator, the ctenophore Beroe ovata, arrived and established in the Southern and Middle Caspian providing a chance for ecosystem recovery, as has already happened in the Black Sea.

Calculation and modeling of 232Th distribution in Gorgan Bay in the Caspian Sea.

The aim of this study was to obtain a relationship that can estimate the emission pattern of 232Th in calm and low pressure aquatic environments such as Gorgan Bay. The 232Th emission pattern in sediments near the outlets of Gaz and Qarasu rivers using experimental data measured by gamma radiation spectrometry using high purity germanium (HPGe) detector and quasi-experimental model recommended by IAEA 2001 as well as the concentric circular diffusion model proposed by authors was investigated. The mean specific activity of 232Th in sediment samples for Gaz Block and Qarasu Block is 30.46 Bqkg-1 and 28.80 Bqkg-1 for, respectively. In Gaz Block, for model1: the average of CsModel1 was 29.03 Bqkg-1 and the mean relative error is 10.76%. For model2: the average of CsModel2 was 30.34 Bqkg-1 and the mean relative error is 7.58%. In Qarasu Block, for model1: the average of CsModel1 was 27.48 Bqkg-1 and the mean relative error is 12.08%. For model2: the average of CsModel2 was 34.17 Bqkg-1 and the mean relative error is 38.99%. The results of this research show that diffusion models 1 and 2 in the calm environment of Gorgan Bay can accurately predict 232Th diffusion. But as increase the amount of turbulence and interference effects in the environment, the accuracy of these two models decreases. These two models can be used in similar calm aquatic environments in other parts of the world.

Contamination assessment and spatial distribution of heavy metals in the Sefidrud Delta coastal lagoons, Caspian Sea, N Iran.

Three coastal lagoons on the Sefidrud Delta, Caspian Sea, were investigated to evaluate heavy metal pollution in sediments. Amirkola Lagoon is located in the eastern part of the delta (abandoned delta lobe) and is aged more than 500 years, whereas Kiashahr and Zibakenar lagoons are in the western or active part delta lobe and formed in the last decades. One hundred six sediment samples and three sediment cores were taken from studied lagoons. The samples were analyzed by ICP-OES. Geo-accumulation index (Igeo), contamination factor (CF), degree of contamination (Cdeg), pollution load index (PLI), and Potential ecological risk index (RI) were employed to determine heavy metal pollution for Co, Cr, Cu, Ni, Pb, V and Zn. Nonparametric statistical analysis (Two-step cluster analysis, analysis of variance, and T-test technique) was used to discriminate the pollution sources. Based on contamination indices, the Kiashahr and Zibakenar lagoons show significant to moderate contamination with Co, Cu, Pb, Zn, and V, whereas the Amirkola Lagoon samples show the lowest metal contamination. PLI values demonstrated metal contamination in the Kiashahr and Zibakenar lagoons but no contamination in the Amirkola Lagoon. Although there was a notable rise in RI values from Amirkola to two other lagoons, all indicated low ecological risk. Statistical methods designated the unique interpretation of contaminant sources. Although the same geogenic origin of sediments in the Sefidrud Delta and lagoons deposits, Co, Zn, and Pb show anthropogenic sources in the newly-formed Kiashahr and Zibakenar lagoons.

Meta-analysis and health risk assessment of toxic heavy metals in muscles of commercial fishes in Caspian Sea.

Heavy metals from contaminated seafood can have serious consequences for human health. Several studies on the amount of heavy metals in Caspian Sea fish have been conducted to ensure their food safety. This meta-analysis aimed to investigate the levels of five toxic heavy metals; Lead (Pb), Cadmium (Cd), Mercury (Hg), Chromium (Cr), and Arsenic (As) in muscles of commercial fishes of the Caspian Sea with assessing their health risk of developing oral cancer in terms of fish collection place and fish type. A systematic search was performed, and the random effect model was applied for meta-analysis. Finally, 14 studies with 30 different sets of results were included. Our results showed that the pooled estimates for Pb, Cd, Hg, Cr, and As were 0.65 mg/kg (0.52, 0.79), 0.08 mg/kg (0.07, 0.10), 0.11 mg/kg (0.07, 0.15), 1.77 mg/kg (1.26, 2.27), and 0.10 mg/kg (- 0.06, 0.26) respectively. The levels of Pb and Cd were higher than their (FAO/WHO) maximum limits. The Estimated Daily Intake (EDI) of Pb and Cd in Mazandaran, and Hg in Gilan were more than Total Daily Intake (TDI) limits. The consumers' non-carcinogenic risk (THQ) for Hg in Mazandaran and Gilan, and As in Gilan, was unsafe. Carcinogenic risk (CR) for Cr and Cd in all three provinces, and for As in Mazandaran and Gilan, was greater than 1*10 - 4 and was unsafe. The lowest and highest risk levels of oral cancer were for Rutilus kutum and Cyprinus carpio respectively.

Ecological environment monitoring for sustainable development goals in Gomishan international wetland, Gorgan Bay, Caspian Sea.

Monitoring of coastal ecosystems is of particular importance for sustainable development and environmental management. Remote sensing, using satellite imagery, can play an important role in these studies. In this study, changes of qualitative parameters in Gomishan wetland and Gorgan Bay located in the southeast of the Caspian Sea were investigated using Landsat images. Based on the results of the range of chlorophyll-a and water temperature changes in both ecosystems, there was an increasing trend. Evaluating of Secchi disk (transparency) ranges showed a decreasing trend until 2018. Also, among the studied years, 2009 has the lowest fluctuations. Overall, the findings of this study showed that changes in water quality parameters of Gorgan Bay and Gomishan wetland had been affected by ecological conditions and human activities such as industrial-domestic and agricultural effluents. Also, satellite data in such coastal ecosystems at different time intervals have valuable results and can be given special attention for the study of similar ecosystems.