Benthic Fish Research Articles

Microplastic bioaccumulation in estuary-caught fishery resource

The environmental behavior of microplastics (MPs) in estuaries with saline and freshwater intersections is extremely complex. This increases the chance of MP ingestion by fishery resources, posing potentially tremendous health risks for humans. Herein, a total of 105 fishes from 14 different species, and 86 crustaceans (including shrimps and crabs) from five different species were sampled in the Yangtze River estuary and offshore, and MP bioaccumulation, accumulative organ, and the influencing factors were comprehensively studied. The results elucidated that MP accumulation in benthos was significantly higher than that in pelagic animals due to the lower acceptance threshold, assimilation efficiency and egestion rate for benthos. The MP content in crustaceans with the burrowing favoring the MP retention was significantly higher than that in fishes. MPs ingested by fish can accumulate in skin, gills and viscera rather than muscles. Most MPs accumulated in fishery resources were cellulose and polyethylene terephthalate characterized by black and gray fibrous and lengths ranging from 0.1 mm to 1 mm. The gill retention capacity of pelagic fish to smaller-size (<0.1 mm) MPs was pronouncedly stronger than that of benthic fish. It was more accurate to assess the ecological risk of MPs in terms of the maximum size of MPs accumulated in organisms. Compared with the offshore area, the incidence of MP uptake was higher in the estuary owing to anthropogenic impacts. This study helps understand the transfer of MPs in aquatic food webs and offers a foundation for assessing the risk of human exposure to MPs.

Species richness and functional attributes of fish assemblages across a large-scale salinity gradient in shallow coastal areas

Abstract. Coastal ecosystems are biologically productive, and their diversity underlies various ecosystem services to humans. However, large-scale species richness (SR) and its regulating factors remain uncertain for many organism groups, owing not least to the fact that observed SR (SRobs) depends on sample size and inventory completeness (IC). We estimated changes in SR across a natural geographical gradient using statistical rarefaction and extrapolation methods, based on a large fish species incidence dataset compiled for shallow coastal areas (&lt;30 m depth) from Swedish fish survey databases. The data covered a ca. 1300 km north–south distance and a 12-fold salinity gradient along sub-basins of the Baltic Sea plus the Skagerrak and, depending on the sub-basin, 4 to 47 years of samplings during 1975–2021. Total fish SRobs was 144, and the observed fish species were of 74 % marine and 26 % freshwater origin. In the 10 sub-basins with sufficient data for further analysis, IC ranged from 77 % to 98 %, implying that ca. 2 %–23 % of likely existing fish species had remained undetected. Sample coverage exceeded 98.5 %, suggesting that undetected species represented &lt;1.5 % of incidences across the sub-basins, i.e. highly rare species. To compare sub-basins, we calculated standardized SR (SRstd) and estimated SR (SRest). Sub-basin-specific SRest varied between 35 ± 7 (SE) and 109 ± 6 fish species, being ca. 3 times higher in the most saline (salinity 29–32) compared to the least saline sub-basins (salinity &lt; 3). Analysis of functional attributes showed that differences with decreasing salinity particularly reflected a decreasing SR of benthic and demersal fish, of piscivores and invertivores, and of marine migratory species. We conclude that, if climate change continues causing an upper-layer freshening of the Baltic Sea, this may influence the SR, community composition and functional characteristics of fish, which in turn may affect ecosystem processes such as benthic–pelagic coupling and connectivity between coastal and open-sea areas.

Features of bile acid metabolism in fish

The fish liver is an important organ involved in the complex metabolism of bile and bile acids. The biochemical reactions that occur during this process directly depend on the functional state of the digestive system and fish nutrition. Knowledge of the features of bile acid metabolism will allow designing the cheapest and at the same time effective drugs for the pharmacological correction of hepatopathy. The composition of bile acids depends on the type of food, so in fish such as pike, perch, carp, cholic and deoxycholic acids conjugated with taurine are more common. In predatory fish, cholic acid predominates, in contrast to benthivorous fish. Substances secreted with bile do not participate in the general metabolism of tissues, so that hepatocytes do not need to constantly secrete large volumes of bile.The metabolism of bile acids is carried out by the liver and is called the enterohepatic circulation. It all starts with the biological precursor of bile acids - cholesterol. Cholesterol in the body is formed during the absorption of lipids in the intestine. Two-thirds of exogenous cholesterol is excreted from the body in the form of bile acids. As a result of transformation by hepatocytes, primary bile acids are formed - cholic and chenodioxycholic. Then they are cojugated with taurine or glycine in the C-24 region of the carboxyl group and are excreted from hepatocytes continuously through the bile ducts to the gallbladder and further to the intestine. In the intestine, under the influence of microbial metabolites, they are hydroxylated and converted into secondary bile acids. Cholic becomes deoxycholic, and chenodisoxycholic becomes lithocholic. A small amount of bile acids are in a free state and form paired compounds. 90% of bile acids in the intestine form complexes of choleic acids in combination with fatty acids, which are absorbed through the wall of enterocytes. In enterocytes, these complexes again disintegrate and bile acids again enter the liver through the portal vein. Thus the circle of metabolism is closed.

Determination of Recharge Areas That Supply Decades Old Groundwater to Creeks Inhabited by the Threatened Okaloosa Darter

The Okaloosa darter (Etheostoma okaloosae) is a diminutive, perch-like, benthic fish that inhabits only six small, clear, and shallow creek systems that flow almost entirely within Eglin Air Force Base in the panhandle of northwest Florida. Listed as Endangered by the U.S. Fish and Wildlife Service (USFWS) in 1973, improvements in erosion control and habitat restoration led to the Okaloosa darter being downlisted from Endangered to Threatened in 2011. However, the long-term management of the species is hampered by the lack of knowledge of the spatial extent of the recharge areas that ultimately support creek flow through groundwater discharge. To address this lack of data, we collected groundwater samples from the sand and gravel aquifer beneath 11 headwater and 11 downgradient sites across six creek basins during February and December 2020. The groundwater samples were collected from 1 to 1.2 m beneath the creek bottom. Concentrations of sulfur hexafluoride (SF6) were analyzed and used to calculate groundwater age (residence time), and indicated that at the 11 headwater sites, recharge occurred between 11 and 28 years ago. Groundwater ages in downgradient parts of the same creeks indicated that recharge occurred between 5 and 25 years ago. When combined with representative values of hydraulic conductivity for the sand and gravel aquifer, the ages reveal that the extent of the maximum recharge distance from the sampling sites ranged from about 222 to 2011 m from the creeks. This new information can be used by natural resource managers as additional evidence to support the USFWS Recovery Plan and proposed delisting of the Okaloosa darter from the Endangered Species List. Moreover, these results may also be useful to fisheries biologists to incorporate groundwater inputs to facilitate fisheries management.

Preliminary screening of microplastic contamination in different marine fish species of Taif market, Saudi Arabia.

Microplastics (MPs), as a physical anthropogenic contaminant, represent a serious, human health concern due to their toxicity and ability to act as vectors for other pollutants and pathogens. This study aimed to screen for MP contamination in marine fish in Taif market, Saudi Arabia. A total of 22 fish species were used according to their different marine habitats and feedings. We have focused on extracting MPs from gills and muscles using KOH digestion. Nile red dye was used for the MP identification under fluorescence microscopy followed by the Fourier-transform infrared spectroscopy analysis. This study has reported MP contamination in gills and muscles of all the studied fish, in which poly(vinyl butyral) (PVB) was present in epipelagic species, poly(vinylidene fluoride) (PVDF) and poly(2,4,6,-tribromostyrene) (PtBS) were present in pelagic species, and PtBS and chlorosulfonated polyethylene were present in demersal/benthopelagic species. Moreover, benthic fish samples contain PtBS particles; reef-associated species have three different MP particles/fiber PtBS, PVDF, and poly(vinyl formal) and the rest of the studied species samples contain PtBS. The results highlight that the MP pollution increased to reach different species from the pelagic species to the benthic ones. PtBS as a type of polystyrene was the most dominant MP found in most species.

Rapid response of the nearshore round goby population to temperature declines associated with upwelling events in Lake Ontario

Upwellings occur in all the Great Lakes in response to prolonged wind events. Several studies have modeled or measured changes in abiotic conditions associated with upwellings, but few direct observations of fish responses have been documented. Video-capture techniques were used in conjunction with moored temperature loggers to link the disappearance of benthic round gobies to temperature declines during upwelling events along the southern Lake Ontario nearshore in summer of 2019. Benthic water temperatures declined by as much as 18 °C within 18 h over as many as nine events. Round goby density estimates were as high as 50/m2 prior to upwellings, but declined to as low as 0/m2 during the events. Using just nine observation dates, ARMA trend analysis suggested a relationship between benthic temperature and round goby abundance (AIC = 78.7, t = 2.21, P = 0.063). Although the actual response of gobies to rapidly declining temperatures was unknown, this population was unobservable in our sample area during upwellings, yet returned to pre-upwelling densities within days. Understanding the magnitude and frequency of fish responses to these events can improve our understanding of the potential for this non-native benthic fish to affect the nearshore environment.

Size matters? Species- and size-specific fish predation on recently established invasive quagga mussels Dreissena rostriformis bugensis Andrusov 1897 in a large, deep oligotrophic lake.

Since its first appearance in Lake Constance in 2016 the invasive quagga mussel Dreissena rostriformis bugensis has come to dominate the mussel community and now occurs in hyperabundant densities over the whole lake bottom. A lake-wide field study was conducted between 2019 and 2020 to obtain a systematic insight into the importance of this novel source of potential prey for the native fish community. In total 664 fish of 20 different species were caught and their digestive tracts were analysed. Meanwhile, quagga mussels were sampled to assess their calorific energy value by size and season. Regressions of septum length on maximum valve length were used to evaluate size-specific mussel consumption by the three dominant quagga-eating fish species. The study shows that nearly all benthivorous fish are able to forage efficiently on quaggas. However, in the case of one keystone species with very high commercial interest, the benthic whitefish Coregonus spp., quagga consumption is more limited as only individuals larger than 35 cm consumed quaggas in relevant amounts. The energy content of quagga mussels is positively size dependent with seasonal effect and elevated values during summer for medium- and large-sized mussels. Even at its peak, the calorific value of quaggas by weight is much lower than that of endemic aquatic invertebrates, while single mass is high. Future implications for fish stocks, food web integrity and possible fishery management options are discussed.

Natural cues for invertebrate and fish hearing: Particle motion measurements on coral reefs

Coral reef soundscapes are increasingly studied for their ecological uses by invertebrates and fishes, their applications for monitoring habitat quality, and to investigate effects of anthropogenic noise pollution. Few examinations of aquatic soundscapes have reported particle motion levels and variability, despite their relevance to invertebrates and fishes. We quantified ambient particle acceleration from orthogonal hydrophone arrays over several months at four coral reef sites in the U.S. Virgin Islands, which varied in benthic habitat and fish communities. Temporal trends of particle acceleration were similar to those of sound pressure, and the strength of diel trends in both metrics significantly correlated with percent coral cover. Low frequency (&amp;lt;100 Hz) and high magnitude empirical particle acceleration levels diverged from plane wave approximations. Particle acceleration levels were also determined for boat and example fish sounds. Comparisons with particle acceleration derived audiograms suggest greatest capacity of invertebrates and fishes to detect soundscape components below 100 Hz, and potentially poorer detectability of soundscape cues by some invertebrates compared to fishes. Based on our results, we discuss research questions in soundscape ecology for which reporting of particle motion is essential versus those for which sound pressure may suffice.

Питание окуневых рыб (Percidae) в малом озере бассейна Онежского озера

The article s focuses on studying the fish nutrition, which is one of the ways to identify the patterns of fish onto- and phylogenesis, as well as the patterns of fish abundance and using food resources in the water bodies. Nutrition determines the key physiological and biochemical reactions in the fish body in a qualitative and quantitative sense, which finally affects the growth of both individual organisms and the entire population. The results of these studies are of practical importance in the work of fish protection authorities. Information about the fish feeding in the small water bodies of Lake Onega basin is practically absent in the literature. There are presented the results of the studies carried out within the framework of forecasting and economic and contractual issues of the Northern Water Problems Institute of the Karelian Research Centre of the Russian Academy of Sciences (NWPI KarRC RAS) and Petrozavodsk State University (PetrSU) on assessing the nutrition of perch species (perch, ruff) in the lakes of the Konchezero group (South Karelia) - the lower reaches of the river Shuya belonging to the catchment area of Lake Onega. The work was carried out by the specialists of the NWPI KarRC RAS in 2018–2020. The main hydrological and ichthyological indicators of Lake Urozero have been studied. It is found that in the diet of perch in Lake Urosero there appear larvae Chironomidae, Ephemeroptera and aerial insects, and the latter having the maximum index of relative importance. The diet of ruff caught in Lake Urozero differs widely: along with benthic organisms fish eggs were also present. Ruff’s nutrition is more abundant: the index of filling its stomach averages 225.3 0/000 against 51.2 0/000 in perch. Perch longer than 13 cm is a typical ichthyophag in Lake Urosero. It is typical for the Karelian lakes that the transition of perch to predation is ob-served when reaching the size (on average) 15 cm.

Signs of the times: Isotopic signature changes in several fish species following invasion of Lake Constance by quagga mussels

Since the arrival of the invasive quagga mussels Dreissena rostriformis bugensis in Lake Constance, significant changes in the zooplankton and benthic invertebrate community were observed. Five years later the quagga mussel has become the dominating species of the benthic community. Its effects on other components of the food web, especially those at higher trophic levels such as fish, remain unclear around the world. To evaluate the actual impact of quaggas on the local food web of Lake Constance, the stable isotope compositions of pelagic whitefish and different benthic fish species from before and after the quagga invasion were compared. A significant increase in δ13C was detected in pelagic whitefish one year after the establishment of the quagga mussel in the lake. This change was most likely the consequence of an increase in benthic-derived nearshore primary production and a shift towards more littoral feeding, than a change in dietary composition. Stomach content analysis of contemporary samples revealed that pelagic whitefish (Coregonus wartmanni) still feed exclusively on pelagic zooplankton. In contrast, benthic whitefish (Coregonus macrophthalmus), roach (Rutilus rutilus) and tench (Tinca tinca) show today high levels of quagga consumption. However, this behaviour alone could not explain the observed differences in δ15N from periods before and after the quagga invasion. The results suggest that energy sources and pathways have changed considerably for both pelagic and benthic dwelling fish species in Lake Constance following the establishment of quaggas.

Depth and benthic habitat influence shallow and mesophotic predatory fishes on a remote, high-latitude coral reef

Predatory fishes on coral reefs continue to decline globally despite playing key roles in ecosystem functioning. Remote atolls and platform reefs provide potential refugia for predator populations, but quantitative information on their spatial distribution is required to establish accurate baselines for ongoing monitoring and conservation management. Current knowledge of predatory fish populations has been derived from targeted shallow diver-based surveys (<15 m). However, the spatial distribution and extent of predatory fishes on outer mesophotic shelf environments has remained under described. Middleton Reef is a remote, high-latitude, oceanic platform reef that is located within a no-take area in the Lord Howe Marine Park off eastern Australia. Here we used baited remote underwater stereo video to sample predatory fishes across lagoon and outer shelf habitats from depths 0-100 m, extending knowledge on use of mesophotic depths and habitats. Many predatory fish demonstrated clear depth and habitat associations over this depth range. Carcharhinid sharks and Carangid fishes were the most abundant predators sampled on Middleton Reef, with five predatory fishes accounting for over 90% of the predator fish biomass. Notably, Galapagos shark (Carcharhinus galapagensis) and the protected black rockcod (Epinephelus daemelii) dominated the predator fish assemblage. A higher richness of predator fish species was sampled on reef areas north and south of the lagoon. The more exposed southern aspect of the reef supported a different suite of predator fish across mesophotic habitats relative to the assemblage recorded in the north and lagoonal habitats, a pattern potentially driven by differences in hard coral cover. Biomass of predatory fishes in the more sheltered north habitats was twice that of other areas, predominantly driven by high abundances of Galapagos shark. This work adds to the growing body of literature highlighting the conservation value of isolated oceanic reefs and the need to ensure that lagoon, shallow and mesophotic habitats in these systems are adequately protected, as they support vulnerable ecologically and economically important predator fish assemblages.

The patterns of trophic transfer of microplastic ingestion by fish in the artificial reef area and adjacent waters of Haizhou Bay

Plastic pollution has become a threat to the global marine environment. Many studies have shown that marine organisms are at risk of plastic ingestion, but there is still a lack of relevant research in the artificial reef area and adjacent waters of Haizhou Bay, located in the western Yellow Sea. The study of MPs will provide useful information for MPs pollution in the artificial reef food webs, as well as the understanding of MPs trophic transfer by reef fish. In this study, we quantified plastic ingestion by marine fish in artificial reef areas and adjacent waters (Natural area, NA; Aquaculture area, AA; Estuary area, EA; Artificial reefs area, AR and Comprehensive effective area, CEA) and analysed the related possible influencing factors. Of the 146 fish samples examined, 100% of fish ingested plastics, and 98.9% of these particles were microplastics (MPs) (<5 mm), with 3.00 ± 2.63 pieces/fish. The main types and colours of MPs were fibre (95.9%) and blue (84%). The MP quantity of AR and AA were significantly higher than that of CEA (P < 0.05) and there is no significant difference among other habitats. The MP ingestion by pelagic fishes was significantly lower than that of demersal fishes (P < 0.05). MP ingestion by omnivores was significantly higher than that by carnivores and planktivores (P < 0.05). The body length (body weight) of four species (Larimichthys polyactis: 17.7–16.7 cm (16.01–59.41 g); Collichthys lucidus: 8.1–14.3 cm (19.65–56.92 g); Tridentiger barbatus: 5.9–9.2 cm (3.37–19.1 g); Cynoglossus joyneri: 10.1–18.7 cm (5–45 g)) had no significant correlation with MP ingestion (P > 0.05). Our results showed that MPs in this region are ubiquitous (i.e., the MP ingestion rate was as high as 100%). We infer that there is a transfer mechanism in MPs from pelagic to benthic fish in this area, and there is weak biomagnification with the trophic transfer of the food chain (TMF = 1.62). However, more practical studies still need to verify whether MPs are actually transferred to humans through trophic transfer from the marine food web.

Validating a narrow codend cover and improving selectivity in south-eastern Australian fish trawls targeting eastern school whiting, Sillago flindersi

As part of attempts to improve selection among south-eastern Australian benthic fish trawls, an experiment was done to assess: (1) for confounding effects of a narrower-than-recommended hooped cover over a conventional trawl codend; and then (2) the associated size selection of eastern school whiting, Sillago flindersi; and (3) if this could be improved by inserting a large panel of smaller square-shaped mesh. The narrow cover was required to avoid contacting the seabed and did not affect trawl wing-end spread or catching efficiency. Despite a stretched mesh opening (SMO) of 96 mm and much larger than all S. flindersi (11–26 cm total length; TL), the conventional codend had a low 50% size at retention (L50) of 16.8 cm TL (selection range of 5.9 cm), which was close to the minimum marketable length. The capture of small S. flindersi by the large-meshed codend was attributed to an excessive increase in circumference (from 100 to 200 meshes) and a legally permitted ‘catch-separating’ rope to restrict fractional mesh openings to <~21%. Replacing ~1/4 of the 96-mm SMO netting in the codend and anterior extension with a panel of square-shaped mesh (~42-mm SMO hung on the bar) marginally (p = 0.065) improved size selection for S. flindersi (by allowing some fish <~15 cm TL to escape). Increasing the size of mesh in the panel to ~47 mm hung on the bar might allow more smaller S. flindersi to escape. But using a smaller mesh size throughout the entire codend, concurrent with other gear or spatio-temporal controls when targeting S. flindersi might be a more coherent management option than retroactively handicapping the existing large-mesh codends.

Socio-ecological systems modelling of coastal urban area under a changing climate – Case study for Ubatuba, Brazil

Understanding the complex dynamics between society and nature is a critical contribution of ecological modelling. Integrated views of human-nature relations as well as tools and frameworks for studying these relations are gaining ground. A socio-ecological systems (SES) perspective therefore embraces both social and environmental factors that uses nonlinearities, feedbacks, models, and multi-level networks for understanding and studying those phenomena. When undesired drivers as climate change are also taken into account, the most urgent question is how these critical socio–ecological systems will behave given the stresses they endure. This work had the objective of creating a new simulation of a coastal SES from Brazil that is able to integrate several climatic and social variables through a dynamic and coupled model, and forecast its behavior in the future according to scenarios. Specifically, a systems dynamics simulation model using MIMES (Multiscale Integrated Model of Ecosystem Services) was developed for Ubatuba, a coastal city highly dependent and influenced by tourism. Results showed good correspondence between the model and the data when testing several environmental inputs (wind speed and direction, cloud cover, sea surface temperature, precipitation patterns). The model simulated the population dynamics of 15 biological groups from 2010 to 2100 under different scenarios. Climate change will reduce most of populations in a range from −0.13% (± 0.0%) to −10.31% (± 0.0%). There are groups where the influence of climate change is not significant (Bivalve, Brachyuran, pelagic feeding fish and benthic feeding fish) with variations from 0 to 2% and others with moderate significance (Phytoplankton, Zooplankton, and Enterococcus) with variations >2%. Tourists reacting to water quality degradation is very relevant in Enterococcus population (with a reduction of 34%). Results show the urban activities strongly influencing the biological populations and that these impacts depend on the scenario context. This suggests a policy that limits the number of tourists and increases the water quality at the same time. Therefore, the model's spatial simulation of this complex socio-ecological system can be used to develop an integrative decision-making tool to help the city manage its natural capital and adapt to its changes.

Metals Bioaccumulation in 15 Commonly Consumed Fishes from the Lower Meghna River and Adjacent Areas of Bangladesh and Associated Human Health Hazards.

The lower Meghna River, the easternmost part of the Ganges Delta, faces severe anthropogenic perturbations as it receives a huge discharge and industrial effluents. To measure the metal concentrations and human health hazards, edible tissues of 15 commercially important fish species were collected from the local fish markets and the lower Meghna River, Bangladesh. Trace and heavy metals such as Pb, Cr, Cu, Zn, Mn, Fe, Hg, Ni, Ca, Co, Se, Rb, Sr, and As were detected using the Energy Dispersive X-ray Fluorescence (EDXRF) method. The hierarchy of mean metal concentrations obtained was: Fe (162.198 mg/kg) > Zn (113.326 mg/kg) > Ca (87.828 mg/kg) > Sr (75.139 mg/kg) > Cu (36.438 mg/kg) > Se (9.087 mg/kg) > Cr (7.336 mg/kg) > Mn (6.637 mg/kg) > Co (3.474 mg/kg) > Rb (1.912 mg/kg) > Hg (1.657 mg/kg) > Ni (1.467 mg/kg) > Pb (0.521 mg/kg) > As (BDL). Based on the metal concentration obtained, the carnivorous species contained more metals than omnivores and herbivores. Similarly, the euryhaline and benthic feeder fishes had more metals than the stenohalines and demersal fishes. The metal pollution index (MPI) suggested that the highly consumed fish species Tilapia (Oreochromis mossambicus) and Rui (Labeo rohita) accumulated higher metals than other fishes. Both the Targeted Hazard Quotient (THQ) and Hazard Index (HI) values for adult and child consumers were <1, indicating that consumers would not experience the non-carcinogenic health effects. Although children were more susceptible than adults, carcinogenic risk (CR) exposure of Cr for all the consumers was found in the acceptable range (10−6 to 10−4), but the CR exposure of Pb was negligible for all the consumers. The correlation, principal component analysis (PCA), and cluster analysis were conducted to identify the sources of metals identified from the fish tissue. The results indicated that the probable sources of the pollutants were anthropogenic, arising from agricultural activities, electroplating materials, and lubricants used near the study area. However, the present study showed a different metal concentration in the samples at different levels but within the threshold levels non-carcinogenic and carcinogenic health risks; hence, the fishes of the area, in general, are safe for human consumption.

Ecosystem effects of invasive crayfish increase with crayfish density

Abstract The nature and extent of effects of increasing densities of non‐native species on stream ecosystems remain poorly understood. Non‐native crayfish are among the most invasive aquatic species and we hypothesised that, in temperate streams, the extent of trophic modification increases with non‐native crayfish density. Instream flow‐through mesocosms in the River Lune, north‐east England, were used over a 47‐day period in summer to measure density effects of invasive signal crayfish Pacifastacus leniusculus on different ecosystem components (benthic fish, macroinvertebrates, algal biomass, and leaf litter breakdown). Effects were measured through three density treatments (low, medium, and high; four, eight, or 12 crayfish with five bullhead Cottus perifretum per 1.5 m2) and two control (crayfish and fish absent; crayfish absent and benthic fish present) groups. Impacts of crayfish on macroinvertebrates (density, taxonomic composition), fish (growth, diet), algal standing stock, and decomposition rates increased with crayfish density. Direct effects of increased crayfish density were more important than indirect trophic cascade effects. Despite similar invertebrate abundance and richness across enclosures before introducing crayfish and bullhead, they differed significantly from controls at the end of the study, with &gt;80% reduction in macroinvertebrate abundance recorded in the high‐density group. Stable isotope (δ15N, δ13C) analysis showed that the trophic niche of bullhead, but not signal crayfish, changed when the species were in sympatry. Bullhead in treatment enclosures occupied a lower trophic position in the food web than those from the control group. Bullhead in the high‐density group lost 4.2% of body mass over the study period, confirming the existence of resource competition. Leaf litter break down was 59.2% faster, and algal biomass was 91.4% lower in the treatment with the highest crayfish density compared to the control without study animals. This study indicates that signal crayfish, even at a low density, can strongly alter multiple ecosystem components in streams, and emphasises the need for minimising the spread of invasive crayfish within and between streams.

Amplitude of undulating fin in the vicinity of a wall: Influence of unsteady wall effect on marine propulsion

To investigate the role of the amplitude of an object under the unsteady wall effect in fluid dynamics, we modelled an undulating fin near a wall in a two-dimensional Cartesian coordinate system. The fin was tethered in a uniform flow and controlled by a user-defined function program. The unsteady wall effect improved the propulsion force and propulsion efficiency at different amplitudes, but the lift force behaved differently. We determined the critical amplitude for the model, below which the lift force is positive within an appropriate off-wall distance range. At amplitudes larger than the critical amplitude and as the off-wall distance decreases, the average lift force is, however, always negative, causing the undulating fin to overturn towards the wall and lose stability. The essence of propulsion and lift variation lies in the change in the shape of the space between the wall and the fin, which affects the fluid flow structure and pressure distribution. In addition, some interesting phenomena related to the vortex core arrangement and pressure distribution were introduced at different amplitudes caused by the unsteady wall effect. The present results may provide new insights into the behaviours of benthic fish, reducing their undulating amplitudes and pitch angles near walls.

Metal-associated human health risk assessment due to consumption of pelagic and benthic ichthyofaunal resources from the highly contaminated Cuddalore coast in Southern India

We present seasonal variation of four metals (Cd, Cu, Pb, and Zn) in nine pelagic and three benthic fish species from the highly polluted Cuddalore coast in Tamil Nadu, India. Metals were assessed using atomic absorption spectrometry and detected in all fish species, in at least one season, except Iniistius cyanifrons where cadmium was not detected throughout. In both benthic and pelagic fish, order of metal concentration was Zn > Cu > Pb > Cd. Multivariate statistical analysis revealed that metals may have originated from both natural and anthropogenic sources. Health risk assessment revealed that consumption of fish from Cuddalore coast does not pose health risk for now; however, hazard index values (pelagic = 0.97; benthic = 0.90) are in borderline. Even a slight increase in metal concentration in fish can prove hazardous for human consumption. Sooner or later, eating fish from Cuddalore coast may pose a considerable health risk to humans if metal pollution is not held at Bay.

Acute damage from the degradation of Ulva prolifera on the environmental microbiota, intestinal microbiota and transcriptome of Japanese flounder Paralichthys olivaceus

Green tide outbreaks caused by overgrowth of Ulva prolifera in the Yellow Sea of China can cause serious ecological stress with concomitant economic hardships, especially to marine fisheries. In this study, short-term effects (14 days) were evaluated using fresh algae U. prolifera (FU), and a 7-day assessment of the effects of decomposing U. prolifera (DU) algal effluent was conducted to determine the effects on the environmental and intestinal microbiota, intestinal transcriptome and mortality of the commercial marine benthic fish, Japanese flounder (Paralichthys olivaceus). The results revealed that algal degradation altered the microbial community structure of fish farm water and fish intestines and increased the relative abundance of the pathogens Flavobacteriaceae in water and Vibrio in fish intestines. Fish intestinal tissue structure appeared to be damaged, as indicated in pathological sections, and transcriptome analysis showed intestinal inflammation after exposure, which may have caused an increase in fish mortality. The degradation of U. prolifera led to a bloom of potential pathogenic bacteria and the inflammation of fish intestines, which resulted in disease in the flounder population that reduced fish harvests and might pose a potential health threat.

Sediment Disturbance Negatively Impacts Methanogen Abundance but Has Variable Effects on Total Methane Emissions.

Methane emissions from aquatic ecosystems are increasingly recognized as substantial, yet variable, contributions to global greenhouse gas emissions. This is in part due to the challenge of modeling biologic parameters that affect methane emissions from a wide range of sediments. For example, the impacts of fish bioturbation on methane emissions in the literature have been shown to result in a gradient of reduced to enhanced emissions from sediments. However, it is likely that variation in experimental fish density, and consequently the frequency of bioturbation by fish, impacts this outcome. To explore how the frequency of disturbance impacts the levels of methane emissions in our previous work we quantified greenhouse gas emissions in sediment microcosms treated with various frequencies of mechanical disturbance, analogous to different levels of activity in benthic feeding fish. Greenhouse gas emissions were largely driven by methane ebullition and were highest for the intermediate disturbance frequency (disturbance every 7 days). The lowest emissions were for the highest frequency treatment (3 days). This work investigated the corresponding impacts of disturbance treatments on the microbial communities associated with producing methane. In terms of total microbial community structure, no statistical difference was observed in the total community structure of any disturbance treatment (0, 3, 7, and 14 days) or sediment depth (1 and 3 cm) measured. Looking specifically at methanogenic Archaea however, a shift toward greater relative abundance of a putatively oxygen-tolerant methanogenic phylotype (ca. Methanothrix paradoxum) was observed for the highest frequency treatments and at depths impacted by disturbance (1 cm). Notably, quantitative analysis of ca. Methanothrix paradoxum demonstrated no change in abundance, suggesting disturbance negatively and preferentially impacted other methanogen populations, likely through oxygen exposure. This was further supported by a linear decrease in quantitative abundance of methanogens (assessed by qPCR of the mcrA gene), with increased disturbance frequency in bioturbated sediments (1 cm) as opposed to those below the zone of bioturbation (3 cm). However, total methane emissions were not simply a function of methanogen populations and were likely impacted by the residence time of methane in the lower frequency disturbance treatments. Low frequency mechanical disruption results in lower methane ebullition compared to higher frequency treatments, which in turn resulted in reduced overall methane release, likely through enhanced methanotrophic activities, though this could not be identified in this work. Overall, this work contributes to understanding how animal behavior may impact variation in greenhouse gas emissions and provides insight into how frequency of disturbance may impact emissions.