Coastal Fish Species Research Articles

Restricted connectivity for cobia Rachycentron canadum (Perciformes: Rachycentridae) in the Western Atlantic Ocean

AbstractCobia (Rachycentron canadum) is a coastal pelagic migratory fish species of tropical and subtropical waters, where it is an important game fish and it has been commercially expanded in offshore aquaculture systems. Understanding population connectivity is of utmost importance to the sustainable use and conservation of aquatic resources, and information on genetic diversity and structure is key element in unraveling differentiation when no clear physical barriers exist. In the present study, cobia genetic diversity and structure were depicted using mitochondrial DNA cytochrome b sequencing and microsatellite genotyping in samples from the Southwestern Atlantic and showed that a major single population inhabits the southern hemisphere. Cytochrome b sequencing also suggested that the Indian Ocean is the center of origin for this species' diversification. A hierarchical analysis of AMOVA compared sampling locations from the Northwestern Atlantic (from a previous study) with the Southwestern ones using nine shared microsatellite markers. Differentiation among groups (FCT = 0.41), Bayesian clustering analysis, and complementary ordination analyses (by discriminant analysis of principal components [DAPC] and factorial correspondence analysis [3D‐FCA]) presented a clear separation between the two hemispheres, supported by a Lagrangian model that explained the ocean dynamics over larval retention on the Western Atlantic. Another genetic subgroup intermingled with the main Southwestern group may also exist further south, probably associated with the Vitória‐Trindade Ridge and the local current systems. The distribution of this species in metapopulations is of extreme relevance for fisheries and fish hatcheries management in the Atlantic Ocean.

Reviewing Introduction Histories, Pathways, Invasiveness, and Impact of Non-Indigenous Species in Danish Marine Waters

Non-indigenous species (NIS) are of concern for biodiversity conservation and ecosystem functioning. We present an updated list of NIS, including cryptogenic species, from Danish marine waters containing 123 species. Benthic invertebrates (36%) and phytoplankton (28%) dominate the list, but fish (15%) and macroalgae (13%) are also important. The Limfjord in Northern Jutland emerges as a hotspot for the introduction of NIS. Data from multiple sources were included, i.e., the National Monitoring Program (NOVANA), the National Fish Atlas project, the citizen science project Arter.dk, research articles, and annual national reports of the ICES working group ITMO. Forty-six NIS species were subject to expert judging using a modified Harmonia protocol; 19 were found to fulfil the four selected criteria identifying a species as being ‘invasive’. Additionally, 38 species, not yet recorded in Danish waters, were evaluated using the same method, and 31 were found to fulfil the ‘invasive’ criteria. For nine selected species, introduction history, distribution maps, and time-series diagrams are presented. Our data document that the national monitoring efforts should be expanded to record macrozooplankton, coastal fish, and mobile epibenthic species. Furthermore, the national data repository, Arter.dk, should be expanded to enable more detailed documentation of new NIS records.

Spatial variability in the structure of fish assemblages associated with Laminaria hyperborea forests in the NE Atlantic

Understanding fish-habitat associations is critical for ecosystem-based approaches to management and conservation. Kelp species, which are estimated to inhabit around 25% of the world's coastline and underpin highly productive and biodiverse ecosystems, are widely recognised as important nursery and foraging habitats for coastal fish species. However, quantitative assessments of fish assemblages within kelp forests are lacking for many regions. Here, we used Baited Remote Underwater Video (BRUV) and Underwater Visual Census (UVC) to quantify fish assemblages in Laminaria hyperborea forests at eight shallow subtidal rocky reefs that spanned 9° of latitude in the United Kingdom (UK). Fish assemblages were a ubiquitous and conspicuous component of kelp forest communities at all sites. BRUV surveys recorded marked regional-scale variability, with latitudinal shifts in assemblage structure and particularly distinct assemblages recorded in southwest England. These patterns were largely due to greater abundances of Pollachius spp. (i.e. saithe and pollock) in northern regions and higher numbers of Gobiusculus flavescens (two-spotted goby) and labrid species (i.e. rock cook, goldsinny and ballan wrasses) in southern regions. Unlike BRUVs, UVC surveys did not detect significant regional-scale variation in assemblage structure but did detect significant site-level differences, highlighting differences between the two techniques. BRUV surveys also recorded clear latitudinal trends in richness, with more taxa recorded at lower latitudes. Fish assemblages in the NE Atlantic have been, and will continue to be, impacted by ocean warming and fishing activities. Greater spatiotemporal coverage of kelp forest surveys and ongoing robust monitoring is needed to better understand and manage future ecological changes.

Impacts of marine fishing ban on the ecology of hilsa In the Nijhum Dwip Seascape in Bangladesh

Bangladesh government has imposed a 65-day marine fishing ban since 2015 to conserve marine fisheries, particularly to boost hilsa (Tenualosa ilisha) production. However, the ecological impacts of the marine fishing bans on water quality and hilsa’s growth are not assessed yet. Thus, this study aims to contribute here using data from coastal waters and fish from pre-contacted fishers in the Nijhum Dwip seascape during and outside the fishing ban in 2021 – 2022. Data were analyzed using R software. The measured mean dissolved oxygen, temperature, pH, electrical conductivity, total dissolved solids, and transparency of the sample water were 7.1 ± 1.13 mg/l, 31.1 ± 0.71°C, 8.45 ± 0.07, 40000 ± 2828 μS/cm, 18000 ± 1414 mg/L and 63.5 ± 2.12 cm at 1 week prior to the ban ends (July) and 8.45 ± 0.21 mg/l, 22.35 ± 0.49°C, 8.45 ± 0.07, 20500 ± 1060.66 μS/cm, 10350 ± 212.13 mg/l and 63.5 ± 7.78 cm before the ban starts (February). The values might be varied due to seasonal differences. The mean length (38 cm) and weight (601 g) of sampled hilsa during the ban periodwere comparatively larger than the mean length (29 cm) and weight (229 g) of hilsa which were sampled during the outside fishing ban period. Therefore, this study concludes that the marine fishing ban has positive impact on the growth and size of hilsa. This study suggests that further research is required to assess the fishing ban’s impact on the growth and production of other coastal and marine fish species across the Bay of Bengal. Dhaka Univ. J. Biol. Sci. 32(1): 33-43, 2023 (January)

Oxidative response to Cd and Pb accumulation in coastal fishes of Pattani Bay

Bioaccumulation of heavy metals can cause physiological and biochemical alterations in aquatic animals. Accumulation of Cd and Pb and oxidative response in the liver and muscle of fish species; Scatophagus argus, Plotosus lineatus, Netuma thalassina and Mugil cephalus were evaluated. Accumulation of Cd, Pb and oxidative response indicated by malondialdehyde (MDA) were significantly higher in the liver than muscle in all coastal fish species. Antioxidative parameters, such as reduced glutathione (GSH), catalase (CAT), and superoxide dismutase (SOD), varied. S. argus exhibited the highest levels of Cd and Pb accumulation, both in the liver and muscle. Simultaneous activation and depression of oxidative defense mechanism was depicted in S. argus’s liver which indicated by positive correlation of Pb to CAT activity and negative correlation of Pb to SOD activity. Positive correlation was significance for Cd and Pb accumulation in the liver and muscle of M. cephalus, which may be used for pollution biomonitoring. The present study indicated the oxidative response to Cd and Pb accumulation was emphasise in liver, while oxidative response varied in each coastal fish species. Highlights Accumulation of Cd, Pb, and oxidative status, i.e., lipid peroxidation level indicated by malondialdehyde (MDA), was significantly higher in the liver than muscle in 4 coastal fish species (Scatophagus argus, Plotosus lineatus, Netuma thalassina, and Mugil cephalus). S. argus exhibited the highest levels of Cd and Pb accumulation, both in the liver and muscle, when compared to other three coastal fish species. The liver’s oxidative response to Pb was high in S. argus, and represented simultaneous activation and depression of antioxidative defense mechanism. A significant positive correlation was revealed for Cd and Pb accumulation in the liver and muscle of M. cephalus, which may be used for pollution biomonitoring.

Brodifacoum Levels and Biomarkers in Coastal Fish Species following a Rodent Eradication in an Italian Marine Protected Area: Preliminary Results.

Brodifacoum is the most common rodenticide used for the eradication of invasive rodents from islands. It blocks the vitamin K cycle, resulting in hemorrhages in target mammals. Non-target species may be incidentally exposed to brodifacoum, including marine species. A case study conducted on the Italian Marine Protected Area of Tavolara Island was reported after a rodent eradication using the aerial broadcast of a brodifacoum pellet. Brodifacoum presence and effects on non-target marine organisms were investigated. Different fish species were sampled, and a set of analyses was conducted to determine vitamin K and vitamin K epoxide reductase concentrations, prothrombin time, and erythrocytic nuclear abnormalities (ENA) assay. In all the examined organisms, brodifacoum was not detected. The results obtained showed differences in vitamin K and vitamin K epoxide concentrations among the samples studied, with a positive correlation for three species between vitamin K, vitamin K epoxide, and fish weight. The prothrombin time assay showed a good blood clotting capacity in the fish. Higher abnormality values were recorded for four species. The results of this study suggest that it is possible to hypothesize that the sampled fish were not likely to have been exposed to brodifacoum and that consequently there are no negative issues concerning human consumption.

Experimentally Determining Optimal Conditions for Mapping Forage Fish with RPAS

RPAS (Remotely piloted aircraft systems, i.e., drones) present an efficient method for mapping schooling coastal forage fish species that have limited distribution and abundance data. However, RPAS imagery acquisition in marine environments is highly dependent on suitable environmental conditions. Additionally, the size, color and depth of forage fish schools will impact their detectability in RPAS imagery. In this study, we identified optimal and suboptimal coastal environmental conditions through a controlled experiment using a model fish school containing four forage fish-like fishing lures. The school was placed at 0.5 m, 1.0 m, 1.5 m, and 2.0 m depths in a wide range of coastal conditions and then we captured RPAS video imagery. The results from a cluster analysis, principal components, and correlation analysis of RPAS data found that the optimal conditions consisted of moderate sun altitudes (20–40°), glassy seas, low winds (<5 km/h), clear skies (<10% cloud cover), and low turbidity. The environmental conditions identified in this study will provide researchers using RPAS with the best criteria for detecting coastal forage fish schools.

Development of modelling and mapping methods to predict spatial distributions and abundance of estuarine and coastal fish species life‐stages in Florida

AbstractSuitability modelling and mapping methods were developed to predict spatial distributions and population abundance of fish and macroinvertebrate species in Florida estuaries and coastal zones. Habitats were mapped in Pensacola Bay, Tampa Bay, and Charlotte Harbor using data from fisheries‐independent monitoring. Starting in 1997, suitability functions from habitat suitability index models were linked to habitat grids to create seasonal maps for early‐juvenile, juvenile, and adult life‐stages. After 2003, habitat suitability models (HSM) were linked to seasonal habitat grids to create seasonal maps validated by reciprocal transfer of suitability functions between estuaries. A quantitative method was used with five factor models and models with fewer environmental factors for four species in 2005 and for 11 species by life‐stages in 2009. In 2006, suitability functions transferred from Charlotte Harbor were linked with habitat grids for Rookery Bay and Fakahatchee Bay and HSM maps produced for three time periods to test transferability to estuaries lacking long‐term monitoring. Analyses in 2012 demonstrated that HSM maps for Tampa Bay derived independently from earlier suitability functions were almost identical to HSM maps created using recent suitability functions. Salinity was the most significant environmental variable for predicting abundance in models for species life‐stages in the Peace River and Charlotte Harbor, although nutrient concentrations from upriver may have influenced species’ abundances associated with low (<5 psu) to moderate (5–10 psu) salinities. Population abundance estimates for Charlotte Harbor were derived from seasonal HSM maps created in 2019 and 2021. The 2021 paper compared changes in seasonal population numbers between Baseline and Minimum Flows associated with projected water withdrawals from the Peace River. Electronic logbooks were developed in 2001 and 2004 to collect data on shrimp fishing vessels and HSM maps for the West Florida Shelf created for 16 months in 2004–2005. Methodologies evolved as enabling technology became available.

Improving assessments of coastal ecosystems – Adjusting coastal fish indicators to variation in ambient environmental factors

The application of ecological indictors for assessing the environmental status of ecosystems play an important role for effective management. However, natural variability may limit the indicators’ ability to provide relevant information about anthropogenic pressures and guide management action. Coastal fish species are not only a resource for commercial and recreational fisheries but also key ecosystem components in the Baltic Sea, and is therefore used as management objectives within the EU Marine Strategy Framework Directive and the HELCOM Baltic Sea Action Plan. A challenge, however, is that the distribution and abundance of coastal fish populations in Baltic Sea is also influenced by spatial and temporal variation in ambient environmental factors. Here, using 16 years of monitoring data, over a latitudinal range of 56 – 66°N along the Swedish Baltic Sea coast, we evaluated the effect of variability in water temperature and depth, and wave exposure for three indicators of environmental status assessment in the Baltic Sea: Abundance of perch, Abundance of Cyprinids, and Abundance of Piscivores. Generalized linear mixed models (GLMM) revealed an overall positive linear relationship between water temperature for all indicators, and overall negative linear relationships to depth and wave exposure. When adjusting indicator values using the parameter estimates from the GLMM models, the variability and 95 % confidence interval for all three indicators were reduced. The adjustment, however, did not have a strong impact on the assessment of the ecological state of the indicator. Our results suggest that adjusting coastal fish indicators to variation in local ambient environmental factors will increase their precision, and hence, the confidence in the assessment of environmental status.

Developing species distribution models for critically endangered species using participatory data: The European sturgeon marine habitat suitability

Increasing knowledge on distribution and habitat selection of coastal fish species is essential for the management of marine environments, and can be provided through the use of Species Distribution Models (SDM). Opportunistic and participatory data, such as recreational or commercial bycatch data, can provide precious information at large scale and low cost to estimate fish spatial distributions, but are subject to biases (e.g. lack of absence data, non-random sampling scheme). The European sturgeon (Acipenser sturio) is a critically endangered diadromous fish and its marine habitat preferences are unknown. The goal of this study was to investigate key variables driving A. sturio distribution and predict its current distribution in inshore waters along the European Atlantic coast. We developed two correlative SDM in A. sturio marine habitats based on incidental observations (2012–2021) and two different sets of environmental predictors. In both attempts, six methods which differ according to the biases they aim to reduce (i.e. oversampled areas or environmental conditions, dependence between calibration and validation datasets) and the input dataset used (i.e. random pseudo-absences or target-group pseudo-absences) were applied at various stages of the model building and evaluation process. By comparing potentially biased and bias-corrected predictions, we found similar satisfactory level of evaluation and spatial patterns of habitat suitability. Marine areas predicted as the most suitable were distributed along the French Atlantic coast, the Seine and Somme bays, and at a lesser extent around the Rhine delta and in some coastal areas of the Cantabrian Sea (Northern Spain). We found a strong influence of the bathymetry, temperature, and salinity as well as an influence of the bottom current velocity and of the distance to the source population in explaining A. sturio marine distribution, while the nature of the substrate was not retained by the models. Results of this study could pave the way toward more integrated conservation measures for this critically endangered fish.

The Key Environmental Factors Shaping Coastal Fish Community in the Eastern Gulf of Finland, Baltic Sea

A highly productive coastal zone plays an important role in various stages of fish life cycles, e.g., spawning migrations, fish reproduction, larval development, juveniles growing, etc. Therefore, coastal biotopes significantly contribute to commercial fish species recruitment. Although the eastern Gulf of Finland is rich in shallow coastal water, its coastal fish communities and the influencing environmental variables are still significantly understudied. We investigated the composition and distribution of coastal fish species and the impact of abiotic and biotic environmental factors in the eastern Gulf of Finland during field surveys in 2011–2017. In total, 34 fish species were recorded at shallows. The coastal fish community demonstrates a low degree of heterogeneity despite a highly heterogeneous environment. Five freshwater species are widely distributed and the most frequent in the area. Three key environmental variables influencing the coastal fish community of the eastern Gulf of Finland were: (i) salinity, (ii) filamentous algae presence, and (iii) macrophytes presence. Fish community structure was also influenced by the sampling season. Discriminating and typifying taxa were performed for each environmental variable. We suggest that obtained results might be useful for future environmental studies in the region and fish community modeling.

Patterns of fish distribution in tropical rock pools at Príncipe Island, Gulf of Guinea

Little is known about the ichthyofauna from intertidal rock pools of the west coast of Africa, especially in the Gulf of Guinea. Rock pools are characteristic habitats of the intertidal zone of structurally complex rocky shores, adding important niche space to coastal fish species. In this study, rock pools of three similar rocky shores of Príncipe Island were sampled to describe the composition, abundance and distribution of fish assemblages and their relation to parameters of pool structure (volume, depth), water mass (temperature, salinity and pH) and biology (algal and coral cover, and biological species richness). A total of 18 fish species and one leptocephalus larva of unknown species, representing 13 families, were observed during sampling. In decreasing order, the five-most-abundant species were the goby Bathygobius burtoni, night sergeant Abudefduf taurus, West African rockhopper Entomacrodus cadenati, sailfin blenny Microlipophrys velifer and Biafra doctorfish Prionurus biafraensis, which together represented 81% of the total number of fish recorded during this study. The four-most-abundant species also proved to be the better adapted to the range of conditions found in rock pools. Overall, larger rock pools with minimal biological cover and higher salinity were found to support higher fish abundance and species richness. Most species individually preferred rock pools with larger volumes, but some presented a degree of habitat specificity, such as the absence or presence of biological cover. Species that were more-active swimmers preferred deeper pools.

Distribution and source apportionment of toxic and trace elements in some benthic and pelagic coastal fish species in Karnaphuli River Estuary, Bangladesh: Risk to human health.

The Karnaphuli River is one of the prime and most important streams in the southeastern part of Bangladesh. The favorable water current and the geographic location have rendered the Karnaphuly River estuary a suitable habitat and a breeding ground for diverse fish species. Reversely, this estuary has been polluted by discharges from many point and non-point sources due to its location in the catchment area of a heavily industrialized area, Chattagram port city. However, published research concerning the status of toxic and trace elements in some commercially important benthic and pelagic coastal fish species in Karnaphuli River estuary was not found in the existing literature. Therefore, it's an important field of study on the assessment of toxic and trace elements concentration in the commercially important benthic and pelagic coastal fish species and their health taxation in the Karnaphuli River Estuary. Energy dispersive X-ray fluorescence (ED-XRF) was used to quantify trace metal concentration in edible parts of the fish species. This study revealed that the rank of the trace metals concentration was as follows (mg/kg): Zn (37.1)>Mn (16.12)>V (11.16)>Cu (9.49)>Rb (5.62)>Pb (2.98)>Cr (1.59)>Co (1.17). The F-test showed that a significant difference at 95% confidence level in the distribution pattern of trace metals concentration among the examined fish species in the study area. The metal pollution index (MPI) in the muscle of fishes were found to be in the following order: L. bata>P. monodon>T. cirratus>M. bleekeri>O. pabda>H. nehereus>L. calcarifer>P. argenteus>P. paradiseus>T. toli, and the MPIs for most of the benthic fish species were higher compared to the pelagic fishes. On the other hand, the examined fish species were significantly bio-accumulative with the highest bio-accumulation factor value for benthic species. The multivariate analysis identified that the sources of the trace metals were associated with anthropogenic activities. For the human health risk assessment concern, estimated daily intake, target hazard quotient and cancer-causing risk were estimated. The results for non-cancer hazardous index values were found to be lower than unity. On the other hand, the total cancer risk data ranging from 1.24E-05 to 1.70E-05 were fallen within the range for the threshold values (1.0E-06 to 1.0E-04). However, considering the suggested values set by the environmental and regulatory agencies, it has been recommended that no significant non-carcinogenic and cancer-causing health risk for humans was seen due to the consumption of the studied fish species.

Application of environmental DNA as a tool for detecting intertidal habitat use by forage fish

Many coastal forage fish species spend most of their life history using the water column, but some species such as Pacific Sand Lance (Ammodytes personatus) and Surf Smelt (Hypomesus pretiosus) have a requirement for intertidal sediments for spawning and or burying. Detection of suitable but typically uncommon intertidal habitats for spawning has historically relied on extensive visual surveys for eggs from large sand samples. In the present study, we developed and validated two new non-destructive qPCR-based tools for detecting Sand Lance and Surf Smelt eDNA from small sand samples. A total of 279 composite transect sand samples were collected from 101 beaches and were tested for eDNA sample integrity using the IntegritE-DNATM test. Initial testing showed that all but 42 of 46 samples passed after an inhibitor clean-up step. Of the 101 beaches sampled 275 times, there were 111 detections of Sand Lance on 52 beaches, and there were 13 detections of Surf Smelt on 10 beaches. One hundred and eighty-one samples were paired with visual egg counts and 76 (42%) of these tested positive for Sand Lance while 9 of 132 (7%) samples tested positive for Surf Smelt. For the 27 paired samples with two or more Sand Lance eggs visually detected there was a significant positive correlation (r = 0.694, p = 0.0001) with eDNA copies per liter suggesting that a larger Sand Lance presence is easily and reliably detected using eDNA. The methods and approaches described herein will serve as a foundation for broad application of eDNA approaches for forage fish species that utilize intertidal benthic habitats.

Life‐history traits and temporal patterns in the incidence of coastal fishes experiencing tropicalization

AbstractClimate change is causing shifts in the geographic distributions of coastal fish species toward higher latitudes. However, local fish communities found in higher latitudes today are not simply those found in lower latitudes in the past because the sensitivity of species to various environmental conditions is different. Responses of fish to environmental conditions differ depending on their life‐history traits such as the maximum population growth rate, age of maturity, and generation time because these traits are constrained by environmental conditions. Here, we investigate associations among temporal patterns in presence–absence (incidence) data, life‐history traits of species, and environmental conditions to elucidate the potential mechanisms behind the effects of climate change on coastal fish communities. In this study, fish monitoring data collected semi‐monthly between 1982 and 2019 from eight major bays in the northwestern Gulf of Mexico were analyzed with generalized additive models. Smooth patterns over seasons and years in the incidence data of 77 species were estimated, and the data were associated with environmental variables. Further, these temporal patterns were associated with the life‐history traits of species. The results show that species that are more common in the summer months (non‐winter spawners) tend to exhibit an increasing trend and that species common during the spring (winter spawners) tend to exhibit a decreasing trend, suggesting the importance of summer conditions in driving tropicalization. Salinity had significant effects on species in general, and longer‐lived species tended to be affected by temperature. These results suggest seasonal differences in the effects of environmental conditions and variation in sensitivity to environmental conditions among different life‐history strategies. These findings represent major steps toward understanding the mechanisms behind the tropicalization of estuarine communities.

ClimateFish: A Collaborative Database to Track the Abundance of Selected Coastal Fish Species as Candidate Indicators of Climate Change in the Mediterranean Sea

ClimateFish: A Collaborative Database to Track the Abundance of Selected Coastal Fish Species as Candidate Indicators of Climate Change in the Mediterranean Sea

Mesoscale assessment of sedentary coastal fish density using vertical underwater cameras

Accurate and precise monitoring of the absolute density (i.e., number of fish per area or volume unit) of exploited fish stocks would be strongly advisable for deriving stock status and for designing proper management plans. Moreover, monitoring should be achieved at relevant (i.e., sufficiently large) temporal and spatial scales. This objective is particularly challenging for data-poor fisheries, as is often the case for recreational fisheries. Therefore, the feasibility of underwater video monitoring (vertical unbaited cameras) for estimating, as a proof of concept, the absolute density (and its ecological drivers) of a coastal sedentary fish species is demonstrated. The absolute density of a small serranid (Serranus scriba) targeted by recreational fishing was estimated along the southern coast of Mallorca Island (nearly 100 km). The median fish density ranged between 111 ind/km2 (Es Molinar) and 14,110 ind/km2 (Cabrera). Absolute density was correlated with fishing exposure, habitat, and depth. Site specific, seemingly long-term, effects of fishing exposure were negatively correlated with fish density, but short-term effects (assessed by the interaction between fishing exposure and before/after the season when recreational fishing occurred in the study area) were not detected. We suggest that the short-term effects of fishing may remain undetected because highly exploited sites could contain fish that are already not vulnerable to recreational fishing gear, irrespective of the short-term fishing pressure exerted. Such a process may explain some hyper-depletion patterns and should preclude the use of fisheries-dependent data for monitoring fish density. The results reported here indicate that monitoring fish abundance with vertical unbaited cameras at large spatial and temporal scales can be a reliable alternative for many species.

A National Scale “BioBlitz” Using Citizen Science and eDNA Metabarcoding for Monitoring Coastal Marine Fish

Marine biodiversity is threatened by human activities. To understand the changes happening in aquatic ecosystems and to inform management, detailed, synoptic monitoring of biodiversity across large spatial extents is needed. Such monitoring is challenging due to the time, cost, and specialized skills that this typically requires. In an unprecedented study, we combined citizen science with eDNA metabarcoding to map coastal fish biodiversity at a national scale. We engaged 360 citizen scientists to collect filtered seawater samples from 100 sites across Denmark over two seasons (1 p.m. on September 29th 2019 and May 10th 2020), and by sampling at nearly the exact same time across all 100 sites, we obtained an overview of fish biodiversity largely unaffected by temporal variation. This would have been logistically impossible for the involved scientists without the help of volunteers. We obtained a high return rate of 94% of the samples, and a total richness of 52 fish species, representing approximately 80% of coastal Danish fish species and approximately 25% of all Danish marine fish species. We retrieved distribution patterns matching known occurrence for both invasive, endangered, and cryptic species, and detected seasonal variation in accordance with known phenology. Dissimilarity of eDNA community compositions increased with distance between sites. Importantly, comparing our eDNA data with National Fish Atlas data (the latter compiled from a century of observations) we found positive correlation between species richness values and a congruent pattern of community compositions. These findings support the use of eDNA-based citizen science to detect patterns in biodiversity, and our approach is readily scalable to other countries, or even regional and global scales. We argue that future large-scale biomonitoring will benefit from using citizen science combined with emerging eDNA technology, and that such an approach will be important for data-driven biodiversity management and conservation.

Linking trophic ecology with element concentrations in a coastal fish community of the Bijagós Archipelago, West Africa

We report the concentration of 13 elements in the muscle and liver of 17 coastal fish species of the Bijagós Archipelago, Guinea-Bissau, and link element concentrations to trophic ecology as assessed by carbon (δ13C) and nitrogen (δ15N) stable isotopes. We found higher concentrations of Hg, Fe, Mn, Cu, Zn, Se and As in liver as compared to muscle tissue, and the opposite pattern for Sr and Ca in all fish species. The concentration of Hg and Se in muscle samples increased significantly with δ15N, suggesting a biomagnification of these elements in this food chain. The concentrations of Ca and Sr, Fe and Cr, Ca and Mn, and Fe and Mn were positively correlated to each other in more than 50% of the studied species. Fish constitute the most important animal protein source for people in Guinea-Bissau, and thus assessing the concentrations of potentially toxic elements is relevant for human health.

Long-Term Monitoring of Diel and Seasonal Rhythm of Dentex dentex at an Artificial Reef

Behavioral rhythms are a key aspect of species fitness, since optimize ecological activities of animals in response to a constantly changing environment. Cabled observatories enable researchers to collect long-term biological and environmental data in real-time, providing relevant information on coastal fishes’ ecological niches and their temporal regulation (i.e., phenology). In this framework, the platform OBSEA (an EMSO Testing-Site in the NW coastal Mediterranean) was used to monitor the 24-h and seasonal occurrence of an ecologically iconic (i.e., top-predator) coastal fish species, the common dentex (Dentex dentex). By coupling image acquisition with oceanographic and meteorological data collection at a high-frequency (30 min), we compiled 8-years’ time-series of fish counts, showing daytime peaks by waveform analysis. Peaks of occurrence followed the photophase limits as an indication of photoperiodic regulation of behavior. At the same time, we evidenced a seasonal trend of counts variations under the form of significant major and minor increases in August and May, respectively. A progressive multiannual trend of counts increase was also evidenced in agreement with the NW Mediterranean expansion of the species. In GLM and GAM modeling, counts not only showed significant correlation with solar irradiance but also with water temperature and wind speed, providing hints on the species reaction to projected climate change scenarios. Grouping behavior was reported mostly at daytime. Results were discussed assuming a possible link between count patterns and behavioral activity, which may influence video observations at different temporal scales.