Fish Assemblage Composition Research Articles

Environmental DNA metabarcoding for fish diversity assessment in a macrotidal estuary: A comparison with established fish survey methods

Fishes are a dominant component of the macrofauna in estuaries and are important for assessing the health of these threatened ecosystems. Several studies have applied environmental DNA (eDNA) metabarcoding to assess the biodiversity of fishes in estuaries. However, none have combined measurement of physicochemical variables with a spatially extensive sampling design across the full salinity gradient. This study aimed to compare spatial fish assemblage composition detected via eDNA metabarcoding of surface water samples with conventional fishing gear surveys in a macrotidal estuary (river Dee, North Wales, UK). In addition, eDNA assemblage composition across seasons was investigated. In autumn 2018, triplicate eDNA samples were taken at 13 stations in a spatially systematic design alongside seine, fyke and beam trawl sampling. In summer 2019, eDNA samples from eight of the 13 original stations were collected again in the upper and lower estuary. DNA was extracted from samples and subjected to metabarcoding analysis using an established assay targeting teleost fishes. The key findings were that in autumn, eDNA detected 17 of the 26 (71%) species caught by fishing gears, which included the most abundant species. Overall, eDNA detected a greater species richness, per 30 samples, than seine or fyke nets (but not beam trawling). Additionally, there was a clear correlation between salinity and assemblage composition, which was consistent across seasons. Overall, the study indicates that eDNA metabarcoding could enhance existing fish sampling methods, by generating a more comprehensive picture of estuarine fish biodiversity and providing additional information for ecological inference and management actions.

Using quantitative soundscape analyses for coral reef microhabitat discrimination

The use of Ocean Sound to describe ecosystems and address ecological questions has increased remarkably during the last decades. The current capacity of recording, storing, and analyzing large amounts of data urges efforts toward developing standards and guidelines to advance underwater soundscape analyses. The development and use of metrics to summarize soundscape attributes have become widespread, but further field-testing and validation are still necessary to identify their ecological relevance resolution. We explore a combination of approaches to determine the performance of ecoacoustic indices and the recently proposed “Soundscape Code” in combination with ecological metrics (habitat and fish assemblage composition) for discrimination between coral reef microhabitats. We collected ecological and acoustic data from Lizard Island (Great Barrier Reef), where we established five transects each with five sampling stations, covering a range of microhabitats from the reef flat zone to the forereef zone, and from high live coral cover to rubble-dominated areas. Conspicuous differences were observed between the soundscapes of the live coral cover and the rubble-dominated areas, demonstrating the potential value of using soundscapes to discriminate between and monitor changes in coral reefs. [Work supported by the BHP-AIMS Australian Coral Reef Resilience Initiative.]

Physical, biological and anthropogenic drivers of spatial patterns of coral reef fish assemblages at regional and local scales

Species abundance, diversity and community assemblage structure are determined by multiple physical, habitat and management drivers that operate across multiple spatial scales. Here we used a multi-scale coral reef monitoring dataset to examine regional and local differences in the abundance, species richness and composition of fish assemblages in no-take marine reserve (NTMR) and fished zones at four island groups in the Great Barrier Reef Marine Park, Australia. We applied boosted regression trees to quantify the influence of 20 potential drivers on the coral reef fish assemblages. Reefs in two locations, Magnetic Island and the Keppel Islands, had distinctive fish assemblages and low species richness, while the Palm and Whitsunday Islands had similar species composition and higher species richness. Overall, our analyses identified several important physical (temperature, wave exposure) and biological (coral, turf, macroalgal and unconsolidated substratum cover) drivers of inshore reef fish communities, some of which are being altered by human activities. Of these, sea surface temperature (SST) was more influential at large scales, while wave exposure was important both within and between island groups. Species richness declined with increasing macroalgal cover and exposure to cyclones, and increased with SST. Species composition was most strongly influenced by mean SST and percent cover of macroalgae. There was substantial regional variation in the local drivers of spatial patterns. Although NTMR zoning influenced total fish density in some regions, it had negligible effects on fish species richness, composition and trophic structure because of the relatively small number of species targeted by the fishery. These findings show that inshore reef fishes are directly influenced by disturbances typical of the nearshore Great Barrier Reef, highlighting the need to complement global action on climate change with more targeted localised efforts to maintain or improve the condition of coral reef habitats.

Environmental filters explain the ecomorphological patterns of stream fish in the southern Amazon

ABSTRACT The ecomorphology reflects morphological variations that may indicate significant ecological processes. In this study, the influence of environmental variables on the ecomorphological composition of stream fish was tested. The study was developed in ten streams within a conservation area in the Juruena River sub-basin, in Mato Grosso state, Brazil. The sampling occurred during the drought period in July 2012. The fish were sampled with simple sieves and trawl nets. We analyzed 17 variables of the physical habitat and 14 morphological indices based on morphometric measurements of the fish. In total, 753 specimens were collected, comprising four orders, 14 families, and 27 species. Only fine sediments influenced the ecomorphological composition of the fish assemblages. This substrate variable acted as a filter for the ecomorphology of fish that usually inhabit slow waters, have a morphology adapted towards a good stabilization capacity and maneuverability, fins capable of large and rapid impulses, and that feed close to the surface. Our results can contribute to the understanding of the ecological processes that drive the composition of fish assemblages in conserved Amazonian streams.

Long‐term monitoring on a new channelized stream section: changes in mesohabitat, composition, and size structure of fish assemblages

The construction of riverine structures (weirs, bridges, or channelization) on riverbeds causes alterations in the flow regime and channel geometry. Once a new stretch is created, species must colonize it. The ecological succession processes that are entailed are decisive for adequate recovery after alterations, and understanding these processes would enable elaborate efficient restoration actions. We analyzed environmental variables and the colonization and succession patterns of fish assemblages in a new channelized stretch of a river from its construction to the present (from 1996 to 2020) in the northern Iberian Peninsula. During the studied period, habitat diversity increased, and mesohabitat became more complex. Depths, depth diversity, and the number of pools in the new channel increased with time. Water temperature decreased because of the new shade provided by riparian forests. The size‐related variables of the fish community (size diversity, mean, and maximum length) increased in the new section, achieving similar values to those in the control section. The slopes of the fish size spectra showed a slow evolution over 25 years from a fish assemblage dominated by small fish to a more size‐diversity fish community. Our results suggest that habitat complexity shape fish assemblage and structure. Moreover, size‐related variables can be effective ecological indicators of fish colonization and succession processes. Finally, small‐scale restoration measures in the riverbed and riparian forest are expected to increase the effectiveness of future restoration projects in rivers.

Spatial and Temporal Variation of Fish Assemblage Associated with Aquatic Macrophytes in Three Small Lagoons of the SOUTH-Eastern, Côte d’Ivoire

Aquatic plants play a crucial role in an aquatic ecosystem partly because these plant communities provide suitable habitats and food items to other aquatic organisms especially fish. The purpose of the present study was to examine spatial variation in fish assemblage structure associated with aquatic macrophytes in Ono, Kodjoboue and Hebe lagoons, three small lagoons of Côte d’Ivoire. Fish were monthly sampled from September 2014 to August 2016 using traps, gill nets, harpoons and hawks. The abiotic parameters namely temperature, transparency, pH, total dissolved solids, conductivity, dissolved oxygen, ammonium-nitrogen, nitrate, nitrite and phosphate were recorded for the characterization of the water mass in the lagoons. Significant variation in water parameters was observed among the sampling lagoons, except for nitrite and ammonium-nitrogen. However, no significant different was obtained between Kodjoboue and Hebe lagoons. A total of 42, 35 and 37 species were recorded respectively in Ono, Kodjoboue and Hebe lagoons, with Perciformes (22 species), Siluriformes (8 species) and Osteoglossiformes (7 species) being the most diverse Orders. Habitats with highly amounts of macrophyte cover provide the optimal environment for many fish and hence, increase the taxonomic richness, abundance, diversity and equitability. The multivariate analysis showed that temperature, dissolved oxygen, nitrate, phosphate, pH and ammonium-nitrogen and macrophyte were key environmental variables and played important roles in determining species composition of fish assemblages.

Characterization of fish assemblages in eleven multi-use reservoirs from North Carolina, USA

Managing impounded river systems is a recurring challenge for aquatic resource professionals because reservoirs serve multiple functions with different ecological and socioeconomic outcomes. However, research on fishes in reservoirs has disproportionally focused on recreationally and economically important species, with less attention directed toward fish assemblages despite the potential for management at the assemblage level. As such, evaluation of relationships between reservoir fish assemblages and biotic and abiotic factors and testing whether assemblage structure is affected by changing environmental conditions may deepen ecological understanding and provide insights for reservoir fisheries management. Our overall objective was to assess these relationships in 11 reservoirs from North Carolina, USA. We sampled fish assemblages in the reservoirs, which spanned five river basins representing a range of habitat conditions, using experimental gillnets and pulsed DC nighttime electrofishing. Multivariate statistical analyses indicated that taxonomic differences in fish assemblage composition among river basins followed a gradient of productivity. The top contributing species to reservoir dissimilarity were bluegill (Lepomis macrochirus), gizzard shad (Dorosoma cepedianum), black crappie (Pomoxis nigromaculatus), and white perch (Morone americana). These four species were positively associated with factors that reflect increasing eutrophic conditions in the 11 reservoirs and could, therefore, serve as indicators of reservoir productivity, anthropogenic influence, and fish assemblage structure, in addition to their key role in reservoir fisheries management. Whereas ­fisheries research has historically focused on assessing fish ­populations, our results illustrate the ecological and management insights derived from simultaneously collecting assemblage- and population-level data. Research on reservoir fish assemblages in relation to biotic and abiotic conditions may help advance fish ecology and management alike.

The Impact of Hydrological Changes on Fish Assemblages in the Zachery Marshes of Southern Iraq

The present study was implemented in the Zachery Marsh as part of the middle marshes north of Bashar Province from January to December 2022 to investigate the impact of the seasons’ oscillation between drought and flooding on fish assemblage abundance, size spectrum, and ecological indices. Three stations were selected to collect samples of fish. The specimens were monthly gathered with different fishing tools, including fixed gillnets, cast nets, and electrofishing. The water temperature ranged from 12.32 to 34.03 °C, the salinity varied from 1.75 PSU to 2.89 PSU, and the pH fluctuated between 7.47 and 8.43. The rate of change in water depth in the low flat regions fluctuated from 27 cm in September to 76 cm in April. The mean water depth in rivers, small pits, and canals varied from 45 cm in October to the highest, 121 cm in March. In the seasonal regions, the average depth ranged from zero in July, August, September, and October to 40 cm in April. The current study documented 18 fish species belonging to 16 genera and 9 families from Zachery Marsh, all of them affiliated with the Osteichthyes class. Cyprinidae was the most abundant family, including six species. The species Planiliza abu, the most abundant species, formed 28.44%, Carassius gibelio constituted 20.27%, and Orechromis aureus represented 18.52%. The dominance index (D3) of the three dominant species was 67.23%. The size spectrum of the most commercial species was determined. The diversity index value ranged from 1.64 in August to 2.08 in June, the evenness index varied between 0.69 in May and 0.91 in December, and the richness index values fluctuated from 1.47 in August to 2.28 in June. Resident species represented 88.02%, seasonal species formed 6.08%, and the occasional fish species counted for 5.90%. The present study concludes that the fluctuation between drought and flooding has a critical role in the composition of fish assemblages, particularly in seasonal marshes that are subjected to extreme conditions. The fish evolve several reproductive strategies in these difficult conditions in order to survive and continue.

The influence of some ecological factors on fish diversity and abundance in Al-Huwyzah marsh / South of Iraq

From January to December 2019, the composition of fish assemblages in Al-Huwyzah marsh was studied in various ways based on the nature of their life-history strategies. In orders to assess the impact of hydrological variations on fish assemblage composition, diversity, and abundance. Water temperature fluctuated from 12°C in January to 33°C in July. Salinity varied from 1.38 g/l in March to 3.87 g/l in November. Hydrogen ion fluctuated from 7.37 in November to 8.18 in December. Monthly fluctuations in water depth were monitored for flat sections and low-lying areas of the marsh. Fish assemblages in Al-Huwyzah marsh were studied to determine the impact of hydrological and environmental changes on the pattern, abundance, diversity, and richness of fish assemblages. Fixed, drift, and cast gillnets were used to catch the fish. Nine thousand eight hundred fifty-three fish specimens belonging to 18 species, 17 genera, ten families, and six orders were caught from the three selected stations. All of which belonged to the Osteichthyes class. Ten fish species were native, and eight were exotic species. The Abu mullet Planiliza abu was the most abundant species comprising 35.74% of the total number of species, Prussian carp Carassius gibelio 19.74% of the total caught, and blue tilapia Oreochromis aureus 19.23%. The dominance index (D3) ratio is 74.71% of the upper abundance of three fish species in the present area. The equilibrium strategists that prefer stable habitats with a long time breeding season include abundant exotic species, and opportunistic strategists comprise one species of present fish assemblage. Keywords: Assemblage of fish; Huwyzah marsh; Hydrological variations

Fish on Fire: Shifts in Amazonian fish communities after floodplain forest fires

Abstract Severe droughts can lead to fires that cause massive tree mortality in even the wettest and most isolated Amazonian forests. After repeated fires, blackwater floodplain forests can remain in an open vegetation state of arrested succession that facilitates a transition towards a white‐sand ‘savanna‐like’ vegetation. These vegetation shifts, from closed‐canopy floodplain forests to open fire scars and eventually white‐sand savannas, may have profound implications for fish communities that depend on floodplain forests for food and recruitment. In turn, changes in fish communities may contribute to the arrested forest recovery after fires as fish are important seed dispersal agents for many floodplain tree species. To explore the impacts of floodplain forest fires on fish communities, we sampled fish in unburnt forests, fire scars, and white‐sand savannas in the middle Rio Negro basin (Brazil) during two consecutive flooding seasons. We compared the abundance, species richness, and the taxonomic and trophic composition of fish assemblages across the three habitat types. We found significant shifts in fish assemblages in fire scars compared to unburnt floodplain forests. Also, as fire scars increased in size, total fish biomass decreased strongly. Fish communities in unburnt floodplain forests seem to be characterized by a higher proportion of smaller and omnivorous fish species than fish communities in burned floodplain forests and white sand savannas. Fish assemblages in fire scars and white‐sand savanna were not significantly different. Synthesis and Applications. Amazonian fish communities change after floodplain forest fires. Unburnt forests have diverse fish communities, with a large proportion of unique and small omnivorous species. In contrast, carnivores and detritivores become more common in fire scars and white‐sand savannas formed after forest fires. Less omnivore fish after forest fires can reduce tree seed dispersal and forest regeneration, affecting ecosystem functioning and the services provided by Amazonian forests. Fish are also a primary source of food and income for people living in Amazonian floodplains. Preventing forest fires is therefore of fundamental importance for the conservation of Amazonian aquatic and terrestrial ecological communities as well as for the livelihood of people.

Shifts in the composition and distribution of Pacific Arctic larval fish assemblages in response to rapid ecosystem change.

The Pacific Arctic marine ecosystem has undergone rapid changes in recent years due to ocean warming, sea ice loss, and increased northward transport of Pacific-origin waters into the Arctic. These climate-mediated changes have been linked to range shifts of juvenile and adult subarctic (boreal) and Arctic fish populations, though it is unclear whether distributional changes are also occurring during the early life stages. We analyzed larval fish abundance and distribution data sampled in late summer from 2010 to 2019 in two interconnected Pacific Arctic ecosystems: the northern Bering Sea and Chukchi Sea, to determine whether recent warming and loss of sea ice has restricted habitat for Arctic species and altered larval fish assemblage composition from Arctic- to boreal-associated taxa. Multivariate analyses revealed the presence of three distinct multi-species assemblages across all years: (1) a boreal assemblage dominated by yellowfin sole (Limanda aspera), capelin (Mallotus catervarius), and walleye pollock (Gadus chalcogrammus); (2) an Arctic assemblage composed of Arctic cod (Boreogadus saida) and other common Arctic species; and (3) a mixed assemblage composed of the dominant species from the other two assemblages. We found that the wind- and current-driven northward advection of warmer, subarctic waters and the unprecedented low-ice conditions observed in the northern Bering and Chukchi seas beginning in 2017 and persisting into 2018 and 2019 have precipitated community-wide shifts, with the boreal larval fish assemblage expanding northward and offshore and the Arctic assemblage retreating poleward. We conclude that Arctic warming is most significantly driving changes in abundance at the leading and trailing edges of the Chukchi Sea larval fish community as boreal species increase in abundance and Arctic species decline. Our analyses document how quickly larval fish assemblages respond to environmental change and reveal that the impacts of Arctic borealization on fish community composition spans multiple life stages over large spatial scales.

Composition and diversity of fish assemblages along a shallow beach of a neotropical coastal lagoon

Coastal lagoons are inland water bodies connected to the sea and influenced by freshwater discharge, so these environments undergo constant changes in physical–chemical water characteristics. Transitional environments are important for promoting breeding, refuge, and food areas, besides serving as possible nursery habitats for fish species. In the present study, we analyzed the structure of the fish assemblages in a shallow marginal area of Mirim Lagoon, which belongs to the Laguna Estuarine System (LES), by seasonally evaluating the composition, structure, and diversity of the assemblages. Fieldwork was carried out between September 2017 and August 2018 with three monthly replicates using a beach seine net. Analyses were conducted to highlight the general patterns of the assemblages and to verify seasonal variations in composition, abundance, and diversity. The common species were defined using a species abundance curve, while the seasonal variation in diversity was evaluated using integrated rarefaction and extrapolation curves that correspond to the three orders of Hill numbers. The differences in the specific seasonal composition were indicated by dbRDA and the existence of statistical differences was tested using a PERMANOVA. In total, 3,556 individuals distributed in 16 families and 26 species were caught, with the predominance of Atherinella brasiliensis, Eucinostomus melanopterus, Coptodon rendalli, Eucinostomus argenteus, Mugi lliza, Anchoa tricolor, and Achirus lineatus that represented approximately 98% of the total. Regarding seasonality, the highest abundance was caught in the winter, while the lowest abundance was caught in autumn. The PERMANOVA indicated differences between spring and autumn and between autumn and winter. The main differences between these seasons are associated with the number of individuals caught, species abundance, and species composition. The presence of juveniles of several fish species, especially non-resident species, demonstrates the importance of the shallow area of Mirim Lagoon as a breeding, growth, and protection site that serves as a possible nursery habitat for these species.

Sound sees more: A comparison of imaging sonars and optical cameras for estimating fish densities at artificial reefs

Imaging sonars are increasingly being utilised in fish surveys in conjunction with or as substitutes for optical instruments. To justify the use of imaging sonars, we must first describe their application, limitations, and efficacy compared to optics. This study compared quantitative data of fish assemblages obtained using imaging sonars operating at four frequencies (0.75, 1.2, 2.1, and 3 MHz) with simultaneous optical camera footage at two artificial reefs. Fish densities were on average three times higher for sonar than optics. Greater detection by the sonar was attributed to site-attached fishes that were camouflaged against the artificial reefs or the adjacent seabed, which could be discriminated by imaging sonar, but not using optics. This suggests that differences in habitat and fish assemblage composition could influence the relative performance and density estimates of imaging sonar versus optics. Several limitations of imaging sonar were identified that need to be accounted for in future survey designs, including: discriminating fishes from benthic growth; an inability to detect fishes within complex habitat structures; and seabed and side-lobe interferences that truncate survey volume. Overall, this study demonstrates the value of imaging sonar for quantifying fish communities and describes limitations and recommendations for their deployment in future surveys.

Effects of small hydropower dams on macroinvertebrate and fish assemblages in southern Brazil

Abstract Hydropower dams affect freshwater biodiversity by virtue of modifying flow regimes and degrading habitat conditions both above and below the water impoundment and diversion structure. In recent decades, there has been a global proliferation of Small Hydropower Plants (SHPs) propelled by incentive policies and a general perception that small dams are less harmful to the environment. However, limited science is available on the effects of SHPs on freshwater biodiversity, which is concerning considering their sheer numbers and the high variability in the size and operation of dams classified as SHPs. We investigated the ecological effects of 12 SHPs on macroinvertebrate and fish assemblages of the Chapecó River Basin, Brazil. Our study included sites located upstream of the SHPs and sites directly affected by their operations (i.e., reservoir, dewatering section and downstream of the powerhouse). This design allowed us to quantify shifts in taxonomic composition and examine the relative role of different SHP attributes (e.g., dam height, reservoir area, age) in explaining these changes. Our results reveal that SHPs modify the composition of both macroinvertebrate and fish assemblages, but the magnitude of such changes vary widely among dams. Both assemblages exhibited directionality in taxonomic shifts, resulting in a gradual replacement of taxa associated with fast‐flowing habitats by other groups more commonly associated with standing waters. We also found that changes in assemblage structureare related to structural (dam height, reservoir area) and spatial attributes (distance from headwaters) of SHPs, although the predictive power of these attributes varied taxonomically and among reservoir, dewatering and downstream sites. Overall, our results demonstrate that SHPs have important and heterogeneous effects on freshwater assemblages, which may manifest individually or cumulatively across the riverscape. This suggests that it is unlikely that a priori classifications of dams based on their structural attributes can replace site‐specific and cumulative impact assessments. The results also shed light on the need for better understanding of how SHP attributes shape their ecological effects, so that a full assessment of the potential environmental impacts of the wide range of "small" dams is possible.

Fish eDNA detections in ports mirror fishing fleet activities and highlight the spread of non-indigenous species in the Mediterranean Sea

Gathering comprehensive marine biodiversity data can be difficult, costly and time consuming, preventing adequate knowledge of diversity patterns in many areas worldwide. We propose fishing ports as “natural” sinks of biodiversity information collected by fishing vessels probing disparate habitats, depths, and environments. By combining rapid environmental DNA metabarcoding (eDNA) surveys and data from public registers and Automatic Identification Systems, we show significant positive relationships between fishing fleet activities (i.e. fishing effort and characteristics of the fishing grounds) and the taxonomic fish assemblage composition in eleven Mediterranean fishing ports. Overall, we identified 160 fish and 123 invertebrate OTUs, including at least seven non-indigenous species, in some instances well beyond their known distribution areas. Our findings suggest that eDNA assessments of fishing harbours' waters might offer a rapid way to monitor marine biodiversity in unknown or under-sampled areas, as well as to reconstruct fishing catches, often underreported in several regions.

Organisation of Fish Assemblage in the Mekong Delta as a Potential Indicator of Salt Water Intrusion

The problem of salt water intrusion into the Mekong Delta is a research topic involving various branches of science. Among the causes of this phenomenon are global sea level rise and regulation of the natural river discharge due to hydropower dam construction. The scale of the delta and its water dynamics complicate instrument-based observations. Meanwhile, communities of living organisms can serve as indicators of environmental heterogeneity. This study aimed to analyze the spatial variability of fish assemblage organisation in the Mekong Delta for use as an indicator of salt water intrusion. The composition of fish assemblages in different parts of the delta were determined by midwater trawl catches during January and April 2021. A total of ~15 thousand individual fish from 74 trawl hauls were captured and analyzed. The null hypothesis was that the fish assemblages in the Mekong Delta are represented by three taxonomic complexes that are localized in the upper course (freshwater), the lower course (brackish) and the middle course (zone of the contact of the fresh and brackish waters) of the delta. The taxonomic composition of the freshwater complex is the most poor and is represented by 9 families. Meanwhile, marginal (the contact zone) and brackish complexes include 26 and 23 families, respectively. Specimens of families Cobitidae, Eleotridae, Plotosidae and Siluridae that are only found in the zone of contact of fresh and brackish waters could be considered as indicator species of its position. The actual boundaries of the brackish and freshwater complexes were determined and the distance from them to the marine delta edge equals 34 and 78 km, respectively. Assessment of the salinity values that correspond to the complex boundaries is a task for future investigation. The position of the boundaries of freshwater and brackish fish taxonomic complexes has a biological basis and could be used as an indicator of salt water intrusion into the Mekong Delta.

Environmental factors in the spatial variability of demersal fish in a subtropical estuary and adjacent continental shelf

Quarterly collections of demersal fish were conducted between 2014 and 2018 on the adjacent continental shelf and in the Paranaguá Estuarine Complex (PEC). Univariate and multivariate statistical analyses were used to determine the abundance, richness, and composition of demersal fish assemblages and to list predictor variables responsible for the variability in these ecological descriptors by applying generalized linear models. The collected specimens of demersal fish (n = 25,179) were distributed across 19 orders, 31 families, and 72 species. Fish richness was explained by the following predictor variables: the percentage of fine sand in the sediment, the richness of the benthic megafauna, and sampling sites. The abundance was associated with the predictor variables of the percentage of very fine sand in the sediment, percentage of silt in the sediment, salinity, and sampling sites. Canonical correspondence analysis showed that the fish assemblage composition was strongly associated with the salinity gradient and positively correlated with benthic megafaunal species richness. As it is one of the last remnants of the Atlantic Forest, declared by UNESCO as a Natural Heritage of Humanity, the patterns observed in this study will support PEC's coastal management of current developmental demands, particularly related to port activities.

Composition and distribution of fish assemblages in a tropical river–estuarine continuum

Composition and distribution of fish assemblages in a tropical river–estuarine continuum

Two for the price of one: eDNA metabarcoding reveals temporal and spatial variability of mussel and fish co‐distributions in Michigan riverine systems

AbstractFreshwater mussels (family Unionidae) are among the world's most endangered taxa, with almost 75% of North American taxa classified as a species of concern, threatened, or endangered. Despite the critical importance of comprehensive distributional data for the conservation of unionids and fishes, these data are often lacking because of the labor and resources associated with traditional survey methods. During their larval stage, unionid mussels use various fish species as obligate hosts, making native fish species vital to unionid persistence and an understanding of host distribution similarly important. Here, we utilized an eDNA metabarcoding approach to evaluate patterns of co‐distribution of unionid mussels and fishes along ~362 km of the densely sampled Grand River network as well as the outlets of 19 tributaries along the eastern shore of Lake Michigan, USA. We detected a total of 21 mussel and 40 fish taxa, with distinctive composition of both mussel and fish assemblages across tributaries and differences in fish taxa between sampling periods. Notably, we detected more mussel taxa within the Grand River watershed than at the outlets of all 20 rivers combined. Within the Grand River network, two fish taxa (Pylodictus olivaris and Cyprinella) were found more frequently in areas of high mussel diversity, and three fish taxa more frequently in areas of low mussel diversity (Umbra, Leuciscidae, and Etheostoma). There was little difference between eDNA detections of mussels from samples collected in June versus August, but we detected significantly more fish taxa in August compared to June. Taken together, our findings demonstrate the value of eDNA metabarcoding for evaluating co‐distribution of ecologically connected taxa. The use of eDNA as a tool for determining distributions of mussels and their obligate hosts may facilitate conservation efforts for these imperiled taxa.

Tropicalization shifts herbivore pressure from seagrass to rocky reef communities.

Climate-driven species redistributions are reshuffling the composition of marine ecosystems. How these changes alter ecosystem functions, however, remains poorly understood. Here we examine how impacts of herbivory change across a gradient of tropicalization in the Mediterranean Sea, which includes a steep climatic gradient and marked changes in plant nutritional quality and fish herbivore composition. We quantified individual feeding rates and behaviour of 755 fishes of the native Sarpa salpa, and non-native Siganus rivulatus and Siganus luridus. We measured herbivore and benthic assemblage composition across 20 sites along the gradient, spanning 30° of longitude and 8° of latitude. We coupled patterns in behaviour and composition with temperature measurements and nutrient concentrations to assess changes in herbivory under tropicalization. We found a transition in ecological impacts by fish herbivory across the Mediterranean from a predominance of seagrass herbivory in the west to a dominance of macroalgal herbivory in the east. Underlying this shift were changes in both individual feeding behaviour (i.e. food choice) and fish assemblage composition. The shift in feeding selectivity was consistent among temperate and warm-affiliated herbivores. Our findings suggest herbivory can contribute to the increased vulnerability of seaweed communities and reduced vulnerability of seagrass meadows in tropicalized ecosystems.