Atherinella Brasiliensis Research Articles

Influence of trophic overlaps and trophic niche amplitude on microplastic intake of fish species in shallow areas of a neotropical coastal lagoon

Plastic pollution is a global challenge that affects all marine ecosystems, and reflects all types of uses and activities of human society in these environments. In marine ecosystems, microplastics and mesoplastics interact with invertebrates and become available to higher predators, such as fish, which can ingest these contaminants. This study aimed to analyze how ecological food interactions (diet overlap and trophic niche amplitude) among fish species contribute to the ingestion of plastic particles. The gastrointestinal contents of six fish species (Atherinella brasiliensis, Eucinostomus melanopterus, Eucinostomus argenteus, Genidens genidens, Coptodon rendalli, and Geophagus brasiliensis) were analyzed to identify prey items and plastic ingestion. Based on the ontogenetic classification, A. brasiliensis, E. melanopterus, and G. genidens were divided into juveniles and adults, and the six fish species analyzed were divided into nine predator groups. Most of the plastics ingested by the fish species were blue microplastic (MP) fibers (< 0.05 mm) classified as polyester terephthalate, polyethylene, and polybutadiene. Considering all the analyzed predators, the average number and weight of plastics ingested per individual were 2.01 and 0.0005 g, respectively. We observed that predators with a high trophic overlap could present a relationship with the intake of MP fibers owing to predation on the same resources. In addition, we observed the general pattern that when a species expands its trophic diversity and niche, it can become more susceptible to plastic ingestion. For example, the species with the highest Levin niche amplitude, E. argenteus juveniles, had the highest mean number (2.9) of ingested MP fibers. Understanding the feeding ecology and interactions among species, considering how each predator uses habitats and food resources, can provide a better understanding of how plastic particle contamination occurs and which habitats are contaminated with these polluting substances.

Phenotypic variation among silverside populations (Atherinopsidae: Atherinella brasiliensis) from distinct environments in Northeastern Brazil

The successful adaptation of populations to a wide range of environments is a central topic in ecology. Based on the assumption that body shape may affect survival, we evaluated to what extent biotic and abiotic factors are capable of inducing morphological changes in Brazilian silverside populations (Atherinella brasiliensis). To reach this goal, we compared 18 morphological traits of specimens from five ecosystems representing three types of environment (estuary, coastal lagoon, reservoir). Populations from estuaries displayed greater anal fin area and greater caudal fin aspect ratio and area. Populations from coastal lagoons had more compressed bodies, larger heads, and slightly broader caudal peduncles. The fish from estuaries and coastal lagoons had longer caudal peduncles, larger pelvic fins and larger eye area. Population from reservoir had more depressed bodies and greater oral protrusion. Food availability explained 31% of the observed ecomorphological patterns. Overall, the morphology of the respective populations was consistent with each type of environment, making it possible to associate phenotypic variation with habitat and feeding patterns, although abiotic factors were more significant than biotic factors. In conclusion, landlocked populations of A. brasiliensis are sustainable and add to current knowledge of phenotypical variability in a species widely distributed along the Western Atlantic coast.

INSIGHTS ON THE INFLUENCE OF PHYLOGENETIC ON THE RELATIVE GROWTH USING &lt;i&gt;Atherinella brasiliensis&lt;/i&gt; AS A TOOL

The lengthí weight relationships (LWR) are important tools for ichthyology, they are useful to demonstrate the environmental influence on growth. In this study we estimate the LWR of the Atherinella brasiliensis in the shallow areas of the São Francisco river estuary and compare the growth of this specie in different environments of the Brazilian coast. Specimens of Brazilian silverside (A. brasiliensis, n = 3483), between 2.1 and 13.6 cm in length, were caught in the shallow areas of the São Francisco River estuary between May 2017 and April 2018. The length-weight ratio of the species was represented by the equation y=0.0047x3.0913. Frequency distribution indicates that the species is present in the shallow areas of the São Francisco River estuary in all its ontogenetic stages and apparently reproduces throughout the year with constant input of recruits into the population. Von Bertalanffy’s growth model and longevity were adjusted to reach asymptotic length (L∞) of 14.7 cm, growth coefficient (K) of 0.91 year-1 and longevity (A95) of 3.25 years. The analysis of variance revealed differences for the maximum total length. However, the differences found between the present study and data available in the literature appear to be caused by environmental and methodological differences.

Long-term trends in the abundance of an estuarine fish and relationships with El Niño climatic impacts and seagrass meadows reduction

El Niño events and their climatic effects vary markedly in intensity due to several factors related to oceanographic and atmospheric conditions in the Pacific equatorial ocean. As a result of fluctuations in the climate system, rainfall and temperature deviate from average conditions which causes severe biological, economic and social impacts worldwide. In this study, long-term (23 years) standardized monthly sampling of Brazilian silverside, Atherinella brasiliensis, resident fish that inhabits the shallow waters of a subtropical estuary, was performed to investigate the temporal variability in its abundance and relationship with local and regional environmental factors associated with El Niño events and temporal changes in seagrass meadows biomass. We investigated the following hypotheses: (i) A. brasiliensis abundance has presented a long-term decreasing trend, (ii) El Niño events with higher intensities are related to a higher decrease in the species abundance in the estuary and (iii) the decline in A. brasiliensis abundance is influenced by reduction of seagrass meadows, which serve as attachment sites for developing embryos of this species. Time series analysis revealed a statistically significant decrease in the abundance of A. brasiliensis, which was characterized by marked decline between 1996 and 2004 followed by a relative stability between 2005 and 2019. Generalized linear mixed models (GLMM) showed that its abundance decreased during high rainfall and lower salinity conditions associated with moderate and very strong El Niño events, but not during neutral and weak events. An additional GLMM also revealed significant effects of seagrass biomass on the fish abundance. In fact, years with marked decline in the fish abundance coincided with lower or absence of seagrass biomass in the estuary, especially between 1997 and 2005. Hence, negative climatic impacts on A. brasiliensis abundance may have been intensified by synergistic effects caused by periods of reduction in seagrass meadows. These findings raise concerns for conservation, especially when we consider that the studied species is ubiquitous in southwestern Atlantic estuaries and that climate disturbances such as El Niño are expected to become more frequent in the future due to rising ocean temperatures driven by global warming.

Spatial and seasonal patterns of the surf-zone ichthyofauna on a tropical Atlantic dissipative coastline

The surf-zone of twelve sandy beaches on a tropical Atlantic dissipative coastline (Sergipe, Brazil) was studied to assess whether fish assemblages may be affected by spatial (proximity to estuaries) and seasonal (wet vs. dry) variations. Sampling locations were classified into sites of greater estuarine (EC) and marine (MC) contribution according to the coastal geomorphology. Samples were obtained by beach seining, and selected environmental variables including distance from estuarine mouths were recorded for each location. A total of 2134 fishes belonging to 21 families and 33 species were collected. The eight most abundant species were Mugil liza, Anchoa januaria, Polydactylus virginicus, Atherinella brasiliensis, Caranx latus, Trachinotus carolinus, Menticirrhus littoralis, and Trachinotus goodei. Species abundance varied significantly between sites and seasons, and taxonomic distinctness only between sites. Distance from estuaries, water salinity and temperature, and rainfall were the best predictors of the spatial and seasonal changes of fish assemblages in the surf-zone of tropical Atlantic dissipative sandy beaches. The occurrence of juveniles and recruits from most of the species recorded supports the nursery habitat hypothesis of shallow surf-zones.

The effect of habitat structure and the interactions between four juvenile fishes and zooplankton-prey in a tropical estuary

Estuaries provide a variety of habitat types for fishes, where abundant food resources and protection from predators have been identified as important drivers of the high abundance of species that use these areas as nursery grounds. However, scientific consensus regarding the role of some habitats as nurseries remains limited. Here, we analyzed the trophic ecology of four juvenile fish species (Atherinella brasiliensis, Anchoa hepsetus, Rhinosardinia bahiensis, and Diapterus rhombeus) that occupy three habitats in a tropical estuary (mangrove fringes, seagrass beds, and mudflats), using samples collected during rainy and dry seasons. The aim of the present study was to investigate whether variations in the diet composition of juvenile fishes were mediated by changes in zooplankton prey availability in these estuarine habitats during the seasonal cycle (rainy/dry). The fish and zooplankton prey were caught at the same time. The analysis suggested that changes in the abundance of zooplankton prey items in estuarine habitats and seasons may have significant effects on fish diet. However, complex habitat structure did not drive predator-prey relationships. Mudflats are the main foraging sites for juvenile fishes in this tropical estuary, while fringe mangrove showed a weak influence on the abundance and diet of juvenile filter-feeders (R. bahiensis and A. hepsetus). The juvenile fish species were dependent on multiple habitats, and no species used only one habitat type exclusively. Understanding the dynamics of prey resources in different estuarine habitats is critical for their conservation, especially in those habitats that are uncommonly considered, such as mudflats.

Brazilian silverside, Atherinella brasiliensis (Quoy & Gaimard,1825) embryos as a test-species for marine fish ecotoxicological tests.

The fish embryo test (FET) is an alternative to the classic freshwater toxicity test used to assess environmental hazards and risks to fish. This test has been standardized and adopted by the Organization for Economic and Cooperation and Development (OECD). As salinity may affect the substances’ toxicity, we describe the development of an alternative euryhaline test species for embryonic ecotoxicological tests: the Brazilian silverside Atherinella brasiliensis (Quoy & Gaimard, 1825). This species is broadly distributed along the coast of South America and is able to inhabit a broad range of environmental and saline conditions. Ours is the first study on the maintenance of a native South American species for natural reproduction and the generation of embryos for tests. The embryos used are transparent and possess fluorescent cells which have only been seen in a few species and which may be used as markers, making it an alternative assessment tool for the lethal and sublethal substances in marine and estuarine environments. We provide a detailed description and analysis of embryonic development under different salinities and temperatures. The embryos and larvae developed in similar ways at different salinities, however as temperatures increased, mortality also increased. We considered the effects of the reference toxicants Zn2+ and SDS using a protocol similar to the FET that was standardized for zebrafish. Brazilian silverside embryos are as sensitive as freshwater, or euryhaline fish, to the surfactant but are more resistant to metals prior to hatching. We were able to show the advantages of the Brazilian silverside as a model for a marine fish embryo test (FETm) with high levels of reproducibility and little contaminated waste.

Swimming behavior of newly hatched larvae of six decapod species (Crustacea: Decapoda)

Abstract Crustacean decapod larvae have developed several adaptations to maximize their survival, including swimming behavior. Swimming improves larvae dispersal and contributes to their response to environmental stresses, including variations in abiotic factors, presence of predators, and search for food. Data on larval behavior can also assist in studies on conservation and in species management in aquaculture. Unfortunately, swimming behavior remains unstudied in many species. The present work aims to analyze the swimming behavior in newly hatched larvae of six common decapod crustaceans in coastal Southeast Brazil (Macrobrachium acanthurus, Macrobrachium olfersii, Emerita brasiliensis, Ucides cordatus, Minuca rapax, and Callinectes danae). The analysis included tests with larval responses to four isolated stimuli: gravity (geotaxis), vertical salinity gradients, low-pressure zones, and presence of the planktivorous fish, Atherinella brasiliensis (only for C. danae and M. rapax). The first two and the last two stimuli were used as indicators of dispersal and defensive behaviors, respectively. All larvae preferred water depth with higher salinity levels. Additionally, negative geotaxis was observed in M. olfersii, M. acanthurus, U. cordatus, and C. danae, being stronger in the last. Both Macrobrachium larvae responded to low-pressure zones, promptly moving away. Callinectes danae and M. rapax larvae avoided contact with the predatory fish by creating avoidance zones around it, even in the absence of light. This is an active defensive behavior that has never been reported for the newly hatched larvae of these two species.

Shore-based competitive recreational fisheries in southern Bahia, Brazil: A baseline study

This study describes shore-based competitive fishing events in Ilhéus, southern Bahia (Brazil), including catch composition, and provides information on the profile of recreational fishers participating in these events. Information was collected in all events promoted by the Clube de Pesca de Ilhéus (CLUPESIL) in 2007-2008. A total of 26 competitive fishing events were organized during this period, with 47 species caught. The top species were: Cathorops spixii, Menticirrhus littoralis, Trachinotus goodei, Eucinostomus melanopterus, Polydactylus virginicus, Atherinella brasiliensis, and Eucinostomus argenteus. These seven species represented 87% of the total catch in number and 78% in weight. Menticirrhus littoralis and Polydactylus virginicus are species of commercial interest and their catch was dominated by juveniles. Local recreational fishers were predominately middle-aged men, who tended to use small hooks and mainly shrimp as bait. They were consumption-oriented, but also released small fishes. During competitions, fishers used even smaller hooks. Most of them perceived shrimp trawling as the main factor affecting recreational fisheries. The use of larger hooks and a minimum size of 20 cm are suggested to decrease the capture of juveniles, mainly those of commercial importance. This study sets a baseline from which new studies can be proposed to access the current status of local recreational fisheries.

Trade-offs between ontogenetic changes and food consumption in Brazilian silverside Atherinella brasiliensis from two tropical estuaries.

Salinity variation in estuarine environments influences the distribution of fish species as well as the availability of food resources to be used by them. This study examines the effect of the range of salinity on the trade-off between growth and feeding intensity of Atherinella brasiliensis from two tropical estuaries (positive and hypersaline). To investigate the effects of salinity, we hypothesized that hypersalinity negatively affects foraging intensity, consumption and prey selection by the Brazilian silverside, leading to differences in body condition. Sampling was carried out using the beach seine method in two areas of the estuaries (upper and lower zone) during rainy and dry periods. A total of 2549 stomachs (1124 for the positive estuary and 1425 for the hypersaline estuary) were examined, and the results indicated a dissimilarity of 92.7% of the diet between environments. In the positive estuary, there was more predation on Calanoida, Gastropoda, Hymenoptera, Ceratopogonidae larvae and Decapoda larvae, while Alga and plant-material characterized the diet in the hypersaline estuary. Significant correlations between the volume of food and salinity were observed in both estuaries. The vacuity index indicated that hypersaline environments presented higher contributions of semifull stomachs, indicating an intense consumption of algae. On the other hand,in the positive estuary, these values were less intense, but the stomachs were always with animal items. The variation found for both environments reinforces the effect of salinity on the physiological mechanism of the populations once the higher proportions of filled stomachs in the hypersaline environment indicate the need for constant and high ingestion of prey to guarantee the pronounced energy expenditure with osmoregulation.

Evaluation of the bioaccumulation kinetics of toxic metals in fish (A. brasiliensis) and its application on monitoring of coastal ecosystems

This study proposes a pro-active approach for evaluations of methylmercury (MeHg), total mercury (THg), arsenic (As), cadmium (Cd) and lead (Pb) in situ bioaccumulation in fish (Atherinella brasiliensis) muscles, using specimens from the external sector of Guanabara Bay as a study case. This approach included an hierarchical sequence: analysis of the pollutants concentrations and their comparison to safety criteria; correlations between specimens concentrations vs length (as a proxy of exposure time); projections of concentrations in key lengths (sexual maturation, asymptotic, length limits for fishing and median of fish population) through polynomial regressions, dose-response analysis (Probit), decreasing curves and incorporation rates (using only three length intervals). The incorporation rates were ascending for MeHg and THg (continued bioaccumulation) and descending for As, Pb and Cd (possible biological dilution). The projections were satisfactory, evidencing their use for an improvement on the risks monitoring of fishing and fish consumption by humans in coastal environments.

Gill parasites of fish and their relation to host and environmental factors in two estuaries in northeastern Brazil

Fish parasites can be good indicators of the quality of water bodies, and their presence or absence can be interpreted as a sign of habitat changes, helping us to diagnose environmental problems. This study was conducted in two estuaries located in the Paraiba state, northeastern Brazil: Mamanguape, an environmental protection area, and Paraiba do Norte, a river with riverside communities along its length. The objective of the study was to determine whether host and abiotic characteristics predict the richness of fish gill parasites and/or the abundance of the most abundant and prevalent parasite species, the copepod Acusicola brasiliensis, testing the species as a possible bioindicator. The fish host species were Anchoa januaria, Atherinella brasiliensis, Mugil curema, and Rhinosardinia bahiensis. Generalized linear models were constructed to test the influence of predictor variables on parasite richness and A. brasiliensis abundance. The predictor variables used in the models were the host relative condition factor (Kn), host length, collection season (rainy or dry), estuary, host species, total phosphorus, and chlorophyll a. Both parasite species richness and A. brasiliensis mean abundance showed a significant relation to water quality parameters, suggesting their possible use as environmental quality indicators.

STRUCTURE OF THE FISH ASSEMBLAGE AND FUNCTIONAL GUILDS IN THE ESTUARY OF MARACAÍPE, NORTHEAST COAST OF BRAZIL

The assemblage and functional structure of the fish fauna of the Maracaí­­pe River, municipality of Ipojuca - PE, was characterized by monthly beach trawls carried out from March of 2012 to February of 2013. A beach trawl net (picaré) was used at three different points of the estuary (EST 1, EST 2 and EST 3) during day and night trawls. The captured specimens were measured and weighed in the laboratory, identified and separated into use and trophic guilds using appropriate literature. Abiotic variables (temperature, salinity, dissolved oxygen, pH, turbidity and chlorophyll-a) were analyzed as for differences between day periods (night and day) and seasons (dry and rainy), and correlated to fish abundance. No difference was detected between day periods (p&gt;0.07 for all variables), but they differed between seasons for most variables (pâ"°¤0.02), and between sampling points only for dissolved oxygen (p=0.03). In one year of collection, 11,513 specimens were captured, belonging to 92 species, 38 families and 15 orders. Gerreidae, Atherinopsidae, Clupeidae, Gobiidae and Hemiramphidae were responsible for 82.9% of the total abundance. The estuary of the Maracaí­­pe River presents a rich ichthyofauna, but with the quantitative predominance of seven species (Atherinella brasiliensis, Eucinostomus argenteus, E. melanopterus, Ulaema lefroyi, Lile piquitinga, Ctenogobius boleosoma and Hyporhamphus unifasciatus). In the estuary, six species classified as vulnerable on the IUCN Endangered Species List were reported. The estuary presents a high diversity of species, most of them marine, carnivorous, and opportunistic, showing the high resilience of this environment. The predominance of juvenile fish underscores the importance of the Maracaí­­pe River estuary for the maintenance of population stocks of coastal species, demonstrating the urgent demand of management of this environment.

Intraspecific food resource partitioning in Brazilian silverside Atherinella brasiliensis (Atheriniformes: Atherinopsidae) in a tropical estuary, Brazil

ABSTRACT We investigated the intraspecific partitioning of food resources of the Brazilian silverside Atherinella brasiliensis in a tropical estuary. A total of 1,099 stomachs were analyzed, and the diet consisted mainly of Gastropoda, Ceratopogonidae larvae, Decapoda larvae, Calanoida, Cyclopoida, Hymenoptera and Brachyura. Ordination of the mean volumetric percentage contribution of preys indicated differences in the dietary compositions between sites and size classes. By SIMPER analysis, we detected high dissimilarity between size classes, suggesting ontogenetic niche shifts: the diet of the early juveniles was based in zooplankton, whereas adults consumed mainly benthic macroinvertebrates. These shifts were related to changes in feeding structures and foraging abilities that show a strong relationship with body size, and showed functional trade-offs in swimming capacity, and feeding strategies used to capture prey. Differences in the diet between size classes and habitat selection by Brazilian silverside are likely strategies to avoid intraspecific competition, clearly related to the abundance and accessibility of resources along the estuarine habitats.

Integrated assessment of sediment contaminant levels and biological responses in sentinel fish species Atherinella brasiliensis from a sub-tropical estuary in south Atlantic

This study combined data of the concentrations of metals, polycyclic aromatic hydrocarbons (PAHs) and pharmaceuticals and personal hygiene products (PPCPs) in the sediments and the biological responses of the Atherinella brasiliensis fish in two different sites and climate seasons in the Estuarine-Lagoon Complex of Iguape-Cananéia, Southeast Brazil. The presence of metals, PAHs, and PPCPs were observed in the sediments demonstrating the contamination throughout the system with contributions of sewage and residues disposal, oil and combustion of biomass and fossil fuels. Higher contaminations were identified in the point of greater human presence (C - Cananéia City), especially during the cold-dry season. The influence of anthropic activities and variations in the estuarine conditions, such as lower hydrodynamics during the lower rainfall period, were observed. In fish, spatial and seasonal changes in the parameters of oxidative stress and biotransformation, genotoxicity and histopathological alterations followed the same trend, with more pronounced responses in C in the cold-dry season. The biological responses of the fish revealed adverse effects in the local species population and indicated the presence of metals, PAHs and PPCPs as stressors. The multivariate analysis and the integrated biomarker response index (IBR) corroborated with these results, also indicating that site C had the worst environmental quality. The present study provides new information about the contamination of the sediments of Estuarine-Lagoon Complex of Iguape-Cananéia and the chronic exposure to contaminants in A. brasiliensis. Therefore, contributing to a better understanding of the local environmental quality with data that can support protective management of the area.

COMPARANDO O USO DA PICARÉ E TARRAFA NA CARACTERIZAÇÃO DA ESTRUTURA DA ICTIOFAUNA DO ENTREMARÉS DE UMA BAÍA SUBTROPICAL

Embora redes-de-arrasto-de-praia (picarés) e tarrafas sejam amplamente utilizadas para amostragem de peixes em habitats marginais costeiros, ainda não há uma comparação entre tais petrechos para a determinação da estrutura da ictiofauna de planí­­cies de maré durante a maré alta. Neste estudo, comparamos a efetividade de uma picaré de multifilamento com a efetividade de uma tarrafa de monofilamento para amostrar a estrutura da ictiofauna do entre-marés de uma baí­­a subtropical do Brasil. A picaré apresentou um melhor desempenho geral. Em comparação com a tarrafa, a picaré amostrou (I) densidade substancialmente maior da espécie localmente dominante, Atherinella brasiliensis; (II) uma média densidade relativamente maior para juvenis das demais espécies localmente conspí­­cuas, i.e., Mugil curema, Eucinostomus argenteus, Harengula clupeola e Oligoplites saurus (III); maiores valores da riqueza média e total; e (IV) melhor tanto a abundí­¢ncia de oní­­voros, quanto o número e a abundí­¢ncia de bentí­­voros. A tarrafa amostrou melhor os pequenos planctí­­voros, especialmente juvenis de Sardinella brasiliensis. Tais resultados poderão dar suporte a um futuro programa de monitoramento da ictiofauna local e enfatizam a grande importí­¢ncia da avaliação do desempenho de amostradores da ictiofauna antes de se iniciar quaisquer atividades de amostragem.

Diet and trophic organization of the fish assemblage from the Mamanguape River Estuary, Brazil

The present work aims to characterize a fish assemblage from a northeastern Brazilian estuary according to its diet and trophic organization along the estuarine-reef gradient. Sampling was performed at the Mamanguape Estuary, and fishes were collected using three types of nets at seventeen sites, grouped into four regions according to salinity range: reefs and the lower, middle, and upper estuary. The most abundant species were Atherinella brasiliensis , Mugil curema , and Sphoeroides testudineus . The highest species abundance and richness was observed for the lower estuary. Zooplankton was the most consumed category, recorded for fortytwo species. Among the guilds, piscivores were the most abundant, followed by crab eaters. Herbivores, mostly represented by Abudefduf saxatilis , had a higher abundance in reefs, being correlated according to ANOSIM analysis to this region, while piscivores and crab eaters showed a high contribution to inner regions of the Mamanguape Estuary.

Growth of the silverside Atherinella brasiliensis in a subtropical estuary with some insights concerning the weight-length relationship.

Specimens of Brazilian silverside (Atherinella brasiliensis, n=9672) with a length range of 1.5 to 14.2 cm were captured in the intertidal areas of the Estuarine Complex of Paranaguá, Brazil, between August 2010 and July 2011. The species' weight-length relationship was represented by the equation W=0.00533 L3.136 with a slightly positive allometry (b>3) and could be divided into two growth stanzas: W = W1 + W2; Stanza 1: W1= SW. (0.005239 L3.152); Stanza 2: W2= (1 - SW). (0.000699 L3.913); Switch-Function: SW = [1 + e1.204 (L - 11.66)]-1. The breakpoint between the first and second stanza (11.66 cm) matches published values for the estimated size at first maturity of adult females. Frequency distributions indicate that the species is present in the shallow areas of the Estuarine Complex of Paranaguá during all phases of its ontogenetic development, with the recruitment of juveniles taking place between October and November. Modal displacement was monitored throughout 12 months. The von Bertalanffy growth model and longevity was estimated as follow: asymptotic length (L∞) of 17.5 cm, growth coefficient (K) of 0.89 (year-1) and longevity (A95) of 3.33 years. We present some considerations with regard to the general methodology for adjusting weight-length relationships.

The rocky reef fishes of Vermelha Beach, a marine estuarine transitional zone at Guanabara Bay, Brazil

Rocky reefs are one of the most important biotopes in Guanabara Bay due to their broad distribution and high species diversity. This study aimed to describe the composition and structure of the fish assemblage associated with rocky reefs in Vermelha Beach (RJ/Brazil), an estuarine-marine transitional zone located at the entrance of Guanabara Bay. Fish were surveyed through underwater visual censuses, conducted by snorkeling divers along 10 m²-linear transects (n = 90). A total of 2.487 fishes were recorded belonging to 29 species in 18 families. Except for Atherinella brasiliensis, all other species are intimately associated with rocky reefs. The present work also stresses the importance of further studies to evaluate the role of periodic influences of estuarine and oceanic waters as structuring factors of the fish assemblages associated with rocky reefs at Vermelha Beach and similar ecosystems.

Opportunity and taxon pulse: the central influence of coastal geomorphology on genetic diversification and endemism of strict estuarine species

AbstractAimSea‐level changes and coastal geomorphology (extension of continental shelves) have affected the pattern of diversification of brackish/freshwater fish populations due to the confluence of basins/estuaries during low sea‐level periods (opportunity) and isolation during high sea‐level periods. It is hypothesized that populations from estuaries in extensive continental shelves, which have greater potential for confluence, should have more opportunities for gene exchange than those in narrow continental shelves. To test this, we assessed the distribution of the genetic diversity and the patterns of diversification of the estuarine silverside, Atherinella brasiliensis, from the Brazilian coast.LocationEight estuaries along the southern and north‐eastern portions of the Brazilian coast.Materials and methodsSequences of the mitochondrial control region (D‐loop) and the cytochrome B were used to assess the distribution of genetic diversity, and these mitochondrial fragments and two nuclear introns were used to assess the patterns of diversification of A. brasiliensis. The palaeochannels that were exposed along the Brazilian coast during the Last Glacial Maximum were reconstructed using bathymetry data and the GIS method.ResultsThe populations of A. brasiliensis from the estuaries of the north‐eastern Brazilian coast (narrower and shallower continental shelf) showed higher levels of genetic differentiation and larger (more haplotypes) endemic lineages than the populations in the southern coast (broader and deeper continental shelf). Furthermore, south coast lineages showed more evidence of genetic exchange among populations, which have resulted in a reticulated relationship between lineages and estuaries. The reconstruction of palaeochannels revealed more connections among southern than north‐eastern basins.Main conclusionsOur results support the hypothesis that continental shelf extension and sea‐level changes have influenced the diversification of A. brasiliensis. By extension, they also support the hypothesis of diversification by taxon pulse, which makes predictions based on the opportunities for expansion during periods of low sea level and the width of the continental shelf. We suggest this as a model for the genetic diversification and distribution of estuarine species along the Brazilian coast and other regions of the world.