Fish assemblages along a morphodynamic continuum on three tropical beaches

Plastic pollution on beaches in an Antillean manatee conservation area, Brazil

The presence of plastic debris along shorelines is a widespread problem, and plastic debris can interact directly with marine wildlife. In northeast Brazil, the Antillean manatees are the most common marine mammals and use estuarine waters mainly as their home range. We aimed to investigate the characteristics of plastic debris on the estuarine-oceanic continuum and the accumulation density of plastic on beaches. The density of plastic debris on beaches located in transitional areas was 7-10-fold greater than that on beaches in estuarine and oceanic areas. Fragments were considered the most abundant form of plastic debris on all the beaches. Our findings could lead to improved pollution management in this marine protected area, principally due to the risks of remobilizing small plastic particles through tides and wind effects that scatter them in resting and feeding manatees areas.

Multiple habitats drive the functional diversity of fish assemblages in a tropical estuary

Understanding estuarine diversity patterns is crucial to highlight the ecological value of coastal ecosystems for fish assemblages. To increase our knowledge, we investigated the functional diversity of fish assemblages in five estuarine habitats (sandy beaches, mudflats, seagrass meadows, mangrove fringes, and estuarine riparian vegetation) in a tropical estuary of Brazil. Functional diversity metrics were assessed considering seven fish functional traits and calculated using functional indices, PCoA (functional spaces), and community-weighted mean (CWM). Then, a unified RLQ and fourth-corner analysis were used to evaluate environment-trait relationships. A total of 27,036 individuals of 119 species were recorded in all habitats. Functional diversity showed similar trends to estuarine habitats, which were more driven by the spatial configuration rather than by their structure, emphasizing the importance of environmental heterogeneity. There was a greater occupation of functional space to habitats located in the lower estuary compared to the upper estuary. Furthermore, body shapes and trophic guilds were the most common traits related to changes in functional diversity between habitats. The RLQ analysis revealed differences in trait composition between habitats influenced by salinity and transparency, although the fourth corner method did not show a significant relationship between fish functional traits and environmental variables. Our results suggest that the mosaic of habitats support the high functional diversity of fishes in tropical estuaries.

Analysis of a hypersaline drought-prone estuary reveals low density and diversity of fish eggs and larvae

We analyzed fish eggs and larvae in an estuary under severe drought conditions. We detected an inverse salinity gradient, with values increasing from the mouth to the upper estuary. Egg densities decreased from the estuarine mouth to the upstream areas following the salinity increase for all three mesh net sizes. This pattern was also found for the density of larvae, which decreased in estuarine regions with hypersalinity (38 to 62). The low diversity constituted only nine fish species, which were classified as anadromous (Anchoa hepsetus), estuarine and marine (Bathygobius soporator, Hippocampus reidi, Eucinostomus sp., and Diapterus auratus), marine estuarine-opportunist (Caranx latus and Bardiella rochus), and marine stragglers (Echeneis naucrates and Haemulon sp.). In addition, we observed an oversimplification of the assemblage to include stress-tolerant estuarine and marine species. Our baseline results suggest that this hypersaline estuarine ecosystem has lower densities and diversity than a healthy mangrove system.

Locally developed models improve the accuracy of remotely assessed metrics as a rapid tool to classify sandy beach morphodynamics

Classification of beaches into morphodynamic states is a common approach in sandy beach studies, due to the influence of natural variables in ecological patterns and processes. The use of remote sensing for identifying beach type and monitoring changes has been commonly applied through multiple methods, which often involve expensive equipment and software processing of images. A previous study on the South African Coast developed a method to classify beaches using conditional tree inferences, based on beach morphological features estimated from public available satellite images, without the need for remote sensing processing, which allowed for a large-scale characterization. However, since the validation of this method has not been tested in other regions, its potential uses as a trans-scalar tool or dependence from local calibrations has not been evaluated. Here, we tested the validity of this method using a 200-km stretch of the Brazilian coast, encompassing a wide gradient of morphodynamic conditions. We also compared this locally derived model with the results that would be generated using the cut-off values established in the previous study. To this end, 87 beach sites were remotely assessed using an accessible software (i.e., Google Earth) and sampled for an in-situ environmental characterization and beach type classification. These sites were used to derive the predictive model of beach morphodynamics from the remotely assessed metrics, using conditional inference trees. An additional 77 beach sites, with a previously known morphodynamic type, were also remotely evaluated to test the model accuracy. Intertidal width and exposure degree were the only variables selected in the model to classify beach type, with an accuracy higher than 90% through different metrics of model validation. The only limitation was the inability in separating beach types in the reflective end of the morphodynamic continuum. Our results corroborated the usefulness of this method, highlighting the importance of a locally developed model, which substantially increased the accuracy. Although the use of more sophisticated remote sensing approaches should be preferred to assess coastal dynamics or detailed morphodynamic features (e.g., nearshore bars), the method used here provides an accessible and accurate approach to classify beach into major states at large spatial scales. As beach type can be used as a surrogate for biodiversity, environmental sensitivity and touristic preferences, the method may aid management in the identification of priority areas for conservation.

Environmental influences on the ichthyoplankton in hypersaline estuaries located in a Semiarid Northeastern Brazilian coast

ABSTRACT Hypersaline estuaries are commonly found in the Semiarid Northeast Brazilian coast. However, the utilization of these estuaries by early life stages of fishes is less well documented. This study aimed to evaluate the effects of environmental factors on the ichthyoplankton, and to describe their spatial and temporal variation in two estuaries (Tubarão and Casqueira). The sampling were diurnally in four excursions carried out during two dry-season months (November and December 2017) and two rainy-season months (May and July 2018). A total of 423 larvae representing 30 species (14 families) and 2,762 eggs (five families) were collected. Although the community structures were similar in both estuaries, there was strong seasonal variation, with higher abundances observed during the dry season. Low rainfall was the primary environmental driver affecting ichthyoplankton in both estuaries. Other environmental factors, such as depth, water temperature, and channel width, were also predictor variables for the distribution of eggs and larvae. The ichthyoplankton was dominated by marine estuarine-dependent species in both estuaries, accounting for 76% of individuals. The presence of the early life stages of typically marine species suggests that hypersaline environments provide important nursery areas and play an essential role for some coastal fish species.

Morphology and molecular evidence support the validity of Pogonias courbina (Lacepède, 1803) (Teleostei: Sciaenidae), with a redescription and neotype designation

The family Sciaenidae comprises about 300 species. The black drum Pogonias cromis was the only valid species of the genus. Herein, Pogonias courbina Lacepède 1803 is redescribed based on morphological and molecular evidence and a neotype is designated. Pogonias courbina is distinguished by the following characters: the occurrence of characteristic thickening of the dorsal spines VII to XI in all specimens larger than 250 mm SL; all pterygiophores in the dorsal-fin laminar, thin; anal-fin pterygiophores slender excluded those of spines; lateral projections of gas bladder with few finger-like projections; genetic distance between both species 1%; exclusive occurrence of characters in six informative sites of COI (58 G; 214 G; 328 A; 331 A; 553C; 580 G). The method Automatic Barcode gap Discovery detected gaps in nucleotid distance congruent with the NJ, MP, and ML tree analysis. Also, advertisement calls are three times shorter in duration in P. courbina than in P. cromis. In addition, two monophyletic groups for P. cromis and P. courbina appear in trees obtained with different methodologies, emphasizing the absence of shared haplotypes. A gap of about 8000 km occurs in the distribution of both species along coastal areas of the Atlantic Ocean.

Composition, density and biomass of fish community from the surf zone as a function of the lunar cycle at Miramar Beach in Cabedelo, Paraíba

ABSTRACT The influence of the moon cycles on the ichthyofauna has been little studied in the surf zone. In this study, the number of species, density and biomass were evaluated as a function of the moon. A total of 49 species distributed in 24 families were captured in two areas of Miramar beach. The mean density was significant high in the weaning and low in the new moon, while density and biomass together showed differences for areas. The most abundant species were Anchoa tricolor and Trachinotus falcatus (new moon), and Anchovia clupeoides showed significant differences in the waning moon. The RDA indicates that turbidity influenced significantly the presence of two species group. The group I were represented by Stellifer brasiliensis, Trachinotus goodei, A. clupeoides, Chilomycterus spinosus and Conodon nobilis that occurred on the waning and new phases in both areas, while the group II were represented by Polydactylus virginicus and Haemulopsis corvinaeformis in the full moon. The surf zones may also be strongly governed by the lunar phases. Therefore, the results found in this study, showed that the biological interactions between the species with turbidity and moon might explain the density and biomass variations for some species in the surf zone.

Feeding ecology of three juvenile mojarras (Gerreidae) in a tropical estuary of northeastern Brazil

ABSTRACT Distributions and feeding ecology of mojarra species from shallow water of a tropical estuary in Northeastern Brazil were observed aiming to investigate differences in distribution and resource partitioning among juveniles of three species of mojarras. Fishes were collected with a beach seine across four sites along a salinity gradient from January to December of 2011. Highest abundances were recorded during the rainy season in the upper and middle estuary. Microcrustaceans, mainly copepods, were the preferential prey items of all mojarras, irrespective of size or hydrological season, suggesting these areas may be important nursery habitats. Juveniles of mojarra used two important mechanisms for exploitation of resources: (1) spatial segregation along the salinity and temperature gradient, such as abundance of Eucinostomus melanopterus increased from downstream to upstream estuary, while Eugerres brasilianus displayed an opposite pattern; (2) differences related to the volumetric proportion of the main prey items, with indications that E. melanopterus and Diapterus rhombeus fed predominantly on Calanoida and Cyclopoida, while the diet of E. brasilianus was dominated by items of infauna. Such strategies were important for resource partitioning, favouring the coexistence of these three species in the estuary.

Temporal patterns in the intertidal faunal community at the mouth of a tropical estuary

The use of intertidal sandy beaches by fish and macrocrustaceans was studied at different temporal scales at the mouth of a tropical estuary. Samples were taken along the lunar and diel cycles in the late dry and rainy seasons. Fish assemblage (number of species, density and biomass), crustaceans and wrack biomass, showed significant interactions among all studied factors, and the combination of moon phase and diel cycle, resulting in different patterns of environmental variables (depth, water temperature and dissolved oxygen), affected habitat use by the different species. Variances in faunal community were detected between seasons, stimulated by salinity fluctuations from freshwater input during the rainy season. These differences suggest an important cycling of habitats and an increase in connectivity between adjacent habitats (estuary and coastal waters). Moreover, the results showed that this intertidal sandy beach also provides an alternative nursery and protected shallow-water area for the initial development phase of many marine and estuarine species. In addition, this intertidal habitat plays an important role in the maintenance of the ecological functioning of the estuarine-coastal ecosystem continuum.