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Functional characteristics of species are of great importance for understanding their roles in ecosystems and can be used to detect long‐term chances in the environment. We evaluated temporal changes (1983–1985 and 2017–2019) in taxonomic and functional indices of the fish fauna in shallow areas of a tropical bay heavily impacted by anthropogenic activities in recent decades. The hypothesis that functional indices change over time as a result of environmental degradation was tested. Our results showed a significant decrease in species richness and abundance over time, and in functional richness, while others functional diversity indices (divergency, evenness, and originality) remained stable. Thirteen functional groups were detected, some of which contained only one species, raising concerns about the loss of ecosystem functions due to ongoing changes. We also observed an increase in beta diversity over time, which may be the result of a decrease in local richness without leading to regional extinctions. Turnover was the most important process in structuring the fish fauna at the evaluated time scale. The relative stability of the functional structure and the higher levels of turnover seem to be related to the dominance of functional groups, within which species replace each other according to their responses to environmental filters that select for specific functional traits. Incorporating functional diversity indices and beta diversity variations in the fish community helped to enhance the existing information about this coastal system by offering improved estimates of biological diversity through diverse approaches. The predominance of turnover identified in the preset study suggests a dynamic and fluctuating species composition within the habitat. In this sense, habitat preservation should prioritize the protection of diverse habitats to accommodate a broad spectrum of species. [ABSTRACT FROM AUTHOR]

As human-induced environmental changes reduce niche opportunities from global to local scales, permanent shifts in species traits alter ecosystem processes. Disentangling multiscale mechanisms driving temporal changes in coastal fish biodiversity is thus critical to conservation aims. From seasonal to multiyear periods, we investigated how local environmental variation and landscape features shape temporal beta diversity (abundance-based and trait-based dissimilarities, and their components of replacement and nestedness) per zones in bays and coastal lagoons, Southeastern Brazil. At larger temporal dimensions, unaccounted processes in individual systems influenced primarily taxonomic dissimilarity, whereas functional responses to variation in marine influence varied between types of system and zones. From 2 years to seasons, taxonomic and functional dissimilarities decreased with abundance-based species replacement, and both trait-based components, respectively. Replacement processes were primarily related to marine influence (transparency, salinity, pH, and tidal phase) at larger temporal dimensions, and habitat availability (mangroves and nearby estuaries) and complexity (forest cover and landscape urbanization) in seasons. Seasonal variations in tidal phase (lower) and pH (higher), respectively, promoted taxonomic (abundance gradients) and functional (fish trait loss) nestedness under shorter environmental gradients. Spatial and temporal balances between marine influence, habitat quality, and seascape connectivity drive temporal dissimilarities in coastal fish assemblages. [ABSTRACT FROM AUTHOR]

Shallow coastal habitats are ruled by fluctuating environmental conditions, which lead to shifts in fish communities. Functional groups of habitat use and trophic strategy were used to address the responses of fish composition and diversity, since comparisons of rich tropical systems are often complex through species-based approaches. We hypothesized that fish groups will have specific affinities in response to the prevailing environmental conditions, especially those reflecting the prevalence of oceanic or estuarine conditions, where guilds of habitat use would perform better as indicators. Despite the importance of other environmental factors (i.e. temperature and transparency), salinity was the key structuring factor irrespective of the coastal lagoon. Although harbouring the greatest biomass of piscivores, the harsh environmental conditions at Araruama lagoon were related to low diversity. A great number of indicator species, typically of marine affinity, was found at the Saquarema lagoon, probably due to the continuous and broad connection to the sea leading to the predominance of euhaline conditions. Despite the presence of non-native species (i.e. Oreochromis niloticus), the Maricá lagoon function as an important refuge for freshwater groups. Our results stressed the key role played by coastal lagoons of varied water conditions in supporting fish diversity at regional levels. [ABSTRACT FROM AUTHOR]

Increases in temperatures over the last century, more intensively after the eighties, were recorded in several databases for the south‐eastern Brazil. These increases are likely to change fish communities in aquatic systems by decreasing abundances, biomass and sizes of some species more sensitive to climate change. Reservoirs may be particularly susceptible to the effects of climate change, as they isolate previously connected areas limiting fish dispersal and migration, as well as increasing water temperature and thermal stratification. We assessed temporal changes in the abundance and biomass of the ichthyofauna in an isolate reservoir (inflowing waters from small tributaries in a highland region) aiming to associate changes with climate effects over three decades (1990, 2000, 2010). Two abundant native species, a loricariid Loricariichthys castaneus (Castelnau, 1855) and a cichlid Geophagus brasiliensis (Quoy & Gaimard, 1824), were selected to assess eventual response to climate changes in their geographical distribution in the Southeast Atlantic Hydrographic Region, considering different carbon emission scenarios using ecological niche models. A decrease in the densities and biomass of the ichthyofauna and of the two selected species were observed in both summer and winter over the three decades, coinciding with increases in temperatures. These decreases were correlated with increases in positive anomalies of temperature, which may be an indicator of climatic changes, although with low explanation of the data variation. The mean size of L. castaneus decreased between the nineties and 2010, whereas no significant trend was found for the size of G. brasiliensis. Our predictions of new area for future adequacy indicated a loss in the distribution area for both species (mainly for G. brasiliensis), considering the most pessimistic scenario for 2050 and 2070, possibly due to climatic changes. Both hydroelectric dams and global warming pose threats to freshwater fish diversity, and both will interact. Changes observed in the fish assemblage over the last decades were essential for an assessment of the consequences of global warming in this type of reservoir combining larger scale studies with future projections. [ABSTRACT FROM AUTHOR]

Estuarine shallow waters have many habitats favouring the colonization and establishment of different fish species. Our study investigated the variability in the composition of these communities by examining beta diversity and evaluated the relationship between fish beta diversity and environmental heterogeneity, which can be dependent on the level of human alteration to which an ecosystem is exposed. Our goal is to provide insights not only on the biodiversity, but also to help develop effective conservation measures. We sampled fish and environmental variables (physicochemical water variables and sediment nutrients and granulometry) in three zones (inner, middle and outer) of Sepetiba Bay, in Southeastern Brazil. The aims of our study were to compare fish communities in the different zones by using beta diversity and to investigate the relationship between environmental heterogeneity and beta diversity. Habitat conditions varied considerably among the zones. Relationships between species and environmental conditions were species-specific, and a weak positive correlation between environmental heterogeneity and beta diversity was found. The highest beta diversity was detected in the inner bay zone, suggesting that relatively more urbanized areas had greater environmental heterogeneity and, thus, higher beta diversity. Our results serve as a 'caution' to reduce the urbanization effects on these environments that sometimes can increase habitat heterogeneity and species richness. The 'weak' relationship suggest that the ecosystems may have been in the 'early stages' of human influences and managers should take into account that anthropogenic impacts would reduce beta diversity because continued degradation would lead to natural habitat reduction. [ABSTRACT FROM AUTHOR]

Multiscale processes through dynamic boundaries drive the local contributions (LCBD; uniqueness in species composition and abundance) and species contributions (SCBD; individual species abundance variation) to fish beta diversity in coastal seascapes. We partitioned LCBD into LCBDRepl (replacement) and LCBDAbDiff (abundance difference), and used model-based approaches to investigate whether seascape size influences environmental and spatial drivers of LCBD, and effects of species (distribution, prevalence, and coastal dependence) on SCBD. Three large bays (bay level) and three zones per bay (zone level), southeastern Brazil, were seascape models during 1 year. At the bay level, more locations had higher LCBD, related to species composition, lower water transparency, and much less to flood/high tides and higher number of estuaries. LCBDRepl was also prevalent and stronger positive effects of transparency and mangrove cover reinforced the importance of environmental filtering and alternative habitats driving local contributions to replacement processes in larger seascapes. Species richness influenced positively LCBD primarily at the zone level, and negative effects of vegetal cover and primarily human settlements suggested species loss under lower heterogeneity. Also, more similar LCBDRepl and LCBDAbDiff evidenced the increasing local contributions to abundance differences in smaller species pools. At both levels, larger- and finer-scale spatial effects evidenced possible influences of dispersal and biotic interactions, respectively, on LCBDRepl and LCBDAbDiff. SCBD was positively related to species prevalence at locations and distribution at both levels. Therefore, multiscale mechanisms dependent and irrespective of seascape size support the critical importance of habitat availability, complexity, and variety to beta diversity of coastal fishes. [ABSTRACT FROM AUTHOR]

Fish and benthic invertebrates are important groups that inhabit shallow coastal areas. Many studies use these two groups separately to answer questions related to environmental relationships, but few assess the correlation between these two groups. This study aimed to assess correlation between richness and composition of fish and benthic invertebrate assemblages and to evaluate their responses to environmental variables in sandy beaches in a tropical coastal area in south-eastern Brazil. We tested for a correlation between fish and benthic invertebrates and evaluated which environmental variables influenced each group. Fish and invertebrate taxonomic richness were not correlated across sites. In addition, the two groups were not significantly correlated, even after controlling the effects of the environmental variables. The taxonomic richness of the two groups were influenced by different set of environmental drivers: fish were influenced mainly by the physicochemical variables, being positively correlated with salinity and dissolved oxygen, and negatively with temperature, whereas invertebrates richness were related mainly to granulometric variables, decreasing in fine and very fine sediment. Fish and invertebrate showed similar patterns with more influence of environmental variables than biotic variables that had comparatively more effects on the invertebrate than on the fish assemblage. Spatial segregation in species distribution along the beaches were found with the Gerreid fish predominating in semi-exposed beaches whereas the sparid Diplodus argenteus, the haemulid Orthopristis ruber and the clupeids Harengula clupeola and Sardinella brasiliensis predominated in the exposed beaches. The Polychaetae families Syllidae and Dorvilleidae, and isopod of the family Cirolanidae predominated in semi-protect beaches, whereas polychaetas of the families Glyceridae and Saccocirridae predominated in the exposed beaches. In this study, we showed that fish and benthic invertebrates are influenced by different environmental variables in tropical sandy beaches and no significant correlation was found between these two taxonomic groups. Our findings are a step to a better understanding of the fish-benthic invertebrate relationship and a contribution to management policies aiming the conservation of tropical coastal areas. [ABSTRACT FROM AUTHOR]

Fragmentation and interconnection of water bodies cause severe changes in the natural flow regime of continental water systems. However, assessments of these impacts on the freshwater fish distribution are still scarce. We investigated whether an artificial flow regime generated by discharges from an aqueduct would promote a longitudinal environmental gradient in an off-river reservoir. We tested the hypothesis that the incoming water from aqueduct discharges promotes environmental gradient between lotic and lentic conditions. We expect that environmental changes and the artificial flow regime promote the structuring of fish assemblage and that the lotic-lentic transition areas present the highest fish species richness. A longitudinal gradient in environmental characteristics with differing fish assemblage structure was found. Temporal changes in the fish assemblages occurred only in areas near the discharge of the aqueduct. The highest fish richness and diversity were recorded in the transition zone during the wet season, associated with the greater environmental heterogeneity of this ecotone, whereas the lowest was found in the lotic zone, probably associated with the altered flow regime. The greatest abundance was recorded in the upper lentic zone in the wet season, whereas the lowest was found in the lower lentic zone in both seasons. Our results corroborate the hypothesis that the artificial flow regime, modulated by the seasonality of discharges and the influence of environmental variables, promotes longitudinal gradients in reservoirs when rivers are not present. The findings are relevant in a scenario where ever more interconnections of aquatic bodies have been diffused around the world. [ABSTRACT FROM AUTHOR]

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The spatial structure of the fish diversity and site-scale and landscape-scale environmental effects were investigated across hierarchical levels in tropical coastal ecosystems. Total diversity (γ) was hierarchically partitioned into α and β components using both the additive and multiplicative methods. A model selection based on the AICc was applied to generalized linear mixed models relating diversity measures to environmental variables and including random effects for hierarchical levels and season. Short-term seasonal effects were negligible. Spatial effects were more relevant at the site level and negligible at the subregion level, due to the high spatial heterogeneity and the natural pooling of ecosystems, respectively. Site-scale environmental effects were more relevant at the subregion level, with eutrophic conditions (continental influence) favoring the species richness (α and γ) and higher absence of species (βA) in oligotrophic conditions (marine influence). At the system level, the positive effect of the distance from the ocean on γ and higher βA in oligotrophic conditions reinforced the positive continental influence on fish diversity. Environmental homogenization processes were most likely associated with the negative effect of the pasture cover on α at the system level, and γ and βA at the site level. The negative effect of the forest cover on the later diversity measure evidenced its relevance to maintain richer but more similar assemblages, whereas the positive continental influence was most likely due to the loss of stenohaline marine species. This study evidenced that disentangling spatial, land use, and marine vs. continental effects on diversity components is critical to understand the primary determinants of the fish diversity in tropical coastal ecosystems. • Spatial and environmental effects were critical for coastal fish diversity. • At the site level, diversity was primarily associated with land use effects. • Multi-scale continental influences affected positively fish diversity within systems. • Diversity was primarily driven by site-scale environmental effects within sub-regions. • The α and additive β components were the major determinants of changes on γ diversity. [ABSTRACT FROM AUTHOR]

Several species of marine fish use different coastal systems especially during their early development. However, these habitats are jeopardized by anthropogenic influences threatening the success of fish populations, and urgent measures are needed to priorize areas to protect their sustainability. We applied taxonomic (Δ+) and functional (X+) distinctiveness indices that represent taxonomic composition and functional roles to assess biodiversity of three different costal systems: bays, coastal lagoons and oceanic beaches. We hypothesized that difference in habitat characteristics, especially in the more dynamism and habitat homogeneity of oceanic beaches compared with more habitat diversity and sheltered conditions of bays and coastal lagoons results in differences in fish richness and taxonomic and functional diversity. The main premise is that communities phylogenetically and functionally more distinct have more interest in conservation policies. Significant differences (P < 0.004) were found in the species richness, Δ+ and X+ among the three systems according to PERMANOVA. Fish richness was higher in bays compared with the coastal lagoons and oceanic beaches. Higher Δ+ was found for the coastal lagoons compared with the bays and oceanic beaches, with the bays having some values below the confidence limit. Similar patterns were found for X+, although all values were within the confidence limits for the bays, suggesting that the absence of some taxa does not interfere in functional diversity. The hypothesis that taxonomic and functional structure of fish assemblages differ among the three systems was accepted and we suggest that coastal lagoons should be priorized in conservation programs because they support more taxonomic and functional distinctiveness. [ABSTRACT FROM AUTHOR]