Fabio Cop Ferreira

This study characterized the composition and structure of fish assemblages in headwater streams of the Guariúma River sub-basin, within Serra do Mar State Park. Ten 100-m reaches were sampled in the Lambari, Guariúma, and Serraria streams using electrofishing. A total of 1,887 individuals and 19 species were recorded. Abundance ranged from 60 to 412 individuals per reach, and species richness from 5 to 15. Shannon diversity ranged from 1.08 to 2.32, and Pielou evenness from 0.49 to 0.86. The results reveal variation in assemblage structure among reaches and differences in patterns of abundance, richness, diversity, and evenness of the ichthyofauna.

Food webs depict the tangled web of trophic interactions associated with the functioning of an ecosystem. Understanding the mechanisms providing stability to these food webs is therefore vital for conservation efforts and the management of natural systems. Here, we first characterised a tropical stream meta‐food web and five individual food webs using a Bayesian Hierarchical approach unifying three sources of information (gut content analysis, literature compilation and stable isotope data). With data on population‐level biomass and individually measured body mass, we applied a bioenergetic model and assessed food web stability using a Lotka–Volterra system of equations. We then assessed the resilience of the system to individual species extinctions using simulations and investigated the network patterns associated with systems with higher stability. The model resulted in a stable meta‐food web with 307 links among the 61 components. At the regional scale, 70% of the total energy flow occurred through a set of 10 taxa with large variation in body masses. The remaining 30% of total energy flow relied on 48 different taxa, supporting a significant dependency on a diverse community. The meta‐food web was stable against individual species extinctions, with a higher resilience in food webs harbouring omnivorous fish species able to connect multiple food web compartments via weak, non‐specialised interactions. Moreover, these fish species contributed largely to the spatial variation among individual food webs, suggesting that these species could operate as mobile predators connecting different streams and stabilising variability at the regional scale. Our results outline two key mechanisms of food web stability operating in tropical streams: (i) the diversity of species and body masses buffering against random and size‐dependent disturbances and (ii) high regional diversity and weak omnivorous interactions of predators buffering against local stochastic variation in species composition. These mechanisms rely on high local and regional biodiversity in tropical streams, which is known to be strongly affected by human impacts. Therefore, an urgent challenge is to understand how the ongoing systematic loss of diversity jeopardises the stability of stream food webs in human‐impacted landscapes.

The organization of fish communities into habitat use groups facilitates a replicable understanding of species distribution due to the distinctive characteristics and ecological roles of these groups. Partitioning beta diversity and assessing both species contribution to beta diversity (SCBD) and local contribution to beta diversity (LCBD) can evaluate the ecological importance of each group and measure the uniqueness of each site. This study aimed to comprehend how different habitat groups within the marine fish assemblage in the Ubatumirim Bay contribute to beta diversity and to correlate the uniqueness of each sampling site to their attributes to better understand the importance of habitat use groups and the community composition variation in the bay. We sampled ichthyofauna at six locations within the bay, employing a shrimp trawl net at varying depths. We categorized the 95 identified species into five distinct habitat groups: reef-associated, pelagic-neritic, demersal, benthopelagic, and pelagic-oceanic, each with different ecological characteristics and preferences. However, no significant differences were detected in SCBD among these groups. An increase in LCBD values was observed with the decrease in mean sediment diameter, indicating a higher environmental complexity, possibly acting as an environmental filter. One of the sampled sites, Couves Island, stood out with a significantly higher LCBD value, which underscores the importance of such diverse environments in maintaining regional biodiversity. These findings can serve as a valuable baseline reference in conservation planning and management, particularly in assessing the effectiveness of the recently established Marine Environment Protection Area. For instance, comparing the current observations with future surveys could quantify the impact of this protection initiative, thus providing evidence of management efficacy and showing the potential effects of impacts (such as predatory tourism) in the Ubatumirim Bay area.

We aimed to study hematological responses of Oreochromis niloticus experimentally exposed to the contaminated water of the Santos-São Vicente Estuary, testing hypotheses that exposure time to estuarine water promotes deleterious effects on hematological parameters and evaluating the use of erythrocytes and leukocytes alterations as environmental biomarkers. Estuarine water was collected from Largo da Pompeba. For the biological assay, 28 juveniles of O. niloticus (red strain) of both genders were randomly selected from commercial pisciculture. For the biological assay, 28 juveniles of O. niloticus of both sexes were randomly selected from commercial fish farms. The juveniles were kept in estuarine water for 72 and 120 hours and, after exposure, blood was collected by puncture of the caudal vein to determine total erythrocytes, hemoglobin concentration, hematocrit, hematimetric indices and total leukocytes, as lymphocyte, neutrophils, monocytes, eosinophils, and basophils were quantified by blood extensions. To test exposure overtime on hematological variables, we performed a two-factor Multivariate Analysis of Variance. Exposure for 72 hours resulted in immunosuppression as seen by the reduced counts of neutrophils, monocytes, and lymphocytes in the bloodstream, whereas after 120 hours the immune system was stimulated with the increase of all leukocyte cell types. Exposure to estuarine water resulted in marked changes in the leukocyte count of O. niloticus, demonstrating that alterations in white blood cells might be more sensitive biomarkers than red blood parameters.

This study provides for the first time information about the reproductive biology of Mimagoniates lateralis, an endangered species of inseminating Neotropical tetra that occurs in blackwater streams of southeastern Brazil. We analyzed 404 individuals, of which 214 were females, 117 were males, and 73 were immature juveniles. The sex ratio was 1.83 females/males. Males were larger than females. The estimated size at first maturation for females was 22.2 mm SL, and for males 23.4 mm SL. We also analyzed 94 ovaries from mature females, and the estimated absolute fecundity was 116.37 ± 26.68 oocytes, the oocyte diameter varying from 0.1 to 1.0 mm. The spawning type was classified as multiple, with two modal values corresponding to different oocyte lots. These data contribute to substantiate future assessments of the conservation status of M. lateralis, as well as future attempts to guarantee the preservation of this species and its natural habitat.

Redundancy analysis is widely used to correlate species matrix against environmental descriptors. This analysis assumes that the response variables have the same continuous linear trend over the whole gradient, which is often not the case. To overcome this issue, we propose the piecewise redundancy analysis (pwRDA). The pwRDA allows the relationship between the response and explanatory variables to break into pieces. The breakpoint between communities is assessed by the split‐moving‐window (SMW) approach. Both analyses are within segRDA package for the R environment. We illustrate the use of segRDA using simulated and empirical examples with a varying degree of discontinuity among communities. SMW results provide consistent estimates for both, number and location of community breakpoints along the gradient. In communities with a sharp transition, the pwRDA models were significantly more informative than the traditional RDA model. For smooth transitions between communities, the pwRDA did not differ from the traditional RDA. The combined use of SMW and pwRDA allows one to identify breakpoints and transition zones among ecological communities along environmental gradients. This approach is particularly relevant when species–habitat associations may differ among communities.

Recent metacommunity ecology research has demonstrated that local communities can be divided into different guilds. We hypothesised that wadeable streams are occupied by fishes that follow distinct metacommunity processes. The mainstem is a river corridor for the potamonic fish guild (PFG) but represents a nonhabitat matrix for the rhithronic fish guild (RFG). Accordingly, the PFG should be filtered out from the headwaters by dispersal limitations or environmental filtering along the longitudinal gradient, and the guild should have a nested pattern of beta diversity. The RFG should be structured by the local species sorting, and the species turnover component should prevail. We sampled fishes in 42 streams distributed in four subbasins that were separated by at least one mainstem channel. We modelled the influences of spatial and environmental predictors using a partial redundancy analysis and variance partitioning and by quantifying the components of beta diversity that were associated with species turnover and nestedness. Both environment and space affected the structure of the RFG, owing to the influence of substrate type, riparian cover and presence of downstream barriers. The PFG was structured by only the influence of downstream barriers. Species turnover predominated within the RFG, and species nestedness dominated within the PFG. Our results support the hypothesis that potamonic and rhithronic guilds coexist in wadeable streams and follow distinct metacommunity assembly mechanisms. Potamonic guilds are structured by regional dispersal from the mainstem channels, whereas rhithronic guilds are sorted by local filtering along the longitudinal gradient in a spatially structured environment.

Considering the need for the Brazilian government to develop tools for environmental monitoring for biodiversity conservancy purposes in the national protected areas system, this paper focuses on determining reference site metrics (or baselines) for adapting the Index of Biotic Integrity (IBI) based on the fish assemblages in the Pantanal National Park (PNP). The habitats in the PNP were grouped into four categories: main rivers, corixos (channels connecting the floodplain), permanent bays, and temporary bays. Fish samplings were performed at 12 points during the dry season (Oct-Nov 2010 and 2011). 146 fish species were identified from the total 18,954 individuals collected with standardized fishing gear. There was no association between the structure of the fish assemblage and categories, suggesting a theory on homogeneity of habitats. The final IBI_PNP consists of nine metrics, most of them were framed in excellent class, some in fair, and none in poor. There was no significant difference in IBI_PNP scores between the two sampled years. This approach provides a direct application for wetland management purposes.