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The functional diversity of phytoplankton communities was studied in two tropical estuaries subjected to anthropogenic pressure, despite one being environmentally protected. We applied functional diversity indices, analysed the dominant morphology traits and explored morphology-based functional groups. The less disturbed estuary showed slightly higher diversity and functional redundancy, during a wet season (on average 1.3 higher). Functional groups including nuisance species were more abundant in the heavily disturbed estuary. During a dry season, results for both systems were similar. Overall, abundance and functional diversity were higher in the upstream areas, associated with the river runoff containing freshwater species and essential nutrients for algae development. In both systems, diatoms were dominant (>75% of the community), however, the group included small and larger individuals, and freshwater to cosmopolitan species. This dominance and the change in traits were associated with sufficient nutrient supply, low light conditions, ressuspension and salinity changes, also associated with river runoff. Overall, the different functional diversity approaches enabled us to improve our understanding of the changes occurring in both systems.

Fatty acids are the main components of lipids and are necessary for the production and permeability of cell membranes, playing an essential role in the physiological responses of organisms. The biochemical composition of zooplankton might be used as bio-indicators of the trophic status of aquatic ecosystems. Aiming to fill the gap of knowledge in tropical estuaries, the main aim of this study was to test if the fatty acid profiles can reveal spatial and temporal shifts in the diet of copepods and therefore can be used as indicators of the trophic status of estuarine systems. We investigated the fatty acids composition of copepod species and their possible food sources along the salinity gradient of two tropical estuaries (Paraiba do Norte and Mamanguape estuaries, northeastern Brazil), during the rainy and dry seasons. We found clear seasonal differences regarding fatty acids composition and concentration in copepods, with maximal concentrations and diversity of total fatty acids during the rainy season. The copepods species were mainly carnivorous in the dry season and omnivorous in the rainy season and, in both estuaries, the diet of most copepods was dependent on food availability. The fatty acid profiles suggest that, in general, feeding patterns of zooplankton change spatially and temporally, reflecting the shifts in their food sources abundance (i.e., dominance among diatoms and flagellates, terrestrial detritus and small animals). We observed a residual proportion of terrestrial detritus and green algae in the diets and these items were only present in the dry season. Furthermore, the food sources in the Paraiba do Norte estuary, a system with high levels of anthropogenic disturbance, showed lower feeding quality, with lower essential fatty acids concentrations. Our study showed that fatty acid profiles can be used as ecological indicator to assess seasonal and spatial shifts in the trophic ecology of copepods in tropical estuaries and to distinguish systems with different levels of human impact in a fast and accurate way.

The aims of study were to 1) evaluate the productivity–diversity relationships (PDR) in reservoir phytoplankton communities in the semi-arid of northeastern Brazil on the local and regional scales; 2) determine the association between regional dissimilarity in species composition and regional mean productivity; 3) test the potential of productivity as well as physical and chemical factors of the water as descriptors of phytoplankton diversity using generalized linear models. Nutrient availability (total nitrogen and total phosphorus) and phytoplankton biomass were used as measures of productivity, whereas species richness as measure of diversity. Unimodal PDR was found when total phosphorus and biomass were considered as measure of productivity. Regional dissimilarity diminished with regional mean productivity. This finding may be attributed to the effect of eutrophication on diminishing the differences in the composition of species between compartments within each reservoir, leading to a loss of diversity in these ecosystems. Moreover, the analysis of the models demonstrated evidence that PDR may be influenced by environmental factors, such as electrical conductivity, total dissolved solids and pH in reservoirs located in semiarid regions of northeastern Brazil.

Macroinvertebrate communities have been widely used as a tool for assessing the environmental quality of freshwater ecosystems, whereas zooplankton communities have been to some extent neglected. However, the importance of using different indicators to achieve a more comprehensive framework of assessment regarding water quality has been recognized. This study compared estimates of species richness (number of species) and the Shannon–Wiener index for data on macroinvertebrate and zooplankton communities in tropical reservoirs and related them to their trophic state. The trop+hic classification was obtained by applying the Carlson index (1977) modified by Toledo et al. (1983), and the index of the Brazilian Society of the Environmental Technology Agency. The comparative response of the different indicators was analyzed using a series of bivariate correlations (Draftsman’s plot). The results illustrate that diversity measures, namely species richness, responded differently when related to the trophic classification of reservoirs, depending on the community considered. The species richness of zooplankton was positively related to hypereutrophic conditions, due to the higher number of rotifer species, including tolerant generalist species and at the same time, as a result of the exclusion of species from other groups, whereas for macroinvertebrates, species richness was negatively related to hypereutrophic conditions. Melanoides tuberculatus , which exhibits a high tolerance and competitive ability under such conditions, was the dominant species in macroinvertebrate communities, which excluded endemic species and reduced local richness and diversity. The same indicators applied to the zooplankton and macroinvertebrate communities might therefore provide contradictory responses regarding ecological quality assessment in tropical reservoirs, which suggest that zooplankton should be taken into account among the biological quality elements considered in the ecological quality assessment, management, and restoration of water bodies.