During low water levels, habitats in river-floodplain systems are isolated from each other and from the main river. Oppositely, floods tend to connect water bodies with distinct hydrological characteristics and, as a result, ecological processes and biological communities tend to be more similar among the distinct habitats that comprise a river-floodplain system. Based on a literature review and also using unpublished data obtained in tropical floodplains, the aim of this paper is to highlight the effects of floods as a process that reduce spatial variability. The usual negative relationship between the coefficient of variation of any ecological indicator (e.g., chlorophyll-a or total phosphorus) and water level is the main result demonstrating a reduction in spatial variability due to floods. Considering physical, chemical or biotic data gathered in distinct habitats within the floodplain, this pattern was found in temperate and tropical regions, subjected to distinct levels of anthropogenic impacts, and at different spatial extents. The main mechanism that accounts for this pattern may be stated as follow. During low water level, the biological communities of each habitat in the floodplain (e.g., lagoons, backwater, streams) follow distinct temporal trajectories due to the effects of local driving forces (e.g., an efficient predator trapped in a lagoon but not in another). Management plans and biodiversity conservation in river floodplain systems will benefit by considering the effects of flood homogenization and increased connectivity peculiar to these unique ecosystems.

1. Although 20% of Brazilian territory is covered by wetlands, wetland inventories are still incomplete. In 1993, Brazil signed the Ramsar Convention but a coherent national policy for the sustainable management and protection of wetlands has yet to be established. 2. Major gaps in the definition of a specific wetland policy are twofold: (1) the lack of standardized criteria by which wetlands are defined and delineated that reflects the specific ecological conditions of the country and (2) the lack of a national classification of wetlands that takes into account specific hydrological conditions and respective plant communities. 3. In recent years, efforts have been made at a regional level to improve public awareness of the ecology of Brazilian wetlands, their benefits to society, and the major threats endangering them. Studies have shown that wetlands play a crucial role in the regional hydrological cycle and provide multiple benefits for local populations. Furthermore, Brazilian wetlands contribute significantly to South American biodiversity. Therefore, wetland conservation and sustainable management should be given high legislative priority. 4. This article provides a synthesis of the current body of knowledge on the distribution, hydrology, and vegetation cover of Brazilian wetlands. Their definition, delineation, and classification at the national level are proposed in order to establish a scientific basis for discussions on a national wetland policy that mandates the sustainable management of Brazil’s extremely diverse and complex wetlands. This goal is particularly urgent in the face of the continuing and dramatic deterioration of wetlands resulting from large-scale agro-industrial expansion, and hydroelectric projects as well as the projected impact of global climate change on hydrological cycles

After much debate, there is an emerging consensus that the composition of many ecological communities is determined both by species traits, as proposed by niche theory, as well as by chance events. A critical question for ecology is, therefore, which attributes of species predict the dominance of deterministic or stochastic processes. We outline two hypotheses by which organism size could determine which processes structure ecological communities, and we test these hypotheses by comparing the community structure in bromeliad phytotelmata of three groups of organisms (bacteria, zooplankton, and macroinvertebrates) that encompass a 10 000-fold gradient in body size, but live in the same habitat. Bacteria had no habitat associations, as would be expected from trait-neutral stochastic processes, but still showed exclusion among species pairs, as would be expected from niche-based processes. Macroinvertebrates had strong habitat and species associations, indicating niche-based processes. Zooplankton, with body size between bacteria and macroinvertebrates, showed intermediate habitat associations. We concluded that a key niche process, habitat filtering, strengthened with organism size, possibly because larger organisms are both less plastic in their fundamental niches and more able to be selective in dispersal. These results suggest that the relative importance of deterministic and stochastic processes may be predictable from organism size.

Neotropical coastal lagoons (NCL) are human-dominated ecosystems. Their distribution along densely populated coastal areas of developing countries makes these systems among the most threatened in the world. Here, we summarize some aspects of the causes and consequences of NCL biodiversity, their functioning, their importance to the surrounding populations, their fragility, and their responses to local and global anthropogenic impacts and the challenges that Neotropical countries face in conserving these systems. Although still scarce and geographically concentrated, a growing body of studies has shown that NCLs are physiographically diversified systems, which harbor a considerable and particular proportion of the Neotropical inland aquatic biodiversity. Despite the fact that coastal lagoons are ecotones that are intricately connected to surrounding environments, they develop mechanisms for structural and functional regulation, which confer to these systems higher productivity and carrying capacities than surrounding ecosystems. Such traits attract residential developments and subsidize local traditional populations with important economic and aesthetic ecosystem revenues such as fisheries and scenic beauty. However, the disorganized human occupation around NCLs are causing profound impacts such as eutrophication, salinization, exotic species introduction, as well as other effects, which are ultimately imposing major habitat degradations and biodiversity extirpations in NCLs. We argue that interdisciplinary conservation strategies, which integrate scientific expertise, government officials, private companies and the general public, are the most likely to overcome the geographic and economic obstacles to NCL conservation.Keywords: coastal ecosystems, ecosystem management, shallow lakes, human impacts, tropical limnology.Lagoas costeiras neotropicais: Uma apreciação sobre sua biodiversidade, funcionamento, principais ameaças e estratégias de conservação ResumoAs lagoas costeiras neotropicais (LCN) estão inseridas em um ambiente antropogênico. Sua localização em regiões costeiras densamente povoadas de países em desenvolvimento coloca estes ecossistemas entre os mais impactados do mundo. Neste trabalho, resumimos vários aspectos relacionados às causas e conseqüências da sua biodiversidade, seu funcionamento e os bens proporcionados à população do seu entorno. Sua fragilidade e as respostas a impactos humanos locais e globais, assim como os desafios para a sua conservação por países neotropicais, também são abordados. Apesar de escassos e geograficamente concentrados, um número crescente de estudos tem mostrado que as LCN são sistemas fisiograficamente diversificados, abrigando uma proporção considerável da biodiversidade dos ambientes aquáticos continentais neotropicais. Apesar de as lagoas costeiras representarem ecótonos bastante conectados ao ambiente adjacente, elas desenvolveram mecanismos próprios de regulação funcional e estrutural, conferindo uma maior produtividade e capacidade de suporte em relação...

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Dissolved organic carbon (DOC) photochemical reactions establish important links between DOC and planktonic bacteria. We hypothesize that seasonal changes in DOC quality, related to the flood pulse, drive the effects of light-DOC interactions on uptake by planktonic bacteria uptake in clear-water Amazonian ecosystems. Water samples from two ecosystems (one lake and one stream) were incubated in sunlight during different hydrological periods and were then exposed to bacterial degradation. Photochemical and bacterial degradation were driven by seasonal DOC inputs. Bacterial mineralization was the main degradation pathway of autochthonous DOC in the lake, while allochthonous DOC was more available for photochemical oxidation. We suggest that sunlight enhances the bacterial uptake of refractory DOC but does not alter uptake of labile forms. We also observed a positive relationship between sunlight and bacterial degradation of DOC, instead of competition. We conclude that photochemical reactions and bacteria complementarily degrade the different sources of DOC during the flood pulse in Amazonian clear-water aquatic ecosystems.

Temporal coherence (i.e., the degree of synchronicity of a given variable among ecological units within a predefined space) has been shown for several limnological features among temperate lakes, allowing predictions about the structure and function of ecosystems. However, there is little evidence of temporal coherence among tropical aquatic systems, where the climatic variability among seasons is less pronounced. Here, we used data from long-term monitoring of physical, chemical and biological variables to test the degree of temporal coherence among 18 tropical coastal lagoons. The water temperature and chlorophyll-a concentration had the highest and lowest temporal coherence among the lagoons, respectively, whereas the salinity and water colour had intermediate temporal coherence. The regional climactic factors were the main factors responsible for the coherence patterns in the water temperature and water colour, whereas the landscape position and morphometric characteristics explained much of the variation of the salinity and water colour among the lagoons. These results indicate that both local (lagoon morphometry) and regional (precipitation, air temperature) factors regulate the physical and chemical conditions of coastal lagoons by adjusting the terrestrial and marine subsidies at a landscape-scale. On the other hand, the chlorophyll-a concentration appears to be primarily regulated by specific local conditions resulting in a weak temporal coherence among the ecosystems. We concluded that temporal coherence in tropical ecosystems is possible, at least for some environmental features, and should be evaluated for other tropical ecosystems. Our results also reinforce that aquatic ecosystems should be studied more broadly to accomplish a full understanding of their structure and function.Keywords: synchrony, temporal coherence, local factors, regional factors, shallow lakes, coastal lagoons. Coerência temporal entre lagoas costeiras tropicais: uma busca por padrões e mecanismos ResumoA coerência temporal (i.e., o nível de sincronismo de uma dada variável ecológica entre unidades ecológicas) tem sido demonstrada para uma vasta gama de variáveis limnológicas em lagos de clima temperado, permitindo que predições sobre a estrutura e o funcionamento destes ecossistemas sejam realizadas. Entretanto, há pouca evidência da coerência temporal de variáveis limnológicas entre ecossistemas aquáticos tropicais, onde a variação climática é menos pronunciada entre as estações do ano. Neste estudo, utilizamos dados de longa duração do monitoramento de variáveis físicas, químicas e biológicas para testar a ocorrência de coerência temporal entre 18 lagoas costeiras tropicais. A temperatura da água e a concentração de clorofila-a apresentaram, respectivamente, a maior e a menor coerência temporal entre as lagoas, enquanto que a salinidade e a coloração da água apresentaram padrões intermediários. Fatores climáticos regionais foram os principais fatores responsáveis pelos padrões de coerência da temperatura e coloração d...

The indicator properties of zooplankton assemblages in a coastal lagoon were evaluated, by means of canonical correspondence analysis, along environmental gradients of trophic state and marine influence caused by anthropogenic impact. Changes in zooplankton species composition were significant indicators of environmental heterogeneity patterns. Species diversity was insensitive to eutrophication but decreased with increasing marine influence. The rotifer species Brachionus plicatilis and Synchaeta bicornis as well as cirriped nauplii were good indicators of mesohaline conditions. The rotifer species Asplanchna brightwelli, Brachionus angularis, Brachionus falcatus, Filinia terminalis, and Polyarthra remata were good indicators of eutrophic conditions. The other species investigated were good indicators of oligohaline and mesotrophic conditions. The rotifer genus Brachionus proved to be a better indicator organism for these environmental gradients than the entire zooplankton assemblage. Hence, this taxon can be considered a target taxon for more intensive monitoring and conservation planning. The method used here to assess the indicator properties of species assemblages and to select target taxa can be widely applied in any aquatic ecosystems to any group of organisms, spatial and temporal scales, and environmental gradients.