Adriano Caliman

Neotropical coastal lagoons: an appraisal of their biodiversity, functioning, threats and conservation management

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.

The prominence of and biases in biodiversity and ecosystem functioning research

The sub-discipline of biodiversity and ecosystem functioning (BEF) has emerged as a central topic in contemporary ecological research. However, to date no study has evaluated the prominence and publication biases in BEF research. Herein we report the results of a careful quantitative assessment of BEF research published in five core general ecology journals from 1990 to 2007 to determine the position of BEF research within ecology, identify patterns of research effort within BEF research, and discuss their probable proximal and historical causes. The relative importance of BEF publications increased exponentially during the period analyzed and was significantly greater than the average growth of ecological literature, affirming the prominence of BEF as a current paradigm in ecology. However, BEF research exhibited a strong bias toward experimental studies on terrestrial plant communities, with significantly lower effort devoted to the functional aspects of biodiversity in aquatic systems, multiple trophic level systems, and animal or microbial communities. Such trends may be explained by a combination of methodological adequacy and historic epistemological differences in ecological thinking. We suggest that BEF researchers should direct more effort toward the study of aquatic systems and animal communities, emphasize long-term and trophically complex experiments, such as those with multi-trophic microbial communities, employ larger-scale field observational studies and increase the use of integrative and theoretical studies. Many technical and analytical methodologies that are already employed in ecological research, such as stable isotopes, paleobiology, remote sensing, and model selection criteria, can facilitate these aims. Overcoming the above-mentioned shortcomings of current BEF research will greatly improve our ability to predict how biodiversity loss will affect ecosystem processes and services in natural ecosystems.

Temporal coherence among tropical coastal lagoons: a search for patterns and mechanisms.

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.

Functional bioturbator diversity enhances benthic–pelagic processes and properties in experimental microcosms

Abstract Widespread declines in biodiversity at both global and local scales have motivated considerable research directed toward understanding how changes in biological diversity may affect the stability and function of the ecosystems on which we rely. However, the research effort devoted to addressing this question in benthic systems has been minimal. In laboratory microcosms, we manipulated the number and composition of 3 functionally distinct benthic invertebrate freshwater species that are bioturbators of sediment over 3 biomass levels. Our objective was to test the effects of bioturbator diversity on rates and reliability of total dissolved P (TDP) flux between benthic and pelagic habitats. Both composition and species richness affected TDP flux. TDP flux was highest in the most species-rich community because of functional complementarity rather than selection effects. Furthermore, species richness enhanced TDP flux reliability by increasing the predictability of the biomass–TDP flux relationship by 30%, on average, for each species added. We attributed these nonadditive effects of invertebrate diversity to a combination of functionally mediated biogeochemical interactions and density-mediated interaction strength. Thus, our results suggest that bioturbator diversity can be important to nutrient cycling in aquatic ecosystems by strengthening benthic–pelagic coupling.

Stoichiometry of benthic invertebrate nutrient recycling: interspecific variation and the role of body mass

Ecological stoichiometry (ES) and allometry offer frameworks for predicting how nutrient recycling varies within and among animal species. Despite the importance of benthic-derived nutrients in most aquatic systems, predictions based on ES and allometry have been poorly tested among benthic invertebrate consumers. Here, we show that the rates and ratios at which three freshwater benthic invertebrate species (a crustacean, an insect, and a polychaeta) recycled nitrogen (N) and phosphorus (P) can be partially predicted by ES and allometry depending on whether data are analyzed intra- or interspecifically. Mass-specific N and P excretion rates were negatively correlated with invertebrate body size both among and within taxa, supporting allometric predictions. However, mass-specific N and P excretion rates were positively and negatively correlated to invertebrate body N and P, respectively, but only when data were analyzed intraspecifically. As a corollary, the mass-specific N:P excretion ratio was positively related to body N:P ratio. Such a contrasting pattern on excretion-mediated N and P recycling suggests that stoichiometric constraints regarding consumer-resource imbalances for the three species utilized in this study may be stronger for P than for N. Our results indicate that the variation in nutrient recycling, which is mediated by taxonomic constraints on stoichiometry and allometry, may substantially help us to understand the importance of benthic detritivorous species to the functioning of aquatic ecosystems.

Biodiversity effects of ecosystem engineers are stronger on more complex ecosystem processes

The relative importance of species richness and identity for the diversity-function relationship remains controversial. We mechanistically explored the potential contribution of ecosystem processes complexity (EPC; i.e., the number of pathways and mechanisms through which an ecosystem process can be directly and/or indirectly affected by species and/or their interactions) to the resolution of this controversy. We hypothesized that the complementarity effects of biodiversity will be stronger and that the diversity-function relationship will be more dependent on species richness as the EPC increases. Using a benthic bioturbator community as a model system we tested these predictions across ecosystem processes that could be ordered according to their complexity (suspended material flux < PO4-P flux < NH4-N flux < bacterioplankton production). Consistent with our predictions, species richness explained an increasing proportion of data variation as EPC increased, whereas the contrary was observed for species composition. Nontransgressive overyielding was not affected by EPC, but the magnitude of transgressive overyielding increased significantly with EPC, indicating that complementarity may be stronger as EPC increases. Our results highlight the importance of considering the interactive role of the characteristics of ecosystem processes in our theoretical understanding of the diversity-function relationship and its underlying mechanisms.

Benthic bioturbator enhances CH4 fluxes among aquatic compartments and atmosphere in experimental microcosms

We utilized laboratory microcosms to evaluate the effects of a benthic sediment bioturbator (Heteromastus similis; Polychaeta; conveyor-belt deposit feeder) on vertical distributions of CH4 in sediment and net CH4 fluxes across sediment-water-air interfaces. The effect of H. similis on sediment CH4 concentration ((CH4)) varied depending on sediment depth and was strongest at higher animal densities. In comparison with defaunated controls, microcosms with the highest density of H. similis exhibited an increase in (CH4) of 3.7-fold, on average, at the sediment surface (0- 2 cm), but these concentrations decreased by ~2-fold in deeper sediment layers (2-8 cm). However, irrespective of sediment depth, the density of H. similis resulted in an overall nonlinear reduction of bulk sediment (CH4). Most of the observed CH4 losses from the sediment were due to CH4 oxidation, but the bioturbatory activities of H. similis also promoted significant increases in (CH4) in both the water column and the microcosm headspace. These results suggest that benthic invertebrates can mediate CH4 turnover between compartments in aquatic ecosystems, with further consequences for the coupling between benthic-pelagic food chains via the methanotrophic-mediated microbial loop, as well as increase CH4 emissions to the atmosphere.

Community biomass and bottom up multivariate nutrient complementarity mediate the effects of bioturbator diversity on pelagic production.

Tests of the biodiversity and ecosystem functioning (BEF) relationship have focused little attention on the importance of interactions between species diversity and other attributes of ecological communities such as community biomass. Moreover, BEF research has been mainly derived from studies measuring a single ecosystem process that often represents resource consumption within a given habitat. Focus on single processes has prevented us from exploring the characteristics of ecosystem processes that can be critical in helping us to identify how novel pathways throughout BEF mechanisms may operate. Here, we investigated whether and how the effects of biodiversity mediated by non-trophic interactions among benthic bioturbator species vary according to community biomass and ecosystem processes. We hypothesized that (1) bioturbator biomass and species richness interact to affect the rates of benthic nutrient regeneration [dissolved inorganic nitrogen (DIN) and total dissolved phosphorus (TDP)] and consequently bacterioplankton production (BP) and that (2) the complementarity effects of diversity will be stronger on BP than on nutrient regeneration because the former represents a more integrative process that can be mediated by multivariate nutrient complementarity. We show that the effects of bioturbator diversity on nutrient regeneration increased BP via multivariate nutrient complementarity. Consistent with our prediction, the complementarity effects were significantly stronger on BP than on DIN and TDP. The effects of the biomass-species richness interaction on complementarity varied among the individual processes, but the aggregated measures of complementarity over all ecosystem processes were significantly higher at the highest community biomass level. Our results suggest that the complementarity effects of biodiversity can be stronger on more integrative ecosystem processes, which integrate subsidiary “simpler” processes, via multivariate complementarity. In addition, reductions in community biomass may decrease the strength of interspecific interactions so that the enhanced effects of biodiversity on ecosystem processes can disappear well before species become extinct.

A global database of nitrogen and phosphorus excretion rates of aquatic animals

Animals can be important in modulating ecosystem-level nutrient cycling, although their importance varies greatly among species and ecosystems. Nutrient cycling rates of individual animals represent valuable data for testing the predictions of important frameworks such as the Metabolic Theory of Ecology (MTE) and ecological stoichiometry (ES). They also represent an important set of functional traits that may reflect both environmental and phylogenetic influences. Over the past two decades, studies of animal-mediated nutrient cycling have increased dramatically, especially in aquatic ecosystems. Here we present a global compilation of aquatic animal nutrient excretion rates. The dataset includes 10,534 observations from freshwater and marine animals of N and/or P excretion rates. These observations represent 491 species, including most aquatic phyla. Coverage varies greatly among phyla and other taxonomic levels. The dataset includes information on animal body size, ambient temperature, taxonomic affiliations, and animal body N:P. This data set was used to test predictions of MTE and ES, as described in Vanni and McIntyre (2016; Ecology DOI: 10.1002/ecy.1582).

Effects of food web structure and resource subsidies on the patterns and mechanisms of temporal coherence in a tropical coastal lagoon: an experimental mesocosm approach

OBJETIVOS: Estudos sobre os padroes e mecanismos de coerencia temporal de variaveis ecologicas entre lagos tem se tornado um tema importante na limnologia. Ate o momento, nenhum estudo testou se e como a oferta de recursos e a configuracao da teia trofica afetam os padroes e mecanismos da coerencia temporal de variaveis limnologicas. Nos conduzimos um experimento de mesocosmos em campo durante 11 semanas para testar as seguintes hipoteses: (i) a adicao de nutrientes reduz a coerencia temporal de variaveis ecossistemicas; (ii) a predacao por peixes potencializa a coerencia temporal de variaveis ecossistemicas e (iii) a coerencia temporal e mais forte para variaveis fisicas (transparencia da agua), intermediaria para variaveis quimicas (concentracao de oxigenio dissolvido [OD]) e fraca para variaveis biologicas (biomassa zooplanctonica total). METODOS: Nos manipulamos a presenca de peixe e a adicao de nutrientes inorgânicos (N e P) em um desenho fatorial 2 × 2 em dezesseis mesocosmos instalados em uma lagoa costeira tropical. A coerencia foi estimada por correlacoes de Pearson par-a-par das trajetorias temporais de cada variavel resposta entre os mesocosmos de um mesmo tratamento. RESULTADOS: A presenca de peixes aumentou significativamente apenas a coerencia temporal da biomassa zooplanctonica, e, contrario as nossas expectativas, a adicao de nutrientes aumentou a coerencia temporal da [OD]. A intensidade dos efeitos da presenca de peixe e da adicao de nutrientes sobre a coerencia temporal foi afetada pela identidade da variavel monitorada, mas nao em um padrao consistente. No entanto, a interacao da presenca de peixe e adicao de nutrientes nao afetaram a coerencia temporal de nenhuma variavel monitorada. CONCLUSOES: Nossos resultados indicam que a predacao de peixes e a disponibilidade de recursos podem afetar significativamente padroes de coerencia temporal, mas tais efeitos dependerao mais de efeitos diretos do fator local sobre a variavel do que da identidade da propria variavel. Concluimos que a eutrofizacao e a sobrepesca podem interferir no acoplamento da dinâmica espaco-temporal de algumas variaveis limnologicas.