João José Fonseca Leal

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.

Life cycle and production of Campsurus notatus (Ephemeroptera, Polymitarcyidae) in an Amazonian lake impacted by bauxite tailings (Pará, Brazil).

Between 1979 and 1989, Lake Batata was subjected to ±50 000 m3 d−1 of bauxite tailings effluent, which impacted about 30% of the lakes area. The present research had as its main goal to study the life cycle and secondary production of Campsurus notatus on the tailings-impacted region of Lake Batata. Campsurus notatus is the species most adapted to the conditions imposed by the bauxite tailings. A central site in the impacted region of Lake Batata was established and sampled at fortnightly intervals between July 1996 and June 1997. The nymphs of C. notatus in the impacted region had a 105-day lifespan, with individuals between 2 and 17 mm in length. Estimated secondary production for C. notatus was 2.5 g DW m−2 yr−1in the impacted region. This was high compared to production rates estimated for other species of ephemeropterans, indicating the degree of successful adaptation of C. notatus to the conditions imposed by the bauxite tailings.Between 1979 and 1989, Lake Batata was subjected to ±50 000 m3 d−1 of bauxite tailings effluent, which impacted about 30% of the lakes area. The present research had as its main goal to study the life cycle and secondary production of Campsurus notatus on the tailings-impacted region of Lake Batata. Campsurus notatus is the species most adapted to the conditions imposed by the bauxite tailings. A central site in the impacted region of Lake Batata was established and sampled at fortnightly intervals between July 1996 and June 1997. The nymphs of C. notatus in the impacted region had a 105-day lifespan, with individuals between 2 and 17 mm in length. Estimated secondary production for C. notatus was 2.5 g DW m−2 yr−1in the impacted region. This was high compared to production rates estimated for other species of ephemeropterans, indicating the degree of successful adaptation of C. notatus to the conditions imposed by the bauxite tailings.

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.

The role of Campsurus notatus (Ephemeroptera: Polymitarcytidae) bioturbation and sediment quality on potential gas fluxes in a tropical lake

About 30% of the total area of Lake Batata (Amazon) was impacted by the disposal of bauxite tailings originated from the process of washing bauxite. This effluent, composed by fine particles of clay and water, settled on top of the natural sediment, originating a new substratum with a different physical and chemical composition. This phenomenon created a new distinct habitat (impacted sediment) influencing the benthic community. The aim of this study was to evaluate the impact of bioturbation by Campsurus notatus (Ephemeroptera: Polymitarcytidae) on potential gas fluxes in the sediment of natural and impacted areas of the lake. The natural sediment had a significantly higher methane concentration when compared to the impacted one. In incubated sediment cores, the presence of C. notatus nymphs resulted in a significant increase in oxygen consumption and methane and carbon dioxide release to the water column. The effect of the presence of nymphs on methane was ambiguous. The C. notatus nymphs strongly decreased methane concentration in natural sediment samples, probably because of the enhancement of the oxic sediment area. However, this effect was not observed in impacted samples. Finally, the new substratum of Lake Batata decreased methane concentration in sediment and water column. C. notatus nymphs demonstrated to have a significant role on gas flux (methane and CO2) from sediment to water column as well as on oxygen consumption in Lake Batata, consequently influencing the carbon cycle in this lake.

Community structure of resting egg banks and concordance patterns between dormant and active zooplankters in tropical lakes

Little effort has been devoted to characterizing the resting egg banks in tropical lakes. In this study, we evaluated the structure of egg banks across 26 Brazilian lakes located in four geographical regions. We also evaluated cross-taxon concordance in species richness and community similarity between dormant rotifers and dormant cladocerans, and searched for concordant patterns between dormant and active communities. We observed 88 taxa among all the hatchlings that belonged mainly to rotifers and cladocerans. Lakes located in the same geographical region displayed more similar dormant communities. Overall, no concordance was observed between dormant rotifers and dormant cladocerans. Concordance in community similarity was observed between dormant and active organisms but only for rotifers and the entire zooplankton community. Resting egg banks were not associated to a set of environmental variables. Our results demonstrate the occurrence of resting egg banks in several tropical lakes. Due to the weak concordant patterns, rotifers or cladocerans found in egg banks should be used cautiously as a surrogate of the other group in zooplankton surveys. Finally, the lack of strong concordance between the active and dormant stages of cladocerans suggests that some species may not receive appropriate cues to induce diapause.

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.

Influence of Campsurus notatus bioturbation on oxygen profile and uptake in sediments of an Amazonian lake impacted by bauxite tailings

Oxygen uptake rates and vertical profiles were determined in sediment taken from natural areas and areas impacted by bauxite tailings in Lake Batata, and in the U-shaped burrows constructed by the nymphs of the benthic ephemeropteran Campsurus notatus, under laboratory conditions. Sediment from impacted and natural areas containing different densities of nymphs of C. notatus (0 to 1,200 ind. m -2 ) were incubated in acrylic cores. In sediment from the natural area, O 2 was present only in the upper 3.5 mm. In the impacted area, the aerobic layer was deeper, with O 2 detected down to 6.5 mm depth. O 2 uptake was twice as high in sediment from the natural area (1.11 mmol O 2 m -2 h -1 ) as from the impacted area (0.61 mmol O 2 m -2 h -1 ). In cores containing nymphs of C. notatus, O 2 uptake was significantly higher than in sediments without C. notatus. The increase in the rates of O 2 uptake was positively correlated with the biomass of the nymphs (g DW m -2 ). The presence of C. notatus resulted in alteration of the O 2 profiles in the sediment of both areas, indicating the importance of these larvae in structuring O 2 profiles in the sediments of Lake Batata.

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.

Biodiversity effects of benthic ecosystem engineers on the spatial patterns of sediment CH4 concentration in an urban Neotropical coastal lagoon

AIM: Biodiversity of sediment bioturbators has been shown to be important for to the magnitude and stability of benthic-pelagic processes. However, no study to date has evaluated the importance of the biodiversity of benthic invertebrate bioturbators to the spatial patterns of sediment CH4 concentration ([CH4]). Here we conducted a laboratorial experiment to test the following predictions: (1) Bioturbator species richness will reduce the sediment [CH4]; (2) individual bioturbator species (i.e. species composition) will have different effects on sediment [CH4]; (3) and both the effects of bioturbator species richness and composition on sediment [CH4] will be dependent on sediment depth. METHODS: We manipulated the number and composition of three functional divergent benthic invertebrate bioturbators species that are widespread in South Atlantic coastal lagoons, in laboratorial sediment chambers containing the sediment and water of an urban impacted coastal lagoon RESULTS: Bioturbator species richness had no overall significant effect on sediment [CH4] when comparisons of sediment [CH4] were made among species richness levels. However, bioturbator species richness significantly reduced sediment [CH4] when species richness levels were compared to the control (defaunated treatments), but this effect was significant only at the deepest sediment layer. Furthermore, bioturbator species composition had significant, but distinct effects on the patterns of reduction in sediment [CH4], depending on the sediment depth and the bioturbator species. CONCLUSIONS: We conclude that both the number and composition of bioturbator species are important to determine the effects of benthic bioturbators on spatial patterns of sediment [CH4], but the strength of these effects depend on species traits that determine interspecific interactions strength across the sediment vertical niche space.