Joan Lluís Pretus

Budgets of organic and inorganic carbon in a Mediterranean coastal lagoon dominated by submerged vegetation

In this article, we studied the fluxes of organic and inorganic (DIC) carbon in a coastal lagoon dominated by highly productive macrophyte meadows (Albufera des Grau, Balearic Islands). Seasonal and annual carbon budgets were performed from estimates of whole-system fluxes, and the fate of organic matter production was evaluated through a stable isotope exploration of the food web. The results showed an extremely intense cycling of DIC, with a turnover between 65 and 13 times faster than water turnover. The metabolic fluxes were the main contributors to the seasonal and annual DIC budgets, which were secondarily affected by calcite precipitation, atmospheric exchange and hydrological fluxes. The inorganic carbon dynamics was strongly determined by the seasonal cycle of the meadows. Accordingly the air–water CO2 flux shifted seasonally, and the lagoon was a sink of atmospheric CO2 during the vegetated period and a source during the period without macrophytes. The high macrophytic production played a minor role in the lagoon food web, which apparently relied on phytoplanktonic or allochthonous organic matter. A fast decomposition of macrophytic biomass appeared to be the main destiny of the annual macrophytic production, which was only secondarily buried in the sediments.

Recent benthic foraminiferal assemblages and their relationship to environmental variables on the shoreface and inner shelf off Valencia (western Mediterranean).

The environmental variables that determine the distributions of benthic foraminiferal assemblages on the shoreface and inner shelf of the north of Valencia province (Western Mediterranean) are identified. The possible influence of variables such as water depth, distance from shore, hydrodynamics, substrate type, carbonate content, organic matter content and human activity is evaluated. Multivariate cluster-Q-type analysis and redundancy analysis (RDA) are used to identify the environmental variables that have the greatest influence on the assemblage distribution. The spatial distribution of the assemblages is closely associated with water depth and substrate. The diversity and abundance of foraminifera shells increase with depth and their conservation improves. The most common species in the study area are Ammonia beccarii, Rosalina globularis, Buccella granulata, Planorbulina mediterranensis, and Lobatula lobatula. The presence of wastewater in the study area has not polluted the foraminiferal assemblages (absence of anomalous shells). The direction of the discharge plume is a potential source of nutrients for deep water.

Ecosystem processes drive dissolved organic matter quality in a highly dynamic water body

The complexity and variability of processes determining dissolved organic matter (DOM) quality is likely to increase in highly dynamic systems such as Mediterranean water bodies. We studied the dynamics of DOM in a Mediterranean lagoon dominated by seasonal submerged vegetation and receiving torrential freshwater inputs. In order to trace changes in DOM quality throughout the year in relation with potential DOM sources, we used spectroscopic techniques including UV–visible absorbance and fluorescence excitation–emission matrices. The quality of the lagoon DOM fluctuates on a seasonal basis between the characteristics of torrential inputs and macrophytes. Humification and aromaticity of DOM increased markedly after the torrential inputs of materials derived from terrestrial vegetation and soils in the catchment. The macrophytes in the lagoon contributed with less humified materials and protein-like compounds. Other minor processes such as seawater entrances, photodegradation or temporary bottom hypoxia translated into sporadic DOM quality changes. These results highlight the need of a whole ecosystem approach to understand changes in DOM quality due to ecosystem processes that might otherwise be exclusively attributed to DOM reactivity.

Convergence of gut microbiotas in the adaptive radiations of African cichlid fishes

Ecoevolutionary dynamics of the gut microbiota at the macroscale level, that is, in across-species comparisons, are largely driven by ecological variables and host genotype. The repeated explosive radiations of African cichlid fishes in distinct lakes, following a dietary diversification in a context of reduced genetic diversity, provide a natural setup to explore convergence, divergence and repeatability in patterns of microbiota dynamics as a function of the host diet, phylogeny and environment. Here we characterized by 16S rRNA amplicon sequencing the gut microbiota of 29 cichlid species from two distinct lakes/radiations (Tanganyika and Barombi Mbo) and across a broad dietary and phylogenetic range. Within each lake, a significant deviation between a carnivorous and herbivorous lifestyle was found. Herbivore species were characterized by an increased bacterial taxonomic and functional diversity and converged in key compositional and functional community aspects. Despite a significant lake effect on the microbiota structure, this process has occurred with remarkable parallels in the two lakes. A metabolic signature most likely explains this trend, as indicated by a significant enrichment in herbivores/omnivores of bacterial taxa and functions associated with fiber degradation and detoxification of plant chemical compounds. Overall, compositional and functional aspects of the gut microbiota individually and altogether validate and predict main cichlid dietary habits, suggesting a fundamental role of gut bacteria in cichlid niche expansion and adaptation.