Drivers of benthic metacommunity structure along tropical estuaries

How tolerances, competition and dispersal shape benthic invertebrate colonisation in restored urban streams

Biotic communities often respond poorly to river restoration activities and the drivers of community recovery after restoration are not fully understood. According to the Asymmetric Response Concept (ARC), dispersal capacity, species tolerances to stressors, and biotic interactions are three key drivers influencing community recovery of restored streams. However, the ARC remains to be tested. Here we used a dataset on benthic invertebrate communities of eleven restored stream sections in a former open sewer system that were sampled yearly over a period of eleven years. We applied four indices that reflect tolerance against chloride and organic pollution, the community's dispersal capacity and strength of competition to the benthic invertebrate taxa lists of each year and site. Subsequently, we used generalised linear mixed models to analyse the change of these indices over time since restoration. Dispersal capacity was high directly after restoration but continuously decreased over time. The initial communities thus consisted of good dispersers and were later joined by more slowly dispersing taxa. The tolerance to organic pollution also decreased over time, reflecting continuous improvement of water quality and an associated increase of sensitive species. On the contrary, chloride tolerances did not change, which could indicate a stable chloride level throughout the sampling period. Lastly, competition within the communities, reflected by interspecific trait niche overlap, increased with time since restoration. We show that recovery follows a specific pattern that is comparable between sites. Benthic communities change from tolerant, fast dispersing generalists to more sensitive, slowly dispersing specialists exposed to stronger competition. Our results lay support to the ARC (increasing role of competition, decreasing role of dispersal) but also underline that certain tolerances may still shape communities a decade after restoration. Disentangling the drivers of macroinvertebrate colonisation can help managers to better understand recovery trajectories and to define more realistic restoration targets.

Taxonomic distinctness and diversity patterns of a polychaete (Annelida) community on the continental shelf of the Southern Gulf of Mexico

The spatial patterns of taxonomic diversity of annelid polychaete species from the continental shelf in the Southern Gulf of Mexico were examined in this study. We used taxonomic distinctness and its spatial variations to explore the diversity patterns and how they change between Southern Gulf of Mexico regions. In addition, using taxonomic distinctness as a dissimilarity measure and Ward's Clustering, we characterized three distinct faunal assemblages. We also investigated patterns of richness, taxonomic distinctness, and distance decay of similarity between sampling stations as a ß-diversity measure. Finally, we examined the spatial relationships between polychaete assemblages and environmental variables to test the relative importance of spatial and environmental components in annelid polychaete community structure from the Southern Gulf of Mexico. We used a combination of eigenvector-based multivariate analyses (dbMEMs) and distance-based redundancy analysis (dbRDA) to quantify the relative importance of these explanatory variables on the spatial variations of taxonomic distinctness. The significance level of spatial and environmental components to the distribution of polychaete species showed that the combined effect of spatial processes and sediment characteristics explained a higher percentage of the variance than those parameters could alone.

Mangrove interaction with saltmarsh varies at different life stages

Mangroves and saltmarshes are two of the most relevant coastal habitats for humans. These ecosystems offer several services like coastal protection, climate mitigation, and nursery habitats for many artisanal and commercially exploited fish, crabs, and shellfish. They mostly dominate different latitudinal ranges but in several places around the world they co-occur and interact. Here, we summarize the current scientific knowledge on mangrove-saltmarsh ecological interactions and propose a conceptual model. We screened 1410 articles from 1945 to 2022 and selected 29 experiments that assessed mangrove-saltmarsh ecological interactions. Both positive and negative interactions are observed but there is variation along different mangrove life stages. Higher retention and establishment of mangrove propagules are found inside saltmarshes than on bare flats, i.e. facilitation, and these effects are higher at grass than at succulent saltmarsh species. Mangrove seedlings, saplings, or trees mostly compete with saltmarshes, negatively affecting mangrove growth. We propose a model with different outcomes considering the interaction between different mangrove's life stages and saltmarsh forms and discussed these interactions in the light of anthropogenic threats and climate change.

Assessing the Zooplankton Metacommunity (Branchiopoda and Copepoda) from Mediterranean Wetlands in Agricultural Landscapes

Mediterranean wetlands are suitable ecosystems for studying metacommunity theory, since they are isolated ecosystems within a land matrix with well-established limits, often with watersheds destined for agricultural uses. The zooplankton community of wetlands in agricultural landscapes is the result of processes that operate in a different multiscale context. We selected 24 ponds in Alto Guadalquivir region (SE Spain) with different local environmental variables (biological, limnological and land uses). The zooplankton community of the wetlands under study consists of a total of 60 species: 38 branchiopods and 22 copepods. This community (total, branchiopods and copepods) was analysed through two different and complementary metacommunity approaches. The pattern approach determines the species distribution along environmental gradients, and the mechanistic approach considers the involved processes, such as environmental control and dispersal limitation. The results indicated a nested metacommunity, in which five limnological variables, three land uses and six spatial variables are the main drivers that explain zooplankton distribution in these wetlands. In conclusion, species sorting and dispersal processes play a role in the structuring of the zooplankton metacommunity. This conclusion has implications for the development of adequate management policies on Mediterranean wetland protection and diversity conservation in agricultural contexts.

A glimpse into the trophic ecology of deep-water sharks in an important crustacean fishing ground

Deep-water sharks are among the most vulnerable deep-water taxa because of their extremely conservative life-history strategies (i.e., late maturation, slow growth, and reproductive rates), yet little is known about their biology and ecology. Thus, this study aimed at investigating the trophic ecology of five deep-water shark species, the birdbeak dogfish (Deania calcea), the arrowhead (D. profundorum), the smooth lanternshark (Etmopterus pusillus), the blackmouth catshark (Galeus melastomus) and the knifetooth dogfish (Scymnodon ringens) sampled onboard a crustacean bottom-trawler off the south-west coast of Portugal. We combined carbon and nitrogen stable isotopes with RNA and DNA (RD) ratios to investigate the main groups of prey assimilated by these species and their nutritional condition, respectively. Stable isotopes revealed overall small interspecific variability in the contribution of different taxonomic groups to sharks' tissues, as well as in the origin of their prey. S. ringens presented higher δ¹⁵ N and δ¹³ C values than the other species, suggesting reliance on bathyal cephalopods, crustaceans and teleosts; the remaining species likely assimilated bathy-mesopelagic prey. The RD ratios indicated that most of the individuals had an overall adequate nutritional condition and had recently eaten. This information, combined with the fact that stable isotopes indicate that sharks assimilated prey from the local or nearby food webs (including commercially important shrimps), suggests a potential overlap between this fishing area and their foraging grounds, which requires further attention.

Polychaete (Annelida) Diversity Patterns in Southern Gulf of Mexico: The Influence of Spatial Structure and Environmental Variables

A comprehensive database was built to examine the spatial diversity patterns of polychaete species from the continental shelf in Southern Gulf of Mexico. Using Cluster and nMDS analysis we found the composition of polychaete species to be different between the terrigenous and carbonate regions of the Gulf. To test the relative importance of spatial and environmental components in the polychaetae community structure in the Southern Gulf of Mexico, we examined the spatial relationships between polychaetae assemblages and environmental variables over broad geographical scales. A distance-based redundancy analysis (dbRDA) and variation partitioning was used to quantify the relative importance of these explanatory variables on the spatial variations of species richness and composition. Variation partitioning is an important tool to investigate the importance of spatial structure to species distribution in communities, but it has not yet been used in marine ecosystems. The significance level of spatial and environmental components to the distribution of polychaete species showed that the combined effect of spatial processes and sediment characteristics explained a higher percentage of variance than those parameters could alone.

The presence of Pseudogymnoascus destructans, a fungal pathogen of bats, correlates with changes in microbial metacommunity structure

Metacommunity theory provides a framework for how community patterns arise from processes across scales, which is relevant for understanding patterns in host-associated microbial assemblages. Microbial metacommunities may have important roles in host health through interactions with pathogens; however, it is unclear how pathogens affect host microbial metacommunities. Here, we studied relationships between a fungal pathogen and a host-associated microbial metacommunity. We hypothesized that a fungal pathogen of bats, Pseudogymnoascus destructans, correlates with a shift in metacommunity structure and changes in relationships between community composition, and factors shaping these assemblages, such as ecoregion. We sampled bat cutaneous microbial assemblages in the presence/absence of P. destructans and analyzed microbial metacommunity composition and relationships with structuring variables. Absence of P. destructans correlated with a metacommunity characterized by a common core microbial group that was lacking in disease positive bats. Additionally, P. destructans presence correlated with a change in the relationship between community structure and ecoregion. Our results suggest that the fungal pathogen intensifies local processes influencing a microbial metacommunity and highlights the importance of cutaneous microbial assemblages in host-pathogen interactions.

Bioaccumulation of Per- and polyfluoroalkyl substances (PFASs) in a tropical estuarine food web

The biomagnification of per- and polyfluoroalkyl substances (PFASs) was investigated in a tropical mangrove food web from an estuary in Bahia, Brazil. Samples of 44 organisms (21 taxa), along with biofilm, leaves, sediment and suspended particulate matter were analyzed. Sum (∑) PFAS concentrations in biota samples were dominated by perfluorooctane sulfonate (PFOS, 93% detection frequency in tissues; 0.05 to 1.97 ng g^-1 ww whole-body (wb)), followed by perfluorotridecanoate (PFTrDA, 57%; 0.01 to 0.28 ng g^-1 ww wb). PFOS precursors such as perfluorooctane sulfonamide (FOSA, 54%; 0.01 to 0.32 ng g^-1 ww wb) and N-ethyl perfluorooctane sulfonamide (EtFOSA; 30%; 0.01 to 0.21 ng g^-1 ww wb) were also detected. PFAS accumulation profiles revealed different routes of exposure among bivalve, crustacean and fish groups. Statistics for left-censored data were used in order to minimize bias on trophic magnification factors (TMFs) calculations. TMFs >1 were observed for PFOS (linear + branched isomers), EtFOSA (linear + branched isomers), and perfluorononanoate (PFNA), and in all cases, dissimilar accumulation patterns were observed among different trophic positions. The apparent biodilution of some long-chain PFCAs through the food chain (TMF < 1) may be due to exposure from multiple PFAS sources. This is the first study investigating bioaccumulation of PFASs in a tropical food web and provides new insight on the behavior of this ubiquitous class of contaminants.