Submarine outfall and new sewage treatment plant modulate the response of intertidal benthic communities in a SW Atlantic area.

Spatio-temporal responses of the intertidal macrobenthic community to the effects of a submarine outfall (SO) and a new sewage treatment plant (EDAR) were evaluated, analyzing changes in macrofaunal assemblages and community structure. Study was conducted in a SW Atlantic coastal area in 4 stages: BSO (Before the SO), Du (During the construction of the SO), ASO (After the SO start-up) and AEDAR (After the treatment plant start-up). Boccardia proboscidea and Brachidontes rodriguezii contributed most to the differences between all stages at the site nearest to the discharge point. Number of individuals was highest at BSO and Du. Richness and diversity were lowest at the BSO and highest at the Du. Furthermore, the richness decreased slightly, and the diversity increased at AEDAR. Evenness was highest at the BSO and AEDAR. The nestedness was the dominant process driving the differences between the BSO stage community and the rest of the stages. SO affects the composition and structure of the intertidal macrobenthic community near the outfall area, as organic matter discharge further offshore favour the development of a more diverse intertidal community, including species sensitive to organic enrichment.

Macro-, meso- and microplastic abundance in sandy beaches and factors influencing their distribution in an SW Atlantic resort.

The present study recorded the abundance of plastic debris in marine sediments of tourist beaches in the Southwest Atlantic (Argentina). We aimed to determine the abundance of macro-, meso- and microplastics in different beaches, considering different anthropogenic and natural factors. Generalized Linear Mixed Models (GLMMs) were performed and the explanatory factors were: Beach Morphology; Grain Size; Recreational Use Level; Continental Water Discharge, Location, Distance Urban Centre and Season. The Continental Water Discharge was the factor responsible for the highest abundance of plastic debris on the beach surface. Beaches with fine granulometry, between groins, with high to very high intensity of recreational use, tend to accumulate and/or retain greater amounts of plastic debris. The seasonal factor influences the abundance of plastic waste in the central zone between the pre-summer and post-summer seasons, despite the cleaning effect of the city goverment. In beaches with greater anthropogenic pressure, the influence of this factor on the abundance of litter is altered.

Submarine outfall effect on subtidal macrobenthic communities in a southwestern Atlantic coastal city.

Submarine outfalls are an effective alternative for the final discharge of wastewater. The aim was to evaluate the subtidal macrobenthic community's responses and the changes in bottom sedimentary dynamics due to submarine outfall (SO) location. Sampling stages were: before SO (BSO), after SO (ASO) and after treatment plant (AEDAR). Sampling sites were determined at different distances from the coastline (coastal, oceanic, and reference) on both sides of the pipe (North and South). Species shifts (from tolerant to sensitive) were observed along with a decrease in organic matter in the AEDAR Stage. There were changes in the sedimentary dynamic with sediment accumulation on the South side of the SO (finest sediments) and erosion on the North side (coarsest sediments) in the ASO and AEDAR Stages. Species turnover was higher than nesting in all stages. Functional trait analysis allowed the identification of temporal variations in benthic communities. The body size, development mode, feeding mode, habit, adult mobility and tolerance to pollution were useful functional traits to detect changes through Stages (BSO, ASO, and AEDAR). Biotic indices classified the sites as slightly disturbed, indicating a slight improvement in the AEDAR Stage.

Factors driving the abundance and distribution of microplastics on sandy beaches in a Southwest Atlantic seaside resort.

Microplastics are currently considered widespread marine pollutants, accumulating in sediments and shorelines around the world. Spatial distribution of microplastics in marine sediments is consequence of a combination of multiple factors (naturals and anthropics). We evaluated the drivers' factors of the abundance and distribution of two microplastics morphotypes (fibers and fragments) in surface sediments (5 cm deep) on SW Atlantic beaches with different plastics waste contribution along the coastline. Beach geomorphology, sediment grain size, distance to the urban area, continental waters discharge and human activities were the analyzed factors. Fibers abundance was significantly highest in pocket beaches, moderately exposed and closest to the urban center, while the fragments abundance was highest in beaches with stormwater outfall. The fine sand and the high recreational level were also factors driving the abundance of both morphotypes. Therefore, plastic morphotype and abundance vary according to the determining factors.

The boom-bust dynamic of the invader Boccardia proboscidea mediated by sewage discharge: The response of the intertidal epilithic community in the Southwest Atlantic.

Biological invasions produce an invader population boom but are often followed by an invader population bust. The decrease of the invader abundance ends with the coexistence of native species and the invader or with repeated boom and bust events. In the southwest Atlantic, the polychaete Boccardia proboscidea invaded the coasts influenced by sewage discharge. We studied the change in the intertidal benthic community during the boom-bust dynamic of the Bo. proboscidea invasion. During the boom, the invader polychaete was dominant forming monoculture reefs. Species richness, diversity, and evenness indices decrease in the boom phase. During the bust of the Bo.proboscidea invasion, the decrease of organic matter allowed Br. rodriguezii to coexist with Bo. proboscidea. Beta diversity comparing boom with the bust phase showed a greater nesting (nestedness component); reflecting a process of species loss. We found that both boom and bust phases of the polychaete Bo. proboscidea invasion were mediated by sewage.