Impact of offshore gas platforms on the structural and functional biodiversity of nematodes

Assessing the potential of nematode metabarcoding for benthic monitoring of offshore oil platforms

Environmental DNA metabarcoding is gaining momentum as a time and cost-effective tool for biomonitoring and environmental impact assessment. Yet, its use as a replacement for the conventional marine benthic monitoring based on morphological analysis of macrofauna is still challenging. Here we propose to study the meiofauna, which is much better represented in sediment DNA samples. We focus on nematodes, which are the most numerous and diverse group of meiofauna. Our aim is to assess the potential of nematode metabarcoding to monitor impacts associated with offshore oil platform activities. To achieve this goal, we used nematode-optimized marker (18S V1V2-Nema) and universal eukaryotic marker (18S V9) region to analyse 252 sediment DNA samples collected near three offshore oil platforms in the North Sea. For both markers, we analysed changes in alpha and beta diversity in relation to distance from the platforms and environmental variables. We also defined three impact classes based on selected environmental variables that are associated with oil extraction activities and used random forest classifiers to compare the predictive performance of both datasets. Our results show that alpha- and beta-diversity of nematodes varies with the increasing distance from the platforms. The variables directly related to platform activity, such as Ba and THC, strongly influence the nematode community. The nematode metabarcoding data provide more robust predictive models than eukaryotic data. Furthermore, the nematode community appears more stable in time and space, as illustrated by the overlap of nematode datasets obtained from the same platform three years apart. A significative negative correlation between distance and Shannon diversity also advocates for higher performance of the V1V2-Nema over the V9. Overall, these results suggest that the sensitivity of nematodes is higher compared to the eukaryotic community. Hence, nematode metabarcoding has the potential to become an effective tool for benthic monitoring in marine environment.

Impact of historical sulfide mine tailings discharge on meiofaunal assemblages (Portmán Bay, Mediterranean Sea)

Portmán Bay is one of the most contaminated and chronically impacted coastal marine areas of the world. Here, from the 1957 to 1990, about 60 million tons of mine tailings from the processing of sulfide ores were dumped directly at the shoreline. The resulting deposit provides a unique opportunity to assess the impact of mine tailings on coastal marine ecosystems after ca 30 years since the discharge has ceased. We investigated meiofaunal abundance, biomass and biodiversity along a gradient of metal concentration that overlaps with a bathymetric gradient from 30 to 60 m depth. Despite the localized presence of extremely high concentration of metals, the bay was not a biological desert, but, nevertheless, was characterized by evident signs of impact on benthic diversity. Meiofaunal variables increased significantly with decreasing metal contamination, eventually reaching values comparable to other uncontaminated coastal sediments. Our results show that mine tailings influenced the spatial distribution of meiofaunal taxa and nematode species composition. In particular, we report here that the bay was characterized by the dominance of nematode opportunistic species tolerant to high metal concentration. The effects of mine tailing discharge on meiofaunal biodiversity and composition were still evident ca 30 years after the end of the mining activities. Overall, this study provides new insights on the potential impact of mine tailings disposal and metal contamination in coastal sediments, and, can also contribute to predict the potential long-term consequences of ever-expanding deep-sea mining industry on benthic environments.

Impact of historical contamination on meiofaunal assemblages: The case study of the Bagnoli-Coroglio Bay (southern Tyrrhenian Sea)

The effects of contaminants on marine organisms have been documented since decades, but the long-term responses and recovery rates of benthic communities to mixtures of contaminants, several years after the cessation of industrial activities, need to be further investigated. Bagnoli-Coroglio Bay (Gulf of Naples, Tyrrhenian Sea) is a typical example of historically contaminated coastal area due to industrial activities stopped at the beginning of nineties. In the present study we carried out a fine spatial scale analysis of the distribution of meiofaunal (and nematodes) assemblages along five bathymetric transects located at increasing distance from the historical source of contamination in relation with the polycyclic aromatic hydrocarbon and heavy metal concentrations present in the sediment. Meiofaunal abundance and biomass changed widely along transects but independent from the distance from the source of contamination. Even when the contamination levels were expected to induce significant detrimental biological consequences, meiofaunal abundance and biomass were similar to those reported in unpolluted benthic coastal areas worldwide. Conversely, biodiversity in terms of meiofaunal taxa richness was generally low (range: 5-8 taxa in 12 of the overall 15 stations investigated). This was explained by the lack of sensitive groups such as ostracods, gastrotrichs and tardigrades commonly encountered in benthic coastal ecosystems, thus reflecting an overall poor/moderate environmental quality of the investigated area. Nematode (structural and functional) diversity was also low, particularly at stations characterized by higher contamination levels. At the same time, nematode species composition did not change significantly among stations suggesting a widespread effect of contaminants able to reduce the variability (i.e., turnover diversity) within the assemblages of the whole study area. Overall, our results indicate that even decades after the cessation of contaminant emissions, benthic biodiversity was affected in terms of both meiofaunal taxa and nematode species. These findings strongly reinforce the call for reducing sources of chronic pollution in marine ecosystems and provide new insights for a better understanding of the ecological recovery of historically contaminated marine environments.

Terrestrial Non-Parasitic Nematode Assemblages associated With Glyphosate-tolerant and Conventional Soybean-Based Cropping Systems

Information about the effects of glyphosate on nematodes is limited and contradictory, while none existing for South African agricultural fields. The abundance and identity of non-parasitic nematodes in the rhizospheres of commercial glyphosate-tolerant and conventional (non-glyphosate-tolerant), soybean cultivars from cultivated fields, and adjacent natural vegetation (reference system) were obtained for two growing seasons. The impact of glyphosate was also investigated on non-parasitic nematodes in a 2-year soybean-maize cropping system. Thirty-two non-parasitic nematode genera were identified from soils of the three field ecosystems, with most of the genera occurring in natural vegetation (28), and less in conventional (23) and glyphosate-tolerant soybean (21). Bacterivores had the greatest diversity in soils of all three ecosystems during both seasons, while fungivores tended to be more abundant in glyphosate-tolerant soybean fields especially during the second season. Soils from the three ecosystems were disturbed and degraded with low abundance and diversity of omnivores and predators. Of the 14 genera identified from the soybean-maize cropping experiment, bacterivores dominated in terms of diversity in non-treated, and fungivores in glyphosate-treated plots. Soils from glyphosate-treated plots were degraded, less enriched and fungal-mediated, while those from non-treated plots were disturbed, enriched, and bacterial-mediated.

Collating science-based evidence to inform public opinion on the environmental effects of marine drilling platforms in the Mediterranean Sea

The use of rigorous methodologies to assess environmental, social and health impacts of specific interventions is crucial to disentangle the various components of environmental questions and to inform public opinion. The power of systematic maps relies on the capacity to summarise and organise the areas or relationships most studied, and to highlight key gaps in the evidence base. The recent Italian technical referendum (2016) - a public consultation inviting people to express their opinion by voting to change the rules on the length of licence duration and the decommissioning of offshore oil and gas platform drilling licences - inspired the creation of a systematic map of evidence to scope and quantify the effects of off-shore extraction platforms on Mediterranean marine ecosystems. The map was aimed as a useful model to standardise a "minimal informational threshold", which can inform public opinion at the beginning of any public consultation. Produced by synthesising scientific information, the map represents a reliable layer for any future sustainable strategy in the Mediterranean basin by: (i) providing a summary of the effects of marine gas and oil platforms on the Mediterranean marine ecosystem, (ii) describing the best known affected components on which the biggest monitoring efforts have been focused, and (iii) strengthening the science-policy nexus by offering a credible, salient and legitimate knowledge baseline to both public opinion and decision-makers. The map exercise highlights the knowledge gaps that need filling and taking into due consideration before future transnational and cross-border monitoring and management plans and activities can be addressed.