The effects of experimental oil-contaminated marine snow on meiofauna in a microcosm

Ecotoxicity of chrysene and phenanthrene on meiobenthic nematodes with a case study of Terschellingia longicaudata: Taxonomics, toxicokinetics, and molecular interactions modelling

Polycyclic aromatic hydrocarbons (PAHs) are toxic for humans and marine fauna alike. The current study assessed the impact of PAHs on the migratory behaviour of meiobenthic nematodes collected from the Bizerte lagoon, Tunisia. The experiment lasted for 15 days and was carried in open microcosms, which comprised a lower, contaminated and an upper, uncontaminated compartment. Three treatments were used, for each of them an untreated control was set up: sediment contaminated with chrysene (116 ng g^-1 dry weight (DW), with phenanthrene (116 ng g^-1 DW) and a mixture of both. The results showed a significant decrease in diversty and abundance in the lower, contaminated compartments compared to the upper zones. The results also highlighted that under an increased stress some species progressively increased in number, these were considered PAH-tolerant species such as Odontophora villoti, some others had an occasionally increased in number were considered as opportunistic species, such as Paracomesoma dubium and the species that showed a progressive decreased in number, such as Metoncholaimus pristiurus and Steineria sp., Terschellingia. longicaudata, and Oncholaimellus sp. were classified as PAH-sensitive. Moreover, an increase in the activity of biochemical biomarkers was observed following the exposure of males and gravid females of T. longicaudata to 29, 58 and 87 ng g^-1 DW of chrysene and phenanthrene paralleled by a higher vulnerability of the latter demographic category. Besides, a significant decrease in fertility of females and an increase in pharyngeal sucking power were observed for both types of PAHs considered. The sex ratio was also significantly imbalanced in the favor of males, which suggest that chrysene and phenanthrene affect also the hormone system of T. longicaudata. The high affinities of these PAHs and their molecular interactions with both germ line development protein 3 (GLD-3) and sex-determining protein (SDP) may justify these results and explain the toxicokinetic attributes.

The exposure to polyvinyl chloride microplastics and chrysene induces multiple changes in the structure and functionality of marine meiobenthic communities

The effects of microplastics and sorbed polycyclic aromatic hydrocarbons at community levels were rarely assessed in laboratory experiments, despite their obvious advantage in reflecting better the natural conditions compared to traditionally single species-focused toxicological experiments. In the current study, the multifaceted effects of polyvinyl chloride and chrysene, acting alone or combined, on general marine meiobenthos, but with a special focus on free-living marine nematode communities were tested in a laboratory experiment carried in microcosms. The meiobenthos was exposed to two polyvinyl chloride (5 and 10 mg.kg^-1 Dry Weight 'DW') and chrysene (37.5 and 75 ng.g^-1 DW) concentrations, respectively, as well as to a mixture of both compounds, for 30 days. The results highlighted a significant decrease in the abundance of all meiobenthic generic groups, including nematodes, directly with increasing dosages of these compounds when added alone. The addition of chrysene adheres to microplastics, making the sediment matrix glueyer, hence inducing greater mortality among generic meiobenthic groups. Moreover, the nematofauna went through a strong restructuring phase following the exposure to both compounds when added alone, leading to the disappearance of sensitive nematodes and their replacement with tolerant taxa. However, the similarity in nematofauna composition between control and polyvinyl chloride and chrysene mixtures suggests that the toxicity of the latter could be attenuated by its physical bonding to the former pollutant. Other changes in the functional traits within the nematode communities were a decline in the fertility of females and an increase of the pharyngeal pumping power following exposure to both pollutants for the dominant species. The latter results were also supported by additional toxicokinetics analyses and in silico modeling.

Effects of benzo(a)pyrene on meiobenthic assemblage and biochemical biomarkers in an Oncholaimus campylocercoides (Nematoda) microcosm

A microcosm experiment was carried out to determine how benzo(a)pyrene (BaP) may affect marine meiofauna community, with a main emphasis on nematode structure and functional traits. Three increasing concentrations of BaP (i.e. 100, 200 and 300 ng/l, respectively) were used for 30 days. The results revealed a gradual decrease in the abundance of all meiobenthic groups (i.e. nematodes, copepods, amphipods, polychaetes and oligochaetes), except for isopods. Starting at concentrations of 200 and 300 ng/l BaP, respectively, significant changes were observed at community level. At taxonomic level, the nematode communities were dominated at the start of the experiment and also after being exposed or not to BaP by Odontophora villoti, explicable through its high ecologic ubiquity and the presence of well-developed chemosensory organs (i.e. amphids), which potentially increased the avoidance reaction following exposure to this hydrocarbon. Moreover, changes in the activity of several biochemical biomarkers (i.e. catalase 'CAT', gluthatione S-transferase 'GST', and ethoxyresorufin-O-deethylase 'EROD') were observed in the nematode species Oncholaimus campylocercoides, paralleled by significant decreases in CAT activity for non-gravid females compared to controls at concentrations of 25 ng/l BaP and associated with significant increase in GST and EROD activities for both types of individuals.

Impact of treated sewage on meiobenthic nematodes: a case study from the Tunisian Refining Industries Company

Abstract The main objective of the current study was to assess the impact of the water taken from the ‘Tunisian Refining Industries Company’ on meiobenthic nematodes, before and after a series of treatments in decantation basins followed by its discharge in Bizerte bay, Tunisia. The comparison of environmental parameters of the two types of water was clearly indicative of an improvement in the quality of treated waters after a significant reduction in their loads in hydrocarbons. Overall, the water retained a good quality after being treated by ‘Tunisian Refining Industries Company’ before discharge in the sea. At the end of the experiment, differential responses were observed according to the richness of sediment in organic matter and hydrocarbons. Thus, it was apparent that the nematode assemblage exposed to the treated waters was closer to controls and associated to higher values of abundance, than that under untreated ones. It was also assumed that the species Microlaimus honestus De Man, 1922, Paramonohystera proteus Wieser, 1956 and Cyartonema germanicum Juario, 1972 are sensitive bioindicators of bad environmental statues and of hydrocarbon presence in the environment. On the other hand, Metoncholaimus pristiurus (Zur Strassen, 1894) Filipjev, 1918 would rather be classified as a positive bioindicative species of this type of pollutants.

Effectiveness of Shewanella oneidensis bioaugmentation in the bioremediation of phenanthrene-contaminated sediments and possible consortia with omnivore-carnivore meiobenthic nematodes

This study was conducted to assess the impact and efficiency of the bioaugmentation as a bioremediation technique in annoying effects of a polycyclic aromatic hydrocarbon (phenanthrene) on a community of free-living nematodes from Bizerte bay (Tunisia). For this purpose, closed microcosms were exposed to three doses of phananthrene (0.1 μg kg^-1, 1 μg kg^-1 and 10 μg kg^-1), in combination or not with a strain of Shewanella oneidensis. After 40 days of the exposure, results were obtained at the numerical, taxonomic and feeding levels. The results of univariate analyses revealed significant decreases in most univariate indices for phenanthrene treated communities compared to controls, with a discernible increase in the proportion of epistrate feeders. After bioaugmentation, similar patterns were observed for univariate and multivariate analyses, with the exception of the highest treatment, which showed no difference from the controls. The results obtained showed that the bioaugmentation with Shewanellea oneidensis was highly effective in reducing the negative impact of the highest dose of phenanthrene (10 μg kg^-1 Dry Weight) tested on meiobenthic nematodes. Furthermore, a combination of Shewanellea oneidensis and four omnivore-carnivore nematode taxa could be suggested as an effective method in the bioremediation of phenanthrene-contaminated sediment.

Planted mangroves cap toxic petroleum-contaminated sediments

Mangroves are known to provide many ecosystem services, however there is little information on their potential role to cap and immobilise toxic levels of total petroleum hydrocarbons (TPH). Using an Australian case study, we investigated the capacity of planted mangroves (Avicennia marina) to immobilise TPH within a small embayment (Stony Creek, Victoria, Australia) subjected to minor oil spills throughout the 1980s. Mangroves were planted on the oil rich strata in 1984 to rehabilitate the site. Currently the area is covered with a dense mangrove forest. One-meter-long sediment cores revealed that mangroves have formed a thick (up to 30 cm) organic layer above the TPH-contaminated sediments, accumulating on average 6.6 mm of sediment per year. Mean TPH levels below this organic layer (30-50 cm) are extremely toxic (30,441.6 mg kg^-1), exceeding safety thresholds up to 220-fold which is eight times higher when compared to top layer (0-10 cm).

Ecological quality assessement of marinas: An integrative approach combining biological and environmental data

The importance of marinas as infrastructures for recreational boating is increasing substantially. However, information on their soft-bottom benthic communities, a key tool for managing programmes, is still scarce. We combined environment features with macro- and meiofaunal soft-bottom community information for assessing the ecological status of marinas with an integrative approach. To address this issue, we focused on eight marinas of the Southern Iberian Peninsula. Macro- and meiofauna data revealed high benthic heterogeneity at a spatial scale. The environmental variables which correlated best with macrofauna were mainly phosphorus, granulometry, and total organic carbon, and secondarily important variables were faecal coliforms, the biocide Irgarol, and heavy metals; total hydrocarbon concentration was also significant for meiofauna. Annelida was the dominant phylum in terms of number of species (37%) and abundance (66%) and were better descriptors of the environmental conditions than Arthropoda and Mollusca. Although identification to the species level is desirable and mandatory for assessing biological pollution, significant differences among marinas and correlations between fauna and abiotic variables were already detected at the level of family and order. This implies that biota assessment at higher levels may still be useful in monitoring programmes limited by time and budget constraints. The major novelty of this study lies in the development of an integrative assessment method based on the following selected ecological indicators: Marinas Environmental Pollution Index (MEPI), Biocontamination Index (BCI), macrofaunal biotic indices (AMBI, M-AMBI, BENTIX, MEDOCC and BENFES), macrofaunal taxa richness and Shannon-Wiener's diversity, and nematode:copepod index. This approach was able to discriminate marinas of the Southern Iberian Peninsula based on their ecological status, which ranged from poor to good. The method can be useful to design standards for assigning "sustainable quality seals" to those marinas with better values of ecological indicators.

Nematode traits after separate and simultaneous exposure to Polycyclic Aromatic Hydrocarbons (anthracene, pyrene and benzo[a]pyrene) in closed and open microcosms

The majority of experimental studies carried out to date, regarding the effects of pollutants on meiofauna have been conducted by means of closed systems, and rarely using open ones. The current work explored the impact of three Polycyclic Aromatic Hydrocarbons (PAHs), anthracene, pyrene and benzo[a]pyrene, applied alone or combined, on meiobenthic nematodes using both systems. The results revealed that single PAHs impacted the nematofauna similarly in closed or open systems with a higher toxicity observed for benzo[a]pyrene. However, the closed microcosms contaminated with PAHs became organically enriched, resulting in more non-selective deposit feeders and omnivores-carnivores. Taxonomic and functional effects related to combinations of PAHs were close to those of individual treatments in closed systems, however, for open ones, the outcomes were different. The caudal morphology influenced the response of taxa during their avoidance/endurance of hydrocarbons in open systems where the effects of PAHs mixtures appeared not only additive but also synergetic. Based on the results of the study, the use of open systems is preferred to closed ones as the research outcomes were more accurate and representing better conditions prevailing in nature.

The individual and combined effects of cadmium, polyvinyl chloride (PVC) microplastics and their polyalkylamines modified forms on meiobenthic features in a microcosm

A microcosm experiment was carried out to study the ecotoxicity and interactions between heavy metals and polyvinyl chloride microplastics. Fifteen treatments were tested and results were examined after one month. In details, this work aims to study the ecotoxicological effects of cadmium (10 and 20 mg kg^-1 Dry Weight DW), polyvinyl chloride (PVC) and its modified forms; PVC-DETA (PD) and PVC-TETA (PT) (20 and 40 mg kg^-1 DW), separately and in mixtures, on meiofauna from Bizerte lagoon (NE Tunisia) with focus on nematode features. The results obtained showed that individual treatments were toxic for meiofauna and particularly for free-living nematodes. No clear trends characterized the numerical responses but significant reductions were observed for diversity indices. Moreover, the binary combinations of contaminants have a lesser toxic effect compared to their individual effects. This effect could be related to the high-capacity chelating ability of PVC and its polymers against cadmium.