Impact of two plastic-derived chemicals, the Bisphenol A and the di-2-ethylhexyl phthalate, exposure on the marine toxic dinoflagellate Alexandrium pacificum

The effects of two plastic-derived chemicals: Bisphenol A (BPA) and di-2-ethylhexyl phthalate (DEHP) were assessed on abundance and physiological responses of the marine toxic dinoflagellate Alexandrim pacificum. During 7 days experiment, A. pacificum was exposed to different levels of BPA and DEHP (separately and in mixture). The responses were evaluated and compared with controls. Results showed that A. pacificum was highly sensitive to this contaminants comparing to other phytoplankton species. BPA and DEHP caused the decrease of the biomass (1.2 to 50 times lower relative to the controls), as well as the perturbation of the photosystem and the photosynthetic activity. Nevertheless, our results show a recovery of contaminated cells activity depending on exposure time and BPA and DEHP contamination. This could be related to an adaptation to induced stress or a degradation of BPA and DEHP in the medium

Seasonal variability of picophytoplankton under contrasting environments in northern Tunisian coasts, southwestern Mediterranean Sea

Highlights: • Picophytoplankton was able to grow under a wide range of environmental conditions varying seasonally. • Picophytoplankton variability was more marked in the bay than in the lagoon. • Picophytoplankton decreased in the lagoon under enhanced anthropogenic stress. • Synechococcus, the most abundant group of the community, was frequently present in both ecosystems during the monitoring. We investigated at the single cell level during 16months (June 2012 to September 2013) the temporal distribution of picophytoplankton (picoeukaryotes, Synechococcus and Prochlorococcus) communities in two contrasted ecosystems: the Bay of Bizerte characterised by an oligotrophic regime typical of the Mediterranean Sea and the Bizerte Lagoon that exhibits a mesotrophic/eutrophic state. We aimed at depicting seasonal variations and quantifying the relationships between the environmental factors and the structure and abundance of picophytoplankton communities. Results showed that picophytoplankton groups were able to grow under a wide range of environmental conditions varying seasonally, although their abundances and contributions to the total chlorophyll biomass significantly varied and showed importance in the Bay of Bizerte. Synechococcus was the most abundant group reaching 225*103 cells·cm-3 in the Bay and 278*103 cells·cm-3 in the lagoon. This group was present all over the year in both ecosystems. Structural equation model results pointed out a different configuration regarding the picophytoplankton environmental drivers. The complexity of the configuration, i.e. number of significant links within the system, decreased under enhanced eutrophication conditions. The less exposure to anthropogenic stress, i.e. in the Bay of Bizerte, highlight a larger role of nutrient and hydrological conditions on the seasonal variations of picophytoplankton, whereas a negative effect of eutrophication on picophytoplankton communities was unveiled in the Bizerte Lagoon. We stress that such influence may be exacerbated under expected scenarios of Mediterranean warming conditions and nutrient release in coastal ecosystems