Thursday September 23th, 2021, 5pm GMT+2
Back to the past: sedimentary archives revealed dinoflagellate communities shifts and species adaptations due to human impact in the Bay of Brest (France)
1 Ifremer, DYNECO Centre de Brest, France
The study of dinoflagellate remains (viable and fossilised resting stages, sedimentary ancient DNA) across stratified layers of marine sediment cores allows the assessment of centuries-old community and population dynamics. When resting stages can be revived from ancient sediments and monoclonal strains are established and compared to contemporary ones, species physiological and genetic adaptation patterns evolved across time can be inferred. Environmental and experimental observations can be related to other paleo-ecological proxies, such as organic and inorganic pollutants, to determine whether the observed dinoflagellate community and species variations are an effect of human impact. In the Bay of Brest (Brittany, France) paleogenetic studies allowed ca. 1400 years of retrospective analyses of dinoflagellate community and harmful species. Heavy metal pollution traces in sediments ascribed to the World War II period coincided with irreversible dinoflagellate community shifts. After the war and especially from the 1980’s to 1990’s, dinoflagellate genera shift followed chronic contaminations of agricultural origin and the harmful species Alexandrium minutum progressively developed across the 20th century (Siano et al., 2021). In order to assess the physiological adaptations of modern populations to the increase in eutrophication and to the progressive phosphorous limitation that occurred in the area across the 20th century, resurrection ecology experiments were carried out on buried cysts of A. minutum and, for comparison, on Scrippsiella acuminata and S. donghaienis. Using a plant seed-inspired priming approach, 150-year old cyst revivification and an increase in the number of revived cells were obtained by stimulating germination using melatonin and gibberellic acid (Delebecq et al., 2020). Metabolomics profiles of A. minutum strains of the eutrophication (1980’s) and post-eutrophication period (2000’s) cultivated in P-depleted conditions were similar, conversely to those of S. donghaienis strains that were significantly different for 27 lipophilic compounds. However, when the alkaline phosphatase (AP) activity was measured at single cell level with an ad-hoc developed microfluidic systems and in P-depleted culture conditions, consistent differences were observed between strains of the pre-eutrophication (1940’s) and the beginning of the post-eutrophication period (1990’s), both in A. minutum and S. acuminata. For both species, total AP in the 1990’s decade was significantly lower than in the 1940’s. Considering that the AP is produced in P limitation, these results suggest that both species would have adapted to the decreasing concentration of phosphorus in the environment. Alexandrium minutum produced less AP, meaning that this species would perform better in P limitation, likely thriving upon internal phosphorous stocks, an adaption that would explain its ecological success in recent time in the Bay of Brest (Girault et al., 2021). These results suggest that the evolution of specific biological traits in dinoflagellate species is a key factor to explain multiannual species dynamics and that paleo-ecological approaches can help unveiling and understanding this process.
- Delebecq, G., Schmidt, S., Ehrhold, A., Latimier, M., Siano, R., 2020. Revival of ancient marine dinoflagellates using molecular biostimulation . Journal of Phycology 56, 1077–1089.
- Girault, M., Siano, R., Labry, C., Latimier, M., Jauzein, C., Beneyton, T., Buisson, L., Del Amo, Y., Baret, J.-C. (2021). Variable inter and intraspecies alkaline phosphatase activity within single cells of revived dinoflagellates. Isme Journal 15, 2057–2069.
- Siano, R., Lassudrie, M., Cuzin, P., Briant, N., Loizeau, V., Schmidt, S., Ehrhold, A., Mertens, K.N., Lambert, C., Quintric, L., Noël, C., Latimier, M., Quéré, J., Durand, P., Penaud, A., 2021. Sediment archives reveal irreversible shifts in plankton communities after World War II and agricultural pollution. Current Biology 31, 2682–2689.