Non-synergistic effects of water-soluble crude oil and enhanced ultraviolet-B radiation on a natural plankton assemblage

Abstract

The present study demonstrates the effects of the water-soluble fraction (WSF) of a crude oil, enhanced ultraviolet-B radiation (UVBR: 280 to 320 nm), and the combination of WSF and enhanced UVBR on a natural plankton assemblage (<150 μm) isolated from the lower St. Lawrence Estuary. To study the separate and dual effects of WSF and UVBR, 12 microcosms (9 l) were immersed in the water column of larger mesocosms (polyethylene bags; 1800 l), providing 4 treatments, each in triplicate: (1) NUVBR + WSF (natural UVBR with WSF), (2) HUVBR + WSF (enhanced UVBR with WSF), (3) NUVBR (natural UVBR without WSF), and (4) HUVBR (enhanced UVBR without WSF). During 5 d we monitored the incident radiation, WSF and nutrient concentrations, abundance and production of heterotrophic bacteria and phytoplankton. Strong deleterious effects of WSF and lower effects of UVBR were observed on the phytoplankton assemblage, with a decrease in growth rates accompanied by an increase in mean cell size which reflected a perturbation of the cell division cycle. Using the NUVBR treatement as reference conditions, the above effects resulted in a reduction of 84, 79 and 60% of total abundance of the phytoplankton fraction < 20 μm in the HUVBR + WSF, NUVBR + WSF and HUVBR treatments, respectively. Significant higher values of bacterial abundances were observed in the WSF-added treatments compared to NUVBR without WSF. However, bacterial thymidine incorporation exhibited diel variations, suggesting cumulative UVBR-induced DNA and/or PAHinduced DNA damages, and possible repair mechanisms with the co-occurrence of more available growth substrates from stressed phytoplankton. The absence of significant differences between both WSF-added treatments under the 2 different UVBR conditions suggests that there is no additive interaction between WSF and UVBR. This study provides therefore the first evidence of a non-synergistic interaction between both stresses, and suggests that UVBR-induced effects on marine microorganisms can be completely masked by the strong deleterious effects of soluble petroleum hydrocarbons.KEY WORDS: Ultraviolet radiation · Dissolved hydrocarbons · Non-synergistic effect · Phytoplankton · BacteriaResale or republication not permitted without written consent of the publisher

Functional and structural responses of marine plankton food web to pyrene contamination

“…Pigment analyses confirmed such a change in exposed communities; diatoms were left to dominate the 250 nmol l -1 community together with green algae, whereas prymnesiophytes and cryptophytes declined compared to the control community. This is in contrast to other findings, in which diatoms were found to be more sensitive to a mixture of hydrocarbon compounds than other algal groups (Nayar et al 2005, Sargian et al 2005. The discrepancy may be caused by the more complex contamination used in those studies, or to the 'rough' characterisation of phytoplankton communities by the pigment analyses used in this study.…”

Plankton stress responses from PAH exposure and nutrient enrichment

“…Diatoms dominated the communities after pyrene exposure at the expense of cryptophytes and dinoflagellates, which were more sensitive to pyrene. These results are consistent with our previous study (Hjorth et al 2007), but contrary to other findings (Nayar et al 2005, Sargian et al 2005. The combination of low total photosynthetic activity and high algal specific activity up until Days 4 through 5 for Py and NuPy communities usually suggests a shift in species composition towards more tolerant species (Hjorth et al 2007).…”

Enhanced bacterioplankton activity after the ‘Prestige’ oil spill off Galicia, NW Spain

“…At first, abundance values were within the range observed before the spill. This result agrees with other field studies in open waters (Delille & Siron 1993) but contrasts with those reported for laboratory experiments with oil-treated microcosms, in which total number of bacteria increased significantly after contamination with water soluble hydrocarbons (Medina-Bellver et al 2005, Sargian et al 2005. Such difference could be due not only to the variable toxicity of the different hydrocarbons involved in each case study, but also to their concentrations and time of exposure for the bacterioplankton.…”