Increasing demands for and utilizations of petrochemicals have resulted in an increase in levels of petroleum hydrocarbons in marine, coastal and estuarine environment. Maritime oil contamination usually caused by maritime incidents has catastrophic impacts on the marine environment. More generally, merchant ships can have a significant environmental impact due to on-going human activities, e.g. air and sea pollutions caused by oil, fuel, waste disposal, and the effects of ballast water exchange processes. The oil contamination in the marine environment can pose a significant threat to marine life, especially the phytoplankton. As one of the most important marine planktons, phytoplankton possesses the basic status and function in the marine food chains, and also plays an important role in dynamics of material and energy fluxes. It is therefore very important to study the impact of oil pollution on marine phytoplankton.
The effect of oil pollution on marine planktonic organisms has been studied both in the laboratory and in the field. The median effective concentrations (EC₅₀) of certain kinds of microalgae exposed to oil were measured and the toxicities of different oil components and oil products were compared. Field researchers investigated the changes in phytoplankton after oil spillage in certain sea areas. Some researchers focused on the gene or protein levels of certain types of microalgae exposed to oil contamination, and others discussed whether the environmental factors such as ultraviolet radiation (UV) in natural sunlight enhanced the oil toxicity or not. However, the responses of phytoplankton community under the stress of oil contamination have not been highlighted yet. Our work is to simulate oil contamination on the natural phytoplankton community and study the community growth. The objectives of this paper are to study the influences of oil pollution on the ecological effects of marine phytoplankton, and provide the basis data for the loss assessment of marine living resources and marine ecosystems caused by oil spills and oil pollution.
In four seasons from November 2008 to July 2009, the experimental phytoplankton was collected from the Yueqing Bay in Zhejiang Province. Eight groups of crude oil water accommodated fraction (WAF) were set to perform the 15-day culture experiments of phytoplankton. The chlorophyll a and cell density of phytoplankton were measured at every 24 h to reflect the growth change of phytoplankton community.
It is indicated that crude oil pollution of high concentration (≥2.28 mg/L) would greatly restrain the growth of phytoplankton (P＜0.001) shown by decreased chlorophyll a content and cell density, while crude oil pollution of low concentration (≤1.21 mg/L) would promote the growth of phytoplankton instead. The chronic toxicity of crude oil to phytoplankton have seasonal differences due to different natural water temperatures, e.g. phytoplankton is less tolerant to pollution in summer than in winter because of higher temperature. There is a close relationship with positive correlation between the chlorophyll a and cell density of phytoplankton (P＜0.001). In addition, the impact of crude oil pollution on phytoplankton varies with time. The phytoplankton communities with low concentration crude oil pollution could recover to grow, as the oil hydrocarbons were decompounded in the anaphase of culture period.