The effects of crude oil and Corexit 9527 on marine phytoplankton in an experimental enclosure

• Published in: Marine environmental research 1986, Vol.18 (2), p.93-109
• Main Authors: Harrison, P.J., Cochlan, W.P., Acreman, J.C., Parsons, T.R., Thompson, P.A., Dovey, H.M., Xiaolin, Chen
• Format: Article
• Language: English
• Subjects: Animal, plant and microbial ecology; Applied ecology; Biological and medical sciences; Ecotoxicology, biological effects of pollution; Fundamental and applied biological sciences. Psychology; Marine and brackish environment
• ISSN: 0141-1136; 1879-0291
• DOI: 10.1016/0141-1136(86)90002-4

The effects of a dispersant, Corexit 9527, plus Prudhoe Bar crude oil and the effects of the dispersant only on natural assemblages of marine phytoplankton in three large experimental ecosystem enclosures (CEEs) were studied. The oil and dispersant were added to a layer between 2 and 4 m depth yielding initial concentrations of 4·5 and 2·0 mg litre −1, respectively. The enclosures remained undisturbed for the 17-day experiment except for sampling at 2- or 3-day intervals. Nutrient concentrations, nitrogen transport rates, chlorophyll a, primary productivity, phytoplankton sinking rates, species composition and cell numbers were followed over the course of the experiment. In the enclosure with oil and dispersant, diatom growth was suppressed and the phytoplankton were dominated by microflagellates such as haptophytes, chrysophytes and a prasinophyte. The diatoms appeared healthy under the microscope and the total number of species was similar species that was affected by the oil. Pennate diatoms, amoebae, zooflagellattes (e.g. bodonids) were more abundant than in the control enclosure. The phytoplankton saccessions in the enclosure receiving only dispersant and in the control enclosure were very similar, but markedly dijferentm from that in the oil-plus-dispersant enclosure. A diatom bloom commenced in both the control and the enclosure receiving only dispersant by day 2 and collapsed by day 11 due to nutrient exhaustion (nitrate and silicate). Nitrate it was not exhausted in the enclosure containing oil and dispersant until the end of the experiment (day 17) and consequently primary productivity and nitrogen transport rates increased with time. This observation is in contrast with the control and dispersant only enclosures were primary productivity and nitrogen transport rates declined dramatically in the middle of the experiment due to the exhaustion of nitrate and silicate.