Effects of Macondo oil on growth rates of Gulf of Mexico phytoplankton.

The water samples were collected from coastal waters at Cocodrie, LA. In the laboratory, one-milliliter aliquots of the coastal water were used to inoculate 125-milliliter glass flasks containing artificial seawater (Instant Ocean) enriched with inorganic nutrients and vitamins according to the protocol for f/2 medium (Guillard, 1975). All experiments were run in triplicate. The control flasks received no added oil. The treatment flasks received oil at concentrations ranging from 0.1 to 19.2 parts per million according to the protocol of Singer et al. (2001). The flasks were incubated in front of a bank of fluorescent lamps that provided about 300 micro-mol quanta per square meter per second of visible light on a continuous basis. The temperature was 20 ± 1 C. The growth of the phytoplankton was monitored via optical density (OD) measured at a wavelength of 750 nm on a spectrophotometer. Growth rates were estimated from the slope of the natural logarithm of the OD during the period of time, typically several days, during which the cells were in log phase growth. OD measurements were made at intervals of 12 hours.