With the oil spill continuing, we have to contemplate what effect the addition of the petroleum in the water column may have on the ecosystem. Hydrocarbons consist of hydrogen and carbon to a large extent, and as we all know they are rich in energy. Bacteria will therefore use that energy, and decompose the hydrocarbons – if they can. Two factors are limiting: The bacteria will also need oxygen for their respiration, which means that the oil increases the biological oxygen demand (BOD) in the sea. This may stress out higher life forms in the upper level of the ocean. On the ohter hand, phytoplankton (organisms that synthesize organic material using sunlight) are not dependent on oxygen since they generate oxygen – in daytime, that is.
Furthermore, the bacteria will need additional nitrogen. As biologically available nitrogen often is a limiting nutrient in the sea, this rather than oxygen might limit their growth – especially since oxygen is introduced from the surface when the wind blows. If the nitrogen level is low, the relative advantage falls thus to phytoplankton that can fixate inorganic nitrogen. Among those we note cyanobacteria, also known as blue-green algae. Cyanobacteria also occur as a symbiont in diatoms. (Diatoms are green unicellular algae, basically.)
Following this line of reasoning, one could predict that there might occur a large algal bloom in the Gulf, either of green diatoms (with a symbiont), or of so-called blue-green algae: cyanobacteria. Following an algal bloom there is an BOD shock in the lower layers, as the dead algae sink to the sea floor. In the worst case this could lead to large bottom areas getting anoxic conditions.
The water quality of the Gulf Stream would also be affected. Future researchers might find the evidence for such an event as far north as Bermuda, in sediment cores from the sea floor. By studying what happens now, scientists may be able to get a better idea of what transpired in the past, and thus gave rise to the sedimentary conditions that we see in cores already retrieved. As bad as this is for the environment, it does provide a research opportunity that it would be foolish to miss out on.
So get to work with monitoring and analysis, ya’ll!
PS. Check out this study of the effects of an oil spill in the Swedish archipelago near the Askö marine field station. They noted a significant increase in the amount of bacteria, and a bloom of phytoplankton. In that area P, not N, is the limiting nutrient.