The Davis Strait - DCE - Nationalt Center for Miljø og Energi

A study of the density and distribution of chlorophyll (as a measure of primary
productivity) in the Disko Bay area in spring 2006 (Mosbech et al.
2007) indicated wide spatial and temporal variability in chlorophyll levels
and that high chlorophyll levels (spring bloom) are distributed over large
areas. Moreover, areas of high importance for primary production vary both
between seasons and between years, depending for example on ice conditions.
An oil spill therefore has at least the potential to impact small and localised
primary production sites, while primary production as a whole will
only be slightly impacted even during a large spill in open waters. Additional
information about primary productivity is available for the area
around Nuuk, including Fyllas Banke (Greenland Climate Center), and this
information should be included in an updated version of this assessment.
11.2.2 Oil spill impacts on benthic flora
The direct impact of an oil spill is an expected mass mortality among
macroalgae and benthic invertebrates on oiled shores from a combination of
chemical toxicity and smothering. Another more subtle way oil spill can impact
algae is by petroleum hydrocarbons interfering with the sex pheromone
reaction, as observed in the life history of Fucus vesiculosus (Derenbach &
Gereck 1980).
There are different reports on the impact of oil contamination on macroalgal
vegetation and communities. After the Exxon Valdez oil spill in 1989 in
Alaska macroalgae cover in the littoral zone (mainly Fucus gardneri) was lost.
It has taken many years to fully re-establish these areas with years with fluctuations
in Fucus cover, and some areas are still considered as recovering
(NOAA 2010). These fluctuations may be a result of the grazer-macroalgae
dynamics, as was shown after the Torrey Canyon accident off the coast of
Cornwall, UK (Hawkins et al. 2002). For Prince William Sound the fluctuations
were considered to be a result of the homogeneity of the evolving Fucus
population (e.g., genetics, size and age), which made it more vulnerable
to natural environmental impacts (e.g., no adult Fucus plants to protect and
assure recruitment), and resulted in a longer time span for Fucus population
heterogeneity to recover (Driskell et al. 2001).
In contrast, no major effects were observed in a study on the impact of crude
and chemically dispersed oil on shallow sublittoral macroalgae at northern
Baffin Island, conducted by Cross et al. (1987).
The scenarios of the Exxon Valdez accident and the Baffin Island Oil Spill
(BIOS) study differ in that the Exxon Valdez oil spill included heavy oil,
while in the case of BIOS the oil tested was a medium crude oil (Sergy &
Blackall 1987). Furthermore, the BIOS studies on macroalgae were conducted
in the upper sublittoral, and not in the littoral zone where the most dramatic
impacts were observed in connection with the Exxon Valdez oil spill
(Dean & Jewett 2001).
Cleaning of the shoreline may add to the impacts of oil contamination. After
the Exxon Valdez oil spill adult Fucus plants were coated with oil but did not
necessarily die. Part of the cleanup effort involved washing shores with
large volumes of high-pressure hot seawater. This treatment caused almost
total mortality of adult Fucus and probably scalded much of the rock surface
and thereby Fucus germlings. In the long term, though, no significant difference
was observed on Fucus dynamics at oiled and unwashed versus oiled
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