The effect of under ice crude oil spills on sympagic biota of the Arctic: a mesocosm approach

Abstract

The Arctic marine environment is facing increasing risks of oil spills due to growing maritime activities such as tourism and resource exploration. Encapsulation and migration of spilled oil through the brine channel system in sea ice poses significant risk to ice-associated biological communities. The first objective of this study was to establish mesocosms that allow the growth of artificial sea ice leading to sea ice physical properties similar to young natural sea ice. In addition, the mesocosms should be capable of growing and maintaining a sea ice community. Six sea water tanks with 360 l capacity each were inoculated with biological cultures collected from landfast sea ice near Utqiaġvik AK in April 2014 (year 1) and March 2015 (year 2). The two experiments lasted 24 and 27 days, and final ice thickness reached a mean value of 33 cm. The light conditions under the ice mimicked natural spring irradiances of 15 umol photons m² s⁻¹. Different inoculation approaches for ice biota were used. In year 1 we did not observe any algal growth. In year 2, biological characteristics in the ice prior to oil release (chlorophyll a, Extracellular Polymeric Substance (EPS) concentrations and algal and bacterial abundances) were similar to natural concentrations from early spring first year ice. The second objective was to evaluate the impact of Alaska North Slope crude oil on sea ice biota. Two different oil spill scenarios were tested in the mesocosms: discrete oil lenses and dispersed emulsions. Tanks were sampled prior to oil release and 13 or 10 days post-release in year 1 and year 2, respectively. In year 1, bacterial abundances increased after oil release, while establishment of algal populations was unsuccessful. In year 2, algal growth rates and EPS production increased over time in the control tanks, while they did not change in the oil exposed tanks. Differential response of bacteria and algae between year 1 and 2 not only point to the potential of nutrient competition, but also to the need of measuring several biological properties to detect effects of oil exposure in the event of a spill. Future studies can build upon the developed experimental framework including biological responses to low, sub-lethal oil dosing.