Assessing Sub-Lethal Impacts of Petroleum Compounds on Marine Benthic Systems
Petroleum and its different distillates commonly end up in the marine environment. One source of these additions is discharges originating from shipping activities; accidents, ship wrecks, operational spills etc. Depending on several different factors that govern the fate of petroleum released into the marine environment the effects of the discharge will differ, from acute toxic to long term sub-lethal effects. While effects on biota from large spills have thoroughly been investigated in the past long term sub-lethal effects are somewhat less examined. Therefore the objective of this thesis has been to develop and apply a method to analyze what effects low concentrations of petroleum, which often ends up in marine sediments, have on benthic sediment biota. Ecotoxicological endpoints that were evaluated were density changes of meiofauna and variations in the microbial community function, measured as inorganic nutrient fluxes over the sediment-water interface the potential to perform a metabolic process. These types of organisms are two important key players in marine benthic sedimentary habitats, performing ecosystem services such as degradation of organic matter, recycling of nutrients and various pollutants and they constitute a carbon link to higher trophic levels.
As manual classification of meiofauna is very time-consuming process including an extended learning process for the taxonomist, this thesis is in its first part focused at the field of automatic classification. To classify meiofaunal communities a novel technique was developed where the image analysis software ZooImage was adapted to automatically classify higher taxonomic taxa of meiofauna, with successful results. The technique was evaluated by classifying meiofaunal communities from five different depths in the Gullmar Fjord, Sweden. The accuracy of the analyses was tested using ZooImage’s internal 10-fold cross-validation method, and by comparing digitalized samples from the different sites with manually classified samples. Sufficient taxon diversity was used, allowing multivariate statistical analysis to reveal differences in the meiofauna communities between different depths. Dissimilarities were mostly owing to changes in salinity with increasing depth.
The second part of the thesis is dedicated to evaluate effects of minor additions of a petroleum product with low concentrations of PAHs, a group of substances which can incur lethal and sub-lethal effects in biota. Here the common Swedish MK-1 diesel was used, which contains 370 times less PAHs than its European Union counterpart. Sediment meiofauna and microorganisms were incubated in microcosms for 60 days and exposed to diesel in different concentrations, 0.2, 2.0 and 20 times the background levels of PAHs in control sediment from the Gullmar Fjord. Meiofaunal community effects were evident after 30 and 60 days, with increasing differences, in treatments with 2.0 and 20 times the background levels of PAHs. Pronounced changes in inorganic fluxes were detected in the latter PAH treatments, resulting in lowered ΣNOx, silicate and phosphate fluxes. The most sensitive endpoint, potential nitrification, was affected in the two highest concentrations after two days as well as in all treatments at day 30 and 60. This suggests an altered community of meiofauna with lowered activity and a microbial community with reduced inorganic flux recycling capabilities, effects that have the possibility of cascading upwards in the food web.
The ecotoxicological endpoints included in this evaluation method, with the use of automatic classification of meiofauna, have shown to be strong tools in assessing effects of small scale discharges of petroleum products. This method can be used further to continue evaluating effects of other anthropogenic stressors, commonly ending up in these marine systems.
Keywords: community response, meiofauna, microbial community, petroleum, automatic image analysis, inorganic fluxes, sub-lethal effects, PAH