Seasonal variation in sensitivity of krill to oil

As the present oil and gas activities increase in the high north, so do the potential impacts of produced water and associated oil pollution on marine organisms. Krill are key organisms in temperate and Arctic ecosystems, and constitute an important link in marine food webs. Therefore, it is of vital importance to understand their resilience to oil concentrations typical for PW discharges. We have examined the sensitivity of the Northern krill, Meganyctiphanes norvegica, collected during three seasons to chronic low level oil exposure. Increased mortality of krill has earlier been documented after two weeks exposure to 0.54 mg/L oil (RCN 204023). In SeaSens adult krill (WP1) and krill larvae (WP2) were exposed to two lower oil concentrations (0.01 mg/L and 0.10 mg/L). When oil compounds in the produced water are exposed to solar UV irradiation more toxic compounds can be produced due to photomodification. In the spring experiments with adult krill and early life stages we included a treatment where 0.01 mg/L was exposed to UV light to investigate if photomodification could increase the toxicity of oil concentrations relevant for produced water discharges. WP1. Effects on adult krill. Krill accumulated considerable concentrations of oil components after two weeks exposure to 0.01 mg/L and 0.10 mg/L; 350 and 4400 µg/kg wet weight respectively of alkylated naphthalens and phenanthrenes. The only clear negative effect detected in oil exposed adult krill was that a larger fraction of the krill (27-80%) exhibited digestive gland pathologies (enhanced apoptosis and pathology of digestive tubules) compared to the control (7-13%). We recommend analysis of digestive gland histopathology for monitoring the effects of oil on krill in the field. There were no significant effects of oil on survival, feeding rate, respiration rate, lipid content, fatty acid composition, oxidative stress (MDA: malondialdehyde and AOPP: advanced oxidation protein products) or gene expression of seven selected genes in any of the three experiments with krill collected from the field at different times of the year. WP2. Effects on larvae. Krill embryo and larvae were exposed for 21 days to the same oil treatments as the adult krill. Hatching success, larval development (shifts in ontogenetic stages and size), feeding and individual fatty acid stable carbon isotope signatures were investigated. There were no significant effects of oil on hatching success (ranging from 61-73%), stage development timing (the larvae reached the Calyptopis 1 stage by day 21 in all treatments), length (mean length of the Nauplius 1 og Nauplius 2 ranged from 470-491 µm) and larval survival (ranging from 70?94%). This suggests high resilience for embryo and non-feeding krill larvae to oil concentrations in the range 0.01-0.10 mg/L. In support, similar fatty acid evolution patterns were observed in all treatments with an ontogenetic shift in profiles. However, feeding rates and motility of the final Calyptopis 1 larvae were significantly impaired at 0.10 mg oil/L compared to control conditions. The results show that the feeding larval stage of krill was more sensitive to oil than the early non-feeding life stages. The response of adult and larval krill to 0.01 mg/L oil was the same with or without UV exposure of the oil, indicating that photomodification of oil at the relatively low oil concentrations relevant for produced water discharges may not be a problem. WP3. Oil did not cause increased mortality in WP1 and WP2, hence we rather used results from a previous experiment where shrimp larvae (Pandalus borealis) were exposed to oil as input to the population model. We have assumed that 10 % of the larvae will be chronically exposed to produced water with 0.06 mg/L oil and that 25% of these larvae will die of the exposure like in the shrimp larvae experiment. In earlier projects, we have also tested the effects of ocean warming and ocean acidification and have concluded that the mortality of shrimp larvae will increase at the future climate scenario. In addition, it is likely that the shrimp will experience more frequent recruitment failures in the future because embryo and larvae develop faster and may hatch when food availability is low (mis-match). We have assumed a 50% decrease in recruitment of shrimp larvae in 25% or 50% of the years in the future climate scenarios. The simulation results show that the decrease in recruitment, due to several factors but mainly to climate change, has a stronger impact on the future population (10-30% decrease in abundance) compared to the chronic discharge of produced water (1-5% decrease in abundance). The effects of decreased recruitment and pollution are additive and give a clear decreased abundance in shrimp population in all the scenarios. It is important to be aware that global environmental changes could make marine organisms more vulnerable to local pollution like oil from produced water.

In this project we will study the seasonal variations in krill (Meganyctiphanes norvegica) sensitivity to oil concentrations relevant for produced water (PW) discharges. Krill are key organisms in temperate and Arctic ecosystems, and constitutes an import ant link in marine food webs. Abiotic factors (e.g. temperature and light) and biotic factors (e.g. lipid storage and reproductive status) vary with season and can potentially affect how krill respond to pollutants. These variations may affect accumulatio n of oil components and hence krill plasticity of response and sensitivity to oil. In WP1 adult krill will be collected from the field in all seasons and used for both baseline analysis and oil exposure experiments. Also, method optimization for analysis of biomarkers for future field monitoring of PW discharges will be done. We will look at the seasonal variation in lipid content and composition, gene expression, oxidative stress, histology (gills, digestive gland), respiration, and feeding rate. Accumul ation of oil components (polycyclic aromatic compounds) in tissues of krill will be measured. Field baseline data will be used to interpret biomarker responses in the laboratory. In WP2, we will investigate the sensitivity of early life stages of krill to oil. The results will be compared to the response thresholds measured in adult krill in WP1. For the spring and summer scenarios, we will investigate if photomodification of oil components in PW contributes substantially to krill sensitivity in Northern areas. Data from the experiments in WP1 and WP2 will be used in WP3 for analyzing (environmental) risk assessment scenarios and modeling krill population dynamic under seasonal conditions. This project will provide new insights into the sensitivity and re silience of a keystone species to current PW discharges.