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Chronic oil pollution related to gas and oil drilling activities is increasing in the sea due to the rising offshore petroleum industry activity. Among marine organisms, zooplankton play a crucial role in the marine ecosystem and therefore understanding the effects of crude oil chronic exposure on zooplankton is needed to determine the impact of oil in marine environments. The present study reports on the effect of crude oil on adult northern krill, Meganyctiphanes norvegica, collected during three seasons. Their sensitivity to oil was examined with oil concentration of 0.01 versus 0.1 mg oil L− 1 and photo-modified oil in flowing seawater maintained in the dark for 2 weeks at in situ temperature. Oil (polycyclic aromatic hydrocarbons, PAHs) entered the krill (on average, 350 and 4400 μg·kg− 1 wet weight in low and medium oil treatments respectively) and a larger fraction of the krill exhibited digestive gland pathologies (enhanced apoptosis and pathology of digestive tubules) in oil treatments (27–80%) compared to a significantly lower fraction (7–13%) in treatments that received no oil. However, 2-week oil exposure at these concentrations did not significantly decrease survivorship or impair basic functioning such as feeding and respiration rates. Similarly, there were only limited changes in the transcription of 7 selected genes from head tissue. Additionally, although there was significant seasonal variation in krill total lipid content and fatty acid composition, there was no treatment effect on both these parameters, which suggests limited oxidative stress under experimental conditions. Furthermore, there was no significant treatment effect on two direct measures of oxidative stress (MDA: malondialdehyde and AOPP: advanced oxidation protein products) in any of the seasons. Nevertheless, histology clearly revealed enhanced digestive gland pathologies in krill even at low concentrations. Although krill with such pathologies continue to survive, their accumulation of PAHs may be transferred up the food chain, impacting their predators and the wider ecosystem.

Analyses of the benthic foraminifera encountered in a piston core and box core collected from the Frisian Front area in the southern North Sea (53°42'N, 4°30'E) revealed that subtidal conditions began at ∼6240 B.P. No large scale changes were observed in the foraminiferal compositions since then, but distinct variation in their densities occurred. Lateral transport from the south is effective, as implied by the presence of reworked Cretaceous foraminifera; there is very little long-term Recent sediment accumulation in this area. Fluctuation in the Holocene foraminiferal densities reflects both the variation in local production of tests and the supply of tests from the south.

Densities of living (stained) benthic foraminifera in the southern North Sea were found to be enriched in areas with high organic carbon content. Enriched densities were not restricted to the surface sediment (0–1 cm) but also extended into deeper layers (down to 25 cm). Foraminiferal populations were larger in June than in February. This will be caused by a spring increase in temperature and organic carbon input. This seasonal effect is also clearly reflected in the deeper layers. There is no well-defined depth stratification of species within the sediment, their vertical distribution being governed primarily by the burrowing activities of macrofauna. Therefore, the maximum depth at which living benthic foraminifera are encountered can be used as an indicator of bioturbation depth.

During culture experiments of various calcareous foraminiferal species, an unidentified heteromorphic, monothalamous, soft-shelled foraminiferid, without any agglutinated matter was observed to feed and increase in size. When offered empty quinqueloculine tests, it rapidly crawled into one and appeared as a typical livingQuinqueloculina specimen with extended pseudopodia. Apart from being another microhabitat of foraminifera, this would add to the problems associated with the use of protoplasmic stains in distinguishing living specimens of benthic foraminifera from dead, empty shells and emphasizes the need to exercise extreme caution in order to avoid misinterpretations of “living” assemblages, which have consequences for the paleoecological interpretation of fossil assemblages.