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In the brackish water Baltic Sea, oil pollution is an ever-present and significant environmental threat mainly due to the continuously increasing volume of oil transport in the area. In this study, effects of exposure to crude oil on two common Baltic Sea species, the mussel Mytilus trossulus and the amphipod Gammarus oceanicus, were investigated. The species were exposed for various time periods (M. trossulus 4, 7, and 14 days, G. oceanicus 4 and 11 days) to three oil concentrations (0.003, 0.04, and 0.30 mg L−1 based on water measurements, nominally aimed at 0.015, 0.120, and 0.750 mg L−1) obtained by mechanical dispersion (oil droplets). Biological effects of oil exposure were examined using a battery of biomarkers consisting of enzymes of the antioxidant defense system (ADS), lipid peroxidation, phase II detoxification (glutathione S-transferase), neurotoxicity (acetylcholinesterase inhibition), and geno- and cytotoxicity (micronuclei and other nuclear deformities). In mussels, the results on biomarker responses were examined in connection with data on the tissue accumulation of polycyclic aromatic hydrocarbons (PAH). In M. trossulus, during the first 4 days of exposure the accumulation of all PAHs in the two highest exposure concentrations was high and was thereafter reduced significantly. Significant increase in ADS responses was observed in M. trossulus at 4 and 7 days of exposure. At day 14, significantly elevated levels of geno- and cytotoxicity were detected in mussels. In G. oceanicus, the ADS responses followed a similar pattern to those recorded in M. trossulus at day 4; however, in G. oceanicus, the elevated ADS response was still maintained at day 11. Conclusively, the results obtained show marked biomarker responses in both study species under conceivable, environmentally realistic oil-in-seawater concentrations during an oil spill, and in mussels, they are related to the observed tissue accumulation of oil-derived compounds.

Gammarid amphipods are a crucial link connecting primary producers with secondary consumers, but little is known about their nutritional ecology. Here we asked how starvation and subsequent feeding on different nutritional quality algae influences fatty acid retention, compound-specific isotopic carbon fractionation, and biosynthesis of omega-3 and omega-6 polyunsaturated fatty acids (PUFA) in the relict gammarid amphipod Pallaseopsis quadrispinosa. The fatty acid profiles of P. quadrispinosa closely matched with those of the dietary green algae after only seven days of refeeding, whereas fatty acid patterns of P. quadrispinosa were less consistent with those of the diatom diet. This was mainly due to P. quadrispinosa suffering energy limitation in the diatom treatment which initiated the metabolization of 16:1 omega 7 and partly 18:1 omega 9 for energy, but retained high levels of eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA) similar to those found in wild-caught organisms. Moreover, alpha-linolenic acid (ALA) from green algae was mainly stored and not allocated to membranes at high levels nor biosynthesized to EPA. The arachidonic acid (ARA) content in membrane was much lower than EPA and P. quadrispinosa was able to biosynthesize long-chain omega-6 PUFA from linoleic acid (LA). Our experiment revealed that diet quality has a great impact on fatty acid biosynthesis, retention and turnover in this consumer.

Qvenild T, Fjeld E, Fjellheim A, Hammar J, Hesthagen T and Lakka H-K. 2021. Upper thermal threshold of Lepidurus arcticus (Branchiopoda, Notostraca) in lakes on the southern outreach of its distribution range. Fauna norvegica 41: 50–88. The Arctic tadpole shrimp Lepidurus arcticus has a circumpolar distribution and the Scandes (Fennoscandian Mountains) marks its southernmost limit in Europe. Within this area, 391 natural and 88 regulated lakes with L. arcticus have been identified, of which 87% are above the treeline. The lakes hosting L. arcticus decrease in altitude from south to north, which results from its temperature preferences. The majority of the locations are at a lower lake air temperature than 11°C which is equivalent to a water temperature near 14°C. This is assumed to be near the upper thermal threshold for L. arcticus. In lakes that exceed this average summer water temperature (1 July – 15 September), sustainable populations seem to be rare. In warmer lakes, life cycle mismatches are assumed to explain the absence of L. arcticus, most likely by affecting the embryo and juvenile stages. The distribution appears to be dichotomous, with one large northern area north of 65°N and one separated southern “island”. Only two locations of L. arcticus are known for the area between latitudes 62.88 and 64.39°N. In this part of the Scandes, the lakes are likely too warm to host L. arcticus as most of them are situated below 700 m a.s.l. This may also be the case in the northernmost region, north of 70°N, where only 11 populations are recorded. Most of the lakes in this area typically occurs below 400 m a.s.l. L. arcticus populations are sensitive to fish predation, and dense fish populations may be another stressor limiting its distribution. In contrast to water bodies in the High Arctic where L. arcticus only exists in shallow, fishless ponds, in the Scandes they co-exist with fish in 97% of the findings. Global warming has already modified the environment of the Scandes, and populations of L. arcticus are at threat in many of the small and shallow water bodies at low altitudes.

Lepidurus arcticus (the Arctic tadpole shrimp) is a vulnerable keystone species in Arctic and alpine water bodies where its occurrence and population size may influence the viability and life history traits of resident salmonids. Using data from a Norwegian mountain hydropower reservoir, Aursjoen, we illustrate how reduced availability of L. arcticus as prey resulted in the reduced condition, growth and delayed maturation of resident brown trout (Salmo trutta). We further link changes in the relative abundance of L. arcticus as prey to changing reservoir conditions, e.g. water level changes in the spring period, thereby establishing an indirect link between reservoir operation regimes and brown trout population traits. While no evidence for decreased brown trout survival was found, the results indicate that alternative brown trout prey resources, i.e. the small chydorid cladoceran Eurycercus lamellatus, do not appear to have successfully offset the caloric loss from reduced consumption of large-sized L. arcticus. Although the fundamental explanation for the observed L. arcticus collapse remains largely unknown, the present findings provide strong evidence that this vulnerable crustacean species can affect the abundance, viability and life history traits of valued resident salmonid populations in oligotrophic alpine lakes and reservoirs exposed to climate- and hydropower-driven changes in water levels and temperature. peerReviewed

This is a post-peer-review, pre-copyedit version of an article published in Hydrobiologia. The final authenticated version is available online at https://doi.org/10.1007/s10750-019-3953-4. Niche diversification of polymorphic Arctic charr can be altered by multiple anthropogenic stressors. The opossum-shrimp (Mysis relicta) was introduced to compensate for reduced food resources for fish following hydropower operations in Lake Limingen, central Norway. Based on habitat use, stomach contents, stable isotopes (δ13C, δ15N) and trophically transmitted parasites, the zooplanktivorous upper water-column dwelling ‘normal’ morph was clearly trophically separated from two sympatric deep-water morphs (the ‘dwarf’ and the ‘grey’) that became more abundant with depth (> 30 m). Mysis dominated (50–60%) charr diets in deeper waters (> 30 m), irrespective of morph. Mysis and/or zooplankton prey groups caused high dietary overlap (> 54%) between the ‘dwarf’ morph and the two other ‘normal’ and ‘grey’ morphs. After excluding Mysis, the dietary overlap dropped to 34% between the two profundal morphs, as the ‘dwarf’ fed largely on deep-water zoobenthos (39%), while the ‘grey’ morph fed on fish (59%). The time-integrated trophic niche tracers (trophically transmitted parasites and stable isotopes) demonstrated only partial dietary segregation between the two deep-water morphs. The high importance of Mysis in Arctic charr diets may have reduced the ancestral niche segregation between the deep-water morphs and thereby increased their resource competition and potential risk of hybridization.

Ecology of the glacial relict macrocrustacean Gammaracanthus lacustris, a rare inhabitant of deep Fennoscandian lakes, is poorly understood. We studied the life cycle and trophic position of this cold‐stenothermic amphipod in Lake Paasivesi, eastern Finland. The study is based on intensive sampling and analyses of fatty acid composition as well as stable carbon (δ13C) and nitrogen (δ15N) isotope ratios. Both day and night, the G. lacustris population occurred at depths below 25 m at temperatures 40 mm and live up to 4 years. The oldest and the largest individuals and females seemed to favour the deepest zones. In October, almost 100% of females with length at least 25 mm (i.e. females presumably at least 1‐year‐old) had an embryo sack with 20–200 eggs or embryos—the larger the female, the more young it had. The developing eggs of G. lacustris had a very high fatty acid content, indicating that the females invest heavily on provisioning their young. Furthermore, the fatty acid composition differed among life stages, and in particular the eggs had a higher proportion of eicosapentaenoic acid than juveniles or adults. The stable δ13C and δ15N isotope ratios and fatty acid biomarkers of the food web, together with visual observations, indicate that G. lacustris is a carnivore that feeds mainly on zooplankton and other relict macrocrustaceans. Due to its high content of essential polyunsaturated fatty acids, G. lacustris is a valuable prey for fish and other predators in the food web. However, as a glacial relict with strict habitat requirements the species is vulnerable to global warming and local environmental changes. These facts should be considered in the management of lakes and their catchments. peerReviewed

Reliktisten makroäyriäisten elintapoja on tutkittu maailmanlaajuisestikin hämmästyttävän vähän eikä etenkään elinympäristönsä suhteen vaativana pidetystä jättikatkasta (Gammaracanthus lacustris) ole tehty julkaisuja juuri lainkaan. Tutkimuksen tavoitteena oli selvittää lajin syvyyskohtaisia koko-, tiheys- ja sukupuolijakaumia sekä eri vuosien ja alueiden välisiä eroja Saimaan Paasivedellä. Lokakuussa 2006 – 2008 30 m alapuolisista vesikerroksista otetuista näytteistä saatiin samalla tietoa myös jäännehalkoisjalkaisen (Mysis relicta) vertikaalijakaumista samoissa olosuhteissa. Myös oka- (Pallaseopsis quadrispinosa) ja valkokatkaa (Monoporeia affinis) tavattiin joitakin yksilöitä. Mahdollisesti jopa neljävuotiaaksi elävän jättikatkan havaittiin suosivan syvimpiä vesikerroksia, sillä keskitiheys kasvoi tasaisesti syvemmälle mentäessä. Myös pituuden ja syvyyden välillä oli positiivinen yhteys, eli erityisesti vanhemmat yksilöt viihtyvät syvemmällä. Syvältä (50 – 60 m) saadut jättikatkat olivat lisäksi useammin naaraita, ja kantavan naaraan alkioiden lukumäärä kasvoi yksilön pituuden myötä. Jättikatkojen pituuksissa ja tiheyksissä oli selviä vuosien välisiä eroja: erityisesti vuonna 2006 jättikatkat olivat monilla syvyyksillä kookkaampia ja niiden tiheys oli suurempi kuin vertailuvuosina. Alueiden väliset erot olivat sen sijaan lähes olemattomia. Kaikkiaan Paasiveden alueella elää arviolta 90 000 000 jättikatkaa. Myös jäännehalkoisjalkaisten isokokoisimmat yksilöt näyttävät viihtyvän syvemmällä kuin nuoremmat, sillä yksilöpituus korreloi positiivisesti syvyyteen. Sen sijaan keskitiheys oli suurimmillaan matalimmissa tutkimussyvyyksissä (30 – 35 m), ja tiheyden ja syvyyden välinen korrelaatio olikin negatiivinen. Vuosien välisiä eroja havaittiin keskipituudessa, joka oli vuonna 2006 lähes jokaisessa syvyysvyöhykkeessä suurempi kuin muina vuosina. Alueiden välisiä merkitseviä eroja ei jäännehalkoisjalkaistenkaan keskitiheyksissä tai -pituuksissa ollut.

Teimme elokuussa 2019 kauan suunnitellun ja unelmoidun retken Käsivarren Lappiin. Tarkoituksena oli käydä etsimässä ja kartoittamassa Lapin uhanalaisia ja vähän havainnoituja äyriäis- ja nilviäislajeja perustuen osin hyvin vanhoihinkin havaintoihin. Hanna-Kaisa Lakka on kartoittanut Enontekiön äyriäispopulaatioita ja niiden ympäristövaatimuksia jo vuodesta 2012 alkaen. Hannu Ormio on kartoitellut nilviäisiä Kilpisjärven ympäristössä vuonna 2011 ja Katriina Könönen on havainnut ensimmäisen lehtijalkaisäyriäisensä 1990-luvulla yliopiston tunturivesikurssilla ja myöhemmin muutamia havaintoja on kertynyt myös kesäisillä lomareissuilla. Yövyimme Kilpisjärven asemalla ja kartoitimme lähialueen lajistoa Mallan luonnonpuistossa ja Saanalla muutaman päivän ajan. nonPeerReviewed

This paper provides an overview of stable isotope analysis (H, C, N, O, Si) of the macro- and microscopic remains from aquatic organisms found in lake sediment records and their application in (palaeo)environmental science. Aquatic organisms, including diatoms, macrophytes, invertebrates, and fish, can produce sufficiently robust remains that preserve well as fossils and can be identified in lake sediment records. Stable isotope analyses of these remains can then provide valuable insights into habitat-specific biogeochemistry, feeding ecology, but also on climatic and hydrological changes in and around lakes. Since these analyses focus on the remains of known and identified organisms, they can provide more specific and detailed information on past ecosystem, food web and environmental changes affecting different compartments of lake ecosystems than analyses on bulk sedimentary organic matter or carbonate samples. We review applications of these types of analyses in palaeoclimatology, palaeohydrology, and palaeoecology. Interpretation of the environmental ‘signal’ provided by taxon-specific stable isotope analysis requires a thorough understanding of the ecology and phenology of the organism groups involved. Growth, metabolism, diet, feeding strategy, migration, taphonomy and several other processes can lead to isotope fractionation or otherwise influence the stable isotope signatures of the remains from aquatic organisms. This paper includes a review of the (modern) calibration, culturing and modelling studies used to quantify the extent to which these factors influence stable isotope values and provides an outlook for future research and methodological developments for the different examined fossil groups. peerReviewed