The effects of environmental changes on contaminant fate in the ecosystem are poorly understood, even in the otherwise well-studied Baltic Sea. This area is considered one of the most polluted in the world and is currently undergoing rapid shifts related to climate change and eutrophication. In this study, we focus on the effects of an altered productivity base and changes in food web structure on contaminant concentrations in the commercially important Baltic herring, which is also a key-species in the ecosystem. In herring of known size and age, collected within the Swedish National Monitoring Program for Contaminants in Marine Biota during the past two to three decades, retrospective analyses of contaminant concentrations and stable isotopes of carbon and nitrogen including amino acid-specific isotope analyses were performed. Partial least squares regression (PLSR) models were applied to dioxins, PCBs, and mercury time series to examine how biological, ecological, and environmental factors (i.e., age, trophic diversity and position, temperature, salinity, proxies of cyanobacterial blooms and ultimate nutrient sources, abundance of relevant benthic fauna as well as biomass and size structure of the zooplankton community) contribute in explaining contaminant concentrations in herring, beyond atmospheric deposition (the main contaminant input in the Central Baltic basin). Our results emphasize that the contaminant burden in Baltic herring is significantly influenced by factors other than atmospheric deposition. Primarily, changes in herring’s trophic ecology, together with nitrogen-fixing cyanobacterial blooms (supporting both growth biodilution and bloom-induced dilution), were linked to dioxin, PCB, and mercury concentrations in fish. Our results support the need to consider all potential ecological synergies and linkages when managing a rapidly changing system such as the Baltic Sea, in order to minimize noxious blooms without compromising the positive impact on contaminant concentrations in fish.

Nitrogen-fixing cyanobacterial blooms worldwide have been shown to support production in primary consumers such as zooplankton and benthic invertebrates, but there have been few estimates on how much of the cyanobacterial nitrogen ends up in secondary consumers, such as fish. Using compound specific analysis of δ¹⁵N in amino acids (CSIA-AA), we have investigated if cyanobacterially fixed (diazotrophic) nitrogen (N) can be traced in higher trophic level organisms such as zooplankton and mysids, and observed in juvenile Atlantic herring (Clupea harengus). At the eutrophied station, the biovolume of N fixing cyanobacteria was higher than at the reference station and the autotrophic population was comprised of a higher proportion of cyanobacteria palatable to zooplankton. The δ¹⁵N ‰ of source amino acids in juvenile herring significantly decreased over the season at the eutrophied station. Bayesian mixing models were used to calculate the percent of diazotrophically-fixed N found in herring muscle tissue in relation to pre-bloom N, and results showed that herring at the eutrophied station had a higher percent (~34 %) of diazotrophically-fixed N in their muscle tissue than fish at the reference station (~18%). A significant relationship was found between the percentage diazotrophically-fixed N in herring muscle tissue and the biovolume of N fixing cyanobacteria in the environment two months prior to the capture date of the fish. This study adds to the mounting evidence that cyanobacteria blooms, a global occurrence, support production at higher trophic levels, including fish.

Den marina miljöövervakningens betydelse för vår kunskap om haven och för samhällets havsmiljöarbete kan inte nog poängteras. Övervakningens långa tidsserier av miljödata gör det möjligt både att förstå hur havet fungerar och att upptäcka förändringar i havsmiljön. Båda är viktiga förutsättningar för att Sverige ska kunna bedriva en vetenskapligt baserad och kostnadseffektiv havspolitik.

Det samordnade recipientkontroll-programmet vid Oxelösundskusten omfattar vattenkemiska analyser (näringsämnen, klorofyll, siktdjup, salthalt), bottenfauna, samt provtagning av sediment, fisk och blåmussla för metaller och PAH:er. Den här rapporten redovisar bottenfauna insamlad 2024 samt två pilotförsök för att undersöka miljöeffekter av förorenat sediment som genomförts under 2023–2024. Övriga parametrar i det samordnade recipientkontroll-programmet presenteras i Walve och Raymond (2024).

Bottenfaunan visar god status för området när det utvärderas med det bentiska kvalitetsindexet BQI. Undersökningar har genomförts fem gånger seden 2006 och vid dessa tillfällen nådde området upp till god status vid alla undersökningar. Däremot visar en undersökning från 1982 att området då endast nådde upp till måttlig status och att faunan var generellt utarmad. Idag är mångfalden och individtätheten betydligt bättre.

Trots att bottenfaunan visar på god status hittas höga halter av metaller och PAH:er i sedimentet. Två pilotförsök har därför genomförts under 2023–2024 för att undersöka miljöeffekter av förorenat sediment. I båda försöken har sediment samlats in i en gradientstudie, där två stationer uppvisar förhöjda miljögifter i sediment och två stationer utgör referens-områden (Dragviksfjärden och Askö).

I det första försöket tillsattes 15 gravida vitmärlor Monoporeia affinis till sedimentproppar från de fyra stationerna. Efter 7 veckors exponering studerades överlevnaden, antal gravida honor, fekunditet per hona, missbildade embryon och döda/outvecklade embryon. Den mest förorenade stationen SS1 närmast SSAB:s verksamhet uppvisade lägre överlevnad, även om skillnaden inte var statistiskt säkerställd, men framför allt färre rekryteringar av nya individer.

I det andra försöket tillsattes 5 uppodlade märlkräftor Hyalella azteca till provburkar med sediment från samma fyra gradientstationer som vitmärlorna exponerades för. Efter 7 dagar analyserades biomarkörer som RNA/DNA-kvot för indirekt tillväxt, ORAC för oxidativ status samt AChE för neuro-toxicitet. På den mest förorenade stationen SS1 förekom hög andel avvikande RNA/DNA-kvoter och AChE-aktivitet samt måttlig ORAC-status. Den referensstation, Askö, där vitmärlorna till reproduktionsförsöket samlades in, visade också på biomarkör-effekter vilket antyder att vitmärlorna redan var påverkade av föroreningar när de samlades in till försöket. 

Undersökningen har beställts av SSAB Oxelösund och utförts av det Marinekologiska laboratoriet (MEL) vid institutionen för ekologi, miljö och botanik på Stockholms universitet (SU) med biomarköranalyser utförda vid institutionen för miljövetenskap vid SU .

Cyanobacterial blooms are intensifying worldwide due to eutrophication and climate change, increasing cyanotoxin exposure to aquatic organisms. This study investigated the physiological, biochemical, and behavioural impacts of cyanobacterial blooms on the three-spined stickleback (Gasterosteus aculeatus), a widespread mesopredatory fish. Adult sticklebacks were exposed for two weeks to naturally collected bloom material dominated by toxic Nodularia spumigena, non-toxic Aphanizomenon sp., or a 50:50 mix. We measured toxin accumulation (NOD_eq), hepatic enzymatic activities (ethoxyresorufin-O-deethylase [EROD], glutathione S-transferases [GSTs], glutathione reductase [GR], and catalase [CAT]), and escape swimming performance (centre-of-mass velocity, angular velocity, distance, and duration) in a multiparametric endpoints approach. Sub-lethal toxin levels in muscle tissue ranged from 0.006 to 0.077 µg g⁻¹ d.w. Results showed that fish exposed to toxic-dominated treatments showed significantly elevated EROD activity (up to 200 % increase), moderate increases in GR and GSTs, and reduced CAT activity compared to controls. Notably, distance travelled during escape responses was reduced by ∼50 % in the high-toxicity treatment and showed an inverse correlation with EROD activity, suggesting a trade-off between detoxification effort and swimming performance. Overall, our results demonstrate that EROD is a sensitive biomarker for cyanotoxin exposure in fish under natural bloom conditions. This finding highlights the need to consider natural cyanotoxin effects when interpreting environmental assessments, particularly given the projected increase in bloom frequency and severity under future climate scenarios.

Anthropogenic pressures are increasing in coastal ecosystems globally, yet identifying robust indicators of change and managing coastal resources can be complicated by phenotypic plasticity and differential life-history responses of key organisms. We illustrate this using biogeochemical and sandprawn (Kraussillichirus kraussi) response metrics along a human recreation gradient (trampling, sandprawn harvesting) in a South African lagoonal ecosystem. Benthic compaction, oxygen depletion and high porewater ammonia concentrations were associated with greatest recreation intensity. Sandprawn abundance was similar across the recreation gradient and body condition was counter-intuitively greater in areas with maximum recreation, but with higher frequencies of embryonic aberrations and arrested development. These findings suggest different vulnerabilities of life-history stages of sandprawns to recreation, with embryonic stages being highly susceptible. We suggest that embryonic aberrations and developmental changes in endobenthic crustaceans may be sensitive bioindicators of recreation-induced changes in sedimentary systems.

Understanding how key-species respond to anthropogenic stress such as chemical pollution is critical for predicting ecosystem changes. Little is however known about the intra-specific variability in the physiological and biochemical traits involved in contaminant exposure responses. Here, we explored this idea by exposing the Baltic amphipod Monoporeia affinis from two sites, one moderately polluted and one more pristine, to a sediment spiked with PAHs and PCBs. We evaluated the amphipods responses related to feeding, growth, a stress biomarker (acetylcholinesterase [AChE] inhibition) and stable isotope (delta C-13 and delta N-15) composition including isotope niche analyses. More adverse responses were expected in animals from the low-pollution site than those from the high-pollution site due to tolerance development in the latter. Amphipods from both populations showed a similar to 30% AChE inhibition when exposed to the contaminant spiked sediment. However, both controls and exposed amphipods from the high-pollution site had higher survival, nutrient uptake and condition status than the amphipods from the low-pollution site, which did not feed on the added diatoms as indicated by their isotope values. We found no signs of population-specific responses in physiological adjustments to contaminants with regard to classic ecotoxicological biomarkers such as AChE inhibition and growth status. Instead, isotope niche analyses proved useful in assessing contaminant stress responses at the population level.

Nitrogen isotope analyses of amino acids (δ15N-AA) are being increasingly used to decipher trophic dynamics. Interpretation of δ15N-AA in consumers relies on the assumption that consumer physiological status and nutritional status of prey have negligible influences on the trophic discrimination factor (TDF), hence a constant TDF value is used in trophic position (TP) equations. Recent experiments have shown that this is not always the case and there is also a need to validate derived TP estimates in the field. We take advantage of the uniquely long time series of environmental monitoring data and archived (frozen) samples from the species-poor Baltic Sea. We analyzed δ15N-AA in similar sized individuals of cod and in its prey herring from four decades, 1980–2018; including time periods where dramatic reduction in condition status of cod has occurred. We expected that TDF in trophic AAs would increase during periods of poor cod condition, resulting in inflated TP estimates. We found that calculated TP and empirical estimates of TDF (difference in δ15N in trophic AAs between cod and herring) for cod increased in recent decades and that this was linked to condition status, herring (prey) lipid content and the hypoxic state of the ecosystem. Statistically adjusting TP for condition and prey lipid content as well as environmental stress (hypoxia) resulted in lower cod TP which better resembled the observed decrease in herring TP in recent decades. TP calculated from stomach analysis data in cod individuals over the same period showed no trend over time and confirmed that adjusted TP estimates mirror the real dietary TP better than unadjusted. By simultaneously measuring condition/nutritional status in both predator and prey it is possible to adjust for them as confounding variables and decipher actual consumer TP, partly overcoming the issues of unknown and variable TDF-values. Our study also highlights the importance of including environmental stressors (here hypoxia) when interpreting TP and reconstructing food webs.

Benthic macrofauna modifies carbon and nutrient retention and recycling processes in coastal habitats. However, the contribution of benthic consumers to carbon and nutrient storage and recycling shows variation over spatial scales, as the benthic community composition changes in response to differences in environmental conditions. By sampling both shallow sandy and deep muddy sediments across a land-to-sea gradient in the northern Baltic Sea, we explored if benthic community composition, stoichiometry and process rates change in response to alterations in environmental conditions and food sources. Our results show that benthic faunal biomass, C, N, and P stocks, respiration rate and secondary production increase across the land-to-sea gradient in response to higher resource quality towards the open sea. The seston δ¹³C indicated terrestrial runoff and δ¹⁵N sewage input at the innermost study sites, whereas more fresh marine organic matter towards the open sea boosted benthic faunal carbon storage, respiration rate, and secondary production, that is, the generation of consumer biomass, which are essential processes for carbon turnover in this coastal ecosystem. Also, biological factors such as increasing species richness and decreasing biomass dominance of the clam Macoma balthica were significant in predicting benthic faunal C, N, and P stocks and process rates, especially at sandy sites. Interestingly, despite the variation in food sources, the benthic faunal C:N:P ratios remained stable across the gradient. Our results prove that human activities in the coastal area can influence the important links between biodiversity, structure, and process rates of benthic communities by modifying the balance of available resources, therefore hampering the functioning of coastal ecosystems.

Invasive species are often generalists that can take advantage of formerly unexploited resources. The existence of such vacant niches is more likely in species-poor systems like the Baltic Sea. The suspension feeding wedge clam, Rangia cuneata, native to estuarine environments in the Gulf of Mexico, was sighted for the first time in the southeastern Baltic in 2010 and a few years later in the northern Baltic along the Swedish coast. To explore possible competition for food resources between R. cuneata and the three native clams inhabiting Baltic shallow soft bottoms, stable isotope and fatty acid analyses were conducted. There was no overlap between R. cuneata and any of the native species in either stable isotope or fatty acid niches. This suggests efficient partitioning of resources; multivariate analyses indicate that separation was driven mainly by δ¹³C and by fatty acids reflecting diatoms and cyanobacteria, respectively (e.g. 16:1ω7 and 18:3ω3). R. cuneata reflected seasonal variation in phytoplankton more than other clams reflecting higher trophic plasticity. In conclusion, the addition of R. cuneata to the Baltic shallow soft bottoms suggests the existence of a vacant trophic niche in these sediment habitats, however the long-term effects on other species and nutrient cycling requires further studies focusing on the population dynamics of R. cuneata and its impact on the Baltic Sea ecosystem.