Arctic coastal benthos long-term responses to perturbations under climate warming.

Climate warming influences structure and function of Arctic benthic ecosystems. Assessing the response of these systems to perturbations requires long-term studies addressing key ecological processes related to recolonization and succession of species. Based on unique time-series (1980-2017), this study addresses successional patterns of hard-bottom benthos in two fjords in NW Svalbard after a pulse perturbation in 1980 and during a period of rapid climate warming. Analysis of seafloor photographs revealed different return rates of taxa, and variability in species densities, through time. It took 13 and 24 years for the community compositions of cleared and control transects to converge in the two fjords. Nearly two decades after the study initiation, an increase in filamentous and foliose macroalgae was observed with a subsequent reorganization in the invertebrate community. Trait analyses showed a decrease in body size and longevity of taxa in response to the pulse perturbation and a shift towards small/medium size and intermediate longevity following the macroalgae takeover. The observed slow recovery rates and abrupt shifts in community structure document the vulnerability of Arctic coastal ecosystems to perturbations and continued effects of climate warming. This article is part of the theme issue 'The changing Arctic Ocean: consequences for biological communities, biogeochemical processes and ecosystem functioning'.

Tissue-specific contaminant accumulation and associated effects on hepatic serum analytes and cytochrome P450 enzyme activities in hooded seals (Cystophora cristata) from the Gulf of St. Lawrence.

The current study aims to assess contaminant levels and tissue burdens in hooded seal (Cystophora cristata) blubber, liver, and blood in association with cytochrome P450 (CYP) enzymes (CYP1A and -3A) and serum analytes (hepatic enzymes like alanine aminotransferase [ALT], aspartate aminotransferase, alkaline phosphatase [AP], and gamma-glutamyltransferase [GGT], serum proteins, and creatine kinase). Contaminant accumulation levels and patterns of polychlorinated biphenyls, chlorinated pesticides, and polybrominated diphenyl ethers (PBDEs) differed between tissues and seal groups, with the highest levels in liver. Pups showed higher liver contaminant levels, especially for PBDEs, than adults. These high levels might be associated with the ingestion of large amounts of contaminated milk and subsequent accumulation in the liver. Adult males and females mainly differed in PBDE levels, which were higher in females, possibly due to a sex-specific diet. The association between blubber contaminant burdens and the diagnostic enzymes ALT, GGT, and AP, and serum albumin, was inconclusive. In contrast, several CYP isoenzymes showed a clear positive relationship with the overall blubber contaminant burden, indicating enzyme induction following exposure to polyhalogenated hydrocarbons. Therefore, liver CYP isoenzymes may serve as a sensitive biomarker for long-term exposure to polyhalogenated hydrocarbons.

Diversity and structure of Chironomidae (Diptera) communities along a gradient of heavy metal contamination in a subarctic watercourse.

Community structure of chironomid larvae was investigated along a gradient of heavy metal pollution in the subarctic lakes of the Pasvik watercourse, bordering Northern Norway and Russia. Sixty taxa were present in the four investigated lakes. Species richness was lower in Lake Kuetsjarvi, nearest the main source of pollution, relative to the more distant lakes, and Simpson's diversity index was similarly highest in the less polluted site with higher maximum depth. The number of orthoclad chironomid species was considerably higher at the least contaminated sites, whereas the relative abundance of Orthocladiinae was highest at the most polluted site. Chironomid density increased with increasing distance from the main source of heavy metal pollution, especially in the subfamilies Tanypodinae and Chironominae, and total chironomid biomass was significantly higher at the least polluted site. Canonical correspondence analysis revealed spatial patterns consistent with species-specific tolerance to the heavy metal concentrations. Protanypus morio, Monodiamesa bathyphila, Chironomus spp., Polypedilum scalaenum gr. and Sergentia coracina seemed to be tolerant to heavy metal contamination, occurring most commonly at the most polluted sites. In contrast, Heterotrissocladius subpilosus, Psectrocladius semicirculatus/sp., Chironomus anthracinus, Pagastiella orophila, Cladotanytarsus iucundus, and Tanytarsus spp. appeared to be more sensitive taxa, being common at the least polluted sites, but rare or absent at the two sites close to the pollution sources. Densities of Procladius (Holotanypus) spp., Tanytarsus spp. and Chironomus anthracinus were negatively correlated with heavy metal concentrations and these taxa appeared to be the best indicators of heavy metal contamination.