Bivalves as indicators of environmental perturbations related to climate and ocean acidification

The aims of this thesis were to increase knowledge on 1) susceptibility of bivalves to environmental perturbations and 2) usage of bivalve shells as sub-annual environmental proxy archives. These objectives were addressed using two experimental settings: 1) an ocean acidification (OA) experiment on bivalve gametes and early larval stages, and 2) year-long bivalve deployments on oceanographic moorings in two fjords in Svalbard followed by geochemical sampling of bivalve shells. The results indicate that Mytilus larvae are sensitive to ocean acidification, but global warming might have a larger impact on the larvae than acidification. Sperm activity of Mytilus galloprovincialis males was negatively affected by the high-end OA scenarios for the year 2100, possibly indicating a reduced fertilization success in low-density populations. Individual males demonstrated different tolerances of OA indicating that Mytilus populations might have the capacity to adapt to moderate reductions in ocean pH. Shell growth rate of Serripes groenlandicus and Ciliatocardium ciliatum correlated with temperature, and the length of the growth season was likely determined by food availability. Both species deposited a prominent winter growth line, which can be used as an indicator of low food availability. Despite the high potential as sub-annual environmental proxies, interpretation of elemental ratios in Serripes groenlandicus and Ciliatocardium ciliatum shells is complicated by multiple internal and external factors: Li/Ca could partly reflect calcium carbonate crystal growth rate, Mg/Ca was loosely connected with temperature, and Ba/Ca could reflect the elemental ratio in seawater. None of these ratios, however, can be used as straightforward proxies of temperature, salinity, fluorescence or shell growth rate. The insights into sub-annual growth of Arctic bivalves and the methods to align sample spots along chronologically deposited materials, as provided by this thesis, can be used in further proxy development studies

Geographic variation in the life history of lane snapper Lutjanus synagris, with new insights from the warm edge of its distribution

Research on life-history variations in widely distributed fish species is needed to understand global warming impacts on populations and to improve fisheries management advice. The lane snapper Lutjanus synagris (Linnaeus, 1758) is commercially important to fisheries in the Western Central Atlantic, where spread information on its life-history traits is available. We studied growth, age, reproduction and mortality of lane snapper in the Guatemalan Caribbean, the warmest part of its distribution range, and collated the new information with published data in a latitudinal analysis extending between 18°S and 30°N. Longevity was estimated at 11 years, and von Bertalanffy growth parameters were asymptotic length (Linf) 45.6 and 42.2 cm for females and males, respectively, the growth coefficient (K) was 0.1 year−1 and the theoretical age at zero length (t0) was −4.4 years. Lane snapper grew slowest in April, prior to the rainy season, and at the onset of the reproductive season, which lasted from May to October. Fifty percent of female and male lane snappers matured at 23 and 17 cm, corresponding to 3.5 and 2.4 years of age respectively. A regional multivariate analysis found seawater temperature to be an important driver of life-history variation. Lane snapper lifespan was shorter at the warm edge of its distribution range, and maximum size and peak reproductive investment were negatively related to sea surface temperature. The trade-offs in lane snapper life-history traits and phenology likely enhance its fitness to differing environments. Interpolation from the present regional estimates to less-studied regions of the Caribbean is useful for preliminary understanding of reaction norms and harvest potentials

Ice-Associated Amphipods in a Pan-Arctic Scenario of Declining Sea Ice

Sea-ice macrofauna includes ice amphipods and benthic amphipods, as well as mysids. Amphipods are important components of the sympagic food web, which is fuelled by the production of ice algae. Data on the diversity of sea-ice biota have been collected as a part of scientific expeditions over decades, and here we present a pan-Arctic analysis of data on ice-associated amphipods and mysids assimilated over 35 years (1977–2012). The composition of species differed among the 13 locations around the Arctic, with main differences between basins and shelves and also between communities in drift ice and landfast sea ice. The sea ice has been dramatically reduced in extent and thickness during the recorded period, which has resulted in reduced abundance of ice amphipods as well as benthic amphipods in sea ice from the 1980’s to the 2010’s. The decline mainly involved Gammarus wilkitzkii coinciding with the disappearance of much of the multiyear sea ice, which is an important habitat for this long-lived species. Benthic amphipods were most diverse, and also showed a decline over the time-span. They had higher abundance closer to land where they are associated with landfast ice. However, they also occurred in the Central Arctic Ocean, which is likely related to the origin of sea ice over shallow water and subsequent transport in the transpolar ice drift. Recent sampling in the waters east and north of Svalbard has found continued presence of Apherusa glacialis, but almost no G. wilkitzkii. Monitoring by standardized methods is needed to detect further changes in community composition of ice amphipods related to reductions in sea-ice cover and ice type

Tidewater glaciers as “climate refugia” for zooplankton-dependent food web in Kongsfjorden, Svalbard

With climate warming, many tidewater glaciers are retreating. Fresh, sediment-rich sub-glacial meltwater is discharged at the glacier grounding line, where it mixes with deep marine water resulting in an upwelling of a plume visible in front of the glacial wall. Zooplankton may suffer increased mortality within the plume due to osmotic shock when brought in contact with the rising meltwater. The constant replenishment of zooplankton and juvenile fish to the surface areas attracts surface-foraging seabirds. Because access to other feeding areas, such as the marginal ice zone, has become energetically costly due to reduced sea-ice extent, glacial plumes may become increasingly important as “climate refugia” providing enhanced prey availability. Here, we investigated zooplankton concentrations within the plume and adjacent waters of four tidewater glaciers in Kongsfjorden, Svalbard, in early August 2016 and late July 2017. Our aim was to compare the zooplankton composition, abundance, and isotopic signatures within the plumes to those in adjacent fjord and shelf waters. Our hypothesis was that the plumes resulted in increased zooplankton mortality through osmotic shock and increased prey availability to predators. The mortality due to osmotic shock in the glacial plume was low (<5% dead organisms in samples), although slightly higher than in surrounding waters. This indicates that plumes are inefficient “death traps” for zooplankton. However, the high abundance and biomass of zooplankton within plume areas suggest that the “elevator effect” of rising glacial water supplies zooplankton to the sea surface, thereby enhancing prey availability for surface-feeding seabirds. Thus, our study provides evidence that glacial plumes are important as “climate refugia” for foraging seabirds. Stable isotope signatures showed that the glacial bay zooplankton and fish community represent a distinct isotopic niche. Additionally, zooplankton mortality associated with the plume estimated over 100-days of melt season supports a flux of 12.8 tonnes of organic carbon to benthic communities in the glacial bays. Benthic scavengers, such as Onisimus caricus and Anonyx nugax, were abundant in the glacial bay, where they feed on sinking organic matter.publishedVersio

Pan-Arctic suitable habitat model for Greenland halibut

Deep-sea marine fishes support important fisheries but estimates of their distributions are often incomplete as the data behind them may reflect fishing practices, access rights, or political boundaries, rather than actual geographic distributions. We use a simple suitable habitat model based on bottom depth, temperature, and salinity to estimate the potential distribution of Greenland halibut (Reinhardtius hippoglossoides). A large presence-only dataset is examined using multivariate kernel densities to define environmental envelopes, which we link to spatial distribution using a pan-Arctic oceanographic model. Occurrences generally fit the model well, although there were gaps in the predicted circum-Arctic distribution likely due to limited survey activity in many of the ice-covered seas around the Arctic Ocean. Bottom temperature and depth were major factors defining model fit to observations, but other factors, such as ecosystem interactions and larval drift could also influence distribution. Model predictions can be tested by increasing sampling effort in poorly explored regions and by studying the connectivity of putative populations. While abundances of Greenland halibut in the High Arctic are currently low, some areas are predicted to be suitable habitat for this species, suggesting that on-going sea-ice melt may lead to fisheries expansion into new areas

Diet and trophic structure of fishes in the Barents Sea: the Norwegian-Russian program “Year of stomachs” 2015 - establishing a baseline

There is a long history of investigations of fish diet in the Barents Sea. The focus has been on commercially important fish species and their food consumption, while diet and interactions of other fishes have been studied only sporadically. In 2015, a large-scale stomach sampling program was carried out for fish species caught on routine monitoring surveys in the Barents Sea during different seasons of the year, supplemented with samples collected from Russian commercial fisheries. A total of 27,657 stomachs from 70 fish species (including two genera) were analysed, providing a baseline on fish diet in the Barents Sea which can serve as a reference for future studies related to climate change. We summarize methodological aspects and diet composition for the studied species. Cluster analysis grouped the fishes in nine trophic groups based on similarities in diet among fish species, while principal component analyses revealed the position of the species and trophic groups along axes reflecting degrees of piscivory, planktivory, and benthivory. The three most distinctly separated groups were piscivores, a group of benthivores feeding on polychaetes, and planktivores feeding on small crustaceans. The latter could be further split into two groups: fishes of Atlantic origin feeding on copepods and euphausiids, and fishes of Arctic origin feeding on hyperiid amphipods. Warming in the Barents Sea were associated with redistribution of water masses, species and increasing biomass of krill and jellyfish. A boreal Meganyctiphanes norvegica, not observed in the northern Barents Sea before, were found in diet of three Arctic fishes (2% of stomachs only). Gelatinous plankton, mainly Ctenophora, were observed in the diet of 1430 individuals from 15 fish species, including two species which have not been reported to eat gelatinous plankton in the Barents Sea before. This work updates our knowledge about trophic structure and interactions in the Barents Sea, providing a baseline for further investigations.publishedVersio

Population structure discovered in juveniles of Greenland halibut (Reinhardtius hippoglossoides Walbaum, 1792)

Understanding the genetic differentiation among populations of most marine fish requires investigating the differences among spawning grounds. However, this can be challenging as spawning grounds for some species are not well known, or spawning fish are difficult to collect. An alternative is to collect juvenile fish in nursery habitats closely associated with potential spawning grounds. Greenland halibut is a deep-dwelling, commercially important species with at least two identified major offshore spawning grounds in the North Atlantic and weak genetic differentiation across the Atlantic. In this study, we sampled juveniles from three sites representing the Davis Strait spawning area in the northwest Atlantic and one site in the northeast Atlantic representing the primary spawning area along the western slope of the Barents Sea. We applied genotype by sequencing and discovered 90 genetic markers that could be used to assess genetic differentiation among the four sites. The northeast and northwest Atlantic showed major genetic differentiation, supporting the existence of the two primary spawning clusters. Additionally, we found genetic differentiation between the three northwest Atlantic samples implying the existence of more than one spawning area in the northwest.publishedVersio

Consequences of Atlantification on a Zooplanktivorous Arctic Seabird

Global warming, combined with an increasing influence of Atlantic Waters in the European Arctic, are causing a so-called Atlantification of the Arctic. This phenomenon is affecting the plankton biomass and communities with potential consequences for the upper trophic levels. Using long-term data (2005-2020) from a high Arctic zooplanktivorous seabird, the little auk (Alle alle), we tested the hypothesis that the Atlantification affects its diet, body condition and demography. We based our study on data collected in three fjords in West Spitsbergen, Svalbard, characterized by distinct oceanographic conditions. In all three fjords, we found a positive relationship between the inflow of Atlantic Waters and the proportion of Atlantic prey, notably of the copepod Calanus finmarchicus, in the little auk chick diet. A high proportion of Atlantic prey was negatively associated with adult body mass (though the effect size was small) and with chick survival (only in one fjord where chick survival until 21 days was available). We also found a negative and marginally significant effect of the average proportion of Atlantic prey in the chick diet on chick growth rate (data were available for one fjord only). Our results suggest that there are fitness costs for the little auk associated with the Atlantification of West Spitsbergen fjords. These costs seem especially pronounced during the late phase of the chick rearing period, when the energetic needs of the chicks are the highest. Consequently, even if little auks can partly adapt their foraging behaviour to changing environmental conditions, they are negatively affected by the ongoing changes in the Arctic marine ecosystems. These results stress the importance of long-term monitoring data in the Arctic to improve our understanding of the ongoing Atlantification and highlight the relevance of using seabirds as indicators of environmental change.publishedVersio

Advice on fishing opportunities for Northeast arctic haddock in 2024 in ICES subareas 1 and 2

Stock Name: Northeast Arctic haddock (ICES areas 1 and 2) The Joint Russian-Norwegian Arctic Fisheries Working Group (JRN-AFWG) advises that when the Joint Norwegian–Russian Fisheries Commission management plan is applied, catches in 2024 should be no more than 127 550 tonnes.publishedVersio