State of the Arctic - Zooplankton in a changing Arctic
- 11:00 Spatial distribution of zooplankton communities in response to riverine terrestrial inputs in Isfjorden, Svalbard
Authors: Emilie Hernes Vereide ( University of Oslo ); Dag O. Hessen ( University of Oslo ); Eva Leu ( Akvaplan-niva ); Janne E. Søreide ( The University Centre in Svalbard ); Maeve McGovern ( Norwegian Institute for Water Research )
Svalbard fjords are characterized by a strong stratification as warm Atlantic water meets cooler and less saline water influenced by freshwater runoff and melting ice. Rising temperatures, increasing melting of glaciers and permafrost thaw are creating changes in the physical and chemical environmental conditions in high Arctic fjords, which will subsequently influence the plankton communities.
We hypothesize a shift in zooplankton species composition, from mainly small- sized, less nutritious to larger- sized high food quality zooplankton along a gradient from freshwater to mainly marine influenced sites. We also expect a decrease in inorganic particles and terrestrial dissolved organic matter (DOM), in addition to an increase in bulk chlorophyll a biomass along the same gradient. The ratio of allochthonous (terrestrial) to autocthonous C (marine) will decrease along the gradient, and we foresee an increase of allochthonous C over the summer with increasing freshwater runoff. Stoichiometric ratios will likely change according to light and nutrient availability, with lowest C:N/C:P of zooplankton and particulate organic matter (POM) closer to the river mouths.
To test our hypotheses, field campaigns were conducted in May, June and August 2018, at 17 stations in Isfjorden along transects from river estuaries and tidewater glaciers to marine stations. Samples were collected for zooplankton community composition accompanied by a range of environmental factors including CTD profiles, light, and various water chemistry analyses. Zooplankton community structure will be analysed in relation to these abiotic factors to assess the impacts of freshwater runoff on zooplankton community structure and nutritious value.
Altogether, this study will provide new insight into the zooplankton community structure in Svalbard fjords, and with increasing temperatures and changing coastal systems, we will gain knowledge on how these communities and their nutritional quality are influenced by increasing and terrestrial inputs.
- 11:15 Climate Change versus genes: Arctic and Atlantic copepod transcriptomics in the Fram Strait
Authors: Maria Scheel ( Aarhus University ); Gareth Pearson ( CCMAR ); Ester Serrao ( CCMAR )
The Arctic Ocean is allegedly the most vulnerable ecosystem under the globally changing climate and is exposed to changing abiotic regimes due to increasing temperatures. The northward shift of aquatic isotherms is followed by polewards distribution range expansions, leading to replacement of polar by boreal-Atlantic species. The most interesting aspect for studies on the temperature sensitivity of zooplankton in Fram Strait is the fact that both boreal-Atlantic and polar plankton communities are dominated by congeneric species, which are characterised by different morphology, trophic relations and lipid content and hence shifts bear potential of trophic cascades. We hypothesised that Atlantic congeners possess higher gene regulation plasticity than polar species under thermal stress of realistic experimental culturing temperatures up to 8 °C. Comparative transcriptomic analysis was executed on the boreal Calanus finmarchicus and Arctic C. glacialis and C. hyperboreus to investigate species-specific gene regulation responses. Based on next-generation sequencing technology with a sequencing depth of >330 million basepairs per species, differential gene expression was found absent for C. glacialis with increasing temperature, though an increase of the heat shock protein 70kDa was calculated. In contrast, the other congeners repressed metabolism pathways of lipids and fatty acids, amino acids, carbohydrates and typical cellular stress response pathways, indicating that 8 °C did not yet induce vital stress. But as the molecular chaperone DnaJ is down-regulated in C. finmarchicus and up-regulated in the polar species, varying temperature sensitivities for protein degradation might be a key for thermal stress responses. Furthermore, varying expression of heat shock proteins and proteins of the minimal stress response indicated a higher thermal resilience and gene expression plasticity in C. finmarchicus than in C. hyperboreus, while C. glacialis might not have suitable gene regulatory machinery to adapt to future ambient thermal stressors.
- 11:30 A flexible life strategy makes the Arctic copepod Calanus glacialis resilient to climate change
Authors: Janne E. Søreide ( The University Centre in Svalbard ); Barbara Niehoff ( Alfred Wegener Institute ); Ksenia Kosobokova ( Shirshov Institute of Oceanology ); Kasia Dmoch ( Institute of Oceanology, Polish Academy of Sciences ); Igor Berchenko ( Murmansk Marine Biological Institute ); Maja K. Hatlebakk ( The University Centre in Svalbard ); Martin Graeve ( Alfred Wegener Institute ); Jørgen Berge ( UiT The Arctic University of Norway ); Malin Daase ( UiT The Arctic University of Norway )
High latitude marine ecosystems experience strong seasonality in incoming light and thus primary production. Herbivorous calanoid copepods of the genus Calanus may comprise up to 80% of the mesozooplankton biomass in Arctic seas. These large copepods build up large lipid deposits during the short, but productive summer and survive the winter by entering a dormant state at depth. The ongoing reduction in sea ice thickness and extent will significantly change the underwater light climate and thus the timing, quantity and quality of primary producers with potential implications for grazers’ reproduction and growth. Up to date we have very limited knowledge on the overwintering ecology and physiology of Calanus spp., and their ability to cope with increased sea temperatures during overwintering. Here we have synthesized more than ten years of data from fjords in Svalbard on C. glacialis seasonal population development and physiological state to determine this species robustness to climate change. This relatively large and fat Arctic copepod prefer seasonal ice covered shelf seas and has evolved somewhat different physiological adaptation and behavior than its sibling species in the deeper oceanic realms, C. finmarchicus in the North Atlantic and C. hyperboreus in the Arctic Ocean. In summary, our findings lead to the conclusion that C. glacialis has a highly flexible life history which is reasonable for a species inhabiting the dynamic Arctic shelf seas that naturally experience large inter-annual variations in sea ice cover and thus the physical (light, temperature) and biological (algal food) environment.
- 11:45 Reproductive rates of small copepods in a changing Arctic: present and future?
Authors: Coralie Barth-Jensen ( University in Tromsø ); Camilla Svensen ( University in Tromsø ); Peter Glad ( University in Tromsø )
Reproductive rates of zooplankton are essential to calculate secondary production of any ecosystem. Temperature is recognized as a major factor influencing reproduction in copepods. Projected warming of Arctic surface waters is estimated between 1.8 and 4°C by 2100. Its suggested consequence is a shift from dominance of larger Arctic copepod species to smaller temperate species in Arctic food webs. The temperature-responses of reproductive rates is well-documented for larger copepods but is understudied for many small copepods species (body length < 1 mm). We investigate the reproduction at cold temperatures of three small copepod species with different reproductive strategies. Egg-hatching experiments were conducted on the egg-carrying Oithona similis and Microsetella norvegica, and egg production experiments were conducted on the broadcast-spawner Microcalanus spp. To the best of our knowledge, our study is the first to present egg-hatching rates for M. norvegica and egg production rates of Microcalanus spp. at low temperatures. Specimens were collected in a high-latitude fjord and incubated at temperatures between 1.3 and 13.2°C in June and August 2017 and March, May, June and August 2018. Typically, an egg-carrying copepod shows a linear increase between temperature and hatching rate. Accordingly, the egg-hatching rates of O. similis increased from 5% day-1 at 1.3°C to 34%.day-1 at 13.2°C. However, the egg-hatching rates of M. norvegica showed a bell-shaped relationship within the temperature range with a peak at 7°C. The average daily egg-production of the broadcast-spawner Microcalanus was 9 ± 3 in May 2018, 6 ± 5 in June 2018 and 12 ± 8 in August 2018 and was temperature independent. The egg hatching time of Microcalanus spp. decreased with increasing temperatures, ranging from 4.3 days at 3°C to 1.6 days at 9.8°C. These results indicate that temperature affects small copepods species differently. While O. similis’ egg-hatching is strongly affected by temperature, additional factors, such as seasons, may influence M. norvegica reproduction. Microcalanus spp. egg production responded to seasonality while its hatching time responded to temperature. Therefore, the predicted increase in Arctic surface waters temperatures will positively affect the reproduction of small copepods irrespective of their reproductive strategies. Because larger Arctic copepod species are negatively affected by an increase in temperature, our study supports the idea of a shift towards smaller copepods species in the Arctic pelagic ecosystem.
Thursday 24th January 2019
11:00 - 12:00