CHASE

Description

The CHASE programme will address the core objective of the NERC Changing Arctic Ocean Program by seeking to understand and predict how ecologically important species will respond to climate change. As the Arctic Ocean is warming, zooplankton such as copepods and krill are undergoing habitat range extensions polewards. This will result in exposure to new and more extreme day-length (photoperiodic) climates of the higher latitudes – known in many terrestrial species to have negative consequences on fitness. We will therefore aim to investigate the behaviour, physiology and genetic responses of copepods and krill to their natural and new photoperiodic environments. We will focus on the circadian biological clock, central in day-length measurement and in orchestrating key seasonal life-cycle events.

To understand large scale ecosystem responses to climate change we need to mechanistically understand small scale individual responses of key organisms driving marine ecosystems and their functional biodiversity. High variability between individuals is an indicator for high adaptive capacity of the population to changing conditions. Due to the ecological relevance of key species their individual variability can give an indication of future ecosystem shifts.

Our approach focusses on the two Arctic key zooplankton groups Calanus finmarchicus / Calanus glacialis (calanoid copepod) and Thysanoessa inermis (krill). We will:

1. characterize the Arctic light climate (spectrum, irradiance) with latitude and season;
2. determine individual copepod and krill behavioural phenotypes with latitude and season;
3. investigate photoperiod as a diapause trigger in copepods;
4. determine the metabolic status of behavioural phenotypes (identified above);
5. provide seasonal characterization of gene expression with a focus on clock mechanisms and the influence of light and;
6. provide indicator genes characteristic for specific life-cycle events, metabolic processes and environmental conditions as well as genetic timekeeping;
7. investigate the effects of light and genetic clock mechanisms on seasonal timing and how the factors may synergistically interact with other environmental and physiological factors and;
8. incorporate these data into life-cycle models to provide a wider, predictive framework for this work.

We will combine a novel, but tested, approach to large scale behavioural screening of activity in copepods and krill with classical physiological investigations on fitness. Activity screening methodology adopted from Drosophila clock research will reveal diel behavioural cycles and rhythms as well as the change of these cycles/rhythms with different photoperiods. We will also use state-of-the-art genetic analyses to characterise the genetic traits of seasonal physiological changes and how light modulates circadian clock and clock related genes. Finally we will incorporate the behaviour, environment and physiological state into existing well-tested individual-based models and dynamic optimisation models to determine the predicted fitness costs of future Arctic climate change scenarios.

The balanced functioning of the Arctic ecosystem is reliant on the success of key zooplankton primary consumers which influence all higher trophic levels, from fish to whales. CHASE aims to understand how such key organisms function in this extreme environment and will develop the predictive tools necessary to assess how climate change will impact their populations in the future. This will be achieved through a combined sampling/experimental/modelling programme, thereby informing future scientific directions, critical in helping manage areas which are rapidly becoming more accessible to increasing resource exploitation. The project is embedded within international Arctic science networks based in the UK, Norway and Germany and will have a legacy of cooperation beyond the lifetime of the funding.

The core objective of CHASE is to understand how the current and future Arctic environments influence the successful functioning of key copepod and krill species at the behavioural, physiological and genetic levels. In order to do so we will address several objectives centred around four key questions:

Q1: How does the behaviour and respiration of copepods C. finmarchicus / C. glacialis and krill T. inermis change over daily and seasonal cycles in the Arctic?

Obj. 1 will determine the seasonal change in Arctic light climate (irradiance and spectrally) across a latitudinal transect in the Barents Sea and in two fjords (Billefjorden, Svalbard and Loch Etive, UK). These measurements will be integrated where appropriate with new observations of the water column from the ArcticPRIZE programme.

Obj. 2 will determine individual krill and copepod behaviours of animals collected from these sites to identify their individual metabolic status.

Q2: What are the drivers of diapause and consequences of a photoperiodic/thermal mismatch in C. finmarchicus / C. glacialis?

Obj. 3 will determine the role of lipid reserves and photoperiod in copepod diapause. Using animals collected from fjords we will behaviourally characterize the non-diapause and diapause phenotypes and lipid content. We will expose copepods to a range of natural photoperiods to determine: a) if there is a critical photoperiod (CPP) triggering diapause; b) if the putative CPP is consistent between individuals and; c) the role of lipid reserves in diapause initiation.

Obj. 4 will determine the consequences of thermal/photoperiodic mismatch in copepods/krill with ship-based crossed experiment mimicking northward geographical shift under increasing potentially unfavourable photoperiods at different temperatures. Changes in behaviour and respiration in these “challenged” animals will be determined.

Q3: What is the role of the circadian clock in controlling the seasonal phenology of C. finmarchicus and T. inermis?

Obj. 5 will characterize physiological performance indicators in relation to environmental parameters (photoperiod, temperature, food supply) in both species.

Obj. 6 will generate seasonal transcriptomes to provide a broad overview of seasonal changes of genes characteristic to initiation, maintenance and termination of copepod diapause, krill winter quiescence and clock gene activity.

Obj. 7 will provide a detailed characterization of the genetic mechanisms involved in the initiation/termination of diapause in copepods with analysis of the expression levels of ‘diapause’ genes whilst Obj. 8 will genetically characterize the seasonal phenology of T. inermis in relation to photoperiod in association with clock and clock related genes.

Q4: What are the life-history and energetic consequences of climate change to copepods and krill under future Arctic climate scenarios?

Obj. 9 will predict optimal DVM patterns as a function of the environment and compare predictions both to observed in situ patterns and displacement experiments. We will develop state dynamic life-history models for C. finmarchicus / glacialis and T. inermis capable of predicting diel vertical migration behaviour and vertical distribution as a function of internal state, life-history and environment to test levels of optimality at different polar latitudes.

Obj. 10 will develop individual based models (IBMs) of copepods and krill with physiological, behavioural and demographic sub-models to determine how environmental change will impact the fitness of individuals. This will make for a unique Polar comparator between climate change projections for Antarctic and Arctic krill and copepods.

Obj. 11 will up-scale the IBMs to include populations models to pan-Arctic scales. Collectively these objectives will provide new, well-validated models that will be merged back into UK and international efforts to project the future of pan-Arctic ecosystems through collaboration with leading modelling groups.