The role of light in the polar night

The role of light in the polar night

Top image: Anna Solvang Båtnes hauling a plankton net in Ny-Ålesund in January 2011. Photo: Cecilie Miljeteig

Anna Solvang Båtnes has studied the role of light in the Arctic marine ecosystem during the polar night, a time of year when it appears completely dark to the human eye. Båtnes performed parts of her fieldwork at UNIS and will defend her PhD thesis in Trondheim on Thursday 26 September.

24 September 2013
Press release from NTNU and UNIS

Anna Solvang Båtnes has studied patterns of diel vertical migration (DVM) of zooplankton, and the vision of selected Arctic organisms was investigated by using hyperspectral imaging as well as behavioural experiments.

During polar night, patterns of bioluminescence and DVM were mapped in Kongsfjorden, Svalbard, using an autonomous underwater vehicle (AUV) as well as zooplankton net hauls. Bioluminescence was, as the first registration during the polar night, documented throughout the water column. Diel changes in bioluminescence over depth were observed, with a significantly greater proportion of the more intense flashes occurring in surface layers during night and at depth during day.

In addition, investigations using acoustic backscatter as well as plankton net hauls, supported that the larger zooplankton, like Calanus spp., performed DVM in Kongsfjorden during polar night.

To investigate the spectral characteristics of the eyes of different organisms, the eyes of live specimens of different copepod and amphipod species were characterised using a hyperspectral imager. The spectral properties of the eyes were found to match the light climate of their habitats, sympagic and shallow-living pelagic species probably absorbing in blue and some in green wavebands, while deeper-living pelagic and hyperbenthic species absorbed mainly in blue. The sensitivity to ambient wavelengths may be part of the explanation to how organisms can stay active during the polar night, when ambient irradiance is very limited.

Response to moonlight and aurora
Calanus spp. is a genus highly important to the Arctic marine ecosystem, and was selected for studies of potential response to extremely low irradiance levels. An experimental setup was developed at NTNU Centre of Fisheries and Aquaculture (SeaLab), and investigations of their phototactic behaviour (behavioural response to irradiance) were performed at UNIS.

The phototactic behaviour of Calanus spp. sampled during polar night was investigated, to start revealing the visual capabilities of polar night acclimated organisms. The investigation suggested that Calanus spp. may respond to irradiance from the night sky down to approximately 40-50 m, moonlight to 100-140 m, and aurora borealis down to 60-100 m depth. Thus, irradiance may be the proximate cue for the observed DVM patterns, and the background irradiance from the sun, moonlight, as well as aurora may affect the pelagic ecosystem during the polar night.

Anna Solvang Båtnes

Anna Solvang Båtnes. Photo: Eva Therese Jenssen/UNIS

The doctoral work has been carried out at the Department of Biology, NTNU, where Professor Geir Johnsen has been the candidate’s supervisor. Professor Jørgen Bergen, The University Centre in Svalbard (UNIS) and University of Tromsø, has been co-supervisor.

Anna Solvang Båtnes will defend her PhD thesis “Light in the dark – the role of irradiance in the high Arctic marine ecosystem during polar night” on Thursday 26 September 2013 at 13:15 in Rådssalen, Hovedbygningen, NTNU.

Related articles:
11.05.2011: Light in total darkness

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