SCUBA welcomes new science columnist Karen Boswarva , who begins her tenure by turning her eyes to the sky , then the sea
OCEANSCIENCE
Rave ‘ till dawn
SCUBA welcomes new science columnist Karen Boswarva , who begins her tenure by turning her eyes to the sky , then the sea
Has anyone else noticed that the nights are slowly drawing in ? The shorter days are signalling that summer is coming to a close , where hibernating in a woolly jumper with a hot brew sounds more appealing than the mandatory torches and icy mask clears that winter tends to bring . These dark evenings have at least been offering us something quite spectacular above sea level .
We ’ ve been very lucky that on at least two occasions this year ( so far ), the whole of the UK from Shetland to the Scillies was treated to one of the greatest natural light shows on planet earth ( unless you ’ re one of the few that slept in and are therefore still kicking yourself for doing so ). The aurora borealis , or northern lights , usually reserved for those with the darkest skies in the far north of Scotland . What an incredible sight it was , as the night sky raved its way into dawn 90s-style , a blaze of flashing green and purple rays of light .
It certainly made us all , including me , get outside and look up . As I stared up in awe , it made me wonder how might its presence be felt underwater ? Do marine animals make use of the light emitted from these solar flares ? Many of the marine animals we come across on a dive are sensitive to light ; you recall the effect when turning a torch on and catching some creature in the light . Some will flee , very quickly mind , while others ( both predator and prey ) will surround you , using you to their advantage in their otherwise darkened world .
The behaviours and physiology of marine animals such as zooplankton and fish attune to even the smallest changes in light , ensuring that ecosystems remain active and functioning all year , from day to night , spring to winter .
Zooplankton are vital to the health of the seas , A biodiverse rich soup that most larger animals ( including us ) rely upon for food . Throughout the summer when there ’ s plenty of daylight hours , these tiny marine animals travel up and down the water column in a daily cycle that follows a circadian rhythm while also adjusting to small changes in ambient light . This is called Diel Vertical Migration ( DVM ). At night they will travel towards the surface to feed , returning to the depths during the daytime to try and hide from predators .
During winter when there are fewer sunlight hours , our seas don ’ t simply lie dormant hiding under a blanket for summer to arrive . Marine animals will make use of any available light to keep to their daily rhythm . An extreme example of this is the polar night , the last remaining undisturbed and pristine dark environment on the planet . To the human eye there is no difference in illumination between night and day . During a polar night , zooplankton will harness light from the moon and stars , in much the same way as organisms generate energy from sunlight , using specialised light detecting cells called photoreceptors .
Meet Karen Boswarva
“ Hello ! I ’ m based in Orkney where I work as a marine habitat mapper and volunteer as Seasearch coordinator for Orkney and Shetland . I learned to dive with BSAC in 2010 , progressing to Instructor , Diving Officer , Regional Training Coordinator , and environment sub-committee member . I ’ m an absolute geek for nature , science and technology , especially the underwater kind . You ’ ll find me anywhere on or under the sea .”
The available light emitted from the sun , moon , stars , and aurora borealis is called ambient irradiance . Scientists tested the light sensitivity of a type of zooplankton called Calanus sp . Calanus is a fat filled copepod – basking sharks find them irresistible – that performs DVM during the polar night . The test consisted of gradually increasing the ambient irradiance of light in the white , blue , green , and red wavebands , recording the Calanus response using a specialised video camera . The Calanus showed high sensitivity to low levels of blue and green light and responded negatively , diving deeper from ambient light levels that mimicked the night sky at depths of 70-80m , moonlight at 120-170 m and aurora borealis down to 80-120 m depth .
Now there ’ s something to ponder next time you ’ re searching blindly for the light switch . �
Northern lights over Orkney ’ s Italian Chapel
PHOTO : PAWEL KUZMA
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