Sea sparkle is a Defence against Enemies
Sea sparkle, the phenomenon of seawater glowing brilliantly at night in breaking waves or when splashing in the water, has always fascinated people. A new study from the University of Gothenburg sheds light on what controls its intensity.
Sea sparkle is caused by thousands of light-emitting single-cell organisms. Now a research team from the University of Gothenburg has shown that the intensity of the glow is controlled by how many enemies there are in the water.
‘The sea sparkle organisms discover their enemies by smelling them and crank up the light intensity when the risk of getting eaten increases. The light protects the cells against their enemies,’ says Jenny Lindström from the Department of Biology and Environmental Sciences and main author of the article.
Defence against Predators
Many marine organisms can glow (bioluminescence), but researchers know very little about why they do it and how the mechanism is controlled.
‘By adding the unique substances that sea sparkle organisms react to, we can examine the mechanisms involved at cell level and the effect of bioluminescence,’ says Erik Selander, researcher at the Department of Marine Sciences, University of Gothenburg.
Despite their small size, microalgae and their copepod enemies, have a language. They communicate effectively with light and scents. Studies show that microalgae such as dinoflagellates can detect chemical substances, copepodamides, that the copepods give off.
Dinoflagellates are the only microalgae that send out flashes of light to prevent being eaten. This phenomenon is known as sea sparkle and mareel. The dinoflagellates send out blue light flashes that last about one-tenth of a second.
‘It is believed that the light surprises the copepods or signals that the dinoflagellates are toxic. Alternatively, the light serves as an alarm that attracts larger animals, such as fish, who gladly eat the copepods,’ says Jenny Lindström.
Loses the Ability to Glow When Grown in Isolation
Several older studies show that dinoflagellates lose some of their ability to glow when grown for a long time without contact with other organisms. The new study shows that dinoflagellates grown in isolation seem to ‘relax’ when not surrounded by copepods threatening to eat them.
‘The glowing dinoflagellates (Lingulodinium and Alexandrium) can smell when there is a large amount of copepods in the water, and if there is, they increase their brightness,’ says Erik Selander.
Approximately 70–80 per cent of all species in the sea use light signals for various purposes, but this is the first study showing that the intensity of the glow can be physiologically regulated in response to the environment.’
Affecting the Balance in the Sea
The microscopic organisms in the sea form the base of the marine food chain. The outcome of the meetings between microalgae and the enemy copepods controls the balance of the marine ecosystem.
The results of the study suggest that light is an important, but costly, defence of dinoflagellates against copepods.
‘If copepods opt not to eat glowing prey, it can have a major impact on the balance of the marine ecosystem and for example contribute to algal blooms of glowing dinoflagellates. Sometimes harmless, fascinating and beautiful, but sometimes with negative consequences such as oxygen deficiency or shellfish poisoning,’ says Jenny Lindström.
Title: Effects of predator lipids on dinoflagellate defence mechanisms – increased bioluminescence capacity.
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Jenny Lindström, researcher at the Department of Biology and Environmental Sciences, University of Gothenburg, tel. +46 (0)703 11 83 96, email firstname.lastname@example.org
Erik Selander, researcher at the Department of Marine Sciences, University of Gothenburg, tel. +46 (0)31 786 26 27, email email@example.com
Picture 1: Millions of sea sparkle organisms glow when researcher Kristie Rigby shakes an algae cultivation bottle.
Picture 2: Glowing dinoflagellates with and without copepodamides. Light from thousands of Lingulodinium sea sparkle organisms. The organisms in the glass container to the right can smell the copepods and therefore glow brighter than those in the left container, which have been cultivated for a long time without contact with enemies.
Portrait pictures taken by Jenny Lindström and Erik Selander.