• Question: @divaamon How comes animals in the dark part of the sea flash blue and pink its really weird. Also why do they have a light above there head wouldn't that attract preditors???

    Asked by reeceherbert to Allan, Angela, Diva, Harriet, Nathan on 29 Jun 2012.
    • Photo: Nathan Langford

      Nathan Langford answered on 29 Jun 2012:

      Hi reeceherbert,

      This is actually really cool – it’s called “bioluminescence” and is a type of “fluorescence”. I wrote more about what fluorescence is in another answer: http://ias.im/87.357 . The quick summary is that atoms and molecules “fluoresce” when you give them a kick of energy somehow and then wait awhile. Once the atoms have absorbed that excess energy they will eventually want to give it up and drop back down into their lowest energy (“laziest”) state. When they do give up the energy, it often comes out and light, and that is called fluorescence.

      As I mentioned in that other answer, there are lots of different types of fluorescence, depending on how you put the energy in. You can use electricity, like in lightning, or heat, like in a candle. But it turns out that you can also use chemical energy and that is how biological animals create light. They have some chemical reaction inside their body which creates the energy that can then be given off as light. As you point out, this happens inside deep-sea fish, but the same things happen in fireflies above ground, for example.

      So why do animals do that? Well, maybe the animals also need some way of seeing down there sometimes, since it is so dark, so they’re a bit like a car with headlights. But another reason why animals might give off light is for communication. For example, I believe that fireflies are thought to use their light to communicate with and attract mates. But you could also imagine other reasons for fish to give off light. They might use it as a defence mechanism, for example, if they were able to give a bright burst of light to confuse a predator. Or if they were a predator fish, they might use the light to attract other fish nearby so that they can then eat them. For example, if you’re thinking of the angler fish, which has a light which floats in front of their head, I think it uses the light as a bait to lure fish close enough to eat. Have you seen Finding Nemo? 😉

      Anyway, I’m sure Diva will know more about the fish side of your question, but I hope that helps from the physics side…

      Cheers,
      Nathan.

    • Photo: Diva Amon

      Diva Amon answered on 5 Jul 2012:

      Hey reeceherbert,

      You are correct. Many deep-sea animals do flash bright colours like pink and blue. This is known as bioluminescence. About 90% of the animals in the deep sea have many small light capsules that have the ability to emit light.

      Deep-sea animals do this for a variety of reasons. Some do it to attract mates like fireflies do on land. The deep-sea is such a huge and dark place that animals need to use cues to signal to mates ‘Hey, I’m here. Let’s have some babies!’.

      Other animals use bioluminescence to stun or temporarily blind animals that may be trying to eat them so they can make a quick getaway. Some may just light up really brightly or some deep-sea squid eject glowing liquids as a distraction. Some deep-sea animals do this in an even more extreme way where they distract their predators by actually dropping a piece of themselves like a leg which will then flash on its own so the predator will instead go after the limb thinking that it is the entire animal.

      Some larger deep-sea predators use their lighting to pretend to be another fish. This will fool fish into investigating their possible prey but then they end up getting eaten by the larger animal. This is known in nature as mimicry.

      Also, you asked about animals that have lights on their heads like for instance the anglerfish. This is another use for bioluminescence – these animals use these lights (called lures….) to lure in prey. The lure dangles close to the fishes mouth and so when smaller fish come to investigate they become lunch!

      Here is a video of my favourite bioluminescent animal in the deep sea – a jellyfish called Atolla wyvillei. Wait until the end of the video to see the bioluminescence without lights on!

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