In an alternate universe, where someone for some reason would present me with the choice of being able to go invisible or to camouflage myself, I would always chose invisibility. In my head this has always been a superior power to camouflage. Is it actually though?
There are limitations to both. The most obvious one being for camouflage, where the setting is crucial. Without any background to camouflage against, say in the middle of the ocean, they would be easy prey. However, the cephalopods who live in these areas, in the deep oceans, are usually colored red or black (Figure 1) (Mäthger and Hanlon 2012). This serves them as an invisibility cloak, as these colors absorb more light than those in other wavelenghts.
Figure 1: A coconut octopus showing off the red skin used in deep waters for camouflage
However, a limitation here is that their heavy coat makes them throw a shadow with light from above. A similar issue is there for transparent cephalopods.
For transparency, the issue is to do with light scattering. When direct light hits these transparent bodies, it is absorbed more so than the background, making them stand out (Zylinski and Johnsen 2011). This direct light can for example come from predatory fish equipped with light emitting organs, known as ‘searchlights’. However, two species have been found to respond to this direct light with color pigmentation, thereby reducing the amount of scattered light and remain in disguise. These two species are the Onychoteuthis banksia (squid) and Japetella heathi (octopus) (Zylinski and Johnsen 2011).
One possible limitation to this adaptation is that essential organs, like digestive tracts, are still exposed inside the transparent body. Whether these give them away, as Tasmin asked in the comment section in my last post, is an interesting question, but was not covered in Zylinski and Johnsens (2011) report. Considering where the two species live (in the lower pelagic areas with low light penetration), the size of them (squid mantle length = 140 mm, octopus mantle length = 80 mm), and the fact that they use pigmentation as a form of disguise against predators with searchlights (Zylinski and Johnsen 2011), makes me assume that some visibility of organs would not regularly give them away. However, without proper research it is hard to say for sure.
Another interesting notion is the fact that the two species respond more slowly than the camouflaged species. Mäthger and Hanlon (2012) redirected the attention onto response time reported in Zylinski and Johnsens (2011) paper and highlighted that these two species reacted in ‘seconds’, while camouflage species have a response time frame of about 300–800 ms. Mäthger and Hanlon presumption is that these two species do not have a direct neural control of their chromataphores (2012), and suggested a new experiment that analyzes the ability of the cephalopods to presumably ‘see with their skin’, performed on Onychoteuthis banksia and Japetella heathi. The idea is to see whether their skin will respond with pigmentation when subjected to bioluminescent light without letting the individual see the light with its eyes. More about this is covered in their paper, if there is any additional interest in the matter.
So who is the winner? At the moment I wish to deliver the prize to the highly adapted Onychoteuthis banksia and Japetella heathi, who have found a way of merging transparency and camouflage. This way they get the mobility entailed in transparency and the ultimate invisibility entailed in camouflage. However, whether response time has any effect on the invisibility, as well as what the cause is for the delayed response, has yet to be studied.
Due to this post being a little late, there will be two posts this week. In the next post we will diverge from the superhero theme and have a look at the cheerleaders of the sea. Yes, you read that right, let’s talk about those pom poms.