So one of my favourite shifts here in South Africa is taking the interns to survey the tide pools. During these shifts, we head to one of several study sites at low tide. From there we lay out a transect rope that runs from the low tide up to the high tide mark. Every five meters we lay out a 1m by 1m square quadrat and record all the invertebrates we see there. Every shift we get data on how the invertebrate community changes depending on position in the intertidal zone.
Why?
Well the purpose is long-term monitoring. The intertidal zone is a pretty extreme place to live. Animals living here spend half their life living underwater dealing with all the usual difficulties of marine life and then the other half of the day exposed to air, an environment they’re not meant for, a place where they’re exposed to extreme temperature, they risk dying out and they can’t readily get food. Living in an extreme environment means that the ecosystem is likely to respond to additional stressers quickly. Changes in the temperature, water quality and human harvesting of species will show up in the data quickly. Its a great way to monitor the health of the local ocean and presents a great way to teach our interns about evolutionary adaptions in the marine environment. We find a lot of cool stuff on our shifts but by far my favourite is the Tuberculated Cuttlefish.
Tuberculated Cuttlefish
These little guys grow to about eight centimetres long. They spend their entire lives living in the intertidal zone and are believed to feed on shrimp although their precise diet isn’t fully understood. They’re very clearly adapted to the intertidal zone too. Their eight arms are short and stubby with a slight webbing in-between. This is much better for moving around all the small rock-pools and maneuvering your way through tight gaps between rocks. They still have longer tentacles that they use for hunting. But whats really cool is that their skin.
Camoflage
Its been a fairly regular occurrence on tide shifts that we’ll be counting the species we see and all of a sudden realize there has been a cuttlefish right next to one of us that has gone unnoticed for ten or so minutes. This is because cuttlefish, like most cephalopods have very special skin. Their skin contains special cells called chromatophores, iridophores and leucophores that the cuttlefish can use for camoflage. Chromatophores are little pigment sacs with muscle around the rim, by contracting or relaxing the muscle, more or less pigment is seen. The Cuttlefish’s skin is covered in millions of these cells. that are controlled directly by the nervous system. This means that a cuttlefish can change colour at the speed of thought!!!
Iridophores and More
These are where it gets really cool. Chromatophores are typically red, yellow or brown. While they can combine these, that still doesnt let them mimic all colours. Iridophores are what cover the rest. Iridophores are stacks of really thin cells that can reflect light at different wave-lengths. This means if viewed from one angle they might appear blue, from another they might appear red.
Leucophores are the last piece of the puzzle. These cells scatter light and therefore appear white. Just like the others, the cephalopod has control over these cells and its thought they use them to increase or decrease the intensity of the colour they’re trying to display. Its the combination of these cells that allow cuttlefish and other cephalopods to camoflage so well.
I’m trying to think of an eloquent way to wrap this post up but honestly, I just wanted to share how flippen cool these animals and their weird skin are. I hope you all found it as fascinating as I do. Here is a videos of a tuberculated cuttlefish to finish on 😀
Catchya next time 🙂
Tomasz Pedlow
Ocean Minded 