Feb 2015

Nudibranch: More than just a Slug!

By Mike Waddington

To the untrained diver everything is exciting, crazy coloured fish, turtle and pristine reefs. However when I have been training new divers it is very difficult to get them excited about what is possibly (in my opinion) one of the coolest things you will see underwater. Nudibranchs are some of the most colourful creatures on earth, which makes them very popular with underwater photographers and divers who seek out macro life. They come in stunning shapes and most divers (once they know what they are looking for) will spend almost an entire diving session looking at a tiny piece of coral trying to find them.

Where can I find Nudibranch?

Nudibranchs can be found in all the oceans worldwide, ranging from tropical coral reefs and to extreme colds such as Antarctica. There is even a species found near the North Pole called the sea angel. They can live in a huge range of depths, they can be found in the intertidal zone, to depths of over 700 meters, although you will find the most species in warm shallow tropical reefs.

How many species of Nudibranch are there?

There are actually over 3000 described species of nudibranch and many have been unnamed. They are often called sea slugs, but many sea slugs actually belong to other taxonomic grounds which are not closely related to Nudibranchs. Nudibranchs are benthic animals, which are usually found crawling over the sand, reef substrate or even the corals themselves. There are certain species that float upside down just under the water’s surface, and some species can swim as well.


Nudibranchs employ various defence mechanisms to help prevent them from being eaten. Over the course of their evolution, they have lost their shells, adopting other defensive techniques. Some species have evolved so their colour mimics the food they prey on (such as sponges or soft corals). Many of them are brightly coloured, so bright they stick out to form their surroundings, which is a natural indicator of either being toxic or highly distasteful. Some Nudibranchs feed on hydroids, and can actually store the stinging cells of the hydroids without harming themselves.

Nudibranchs can also use a variety of chemicals to defend themselves. Some of these toxins are not actually lethal but can incapacitate the attacker while the nudibranch can escape. Other species can release a form of acid from their skin, which is released when the nudibranch is physically touched or irritated by another creature. All known species of Nudibranchs are carnivores. Many feed on sponges, others hydroids. Or many species are known to be cannibals eating other nudibranchs or even their own species!

Physically nudibranchs can look vastly different, apart from their crazy colour variations they vary massively in size too. Although the majority of species are between 4-10 cm some species can grow to 60cm and weigh up to over 1kg! They have tentacles on their heads which they use to smell, taste and touch. They have eyes, but they are around ¼ of a millimetre in diameter that is set into their bodies, which can only deal with light and dark.

If seeking nudibranchs is something that you are interested in, then you should discuss with the dive centre that you are wanting to dive with, as many divers are more interested in seeing an entire dive site than focusing on trying to find some potentially tiny and camouflaged creatures. They can be found all over the world, but some of the best nudibranch diving can be found in Australia, Fiji and Indonesia.

‘Nudibranch: More than just a Slug!’ was written by Mike

Photo Credit: ScubaDiving.com

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Mike Waddington

I first discovered diving in 2008 after going snorkeling on the Great Barrier Reef in Australia. After trying diving at a flooded quarry in England I decided to head out to warmer more interesting waters in Thailand where I ended on the Island of Koh Tao completing my Open Water course. Instantly addicted with money to spend and plenty of time on my hands I decided to continue until I became a Divemaster so I could live what seemed as the perfect life.

After that I headed to the Caribbean to an island called Utila to complete my instructor course, I spent several months out there completing the MSDT internship, teaching students and leading dives. This is also where I discovered my interest in the technical side of diving, taking part in equipment repair courses and learning about blending gasses and running compressors.

With all my new qualifications it was time to head back to where it had all started, Back to Koh Tao where I intended on living the dream. Once I arrived I quickly found a job and started teaching straight away. During my time on Koh Tao I took part in all many technical diving courses, learning how to dive with re-breathers, in caves and even going down to 90m/300ft!


PADI Master Scuba Diver Trainer
PADI/DSAT Tech Deep Instructor
PADI/DSAT Gas Trimix Gas Blender
PADI/DSAT Trimix Diver
TDI Intro to Cave Diver
TDI Advanced Wreck Diver
TDI Inspiration rebreather Decompression Procedures
PADI Professional Videographer
BSAC Compressor Operator
TDI Equipment Service Technician

Dream Dive Locations:

Silfra, Iceland
Cenotes, Mexico
Chuuk Lagoon, Micronesia
Ice Diving in Russia