Nudibranchs the most gorgeous marine animals keep scuba divers fascinated
Author: Georgina Jones of Sea Slug Atlas
Nudibranchs, or sea slugs, are possibly the most gorgeous marine animals of all. The extraordinary variety of their colours and shapes keeps scuba divers fascinated over years of spotting them. South African nudibranchs, like our seas, span a huge range from tropical animals to ones which prefer cooler or even cold water. Some can be found in shallow rock pools and others prefer the deep ocean. They range from animals commonly seen over the entire Indo-Pacific Ocean, to beasts known only from a single Cape reef.
Our understanding of which nudibranchs live where, what they eat, and who eats them is limited. Humans don’t spend that much time underwater and nudibranchs lead swift and interesting lives.
Though all are carnivorous, there’s only a small sub group which actually catches their prey, using a hood adapted from mouthparts for the purpose. Most nudibranchs graze living animals such as hydroids, sea squirts or moss animals. Not having a shell for protection, nudibranchs have developed toxicity as a defence, and in almost all cases, they acquire their toxins from their prey. They are hermaphrodites, i.e. each animal is both male and female. The male body parts develop first so that the nudibranch can donate and store sperm until its eggs are ready to be fertilised. Once this has been done, each species lays a ribbon of eggs which is unique to the species. From these eggs, larval nudibranchs hatch and begin a new life cycle.
SeaKeys* is using observations from beach and sea users to produce a Sea Slug Atlas showing the distribution of these absorbing creatures around the South African coast. You can help by registering as a user on iSpot and uploading any nudibranch images you may have, tagged with Sea Slug Atlas – they’ll need to know where you took the pic, and when, and in this way, we are slowly building up a picture of what nudibranchs we have where around our coast.
*a National Research Foundation funded project, being run over three years through SANBI and involves collaborations with over thirty institutions both governmental and academic, as well as input from the general public