Uncovering marine biodiversity on our shorelines.
Nudibranchs are stunning and bizarre creatures, they occur in an almost unimaginable range and combination of colours, including intense blues, vivid yellows and purples, magenta and scarlet. Australia’s tropical waters abound with a great diversity of species, but it’s our southern shorelines that have offered the greatest assortment of new discoveries.
Divers sometimes refer to nudibranchs as ‘butterflies of sea’. Now I mean no offence to the Lepidopterist community out there (i.e. those that study butterflies) but I’m of the view that nudibranchs put butterflies to shame when it comes to sheer brightness, flamboyance, and a seemingly incongruous combination of shapes, patterns and appendages.
So, what are nudibranchs? What sets them apart from all the other wild diversity of our oceans? Well put simply they are snails and slugs, but they’re about as far removed from your average garden snail or slug as you could possibly imagine. Nudibranch means ‘naked gills’, they are gastropods, that is snails and slugs, but nudibranchs have rearranged their anatomy and lost their protective shell resulting in their gills being directly exposed to the ocean currents.
They occur throughout the world’s oceans from intertidal rock pools to the deepest trenches. Despite their conspicuous colour and lack of agility nudibranchs are surprisingly poorly known to science with relatively few studies into their ecology and biology.
What we do know is that most nudibranchs are carnivores preying upon marine animals including corals, bryozoans, anemones, jellyfish and occasionally they devour each other. The Blue Dragon, one of the few nudis with a common name, is an ocean going, upside down swimming hunter. This species preys upon jellyfish in the ‘blue bottle’ group of jellyfish, the Physalia. Remarkably it can encapsulate the stinging cells of the jellyfish it preys upon and use these in self-defence.
The Blue Dragon heading south as our oceans warm. Image via flickr
The ability to harness the toxic power of the stinging cells of one’s dinner is not however confined to the Blue Dragon. This rather filamentous Flabellina rubrolineata positively bristles with defensive cnidocytes. The white points at the tip of each pink fringed filament are where its cnidocytes reside. This elegant marine ballerina inhabits the shores of Port Phillip Bay, clearly it’s not only tropical waters where bright and intricate examples of these creatures can be found.
Flabellina can be seen at Blairgowrie pier, as can Mexichromis macropus. This species is relatively common and at times has been observed in large numbers within Port Phillip Bay.
Mexichromis macropus. Image via Wiki Commons
And in case you’re wondering, yes they are posturing to exchange barbs as is the mating behavior of some nudibranchs. For those new to the sex life of marine gastropods allow me to explain. Nudibranchs are hermaphrodites, they copulate by inserting their barbed penis into their mate and exchanging sperm.
Simple, and sounds all rather dispassionate but it can be a little more intimate than that for some. A number of nudibranch have been observed stroking each other’s ‘heads’ and caressing each other before copulation, while the more cannibalistic varieties rather quickly ‘uncouple’ and then attempt to eat each other. A rather odd evolutionary strategy I’d suggest.
Bright colours in nature, are often a warning sign of toxicity but I must admit that many Nudibranchs do look rather edible to me. This next species really does remind me a meringue just out of the oven, with slightly browned crispy, wispy peaks. It is referred to by many divers as the confectionary nudibranch. I think the Meringue Nudibranch would be more apt.
Glossodoris atromarginata, often seen on the east coast. Image via Wiki Commons
And if I were to abandon my studies to pursue a career as a manufacturer of confectionary I would surely model my first product on this little guy, Glossodoris cruenta occasionally recorded along the southern Queensland coast.
Glossodoris cruenta. Would anyone care to suggest a common name? Via Wiki Common
I don’t know about you, but to me, this oceanic eye candy has ‘milk bottles’ written all over it. But, Glossodoris cruenta is an uncommon species in Australia. It’s our southern shorelines which are the center of discovery for nudibranch diversity.
Port Phillip Bay and surrounds is renowned for its range of nudibranchs with over 100 new species described over the past few decades. Surprisingly these creatures are relatively easy to find in rock pools and the intertidal zone. Close inspection of anemone beds and fringing marine sponges will more than likely reveal a nudibranch. One of the more common species is Tambja verconis, it’s a conspicuous nudi with unmistakable coloration.
The vast majority of Victoria’s new discoveries have been made by amateur ecologists Bob Burn, a passionate nudi-nerd and builder by trade. So, while exploration of the worlds deep ocean trenches often reveal remarkable new creatures it is equally likely that new nudis will be discovered in rock pools by weekend enthusiasts.
New species await discovery, hiding in plain view. They’re in a rock pool near you.