Environment – In awe of the little things

The nudibranch is a wondrous creature. For a start, many wonder how to pronounce its name correctly.

It’s nudi-brank. Nudibranchs are a type of mollusc gastropod – slugs and snails. All mollusc gastropods have an external shell at one stage of their life cycle, but nudibranchs are a marine species that lack a shell in the adult stage. Mollusc gastropods all have a special protective tissue (the mantle), a foot for locomotion, a feeding organ (radula), and they are hermaphrodites – with both male and female sex organs.

There are around 3000 species of nudibranchs known around the world. From the Arctic to Antarctica, they’re found mostly in shallow shores but also on the surface of the open sea, living in plankton, and in the deep ocean. They can live at 700m deep and have also been seen 2500m down.

They are incredibly diverse and colourful. They range from a few millimetres to several centimetres long, but they make up for size in sheer gaudy freakiness. They sport a range of psychedelic patterns and forms. Their outlandish colours and shapes are why they have attracted names like the ‘clown’ nudibranch (Ceratosoma amoenum), which is usually a soft white colour with orange spots, a frilly rosette at the tail end and a couple of red horn-like antenna at the head. There’s the marigold dorid nudibranch (Neodoris chrysoderma), which is a beautiful bright yellow with white dots and feathery gills.

The blue sea dragon nudibranch (Glaucus atlanticus) looks like something out of Alien. It has limb-like blue spikes and it adheres to the underside of the ocean’s surface (meaning it is neustonic), far out at sea. They predate Portuguese men-of-war jellyfish and absorb the jellyfish toxin to become toxic themselves – and they look like it! There are other nudibranchs that are fluorescent yellow/green and lumpy, black and white patchy; ‘nodulosa’ looks like it sounds. Some are covered in soft green spikes with yellow tips or are stripey black and yellow.

Nudibranchs are also ecologically and biologically remarkable. Their diets are very varied, as is fitting for their diversity and occupation of many habitats. They mainly eat sea sponges and hydroids (small jellyfish), but according to NIWA, every animal group in the sea is predated by one type or other of nudibranchs.

A total of 80 species of nudibranchs have been recorded in New Zealand. More are being discovered all the time, and NIWA suggests there are still possibilities to discover and name nudibranchs never recorded before. They also say nudibranchs can be seen in an area, and then not seen again for 10 years.

When I was at Tiritiri Matangi recently, I saw two types of nudibranch in the rock pools. They were the bright orange Berthellina Citrina and lumpy cinnamon coloured gem nudibranch, Dendrodoris denosoni.

Though I was visiting the island for the birds and reptiles, the nudibranchs reminded me to save some awe for the little things.