The Coral Reef Off Sulawesi, Indonesia Is a Kaleidoscope of Colour
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{SEA SLUGS} nudibranc The coral reef off Sulawesi, Indonesia is a kaleidoscope of colour. The corals seem to fight for space, clamouring in a brilliant profusion of textures, shapes and sizes. I am 10m below the waves, searching for a tiny creature in an immense underwater realm. From my weightless spot several feet from the reef, it’s akin to searching for a needle in a haystack. To my right, I spot a distinct jumble of coral anchored to the sandy bottom. It’s the size of a small car. To me, the isolated coral head seems a more manageable place to step up my search. I exhale a column of bubbles, kick my fins and roll to my right, gently descending until I am only inches away from the coral. Hovering, I scan the nooks and crannies, and almost immediately, my patience is rewarded. Well camouflaged by the vivid sponges, algae and corals around it, is an aptly named Chromodoris magnifica. It’s only 3cm long, but the magnificent pyjama-like orange, blue and white stripes that are characteristic of the species, pack a visual wallop. I am thrilled by the find, but the Chromodoris magnifica is only one species of a huge group of marine invertebrates belonging to the scientific order Opisthobranchia. To the layperson, the finger- shaped, bottom-dwelling animals are known as ‘sea slugs’ or ‘nudibranchs’ (pronounced nooh- dee-branks), and they’re found all over the world. 64 THE SEA Sea LIFE {OCEANOGRAPHY} to in .. ev s. Sea’s Jessica LePoid re he u T as ith markable living tre w t re es os av m e w s’ Travel beneath th an ce e o e of th c hs discover som Chromodoriskuniei t 65 THE SEA – nudibranchs digestive system and a about and are detected by a variety rasping organ – called a of marine life. radula – which is really a In the sea slug’s case, chemical modified mouth. But that’s receptors are located in the rod- where the relationship stops. like rhinophores that protrude In fact sea slugs and land from the front of their bodies. slugs belong to different Rhinophores enable them to detect scientific orders, and the food, enemies and mates as they biggest difference between make their way around their the two lies in their habitat. This is crucial to their Nembrotha purpureolineata evolution. Land slugs survival, as their tiny eyes only crawled out of the sea register dark and light. and evolved lungs and But the rhinophores aren’t Slug of another kind? a respiratory system, the nudibranch’s only marine When I tell people I love sea slugs whilst nudibranchs adaptations. On the back of the I often get a strange look. Most of stayed in their aquatic Glossodoris cincta, away from the time the term ‘slug’ drums up environment. As for why both the creature’s head, is a cluster of visions of the small, mud-coloured groups subsequently lost their appendages. In this species’ case garden variety that invades protective shells; that’s still being they resemble a small feather gardens across the UK. While the debated by scientists. So, while duster. But they can range from nudibranch’s basic shell-less body both land and sea slugs are similar large tentacle-like clusters of type is similar to that of the land in a basic way, in actuality they contrasting colours, to invisible, slug’s (the word slug only refers are quite different creatures. such as in the case of Phyllidra. to their body type) the marine In many instances, the versions are farther apart on the Made for the sea appendages on some nudibranchs’ evolutionary scale than snails and In the wave-dappled sunlight backs add to their magnificent land slugs and they couldn’t be streaming down to my place above appearance, but they aren’t just a more visually different. Many are the coral, I have resumed my pretty adornment; they’re actually covered in such dazzling patterns search. This time my scan reveals gills, which enable them to extract and colours that they look more a multi-coloured Glossodoris cincta oxygen from the water around like undersea jewels than soft- moving sedately, its muscular foot them. And because bits waving bodied molluscs. But in fact, that’s flexing rhythmically to propel it about in the current can act like a exactly what they are. along its perch. lure for curious predators, many Like land slugs, sea slugs I wave my hand gently in the nudibranchs with these types of belong to the scientific class water above its head and watch gills have evolved the ability to Gastropoda. In essence, they’re as two small horn-like projections retract them into in the same group. They both sway in the current. These are the a pocket where evolved from shelled, sea-dwelling nudibranch’s rhinophores. they are safe creatures, and both share several In air, chemical molecules from nibbling. basic characteristics. For instance, float about and are detected by they both possess a muscular foot, animals with scent receptors. which they use for locomotion, In our case, scent receptors are and both have a mantle, which found in our nose. The same encloses their organs. Surprisingly, senario happens in the sea, they also share a fairly complex as dissolved chemicals float Se a PHYLUM: M a-s ali ollu lug nim scs cl : A ropod ass OM ast a if c NGD og ation KI rth hia C S: O anc LA LAS br S BC di S: SU u Ga da : N stropo SS O LA R BC DE SU R: O hia pisthobranc Chromodoris magnifica 66 THE SEA – Phylllidia Phyllidia Chromodoris ocellata elegans annae Nembrotha kubaryana Phyllodesmium Nembrotha Phyllidiella pustulosa briareum aurea Chromodoris Tambja kuniei morosa Chelidonura varians The word nudibranch is made from two Latin words: nudus, meaning naked and branchia, meaning gills. Essentially, nudibranch means ‘naked gills’. Nudibranchs actually belong to a suborder of Opisthobranchia and, to make things really confusing, not all sea slugs are nudibranchs! However, many divers and enthusiasts have come to use the terms ‘sea slug’ and ‘nudibranch’ interchangeably. Glossodoris tropod cincta gas a rtho C S: O LA LAS SS UBC : Gastropoda S t Survival secrets d b an As I check my dive gauges and nu i r chs ascend over the top of the coral head, I can’t help but marvel at how camouflaged sea slugs actually are. When gazing at photos and taking in their dazzling colours and patterns, people often assume they should be easy to spot, but amidst their natural habitat they can be nearly impossible to find, and this is one of the keys to their survival. Their colours, patterns and even shape have evolved over time to provide sophisticated protection from veritable sea of predators. In nature, brightly coloured animals are often harmful, and this is also true of sea slugs. In many cases their brilliant display is a warning to predators to keep away from stinging flesh, foul tastes and panish d poisonous chemicals. r S anc s, o er, h neu ave o S ui de ty t pe ang rgest, m velop bili cies s s he la easu ed the a like chu of t ring the He bran one upw m! xa s is ards of 40c sw ecie im. r sp This particula Ceratosoma trilobatum 68 THE SEA HOME-GROWN NUDIBRANCHS Fabulous sea slugs aren’t just exclusive to warm tropical waters. Many interesting and beautiful specimens can be found Spanish dancer, close to home! Bernard Picton, author of Hexabranchus ‘Nudibranchs of the British Isles’, shares Sanguineus, in action! some of his favourites... Favorinus bilanus nis r Spa h danc s, o er, h neu ave o S ui de ty t pe ang rgest, m velop bili cies s s he la easu ed the a like chu of t ring the H ran ne upw ! Flabellina lineata exab is o ards 40cm s cies of wim spe Janolus cristalus . This ticular par The fascinating thing about incorporate the pigments from some sea slugs is that they get their food into their skin. This their harmful chemicals from the results in camouflage that is so food they eat. These nudibranchs precisely matched, it can be nearly feed on sea anemones, corals, impossible to distinguish them jellyfish and other stinging from their background! organisms and are able to Besides colour and pattern, a store their food’s stinging cells few nudibranchs have developed (nematocysts) and use them in their the ability to cast off body parts in own defence. a process known as autotomy. One But not all nudibranchs are nudibranch is able to quickly drop brightly hued. Many temperate- its mantle, confusing predators and water species are less lurid aiding its escape, while another than their tropical counterparts, species, Phyllodesmium, is able to which makes sense, since their cast off parts that secrete a sticky environment is generally less mucus. These gluey bits are left colourful and bright patterns would behind to wriggle and distract increase their visibility – think of predators while the Phyllodesmium a Hawaiian shirt in the Arctic! In makes its getaway! Rostanga rubra fact, many Arctic and Antarctic Other species, like the sea slugs are snow white and Hexabranchus sanguineus, or Okenia elegans unpatterned, while UK species tend Spanish dancer, have developed towards subtle browns, oranges, the ability to swim. This species peaches and whites. is one of the largest, measuring While the sea slugs that upwards of 40cm, and is usually rely on camouflage as a nocturnal.