seeNow you me ...

For all marine creatures, sustenance is a driving force in their daily lives. The seaweeds require light and nutrients, the herbivores suitable vegetation to graze, and the carnivores are almost constantly on the hunt for prey. For most, the need to eat and avoid being eaten have been major evolutionary pressures, influencing not only where they live and the way they behave, but also the way they look. The latter can be expressed in a variety of ways, including some that would seem to be totally at odds with what might be expected. by John Huisman and Alan Kendrick Photos by John Huisman healthy ecosystem with a diverse range of is a joy to A behold. But essential to this is a balance between the primary producers, the herbivores and the carnivores. Too many, or too few, of one group can impact on the others, upsetting the equilibrium and potentially causing the entire ecosystem to undergo sometimes quite dramatic changes in structure and function. To maintain this fine ecological balance, species have evolved numerous survival strategies, both to keep themselves fed and to avoid being eaten. Here we look at just a few of the myriad ways that marine species have achieved this. NOW YOU SEE ME … “The most obvious strategy to elude predators is to be NOW YOU DON’T inconspicuous – in shape, colour, or both – to blend The most obvious strategy to elude imperceptibly with the surroundings and remain unseen predators is to be inconspicuous – in shape, by any potential predator looking for a meal.” colour, or both – to blend imperceptibly with the surroundings and remain unseen by any potential predator looking for a of the tropical leopard flounder (Bothus colourful mosaic of algae and encrusting meal. One of the best practitioners of this pantherinus) almost precisely matches invertebrates. The wobbegong’s strategy is the flounder, a bottom-dwelling the colours of the sandy seabed where dangerous mouth is even obscured by fish, which has undergone a massive it most commonly occurs. Such cryptic the presence of branched, seaweed-like rearrangement of body parts. Evolution in colouration, or , is common among skin extensions around the front of its the flounder has resulted in a flat body that marine organisms. Of course, this strategy head, which soften its outline and enables can lie snug against the sea floor, while at will only work if the remains still, as it to blend in smoothly with the natural the same time one eye has shifted so that any movement will usually draw attention. surroundings. The shark remains perfectly both sit on the upper side. Interestingly, Cryptic colouration can also be very still, other than sometimes waving its tail the eyes of larval flounder are on both effective for predators, as they can remain to lure smaller fish, before launching a fast sides of their head and this remarkable hidden and lie in wait for unsuspecting and unexpected ambush on prey that stray change occurs as they grow into juveniles prey. The tasselled wobbegong shark too close. on the seabed. The pale, mottled colour (Eucrossorhinus dasypogon) is found in Numerous other species of marine fish northern and can grow up to and invertebrates have evolved cryptic 1.8 metres in length. During the day the colouration. The prickly leatherjacket shark often settles in caves, where its (Chaetodermis penicilligerus) merges strongly patterned blends almost imperceptibly with the background effectively with the rocky seabed and its and has a few seaweed-like frills to complete the effect. The broadclub cuttlefish (Sepia latimanus), which is a cephalopod like octopuses and squid, has the ability to change its skin colour at will, Previous page Main Hermit crabs use empty mollusc shells blending instantly with its surroundings. as their home. When a cuttlefish swims from a reef to a sandy area, its colour will change to match Above A decorator crab (Naxia sp.) with its the new background. It also uses evolving clever camouflage of seagrass and seaweed. colour patterns to communicate with Left Leopard flounders (Bothus pantherinus) other cuttlefish, or as warning signals. have both eyes on one side so they can lay Unsurprisingly, they are often called the undetected on the ocean floor. ‘chameleons of the sea’.

24 LANDSCOPE Above Prickly leatherjackets (Chaetodermis penicilligerus) blend into their environment.

Right Broadclub cuttlefish (Sepia latimanus) change their colour to match their surrounds and to communicate.

NATURAL DISGUISES a home, providing the crab with a mobile that they are distasteful and not to be protective casing that also hides it from eaten. Fish, it seems, are fast learners, Of course if changing colour or potential predators. and an unpleasant encounter with a toxic modifying body shape is not possible, nudibranch ensures they will no longer you can always sequester parts of the EAT ME IF YOU DARE! try them as food. Some nudibranchs surrounding vegetation to hide beneath. While camouflage and remaining produce their own toxins, but others store The decorator crab (Naxia sp.) is inconspicuous are intuitively excellent compounds derived from their own food, expert at attaching pieces of seaweed strategies to avoid predators, there are such as sponges. Such is the case of the and even seagrass to its hard carapace, numerous marine species that have spectacular nudibranch Chromodoris kuniei, resulting in an almost perfect disguise. evolved to be outstandingly bright and which feeds on sponges and uses its toxic The crab selects suitable material from colourful. So how does being so obvious chemicals for its own defence. its surroundings, coats the ends with a help to avoid predation? The answer lies This bright warning colouration, also gland secretion that hardens in seawater, in an unusual phenomenon, not unique known as aposematic colouration, is such and then attaches it to special hooks to the marine environment, but certainly an effective deterrent strategy that many that cover its shell. The algae and seagrass prevalent among marine creatures. Many other species have now evolved apparently even continue to grow, ensuring that species that are poisonous, or at least vivid warning colours, but do not have the the crab looks exactly like a small rock contain distasteful compounds, are also poisonous compounds that are so often when it remains still. the most colourful. These bright colours advertised by such patterns. Why bother Decorator crabs are remarkably warn potential predators that if you eat wasting valuable energy developing toxic attentive to the effectiveness of this me you could die, or if you survive, it will defences, which can otherwise be spent on protection. When moved to a different have been a very unpleasant experience. growth and reproduction, when you can habitat, they rapidly shed the original This strategy is perhaps best developed get the desired outcome with a relatively camouflage and attach materials from by the spectacularly colourful shell-less simple disguise? the new home, ensuring that their molluscs known as nudibranchs, which are Looking like another species is known disguise blends into the most recent much loved by underwater photographers. as , with the imitator known surroundings. Similarly, other crabs can Many nudibranchs make no effort to hide, as the mimic and the species being use anemones, sponges and an assortment and their visibility is accentuated by bright mimicked known as the model. Mimicry of invertebrates as camouflage and colours and bold patterns. They embrace of a toxic species by a non-toxic species protection. In another form of camouflage, this seemingly carefree attitude because is known as , after the hermit crabs adopt empty mollusc shells as their colours signal to potential predators English naturalist Henry Bates, who first

LANDSCOPE 25 recognised the phenomenon in butterflies. Above A Western Australian sea hare ( Batesian mimicry can only be effective if gigantea). the prevalence of the mimic species does Right top and right Nudibranch (Phyllidiella not exceed that of the model, otherwise pustulosa) and flatworm (Pseudoceros potential predators may encounter the imitatus) look almost identical with the flatworm enjoying the protection brought by non-toxic species more often, and not resembling a tropical nudibranch. associate the warning colours with an unpleasant taste. In some cases both the mimic and model are toxic, which serves as a strong reinforcement of the warning distasteful model. These two are not warn off potential predators. Like many to predators to stay away. This type of the only lookalikes; several other species marine , the toxic compounds in mimicry is known as Müllerian mimicry, of nudibranchs are mimicked by other crabs are not produced by the animals after the German naturalist Fritz Müller, organisms, including flatworms, juvenile themselves but are derived from external who, like Bates, worked with butterflies. holothurians (sea cucumbers) and even sources, such as diet or possibly symbiotic Batesian or Müllerian mimicry is often other nudibranchs. bacteria. seen in polyclad flatworms, many of which Not all toxic sea flag their display colours and patterns remarkably toxicity with bright colours. The Western SEAWEED MIMICS similar to those of nudibranchs. Flatworms Australian sea hare (Aplysia gigantea) Mimicry is most often associated with are carnivorous members of the phylum has cryptic colours, but is also toxic. animals, but a few seaweeds are also Platyhelminthes and are common in the This species is short-lived and spawns in excellent at hiding their true identity. In marine environment, where they are often shallow water during summer and early this case, rather than adopting the guise of conspicuous due to their bright colours. autumn. They often wash up in large a toxic species, the seaweeds take on the The flatworm Pseudoceros imitatus numbers on WA beaches, where they appearance of a less palatable organism. mimics the colour pattern of the unrelated attract the interest of dogs. This has led The red seaweed Rhodogorgon was Phyllidiella pustulosa, a tropical nudibranch to numerous poisonings, but fortunately named due to its uncanny resemblance that deters fish predators by secreting most are treatable and the dog survives. to a gorgonian coral, and this mimicry a milky substance containing noxious The toxic red-eyed rock crab (Eriphia deceived seaweed and coral biologists compounds. The flatworm has evolved sebana) seems to be hedging its bets. It has until very recently. Another red seaweed, an almost exact copy of the nudibranch’s a fairly bland colour that merges well with Eucheuma arnoldii, has evolved to mimic colour and patterns, undoubtedly the background, but also has vivid red eyes the very common hard coral Acropora, reaping the benefits of looking like its that standout like beacons and presumably presumably taking advantage of the fact

26 LANDSCOPE that herbivorous predators have little such as the rubbery Titanophora pikeana, by most species, but are eaten by a small interest in eating the stony coral skeleton. can appear strikingly like coralline algae, number of specialists that can tolerate or This disguise is so perfectly rendered that presumably gaining protection from the sequester the active compound. These the algae even has the distinctive bluish similarity. include the red seaweed Asparagopsis, branch tips with a polyp-like structure, a Several seaweeds, like animals, which produces halogenated metabolite distinguishing feature of Acropora corals produce compounds that make them bromide as a chemical defence, but and is in fact the source of its name (the unpalatable to fish. The turtle weed is grazed by the pygmy sea hare Greek word acro means ‘tip’). The alga in (Chlorodesmis fastigiata) produces a (Aplysia parvula). Perhaps surprisingly, the photo was seen recently at Ashmore cytotoxic terpene that deters grazing Asparagopsis is highly prized in Hawaiian Reef, and actually went unnoticed by by fish, but surprisingly the chemical cuisine, where it is known as ‘limu kohu’ seaweed biologist and WA Herbarium stimulates grazing by the aptly named and is used to flavour raw fish and stews. curator John Huisman but was picked up turtle weed crab (Caphyra rotundifrons), The struggle to survive could be by the WA Museum’s coral biologist Zoe which lives exclusively among the described as an ongoing battle between Richards, who was stunned to find that seaweed filaments and feeds on them. species, each evolving novel ways to gain what she thought was a stony Acropora The crab benefits further by its association sustenance while avoiding being eaten. coral was actually flexible. The disguise with the seaweed, as it experiences It’s not surprising that this has resulted clearly confuses more than just potential significantly reduced predation. There are in a seemingly endless array of different grazers! several other examples of seaweeds that strategies, many of which, undoubtedly, Seaweeds can also be protected from are chemically defended against grazing are yet to be discovered by biologists. grazing by producing a calcium carbonate skeleton. Numerous species do this, but it is most well-developed in the coralline red algae, many of which can be rock- hard and bear little resemblance to their more plant-like relatives. Coralline algae are not immune to grazing fishes and often bear teeth marks and scars, but the number of grazers is considerably reduced by their calcified structure. Other algae,

Above and above right Red seaweed (Eucheuma arnoldii) has evolved to mimic a John Huisman is the WA Herbarium’s curator and is a specialist in seaweed . hard coral (Acropora vaughani). He can be contacted at [email protected]. Photo (right) – Zoe Richards/WA Museum Alan Kendrick is the Marine Science program leader at Parks and Wildlife. He can be contacted at [email protected]. Right A red-eyed rock crab (Eriphia sebana).

LANDSCOPE 27