Amazing Facts about Australian
Marine Life
Tony Ayling & Steve Parish Corals • Crustaceans • Sea stars & more
History of
of marine life KINGDOM
PHYLUM
CLASS
ORDER
KINGDOM
PHYLUM
CLASS
Malacostraca
ORDER
POPULAR NAME
Stomatopoda
Mantis shrimps
Cyanobacteria
Mysidacea
Mysids
Foraminifera
Forams
Isopoda
Isopods
Bacillariophyta
Diatoms
Amphipoda
Amphipods
Dinophyta
Dinoflagellates
Euphausiacea
Krill
Chlorophyta
Green algae
Decapoda
Shrimps
Phaeophyta
Brown algae
Lobsters
Rhodophyta
Red algae
Crabs
Fungi
Slipper lobsters
Lichens
Ghost shrimps
Monera Protista
POPULAR NAME
Bacteria
Fungi Plantae
Magnoliophyta
Seagrasses
Animalia
Porifera Hydroida
Hydroids
Siphonophora
Bluebottles
Cnidaria
Hydrozoa
Mollusca
Aplacophora
Aplacophorans
Mangroves
Polyplacophora
Chitons
Sponges
Gastropoda
Gastropods
Bivalvia
Bivalves
Scaphopoda
Tuskshells
Cephalopoda
Squids
Milliporina Stylasterina Anthozoa
Actinaria
Octopus Anemones
Corallimorpharia Jewel anemones
Brachiopoda
Brachiopods
Bryozoa
Bryozoans
Zoanthidea
Zoanthids
Echinodermata Crinoidea
Feather stars
Scleractinia
Stony corals
Asteroidea
Sea stars
Ceriantharia
Tube anemones
Ophiuroidea
Brittle stars
Antipatharia
Black corals
Echinoidea
Sea urchins
Alcyonacea
Soft corals
Holothuroidea
Sea cucumbers
Gorgonians
Ascidiacea
Ascidians
Sea pens
Thaliacea
Salps
Sea jellies
Larvacea
Larvaceans
Cubomedusae
Box jellies
Agnatha
Jawless fishes
Polycladida
Flatworms
Chondrichthyes
Sharks & rays
Ribbon worms
Osteichthyes
Bony fishes
Pennatulacea Scyphozoa Cubozoa Platyhelminthes Turbellaria
Nautilus
Nemertea
Round worms
Reptilia
Reptiles
Annelida
Polychaeta
Polychaete worms
Aves
Birds
Arthropoda
Pycnogonida
Sea spiders
Insecta
Insects
Cirripedia
Barnacles
Copepoda
Copepods
Ostracoda
Ostracods
( Crustacea )
Text: Tony Ayling. Uncredited photography: Steve Parish
Mammalia
Pinnipedia
Seals
Cetacea
Whales
Sirenia
Dugongs
THE FIRST LIFE ON EARTH The planets of our Solar System first formed about five billion years ago but the early Earth was far too turbulent and hot for life to form for the first billion years of its existence. As temperatures dropped, Earth had a dense atmosphere of carbon dioxide, reeking of hydrogen sulphide and methane and this fuelled the first archaebacteria that developed about 3800 million years ago. The first recognisable bacterial fossils are domed stromatolites from Western Australia, dating from 3500 million years ago — structures that were generated by early photosynthetic cyanobacteria. Hordes of these bacteria eventually used up much of the carbon dioxide and generated oxygen, paving the way for the evolution of more complex organisms. About a billion years ago a range of multicellular organisms first appeared, including algae, fungi and the first animals. The advent of sexual reproduction was probably responsible for this sudden multicellular development. The fossil record is strangely bare for the next 400 million years, but an odd faunal group discovered in the Ediacara Hills of South Australia signalled another link in the story of life. The poorly understood Ediacaran animals of 560 to 580 million years ago were probably bottom-living filter-feeders of various kinds.
THE FIRST APPEARANCE OF MODERN GROUPS A mass extinction at the close of the Precambrian 550 million years ago paved the way for the rapid evolution of modern animal groups. Within a remarkably short time sponges, hydroids, corals, sea jellies, worms, crustaceans, molluscs, brachiopods, and echinoderms had all appeared in the amazingly rich seas of the Cambrian Period between 550 to 500 million years ago. In fact, all of the many major divisions of animal life that are still present today evolved in a rush during the Cambrian. This period also saw a rapid increase in diversity with a rise in the number of animals inhabiting Earth’s seas. Most of these animals evolved some sort of skeleton to help to support their larger multicellular bodies. Since the development of invertebrate groups in the Cambrian, there have been several major episodes of extinction that have shaped marine communities — the latest at the end of the Cretaceous when dinosaurs and many other groups died out. Modern forms of marine life have evolved over the past 50 million years but the basic patterns were all laid down more than 500 million years ago.
Below: Dendronephthya soft coral tree
Right, top to bottom: Close Sea Star; Prickly Sea Cucumber, Striped Feather Star; Pectinia Hard Coral.
Dolphins
RIGHT: TONY AYLING
Nematoda
Chordata
Australian marine life
From Steve Parish Publishing’s Amazing Facts: Marine Life ~ www.steveparish.com.au
Introduction
Introduction
Taxonomic chart
Massive sponges
or animals? Kingdom: Monera ( Cyanobacteria ) and Protista Phyla: Foraminifera
Above: Stromatolites
Porifera
GARY BELL/OCEANWIDE IMAGES
Foraminifera
Plants
— simple but effective Phylum: Porifera Above: Sponge oscules
OIL SLICKS? Trichodesmium slicks sometimes become so thick and extensive that they are reported as oil pollution to Great Barrier Reef managers. THE OLDEST FOSSILS: Stromatolite fossils discovered in Western Australia and aged at 3500 million years are the oldest known fossils. FORAMS: Using their food-trapping pseudopods ( “false feet” ) to crawl over the sea bed, forams can move surprisingly quickly. ROCK FORMING: Forams are so numerous, both on the bottom and as plankton in open water, that over half of the calcareous sedimentary rocks on Earth have been formed by accumulations of their skeletons! A CLUE TO OIL: Geologists are particularly interested in the rock laid down by forams. Oil-bearing rocks are often closely associated with forams. SYMBIOTIC: The common benthic coral reef forams ( Marginopora spp. ) rely on tiny symbiotic zooxanthellae for most of their energy requirements.
Many marine organisms are hard to categorise. Plants may look like rocks, animals may look like plants and some species look like nothing else on Earth! The distinctions between some groups of organisms are hard even for scientists to agree on, and so major groupings are constantly changing.
MINUTE BUT ABUNDANT During spring and summer in tropical waters around Australia, vast orangebrown slicks appear on the water surface. They are often mistaken for oil spills or some other form of pollution. In fact, these slicks are blooms of millions of minute cyanobacteria known as Trichodesmium. Cyanobacteria are bacteria that get their food by photosynthesis and it is these photosynthetic pigments that give the slicks their characteristic yellow or orangebrown colour. Extensive Trichodesmium Top: Rock-like algae — crustose corallines slicks inspired early explorers to give the Above: Algae-like animals — the bryozoan Bugularia Red Sea and Yellow Sea their names. Cyanobacteria were also responsible for creating the oldest fossil evidence of life on Earth. Ancient dome-shaped concretions were thought to be the result of physical processes until the stromatolites of Western Australia were discovered. Scientists found that cyanobacterial mats produce a sticky gel that protects them from ultraviolet radiation. This gel traps sediment and becomes opaque to light, so the bacteria migrate to the surface again leaving the sediment to be bonded by calcium carbonate extracted from the seawater. The resultant mounds grow less than 1 mm a year but eventually form the extensive beds of stromatolites that can be seen in the shallow, warm waters of Shark Bay in Western Australia.
TONY AYLING
PINK DISCS Small pink discs with a hole in the middle are often seen on the surface of dead coral on coral reefs. These are benthic Foraminifera ( colloquially known as forams ): single-celled protists that have a calcareous skeleton. Long pseudopodia ( “false feet” ) extend out through holes in the skeleton to trap organic material, which the forams feed on. Left: Marginopora forams Text: Tony Ayling. Uncredited photography: Steve Parish
Conservation Watch Species: 1476 species in Australia; approximately 5500 species worldwide. Habitat: Coral and rocky reefs; some species on sandy bottoms.
the FACTS!
MANY DIFFERENT SHAPES Massive sponges come in a huge variety of shapes, sizes and colours. They may Above: Pink Tube Sponge be shaped like balls, vases, tubes, fingers, nets or plates and range in size from a centimetre to over a metre. Sponges may be rough and hard, or soft and slimy, black or white or all colours of the rainbow. All sponges have an internal skeleton that is made from a mixture of fibres and glass-like silica spicules. These spicules come in many different shapes ( from stars to rods ) and the largest are usually only a few millimetres long. These sharp, irritating spicules help to discourage predation. Sponges eat microscopic phytoplankton and bacteria that they filter from the surrounding water. Water is sucked through a series of small pores on the outside of the sponges into a network of canals lined with special whip-like cells ( choanocytes ). Filtered water exits through larger exhalant openings (oscules) and is jetted away from the top of the sponge colony.
SYMBITOIC ZOOXANTHELLAE: Many tropical sponges have huge numbers of symbiotic algal cells throughout their tissues. These algae get a safe place to live and in return provide the sponge with more than half its food needs. CALCEROUS SKELETON: Most sponges have silica ( glass ) spicules in their skeleton but one group, known as calcareous sponges, have spicules made of calcium carbonate. A CHIP OFF THE OLD BLOCK: Many sponges can reproduce asexually by budding off small spongelets that roll along the bottom with wave and current movement and attach elsewhere. These colonies are genetically identical to the parent sponge.
NO ORGANS Sponges have no organs. How do they reproduce without testes or ovaries? Special reproductive cells scattered through sponges produce either eggs or sperm that are released through the exhalant canals when they spawn. Such a system is highly versatile and different species have different arrangements. Some sponge colonies have separate male and female individuals, while others are hermaphrodites with both male and female cells in the same individual. For most species fertilisation of the egg takes place in the water and a larva develops that later settles to the bottom and begins life as a tiny new sponge. Sponges have a low-energy lifestyle and most species grow very slowly, taking decades to reach a large size.
POISONS: Many sponges produce toxins to make them unpalatable to grazers. AGE OF SPONGES: A few studies have suggested that massive sponges grow very slowly, with no measurable growth detected over 5 years! Large sponges may be hundreds of years old.
Below, left to right: Vase sponge; Volcano sponge.
LEFT & RIGHT: RON & VALERIE TAYLOR
the FACTS!
TONY AYLING
WHAT AM I?
Sponges are the most primitive multi-celled creatures in the animal kingdom. Although they are animals they have no organs, brain, gut or nerves. Instead of organs, sponges have several different specialised cells that carry out all the functions for maintaining life.
SCLEROSPONGES: An ancient group of sponges have a solid silicious skeleton and feel like rock to the touch. They live deep in caves on the Great Barrier Reef or in very deep water.
From Steve Parish Publishing’s Amazing Facts: Marine Life ~ www.steveparish.com.au
Acroporid corals
— the reef builders
— weeds of the reef
Phylum: Cnidaria Class: Anthozoa Order: Scleractinia
TONY AYLING
Stony corals in the order Scleractinia are the basic building blocks of all the world’s coral reefs. These simple anemone-like animals are able to extract calcium carbonate from seawater to create a stony skeleton. The combined effort of millions of colonies gives rise to biological structures that are visible from space!
Above: Staghorn bleaching
Conservation Watch Species: 436 species in Australia; 792 species worldwide. Habitat: Coral and rocky reefs.
Below, top to bottom: Assorted corals; Coral plates; Partly bleached corals.
the FACTS!
LOTS OF REEFS: The Great Barrier Reef is not a single structure but is made up of about 2900 separate corals reefs. BLEACHING EPISODES: Bleaching occurred worldwide during the El Niño event of 1998 and damaged lots of coral reefs. Another episode in the summer of 2002 killed many corals in northern Australia.
These corals are the weeds of the reef, growing quickly and covering all available space. As a consequence of this fast growth, acroporid corals have a relatively thin and porous skeleton. They are fragile and break easily so that even the largest colonies can be completely pulverised during cyclonic weather.
SYMBIOSIS DRIVES LIFE Individual stony coral polyps have a ring of tentacles, very similar to those of sea anemones, that trap zooplankton from the surrounding water. But planktonic food does not provide sufficient energy to build the large carbonate skeletons that form reefs so stony corals rely on the extra energy they receive from the symbiotic zooxanthellae that live within their bodies.
THE MOST ABUNDANT CORALS Acroporids are the most abundant corals on most of the world’s reefs, especially in shallow seas with good water movement. They totally dominate some shallow Great Barrier Reef sites and usually account for more than half of the cover of live corals on slopes less than 10 m deep. There are two major groups of acroporids: the branching Acropora species and the encrusting Montipora species. Acropora corals have a single tubular polyp at the tip of each branch and smaller tubular polyps around the sides. They can form extensive staghorn-like thickets, small branched clumps, large plates or clusters of thick columns. Montipora corals usually form thin sheets, either encrusting, plate-like or vase-shaped and have tiny ( pin-head sized ) polyps. Acroporids are usually pale brown or fawn in colour but can also range from green to blue or pink to orange. These corals usually have their polyp tentacles withdrawn during the day and extend them at night to feed.
Zooxanthellae take waste nutrients and carbon dioxide from the coral animal and use sunlight to generate food, some of which is diverted to the coral host. Stony corals get almost three-quarters of their energy requirements from their zooxanthellae. This whole process is temperature-dependent and provides only enough energy for reef formation where sea temperatures do not drop below 18 ºC for more than a short period during winter. Northern Australia supports large areas of coral reef, including the iconic Great Barrier Reef and Ningaloo Reef near North West Cape, Western Australia.
GROUP SPAWNERS Acroporid corals reproduce sexually as part of the coral mass spawning spectacular that occurs when the water warms up in spring. Each colony is hermaphroditic. As the spawning night approaches, clusters of about eight eggs together with packets of thousands of sperm are gathered together in the body cavity of all the coral polyps. In October or November, about four nights after the full moon, all the acroporid corals release their small pink egg and sperm clumps a few hours after dark. Once the sperm are released, they fertilise eggs from corals of the same species. This fertilised egg then develops into a planula larva and eventually settles to form a new coral colony.
Text: Tony Ayling. Uncredited photography: Steve Parish
When sea temperatures exceed 31–32 ºC, zooxanthellae photosynthesis speeds up and starts to produce toxic compounds that damage the coral host. When this happens, the coral ejects the suddenly toxic algae and so turns stark white — because the algal pigments are the coral’s only natural colour. These white corals are said to be “bleached”. Stony corals can only survive for a few weeks without their zooxanthellae. If sea temperatures drop within that time, the corals can regain their zooxanthellae and survive, but if temperatures remain high the coral will die. Increased sea temperatures associated with global warming have caused several damaging bleaching episodes on Australian coral reefs in the past decade.
From Steve Parish Publishing’s Amazing Facts: Marine Life ~ www.steveparish.com.au
Below, left to right: Montipora whorls; Acropora coral polyps; Acropora staghorn.
LEFT TO RIGHT: TONY AYLING
REEF AGE: Modern stony corals first appeared 24 million years ago at the beginning of the Miocene Epoch but reefs did not develop in northern Australia until about two million years ago.
Phylum: Cnidaria Order: Scleractinia Family: Acroporidae
CORAL BLEACHING
TONY AYLING
SOUTHERN REEFS: Lord Howe Island off the New South Wales coast is home to the most southerly Pacific coral reef, and the Houtman Abrolhos Islands off Western Australia are the site of the most southerly Indian Ocean reefs.
TONY AYLING
MORE TOLERANT: Individual stony corals can live in southern Australia ( where sea temperatures drop as low as 11 ºC ), but they cannot form reefs in these colder waters.
TONY AYLING
REEF AREA: Coral reefs cover more than 250,000 km² of the world’s tropical seas.
Cnidaria
Cnidaria
Stony corals
Above: Montipora incrassata
Conservation Watch Species: 138 species in Australia; 261 worldwide. Habitat: Coral reefs.
the FACTS! COMMON NAMES: Most corals do not have widely established common names but the most abundant acroporid corals are usually known as staghorn corals and plate corals. SIZE OF COLONIES: Acroporid corals do not stop growing, and eventually reach very large sizes. Staghorn Acropora colonies more than 100 m across have been measured on the Great Barrier Reef. RAPID RECOVERY: Although acroporids are easily broken, the scattered fragments often survive. Each broken piece quickly repairs itself, begins to grow rapidly and eventually re-attaches to form a new colony. SUSCEPTIBLE TO BLEACHING: Acroporids are susceptible to bleaching. When the sea temperature rises, acroporids can suffer severe bleaching episodes.
Conservation Watch Species: Number of species unknown; over 50 genera. Habitat: Coral and rocky reefs, often in deep water.
the FACTS!
— quills of the sea floor
Phylum: Cnidaria Class: Anthozoa Subclass: Octocorallia Order: Alcyonacea
Phylum: Cnidaria Class: Anthozoa Subclass: Octocorallia Order: Pennatulacea
Many octocorals have a net-like structure of fine polyp-covered branches that makes an extremely efficient plankton-trapping device. These animals are generally known as gorgonians and orient with the flattened net across the normal current flow to filter the water most effectively.
Sea pens are strange cnidarians that have adapted to life in sand or mud habitats. Many of these animals have a feather-like shape and are named for their resemblance to the feather quills that were once used for writing with ink. Other sea pens look like a small soft coral protruding from the sand bottom.
TOUGH SUPPORTING SKELETON
HOW BIG ARE GORGONIANS? Most gorgonians are less than 50 cm high but some Melithaea gorgonians from the Great Barrier Reef may have fans 1–2 m across. Some deep water gorgonian colonies over 3 m high have been dredged in the Atlantic. ZOOXANTHELLATE: To help provide for their energy needs, a few shallow water coral reef dwelling gorgonians have symbiotic zooxanthellae in their tissues. These are the only species able to compete with stony corals. SEA WHIPS: A few species of gorgonians, including the common genus Junceella ( below ), do not branch and these are usually referred to as sea whips.
Above, top to bottom: Ellisella sp. gorgonian; Annella gorgonian.
BROODED LARVAE
Right, top to bottom: Yellow gorgonian Annella; Red gorgonian polyps; Red gorgonian Ctenocella. Text: Tony Ayling. Uncredited photography: Steve Parish
RON & VALERIE TAYLOR RON & VALERIE TAYLOR
SEA WHIP BUDDING: Most gorgonians do not reproduce asexually; however, sea whips can bud off the colony tips to form propagules that fall to the bottom, attach and begin to grow as a new colony.
Most gorgonians in tropical waters are found in water deeper than 20–30 m or under overhangs where they do not have to compete with corals. In southern Australia sea fans and gorgonians are also found in deep water or under overhangs to avoid competition with seaweeds and kelp. Gorgonians have separate male and female colonies and the males release their sperm into the water shortly after sunset during the breeding season. Females retain their eggs within the polyp body cavity where they are fertilised and begin to develop into planula larvae. When the larvae are almost ready to settle, these brooded larvae are released by the female and settle relatively close to the parent colony.
OOZOOID — THE PEN IN THE QUILL
RON & VALERIE TAYLOR
Gorgonians and sea whips have a central skeleton made of a mixture of calcareous sclerites and a horn-like substance appropriately called gorgonin. The gorgonin provides flexibility to the thin skeletal net — a skeleton composed only of fused sclerites would be too brittle to cope with strong currents, wave surge or being bumped by passing fishes. The proportion of sclerites and gorgonin, as well as the arrangement of the sclerites, differs among gorgonian genera. Coloured body tissue, bearing many expandable feeding polyps, covers the skeleton. Like all octocorals, the polyps have eight large, frilly tentacles that are richly supplied with stinging nematocysts to catch passing zooplankton. With all their tentacles expanded, gorgonians can filter most of the water passing through the holes in their net.
Cnidaria
Sea pens
— plankton-trapping nets
TONY AYLING
Cnidaria
Gorgonians & sea whips
All sea pens have a single modified polyp ( oozooid ) that forms the central support structure of the quill. This axial polyp has a sterile stalk or foot at the base and an upper rachis ( main shaft ) that either directly supports the other polyps or many pairs of “leaves” that bear the polyps. The rachis usually has a strengthening central core of calcareous sclerites. Sea pens have two types of polyps — normal eight-tentacled feeding polyps similar to those of all soft corals, and special siphonozooids that lack gonads and tentacles. Their purpose is to pump water into the central polyp and keep the colony’s hydroskeleton inflated. Sea pens use rhythmic contractions of their foot to burrow the extensible base of the Top: Black sea pen (Sarcoptilus sp.) supporting polyp into Above: Sea pen (Pteroeides sp.) the sand, anchoring Right: White sea pen (Sarcoptilus sp.) the animal firmly and leaving the rachis and feeding polyps extending up into the water column. By turning off the water pumps, the entire animal can withdraw quickly into the sand.
LIFE IN THE CURRENTS Sea pens prefer to live in areas that are regularly swept by currents that ensure them a constant supply of planktonic food. They do not withstand wave surge and either live in protected waters or in depths below the reach of the waves. Many species remain withdrawn in the sand during the day and only emerge at night to feed, although they are often seen feeding on overcast days when there is a good feeding current running. Sea pens often stay beneath the sand if there is no current and it is not worthwhile feeding.
From Steve Parish Publishing’s Amazing Facts: Marine Life ~ www.steveparish.com.au
Above: Sea pen ( Cavernularia obesa )
Conservation Watch Species: Number of species in Australia unknown; over 30 genera and 300 species worldwide. Habitat: Sand and mud habitats, often in deep water.
the FACTS! POORLY KNOWN: Although sea pens are found throughout Australia, they are most abundant in deep water and are rarely seen. Their taxonomy and biology is poorly known and many species remain undescribed. DEEP SEA DENIZENS: Sea pens are most abundant in deep water and have been found at depths of over 5000 m. HOW BIG ARE SEA PENS? Most sea pens only extend 10–20 cm above the sand bottom when they are expanded and feeding ( with a similar length buried in the bottom ). Some deep water species may be 80 cm in length. SEA PEN REPRODUCTION: Sea pens have separate male and female colonies and most species release eggs and sperm into the water during group spawning episodes. A few species brood their larvae within the female polyps as gorgonians do. LUMINESCENCE: When disturbed, sea pens pulsate with a spectacular green-blue light. This luminescence is probably designed to deter would-be predators. PROTECTIVE SCLERITES: Some sea pens have long sharp sclerites arranged along the edges of the colony to provide some protection against predators.
Phylum: Cnidaria Class: Hydrozoa and Cubozoa ( box jellies ) Order: Siphonophora ( Bluebottle or Portuguese Man-of-War )
Phylum: Platyhelminthes Class: Turbellaria Order: Polycladida
Although some sea jellies deliver a painful sting, there are a number of related species that are considered dangerous. The Bluebottle or Portuguese Man-of-War ( Physalia physalis ) can deliver extremely painful stings and cause some distress, but stings from at least two box jelly species can cause death.
There are over 10,000 flatworm species worldwide but most of these are tiny or parasitic and are never encountered. The polyclad flatworms, however, have many large and spectacularly coloured species that may be encountered by shore fossickers or divers, especially on coral reefs around northern Australia.
the FACTS!
COLONIAL DRIFTER The Bluebottle is a colonial hydrozoan unlike other sea jellies, which are single individuals. Specialised polyps share the processes needed for the colony to function. One polyp forms a gas-filled, sail-like float, while other polyps have long blue feeding tentacles covered in stinging nematocysts. Some polyps have shorter tentacles that hold captured prey while separate feeding polyps digest it. Another polyp type contains the colony’s gonads and takes care of reproductive duties. Bluebottles normally live in the open ocean but are sometimes blown into coastal waters and can sting swimmers and divers. A fully grown individual, with a float 30 cm long and tentacles 10 m long, can cause severe pain and other symptoms including vomiting, headaches and general distress.
SWIMMING SPEED: A large Box Jelly can swim at a sustained speed of over 3.5 knots — that’s as fast as an Olympic swimmer! BOX JELLY SIZE: A fully grown Box Jelly may have a bell 23 cm long and tentacles 2–3 m long.
GARY BELL/OCEANWIDE IMAGES
FATALITIES: It is estimated that over 80 people have died in Australia from Box Jelly stings since the late 1800s. Worldwide fatalities may be over 5000 for the same period of time! IRUKANDJI: These tiny box jellies may occur in offshore waters and can cause a very painful sting that gets progressively worse for more than an hour. Cramps, nausea, vomiting and a dramatic rise in blood pressure have led to death in a few cases. Snorkellers and divers should cover up when swimming on the Great Barrier Reef during summer to avoid Irukandji ( Carukia barnesi ) stings.
Left: Bluebottles are armed with venomous tentacles.
Text: Tony Ayling. Uncredited photography: Steve Parish
Left and right: Box Jelly — a lethal invertebrate
Platyhelminthes Left: Swimming P. hankcockanus
Conservation Watch Species: Approximately 150 species in Australia; worldwide unknown. Habitat: All habitats but most abundant on coral reefs.
the FACTS!
MULTI-BRANCHED GUT
SWIMMING FLATWORMS: Flatworms can swim by passing undulations down their bodies in the same way as stingrays.
Flatworms have a very thin, leaf-shaped body, usually with a pair of pseudo-tentacles ( raised body folds ) at the front. They glide smoothly along by beating thousands of minute cilia ( movable hair-like structures ) on their bellies and secreting a mucous trail to slide on. The term “polyclad” refers to the multi-branched gut that extends in a network throughout the body from the dual-purpose mouth and anus located on the worm’s underside. Between the mouth and the gut is a muscular pharynx that can be everted to engulf, crush or suck up prey. Flatworms are predators that feed on a variety of encrusting and mobile invertebrates ( including sponges, bryozoans, ascidians, molluscs and other worms ). The mouth is positioned well back along the underside of the body and flatworms must crawl over their prey to consume it. Once prey is digested, any waste has to be regurgitated back out the mouth.
EATING FROM TEN PLATES AT ONCE: Pseudoceros flatworms have a multi-branched pharynx that can feed on up to ten ascidian zooids at once! HOW BIG ARE FLATWORMS? Many flatworms are small but most of the brightly coloured tropical species are 3–6 cm long. The largest polyclad species is over 15 cm long. SECOND-HAND DEFENCE: Flatworms that feed on cnidarians have a way of storing un-triggered nematocysts in their skin to use in defence against predators.
PROTECTIVE TOXINS
STRANGE MIMICS: Several brightly coloured flatworms share identical colour patterns with nudibranch species ( see page 53 ). As both flatworms and nudibranchs are apparently toxic, the reason for this mimicry is not clear!
Below, left to right: A pair of Pseudoceros hankcockanus; Thysanozoon sp.
RON & VALERIE TAYLOR
Box jellies were formerly placed as a separate order ( in the sea jelly group Scyphozoa ), but are now considered to be sufficiently different to deserve their own class. These jellies all have a square, box-shaped bell with one or a group of tentacles trailing from each corner. They are all strong-swimming hunters that move horizontally through the water and actively seek the fish that form their normal prey. If one tentacle touches a fish, the jelly quickly contracts to grab the prey with as many tentacles as possible and deliver a knock-out dose of their potent fish-killing toxin. The large Box Jelly ( Chironex fleckeri ) is found in inshore waters during the summer months around northern Australia and is common enough and dangerous enough to keep swimmers out of the water in the tropics for six months of the year.
Above: Pseudoceros cf. dimidiatus pair
Many of the brightly coloured tropical flatworms swim brazenly in the open during the day, which can only mean one thing in an environment teeming with keen-eyed predators — they taste terrible! Analysis has shown that these colourful flatworms have a powerful nerve toxin similar to the ciguatera poison found in some coral reef fish. Several small fishes mimic toxic flatworms to share in their predation protection. Flatworms are all hermaphrodites — each individual has both male and female gonads. When two flatworms meet, each one pushes out a penis and delivers sperm into the other’s female opening to fertilise the eggs. The worms then crawl off and glue clusters of sticky eggs onto the surface of prey items that later hatch into tiny young worms.
DEADLY DUO
TREATMENT: Liberal dousing of the stung area with vinegar and immediate medical attention are the recommendations for anyone stung by a box jelly of any type.
— colourful crawlers
TONY AYLING
Species: Approximately 8 species in Australia; approximately 20 species worldwide. Habitat: Open water, mangroves, coastal or offshore.
Flatworms
LEFT & RIGHT: RON & VALERIE TAYLOR
Conservation Watch
BELOW & RIGHT: RON & VALERIE TAYLOR
— dangerous relatives
RON & VALERIE TAYLOR
Cnidaria
Box jellies & Bluebottles
From Steve Parish Publishing’s Amazing Facts: Marine Life ~ www.steveparish.com.au
the FACTS! COMMERCIAL CATCH: Over 10,000 tonnes of Western Rock Lobsters ( Panulirus cygnus ) are caught annually in Western Australia with a commercial value of about $250 million. This accounts for 20% of the value of Australia’s total fishing industry. LONG LARVAL LIFE: The Southern Rock Lobster ( Jasus edwardsii ) may have the longest larval life of any marine creature, spending 1–2 years in the pelagic phase before settling. SENSITIVE ANTENNAE: Rock lobster antennae are sensitive to vibrations and provide a disposable barrier between the lobster and potential threats. WHAT IS THE LARGEST ROCK LOBSTER? The Eastern Rock Lobster is the largest species in the world, reaching a total body length ( with antennae ) of around a metre and weighing up to 15 kg. HOW LONG DO LOBSTERS LIVE? Rock lobsters take about four years to mature and can live for more than twenty years ( if they can avoid getting caught ).
Rock lobsters, or crayfish as they are commonly known, are large crustaceans that are common invertebrate predators and scavengers on coral and rocky reefs around Australia. Most species are caught commercially and together account for almost a third of the value of Australian seafood.
Rock lobsters have five pairs of long legs and very long tapering antennae. Their large eyes are protected by strong curved spines on the front of a large carapace. Rock lobsters have a muscular tail that can be flapped vigorously to propel them rapidly backwards ( to escape from predators ), but normal locomotion is by walking forwards. Rock lobsters usually spend daylight hours sheltering in caves, crevices and overhangs, often in groups, emerging at night to feed on invertebrates and algae. They can undertake quite long migrations to feeding or breeding areas, often gathering together in groups during these marches. In temperate reef communities around southern Australia, rock lobsters are one of the major predators and their removal by commercial fishing has probably significantly altered the ecology of these reefs.
Below: Eastern Rock Lobster ( Jasus verreauxi )
PROLIFIC EGG LAYERS
Left: Western Rock Lobster ( Panulirus cygnus )
Text: Tony Ayling. Uncredited photography: Steve Parish
Arthropoda
RON & VALERIE TAYLOR
Above: Scarlet Cleaner Shrimp ( Lysmata amboinensis )
Hundreds of different shrimps and prawns live in Australian waters. These range from tiny transparent Periclimenes shrimps 1–2 cm long, to the giant Leader Prawns ( Penaeus monodon ) that grow to 35 cm. All shrimps and prawns have five pairs of legs, several of which have nippers, but in some species one pair is larger than the shrimp’s body.
Conservation Watch Species: 36 families in Australia and approximately 750 species. Habitat: Sand and mud habitats; coral and rocky reefs.
FISH CLEANERS
WANDERERS
The male sexual openings are at the base of the lobster’s fifth pair of legs. During mating, males deposit sperm packets ( tarspots ) at the base of the female’s legs. When the female spawns her half million or so eggs, she scratches the tarspots to release the sperm over the eggs then attaches them to the pleopods under her abdomen. The eggs hatch a month or two later and begin their extended pelagic life as phyllosoma larvae. After a year or so, and several moults later, larvae have a final moult and transform into pueruli ( or young lobsters ) that look like tiny versions of adults but are almost white in colour. As with all arthropods, rock lobsters must shed their hard exoskeleton in order to grow, and so they moult regularly throughout their life.
Phylum: Arthropoda Subphylum: Crustacea Class: Malacostraca Order: Decapoda
Bottom: Painted Rock Lobster ( Panulirus versicolor )
the FACTS!
Shrimps have a very versatile body plan and have adapted to many different lifestyles but they have one major problem — they are too tasty and vulnerable. To avoid predators most shrimps are nocturnal and spend the day hiding away from sharp-eyed fishes. Some species have got around this problem by taking up fish cleaning. In exchange for the services they offer, cleaner shrimps are not eaten ( and are active during the day ). Several conspicuously coloured coral reef shrimps engage in regular cleaning activities, including the Banded Coral Shrimp ( Stenopus hispidus ), with its huge red and white banded claws, and the Scarlet Cleaner Shrimp ( Lysmata amboinensis ), with its startling white claws. Both species usually live in pairs and set up cleaning stations at the entrance of a suitable crevice, advertising for clients with their six long white antennae. When a fish client approaches, the shrimps wave their conspicuous claws up and down to encourage them closer. Cleaner shrimps will climb about on the fish’s body nipping off parasites and damaged skin. The shrimps even venture into the fish’s mouth to clean around the teeth and gills — even those of fierce moray eels!
VALUABLE: Prawns in the family Penaeidae are trawled commercially all around Australia with a total value of around $250 million. HOW BIG ARE CLEANER SHRIMPS? Cleaner shrimps have a body length of about 8 cm with 10 cm long antennae. OTHER CLEANERS: Many other shrimps are part-time fish cleaners, including the bright red hinge-beak shrimps ( below ) and many of the Periclimenes shrimps.
LEFT HOLDING THE BABY These shrimps live in pairs and the female is usually larger than the male. During the breeding season, males stick packets of sperm ( spermatophores ) onto the base of the female’s legs where they are visible as a dark black tarspot. After the female spawns, she breaks open the tarspot so the sperm can fertilise her eggs. She holds the sticky green-blue mass of several hundred thousand eggs under her body for about four weeks until they hatch into tiny larvae and disperse.
FULL-TIME CLEANERS? Cleaner shrimps do not usually get all their food needs from cleaning activities. They also browse for any small animals among the bottom growth of sandy and reef habitats.
Below, left to right: Banded Coral Shrimp ( Stenopus hispidus ); Tomato Cod and cleaner shrimp.
RON & VALERIE TAYLOR
Species: 11 species in Australia; approximately 45 species worldwide. Habitat: Coral and rocky reefs, occasionally in sand habitats.
Phylum: Arthropoda Subphylum: Crustacea Class: Malacostraca Order: Decapoda Family: Palinuridae
— little service stations
RON & VALERIE TAYLOR
Conservation Watch
— crustacean scavengers
RON & VALERIE TAYLOR
Above: Southern Rock Lobster ( Jasus edwardsii )
Cleaner shrimps
TONY AYLING
TONY AYLING
Arthropoda
Lobsters
WHERE ARE CLEANER SHRIMPS FOUND? These shrimps have a long larval life and are widely distributed throughout the Indo-Pacific. Banded Coral Shrimps are found from Rottnest Island off Perth all the way around northern Australia to southern New South Wales.
From Steve Parish Publishing’s Amazing Facts: Marine Life ~ www.steveparish.com.au
Above: Juvenile Giant Cuttlefish
Conservation Watch
Phylum: Mollusca Class: Cephalopoda Family: Sepiidae
Phylum: Mollusca Class: Cephalopoda Family: Nautilidae
Floating cuttlebones are found on beaches around Australia and almost every pet parrot has a cuttlebone to chew on. These porous structures are actually the buoyancy adjustment apparatus from cuttlefishes and a highly modified mollusc shell. Cuttlefishes are a type of bottom-living squid common in all Australian waters.
Species: 34 species in Australia; 115 species worldwide. Habitat: Coral and rocky reefs; sandy and muddy bottoms.
the FACTS! COLOUR CHANGE ARTISTS: Like most cephalopods cuttlefishes have amazing control of their colour pattern and can instantly change from almost white to very dark. They can flash different patterns and pass waves of colour over the body and arms.
LAZY SQUIDS
RON & VALERIE TAYLOR
HYPNOTISING PREY: The common coral reef species of northern Australia is the Broadclub Cuttlefish ( Sepia latimanus ). This species adopts an unusual posture and pulses with rapid flashes of white as it approaches prey, seeming to hypnotise them before it strikes.
REPRODUCTION: Cuttlefishes usually have elaborate courtship displays before the male passes a packet of sperm to the female, which she uses to fertilise her eggs. Eggs are attached individually to the bottom, often in bunches under sheltering rocks. A WALKING CUTTLEFISH: The amazing Flamboyant Cuttlefish ( Metasepia pfefferi ) lives on sandy bottoms around northern Australia. When disturbed, it can flash spectacular colours to advertise that it is toxic. This 10 cm long midget has largely given up swimming and walks along the bottom using the two arms and two lobes on its lower body as “legs”.
Text: Tony Ayling. Uncredited photography: Steve Parish
RON & VALERIE TAYLOR
THE LARGEST CUTTLEFISH: Most cuttlefishes are between 15–30 cm long but the Giant Cuttlefish ( Sepia apama ) of southern Australia grows to at least a metre in length and may weigh more than 10 kg. This species is the largest cuttlefish in the world.
Above, top to bottom: Giant Cuttlefish; Broadclub Cuttlefish; Flamboyant Cuttlefish; Pair of Giant Cuttlefishes mating.
— living fossils
Cuttlefishes are broader bodied than squids and have a long fin extending completely down each side of the body. They have the typical cephalopod circlet of eight suckered arms on the head and a pair of much longer tentacles with suckered, club-like ends that can be completely retracted into pouches beneath the head. These long tentacles are used to seize prey, shooting out at least a body length in front of the animal ( much like the tongue of a chameleon ). Captured fishes or crustaceans are held by suckers on the tentacle clubs and drawn quickly back to be grasped by the other eight arms. These arms hold the victim while the cuttlefish uses its chitinous beak (in the centre of the arms), assisted by a typical molluscan tooth radula, to feed. Cuttlefishes are much more relaxed than most squids and usually drift slowly around, using waves of their lateral fins to swim. When more speed is required they use water jet propulsion like other cephalopods.
Above: Pearly nautilus with the hood blocking the shell
Beautiful pearly nautilus shells occasionally drift onto beaches in the tropics. The animals live in depths between 100–500 m around offshore coral reefs and are more ancient than octopuses and squids. Their closest relatives are the extinct ammonites that roamed the seas from 100 to 400 million years ago.
UNUSUAL CEPHALOPODS Pearly nautiluses are very different from other cephalopods and even in a different family from the similarly named paper nautiluses. These animals live in a large coiled shell that is usually cream with red-brown wavy stripes. They have a tough protective warty hood that can be pulled down to completely block the shell opening like an operculum. The simple eyes lack lenses and there are 47 pairs of thin, arm-like tentacles around the mouth. These arms lack the usual cephalopod suckers but have sharp ridges that help to grasp prey. A siphon protrudes over the edge of the shell lip below the arms and is used for water jet propulsion. These cephalopods lack the colour changing chromatophores and inkproducing sacs of other groups. Pearly nautiluses R live close to the bottom where they hunt crabs and LO AY IE T ER L A other crustaceans, fishes, sea urchins and other squids. &V RO N Nautiluses will also scavenge any dead animals and can be Above: Nautilus pompilius caught in baited pots lowered into their deep water habitat. These animals are active day and night but move into shallower water at night.
BUOYANCY CONTROL
CAMOUFLAGE TACTICS Cuttlefishes are often very well camouflaged, with the ability to change colour rapidly to suit different backgrounds. They also vary their skin texture from smooth to warty. Their ability to hover effortlessly in position is an important part of this camouflage tactic and reflects their excellent buoyancy control. The large cuttlebone, embedded under the skin of the back, is a calcareous structure with many narrow compartments that can be variably filled with gas to make fine adjustments to buoyancy. This does limit most cuttles to relatively narrow depth ranges and very few species are found deeper than 400 m.
TONY AYLING
— buoyancy control experts
Mollusca
Pearly nautiluses
RON & VALERIE TAYLOR
Mollusca
Cuttlefishes
Like cuttlefish, pearly nautiluses use their multi-chambered shell for buoyancy control. The animal lives in the open outer chamber but can vary the amount of gas in the sealed inner chambers to control its buoyancy — becoming lighter during nightly forays up to shallower water and heavier during the descent back to the depths. Males are larger than females and have four tentacles fused to form a spadix, which is used to transfer spermatophores to female nautiluses. Females lay single large eggs that take well over a year to hatch.
Conservation Watch Species: Approximately 4 species in Australia; approximately 6 species worldwide. Habitat: Deep water around coral reefs.
the FACTS!
LONG LIVED: Most cephalopods only live for 1–2 years but pearly nautiluses grow very slowly and take 5–15 years to reach maturity, living for well over 20 years. HOW BIG ARE PEARLY NAUTILUSES? The common northern Australian species Nautilus pompilius grows to about 25 cm diameter in north-western parts. It is suspected that this may be a separate subspecies from the smaller-shelled eastern populations. DIFFICULT TO STUDY: Nautiluses are difficult to study as they live in depths beyond the reach of scuba divers. Tagging of trapped and released animals has shown that they can be highly mobile, with one individual reported to have travelled 150 km in twelve months. ENDANGERED: In parts of the Philippines, pearly nautiluses are trapped commercially. Their shells are highly prized by tourists and collectors. These slow-growing animals are easily overfished and local extinctions have occurred. EXTINCT RELATIVES: Ammonites ruled the seas during the Mesozoic Era when giants with shells up to 2 m in diameter headed a diverse range of species. Most ammonites went the way of the dinosaurs at the end of the Cretaceous Period leaving only a few small nautilus species that still survive today.
Left: Head-on view of a nautilus From Steve Parish Publishing’s Amazing Facts: Marine Life ~ www.steveparish.com.au
— radial symmetry Above: Plectaster decanus
— coral killers
Phylum: Echinodermata Class: Asteroidea
Phylum: Echinodermata Class: Asteroidea
Sea stars or asteroids ( not to be confused with orbiting mini-planets ) have a radially symmetrical star-shaped body with five or more thick arms. Most species are pentagonal but a few species have six, eleven or even fifteen arms. There is a double row of mobile tube feet along the underside of each arm.
Although there are a few herbivorous sea stars and some predatory species most members of this group feed on encrusting animals especially sponges, hydroids, corals and ascidians. These attached animals cannot escape and it is easy for the sea stars to evert their stomach over part of a prey colony and slowly digest the edible parts.
approximately 1800 species worldwide. Habitat: Coral and rocky reefs; sandy bottoms.
RON & VALERIE TAYLOR
Conservation Watch Species: 279 species in Australia;
Echinodermata
Crown-of-Thorns
RON & VALERIE TAYLOR
Echinodermata
Sea stars
Above: Giant Tritons are one of the few predators of Crown-of-Thorns.
Top: Nectria ocellata. Above: Fromia monilis.
Conservation Watch
the FACTS! BRIGHT COLOURS: Many sea stars are brightly coloured and some possess toxins that make them nasty to eat. DIFFERENT COLOURS: Many sea stars are very variable in colour. The common coral reef species Linckia laevigata is usually bright blue but may also be green, pink or yellow. PEDICELLARIAE: Many sea stars are equipped with lots of small beak-like structures on their upper surface that can nip predators or discourage larvae of other animals from settling on them. GRAZERS: Many sea stars simply evert their stomach over a patch of bottom and digest any small animals and plants growing there ( as well as consuming any organic detritus ). Others specialise in eating sponges or ascidians. HIGH FECUNDITY: Female sea stars can produce large numbers of eggs. Some large species release over 100 million eggs each year!
Above: Crown-of-Thorns Sea Star
TONY AYLING
Above: Crown-of-Thorns group feeding
CROWN-OF-THORNS SEA STAR
RON & VALERIE TAYLOR
Above: Pentaceraster regulus
Like all echinoderms, sea stars have a tough calcareous skeleton made up of a network of plates and spines. Large numbers of retractable lobes ( papillae ), which are part of the water vascular system, protrude through the skeleton on the upper surface and are used like gills for respiration. The water vascular system also drives the many suckered tube feet that are used for movement, for gripping strongly to the bottom and for the capture and manipulation of prey. Sea stars have two stomachs, the cardiac stomach is a large sac that can be everted out through the mouth to cover or surround their food and digest it outside the body. ( Imagine everting your stomach to cover your plate of food at the dinner table! ) Pre-digested food is then passed into the pyloric stomach, which has many lobed sacs that extend into each arm, for final digestion and storage. This unusual feeding method lets sea stars eat prey that are far too large to be swallowed and also enables them to eat part of a very large food item like a coral colony.
Habitat: Coral and rocky reefs; sandy bottoms.
RON & VALERIE TAYLOR
OUT-OF-BODY DIGESTION
Above: Catala’s Sea Star (Thromidia catalai)
SELF-REPAIR Most sea stars can reproduce asexually by simply splitting in two and regenerating lost arms and organs. Part of the animal holds firmly to the bottom and the rest walks away, tearing the animal apart. The healing powers of sea stars are phenomenal — a complete animal can regrow from a single arm! Sea stars also reproduce sexually by mass spawning of eggs and sperm from separate male and female individuals. Gonads run down each arm and release eggs or sperm through a central pore in the upper surface.
The infamous Crown-of-Thorns ( Acanthaster planci ) is a grazing sea star that feeds on reef corals, everting its stomach to digest a 20 cm diameter patch in a coral colony, absorbing the juices and then moving on to a fresh coral patch. A single Crown-of-Thorns can kill over 5 m² of living coral a year. Population outbreaks sometimes occur and the feeding activities of hundreds of thousands of Crown-of-Thorns can destroy most of the coral on a reef in less than a year. Recovery of coral populations on devastated reefs may take 10–15 years. Female Crown-of-Thorns can produce over 100 million eggs each year and the group spawning of an outbreak population releases many trillions of eggs into the plankton. If the developing larvae encounter ideal conditions and plenty of food during their pelagic phase, millions more sea stars may settle on other reefs and continue the outbreak. Newly settled Crown-of-Thorns feed on crustose coralline algae and only switch to coral feeding when they are 3–5 cm across. There have been three widespread outbreaks of these damaging sea stars on the Great Barrier Reef over the past 40 years.
ORGANIC FOOD DIET A constant rain of fish faeces, dead plankton, mucous strings and assorted other organic material rains onto the bottom around coral and rocky reefs and accumulates on the surface. Some sea stars seek out the organic-rich sediment that collects in the nooks and depressions of reefs and simply evert their stomach over the silt to digest any organic material ( including all the bacteria and any other organisms that are also feeding on the silt ).
the FACTS! TOXIC SPINES: Crown-of-Thorns are named for the hundreds of sharp, highly toxic spines that cover their upper surface. Stings are extremely painful and usually require hospital treatment. HOW BIG ARE CROWN-OF-THORNS? Adults are usually 40–50 cm in diameter but exceptional individuals may reach 80 cm or more. ARE WE RESPONSIBLE? There is considerable dispute among scientists about whether human activities are responsible for creating Crown-of-Thorns outbreaks. Some argue that fertiliser run-off has encouraged the growth of plant plankton that the sea star larvae feed on ( thus improving their survival ) but others say the cycles are natural. PAST OUTBREAKS: Cores drilled into reef sediments show that there were sometimes large numbers of Crown-of-Thorns on reefs more than 5000 years ago.
Left: Pentaceraster sp. Text: Tony Ayling. Uncredited photography: Steve Parish
From Steve Parish Publishing’s Amazing Facts: Marine Life ~ www.steveparish.com.au
— an unlikely ancestor Conservation Watch Species: 757 species in Australia; 2566 species worldwide. Habitat: Coral and rocky reefs.
the FACTS!
Phylum: Chordata Class: Ascidiacea
Phylum: Chordata Class: Ascidiacea
It is hard to imagine why sea squirts ( ascidians ) are included in the same phylum as birds and mammals. As adults, these animals live permanently attached to the bottom as simple filtering sacs with twin siphons, but as larvae they have a basic notochord that is the precursor of our backbone.
Compound ascidians have groups of individuals called zooids, each with their own inlet siphon and digestive system draining into a common exhalant canal. Most of these species are relatively softbodied but their bright colours indicate that some form of chemical predator protection is being employed.
SYMBIOTIC HELPERS
LARVAL BROODERS: Some sea squirt species retain eggs within the body and brood their larvae internally for a time before they are released. Above: Simple ascidian ( Polycarpa viridis )
THE TUNIC OF SOME ascidians has many easily ruptured cells full of acid to discourage predators. Some brightly coloured species also incorporate other poisons for added protection. EDIBLE? Sea squirts are eaten as a delicacy in many parts of the world and are called “sea violets” in Europe. They are reputed to taste like rubber dipped in ammonia!
Right: Purple reef ascidian
TONY AYLING
SEA SQUIRTS: These animals are named for the way exposed intertidal species squirt jets of water out of their closed siphons when they are disturbed.
TUNICATES: The tough flexible bag that encloses simple sea squirts is called a tunic and is made of an unusual polysaccharide appropriately called tunicin. These animals are sometimes called tunicates.
& compounds
THREE TYPES There are three main types of sea squirt. Simple ascidians are solitary individuals with sac-like bodies. Colonial ascidians are groups of individuals with the same body plan as the simple forms ( but joined into a colony by a basal mat ). Compound ascidians are a colony of zooids contained within a common body. Simple ascidians have an inhalant siphon that leads water into a perforated pharynx sac. The numerous slit-like openings are lined with cilia that beat to move water through the sac walls and out through a separate exhalant siphon. Mucous sheets on each side of the pharynx trap plankton from the water and the pharynx sac also acts as a respiratory gill structure. Cilia tracts also move trapped plankton to the mouth and faeces are ejected out the exhalant siphon with the filtered water, up and away from the lateral inhalant siphon. Sea squirts are supremely efficient filterers and can retain particles as small as bacteria.
TADPOLE LARVAE Most ascidians are hermaphrodites and usually only release eggs or sperm at any one time to reduce the risk of self-fertilisation. Sea squirt larvae are tadpole-like with a tail strengthened by a rudimentary reinforcing rod ( notochord ) that reveals the chordate relationships of this group. A central nerve cord runs alongside the notochord ( the precursor of our spinal chord ) and ends in a small brain in the “tadpole” head. These larvae do not feed, and only swim freely for a few hours before they settle to the bottom, re-absorb the tail and metamorphose into tiny sea squirts. Top left and left: Sea Tulips ( Pyura spinifera )
Text: Tony Ayling. Uncredited photography: Steve Parish
Many compound ascidians of coral reefs have symbiotic associations with Prochloron blue-green algae similar to the coral–zooxanthellae relationship. The algae get a secure place to live, and in return share some of their photosynthesis-derived food with the ascidian. The flask-shaped green species Didemnum molle is the most abundant of the symbiotic compound ascidians and is very common on coral reefs around northern Australia. The larvae of these species scoop up some of the symbiotic algae as they are released from the parent and these are incorporated into the new colony after the larvae settle. Symbiotic ascidian species must live in the sun and compete with coral species — but manage to hold their own because they grow quickly and can recover from damage very rapidly.
ASEXUAL REPRODUCTION Colonial ascidians such as the beautiful, almost transparent, Clavellina sp. are colonies made up of large numbers of small, simple ascidian-type individuals. Many of these colonial ascidians are semi-transparent with red, orange or blue highlights. The internal structure of these animals can often be clearly seen, including the perforated feeding pharynx and the long endostyle that produces the mucous sheet which slides up each side of the pharynx to trap planktonic food and transport it to the mouth. The component individuals of these colonies are usually much smaller than their solitary relatives, ranging from 5–25 mm high. Colonies increase in size by budding off new individuals and may be over a metre across. Compound ascidians often reproduce asexually as well, splitting into two halves that develop separately. As a result of this behaviour they are often found in large clusters in preferred habitats. Right: Clavellina colonial ascidian
From Steve Parish Publishing’s Amazing Facts: Marine Life ~ www.steveparish.com.au
Chordata
Ascidians colonials
RON & VALERIE TAYLOR
Chordata
Sea squirts
Above: Compound ascidian
Conservation Watch Species: Approximately 500 species
in Australia. Habitat: Coral and rocky reefs.
the FACTS! MOVING HOUSE: Although they seem to be attached permanently to the bottom ( like all other ascidians ), some compound ascidian colonies can move very slowly along the bottom at about 15 mm per day to separate colonies that have split in two. REPRODUCTION: Most compound ascidians brood their eggs within the body cavity after they are fertilised, and release welldeveloped tadpole larvae. SHORT LARVAL LIFE: Studies have shown that the common green coral reef compound ascidian Didemnum molle (left ) releases its larvae at midday and the larvae only swim for about ten minutes before seeking a shaded spot to settle. DISTRIBUTION CONUNDRUM: The compound ascidian Didemnum molle is common throughout the Indo-Pacific — a mystery considering its ten-minute larval dispersal phase. SPONGE LOOK-ALIKES: Some compound ascidians have very small inhalant holes and are easily mistaken for sponges ( right ).
Glossary
of marine life
ACRORHAGUS (Plural: acrorhagi) Stinging-cell-covered structures on a sea anemone’s defensive-searching tentacles.
TONY AYLING
RESILIENT LIFESTYLE
Above: Spawning clam
Most invertebrate marine animals release lots of pelagic eggs during the breeding season. Some of them produce tens or even hundreds of millions of eggs every year. Almost all of them also have a larval stage that drifts in the plankton for a period ranging from a few days to more than six months. An animal with this type of lifestyle is naturally resistant to sustainable fishing pressure. Such species may be impacted by collectors and fishers in one area but new larvae may drift in from other places (depending on sea currents) to replace them. This is in stark contrast to groups like sharks, whales and Dugongs, which are more vulnerable to external pressures because each female produces only a few offspring during her lifetime, that “invest” much time and energy in each offspring.
TA YL OR
IE
ER AL &V RON
PLANULA (Plural: planulae) A freeswimming cnidarian larval form.
HYDROSKELETON Fluid-filled support structure of many cold-blooded marine organisms.
PLEOPODS Swimmerets. Appendages on the abdomen of a shrimp/lobster used primarily for swimming. Females also use pleopods to carry their eggs.
Above: Distichopora sp.
CHITINOUS Relating to chitin — a natural polymer that helps form the hard exoskeletons of crabs, beetles etc. CILIA Fine, hair-like structures. CIRRI Hairy feeding “legs” of barnacles. COLONY Group of animals of the same species living closely together. COMMENSAL ( RELATIONSHIP ) A relationship between two species whereby one benefits without harming the other. DETRITUS Non-living organic material that accumulates on the bottom ( such as faeces, silt or dead animals ). ELONGATE Drawn out, or long. EVERT To turn inside-out.
Below: Cowrie ( Cypraea arabica )
FORAM Common name for Foraminifera — single-celled organisms with a hard test ( shell ).
Below: Cowrie ( Cypraea teres )
GASTROPOD A class of mollusc. Includes marine snails ( with shells ) and slugs ( without shells ). RON & VALERIE TAYLOR
PINNULE A feather-like appendage.
HERMAPHRODITE An animal or plant with both male and female reproductive organs.
CERATA The branch-like growths on a nudibranch’s body.
Unfortunately, many people still have the view that the sea’s resources are limitless and that we could not possibly have an impact on any marine life by our collecting efforts. We need to think carefully before we kill an animal just because its shell looks beautiful or because we want to make jewellery. Healthy communities of marine life require a healthy environment and we need to ensure that our activities do not have any detrimental impacts on the rich and diverse communities that make Australian seas such special habitats.
PHYTOPLANKTON Plant life that is part of the plankton.
APERTURE The main opening in a mollusc shell.
CARAPACE A shield-like skeleton that covers the body of crustaceans.
MARINE POPULATIONS ARE NOT LIMITLESS
GONOZOOID Reproductive polyp of a hydrozoan.
PHOTOPHORE A light-emitting organ.
HECTOCOTYLUS Modified arm of male cephalopods used to transfer sperm to females.
CALCAREOUS Made of calcium carbonate.
Overfishing or heavy collecting can dramatically reduce numbers of adult marine life species throughout much of their range and can also lead to local extinctions. Fishing for prawns, rock lobsters and abalone is so intense that more than 80% of the available adult stock may be caught each year, and without good management these species would be in serious strife. The Giant Clam ( Tridacna gigas ) has been fished so heavily in many places that it is now extinct on many Pacific islands where it was once common. Fortunately, there are still many Giant Clams in Australia where the species is protected, and it has now been reintroduced to some areas where populations were decimated. Many other molluscs are heavily collected for souvenirs or by shell collectors and some species are now rare in parts of their former range. Other groups of marine invertebrates are collected for display in marine aquariums but this trade is controlled in Australia and has not damaged most species. Black coral trees are now rare in many places around the world because of their value in fashioning attractive, highly polished jewellery. Those species of invertebrates that brood their young are much more vulnerable to collecting and fishing pressure or to impacts such as habitat pollution or destruction. Collecting of the rare brooding cowries from southern Australia has the potential to seriously affect populations and there are now strict limits on collection of these species.
hydrozoan reproductive polyp. The external part of the gonozooid.
AMPULLA ( Plural: ampullae ) Bulblike structure which is part of an echinoderm’s unique water-vascular system for movement.
BENTHIC Living on the sea bottom.
HEAVY FISHING PRESSURE
Glossary
Conservation
Conservation
GONOTHECA (Plural: gonothecae) An extension of the cuticle around a
Text: Tony Ayling. Uncredited photography: Steve Parish
LARVA ( Plural: larvae ) The immature stage of an animal that usually has a different appearance and lifestyle to the animal itself. MADREPORITE A sieve-like opening that permits sea water to enter an echinoderm’s water-vascular system. MANTLE The flap of skin covering a mollusc’s body cavity. MARICULTURE A specialised branch of aquaculture: farming marine life, generally in sea cages or large tanks. MEDUSA ( Plural: medusae ) A freeswimming cnidarian ( such as a sea jelly ). One of two main cnidarian body types. NACRE Mother-of-pearl. NANOPLANKTON Planktonic organisms 2–20 micrometres in size. NOTOCHORD The firm, jelly-like rod that supports the body of some advanced invertebrates and embryonic vertebrates.
PLANKTON Plants and animals that drift in ocean currents ( and are usually microscopic ).
POLYP An individual member of a colonial animal with its own body cavity. PROBOSCIS A long, flexible snout. RADULA The rasp-like tongue of most molluscs. SCLERITE Small skeletal parts embedded in the body of invertebrates. SPICULE Small, sharp skeletal parts. STOLON Stem or stalk. STROMATOLITE Hard, rock-like growths formed by cyanobacteria trapping and binding sediments into distinctive shapes. SYMBIOTIC ( RELATIONSHIP ) A close relationship between two different species where both derive a benefit. VELIGER A plankton-eating larval stage of a mollusc. ZOOID An individual member of a colony of animals such as a hydrozoan or bryozoan.
OPERCULUM A lid that closes off the shell aperture of some gastropods.
ZOOPLANKTON Animal life that is part of the plankton.
PELAGIC Belonging to the open oceans. Oceanic.
ZOOXANTHELLAE Symbiotic singlecelled algae that live in the body tissues of many invertebrates.
PHARYNX The muscular first part of the digestive canal.
From Steve Parish Publishing’s Amazing Facts: Marine Life ~ www.steveparish.com.au