Life in isolated oases Western Australia’s shelf-edge atolls

A major biological survey of Western Australia’s remote offshore atolls has revealed a diverse assemblage of more than 1500 species of marine plants and animals, with many not previously recorded in the State and several new to science.

by John Huisman and Sue Morrison 32 LANDSCOPE LANDSCOPE 33 estern Australia’s remote Marine Park, first declared in 1990 250 square kilometres. Seringapatam Wnorth-west offshore atolls lie and extended four-fold in 2004) and Reef, 23 kilometres north of North on the edge of the continental shelf Mermaid Reef, a Marine National Scott Reef, is a smaller circular reef in deep, clear oceanic waters far from Nature Reserve under Commonwealth with an area of 55 square kilometres. the mainland. The biodiversity of these legislation. Regarded as Australia’s Scott Reef has also been of interest atolls is still poorly known to scientists. best examples of shelf-edge atolls, the to marine scientists for less positive Such remote places are always of great Rowley Shoals provide some of the reasons. In 1998 it suffered a severe interest to biologists, as their isolation best diving and nature-based tourism bout of coral bleaching caused by often leads to the development of found in WA. unusually warm sea temperatures. unusual communities. The interplay of Scott and Seringapatam reefs lie Coral bleaching occurs when the living environmental conditions such as large- more than 300 kilometres north-west tissue of the coral loses its pigmented scale current systems and local climate of Cape Leveque and rise steeply some symbiotic algal cells, which often kills all affect these communities, the former sponges, corals, crustaceans, molluscs, 400 to 500 metres from the sea floor. the coral but leaves its white skeleton largely dictating what species might echinoderms and fish. For some groups, Scott Reef is comprised of South behind. AIMS scientists reported that make the journey, the latter what such as fish and corals, this was a chance Scott Reef, a large crescent-shaped about 80 per cent of Scott Reef’s coral might survive in the new home. Once to revisit and update earlier surveys. formation, and North Scott Reef, cover was lost in this 1998 event. In a species is established, isolation from For others, such as marine plants and with a roughly circular shape. They are 2004, the reef bore the full brunt of the source population may eventually sponges, it was an opportunity to make substantial structures with a combined Cyclone Fay. Three hundred kilometre lead to the evolution of new species, the first known collections. area (including the lagoons) of some per hour winds uprooted coral colonies endemic to that location. In the past, marine scientists and and tore huge reef boulders up to five Research in such remote places researchers from the WA Museum, metres in diameter from the reef’s edge. is expensive. So, when Woodside Department of Environment and AIMS scientists are monitoring the Energy Limited agreed to sponsor Conservation (DEC), Australian reef’s slow recovery from this double Previous page a WA Museum survey of Mermaid Institute of Marine Sciences (AIMS) blow of rare events. Main Gorgonians, soft corals and The Rowley Shoals, Scott Reef Reef Marine National Nature Reserve and CSIRO have made visits to the sponges at Scott Reef. (in the Rowley Shoals), Scott Reef northern atolls to study their habitats Insets Colourful gorgonian coral; and Seringapatam Reef lie on the and Seringapatam Reef, the news and ecology. false clownfish and its anemone home; very edge of Australia’s continental was received with much excitement. sunset over Scott Reef. shelf. Around 15 million years ago the The aim of the survey in September Left on the shelf shelf probably formed the shore of the Above Researchers survey the vast mainland, which was fringed by a reef. 2006 was to document the presence, The three most southerly shelf expanse of Seringapatam Reef at low distribution and, where possible, the atolls, located north-west of Broome, tide, with the brown seaweed spiny tops The atolls were possibly once reefs abundance of the major groups of are known collectively as the Rowley in the foreground. surrounding former headlands. As a marine animals and plants. Specialist Shoals. From south to north, they are result of changes in sea level and other marine scientists were invited to Imperieuse Reef, Clerke Reef (both Below left Smith’s weed. geological processes (probably related to survey and study seaweeds, seagrasses, in the DEC-managed Rowley Shoals Below The green seaweed Halimeda the collision of the Australian and Asian sometimes forms luxuriant meadows. continental blocks), these subsided into Photos – John Huisman the sea, slowly enough for the fringing coral reefs to be maintained. As a result, the reefs built up from the sea floor like high turrets, each enclosing a shallow lagoon. The growth of similar Above Purple anthias at Scott Reef. reefs along the shelf was not sufficient and three species of seagrasses have Photo – John Huisman to keep pace with subsidence and so far been recorded, but the list there are a number of drowned reefs will no doubt grow once the smaller, along the shelf, including one south of cryptic species, mostly growing on animals. Others dominate rocky Imperieuse Reef. the larger seaweeds, are examined in sections of the reef flat, with the brown detail. It is the first time many of these seaweed spiny tops (Turbinaria ornata) Marine plants species have been found in WA waters, almost completely covering parts of None of these atolls had ever been although they have been recorded from Seringapatam Reef. There are plants systematically surveyed for marine tropical reefs in Indonesia and the that grow only in the sandy, mobile plants, so the expedition provided a Philippines. sediments of the lagoon. Some, such as great opportunity for seaweed expert The marine plants come in all lobed halimeda (Halimeda macroloba) and John Huisman to make new discoveries. manner of shapes and sizes. Some, grey-green udotea (Udotea glaucescens), Each species was photographed and such as encrusting coralline algae, are form massive, sand-binding holdfasts to representative specimens collected and extremely important in consolidating help keep them in place. These plants preserved for DEC’s WA Herbarium, reef crests and therefore play a major are also calcified, providing an unusual where they will form an important part role in reef ecology. Others inhabit the defence against herbivorous fish that is of the State’s marine plant collection. gaps in reefs, presumably as a refuge not just due to their crunchy texture. More than 100 species of seaweeds from the many grazing, herbivorous When calcified green seaweeds are

34 LANDSCOPE LANDSCOPE 35 crushed, as might happen in the stomach (Gibsmithia hawaiiensis), with its jelly- outer reef, to squadrons of triggerfish of a parrotfish, the calcium carbonate like body growing from a firm stalk. In and surgeonfish cruising along the would combine with acids in the plant many cases, the evolutionary pressures outer reef perimeter. Elongated painted tissue, producing carbon dioxide gas. that led to the unusual appearance of moray eels slither in and out of crevices For a fish, this is undoubtedly a very these plants can only be guessed at. in the intertidal reef flats and dainty unpleasant experience! Other marine damselfish school around the corals in plants—such as Caulerpa species and Fish the lagoons. Tiny, slender whip gobies the seagrasses paddleweed (Halophila) The reef fish of the north-western shelter between the polyps of sea- and turtle grass (Thalassia)—have atolls overload the senses with their whips on the outer reef. horizontal stems that creep across the stunning range of colours and sheer Fish experts Glenn Moore and sand and attach wherever possible. abundance. Body shapes and sizes Sue Morrison recorded 433 species of Some plants defy categorisation, such vary from gigantic, solid potato cods fish during the surveys, representing copyright photograph removed as the mucilaginous Smith’s weed hanging around the deeper parts of the 59 families. Their diversity tended to increase towards the more northerly atolls, with 290 species recorded at Mermaid Reef and 376 species at Scott and Seringapatam reefs, which agrees with the results of earlier surveys. Typically, the outer reef habitats had a greater diversity of fish species than the lagoons. The most abundant and diverse fish families recorded from all reefs were the damselfish, wrasse, surgeonfish, triggerfish, butterflyfish, rock cod and goatfish. The fish fauna at these atolls has more in common with fish communities of clear-water reefs in Indonesia than Top Barrel sponge. with those of the more turbid coastal difficult to identify. Although corals during this survey that she believed reefs of north-western Australia. Above A delicate comb jelly (Ctenophora). have been well documented during may belong to a different species. According to Barry Hutchins of the Photos – John Huisman earlier surveys, coral biologist David The sponges of Mermaid, Scott and WA Museum, around 36 per cent of McKinney recorded new distribution Seringapatam reefs were documented the fish species occurring at these atolls records for 23 species at Mermaid Reef for the first time in this survey. are not recorded from coastal reefs of and 18 species at Scott/Seringapatam A total of 137 species from 36 families WA. Scott and Seringapatam reefs are reefs, plus a new record for the region— were recorded. In contrast to fish and likely to be important ‘stepping stones’ finger coral (Montipora digitata)—and corals, most of the sponge species were for fish dispersal between Indonesia one new record for WA—Moluccan rare, supporting indications that many and the Rowley Shoals, and possibly particular interest are the depleted mushroom coral (Fungia moluccensis). species are endemic (only found in regions further south. populations of giant clams (Tridacna A total of 273 hard coral species one region). These limited distributions Molluscs species) at Scott and Seringapatam from 14 families were recorded. When are probably due to their short-lived reefs where, under a Memorandum combined with historical records, larval stages, which means the larvae Many molluscs are cryptic, of Understanding, traditional fishers this brings the overall total recorded cannot travel very far, restricting their nocturnal and/or mobile, so are from Indonesia may harvest limited for the region to 291 species. Most dispersal. difficult to observe. WA Museum quantities. coral species found in the atolls are mollusc experts Clay Bryce and Corey Crustaceans Whisson recorded 373 mollusc species widespread Indo–Pacific species with Corals Crustaceans are particularly difficult at the atolls. As with the fish, these clear affinities with coral assemblages Reef-building hard corals are the to observe because most species are species have a greater affinity with of Ashmore Reef and Indonesian essential ‘building blocks’ of these mollusc communities of the Indonesian provinces to the north. cryptic, many are nocturnal, most can north-western atolls. They also provide Archipelago than with those of coastal move quickly, and some live hidden complex structures in which other Sponges waters of north-western Australia. Of within or on the surface of other marine life live or take shelter and Identifying sponges can be animals, algae or the seabed. Collecting form a food source for many species. difficult, as some species are extremely and identifying crustaceans was Both the physical structure of the atolls variable in shape and colour. To therefore very time consuming and and the health of associated marine life make matters worse, most species need required the input of two researchers, therefore depend on the health and to be examined under a microscope Melissa Titelius and Christine Hass. Above left The Rowley Shoals are famed diversity of the hard corals. before they can be identified. This The crustacean fauna of the north- for their large potato cod. Being sedentary animals, corals made it necessary for sponge expert western atolls was poorly known and Left The spectacular tiger cowrie. are in some ways easier to record Jane Fromont to collect samples, for Mermaid Reef had not been surveyed Photos – John Huisman than mobile species but they are often later study, from every sponge she saw at all. This survey documented 153

36 LANDSCOPE LANDSCOPE 37 Above The orange marble sea star (Fromia monilis ). of 15 habitat types (corals, rock, algae, fishing and tourism. It is important Above right Courting olive sea snakes. sponges and so on). The images provide to use a survey method repeatable Two males vie for the attention of a a permanent record of each habitat in regular monitoring programs to female (top snake). Photos – John Huisman and can be compared with those from establish an understanding of such similar surveys in the future. complex and changeable ecosystems. The results showed distinct Such surveys are extremely important. Despite their remoteness, differences between the lagoon and the reefs are of increasing commercial species of crustaceans, including an outer reef habitats, largely related to interest, as they sit upon a huge amazing 98 new records for the region the level of wave action. The outer reefs plus two new species. The most diverse gas reservoir that could potentially generally supported more robust and families at these reefs were the black- generate billions of dollars in revenue. encrusting coral species, while fragile fingered crabs, coral crabs, spider crabs, It is therefore imperative that detailed coral species inhabited the lagoons. hermit crabs and swimming crabs. surveys of the region are undertaken to ensure adequate protection of this Stars of the sea More to uncover delicate ecosystem. Echinoderms—sea stars, brittle The diversity recorded in this survey stars, feather stars, sea urchins and is undoubtedly an underestimate, as sea cucumbers—were not thoroughly many nocturnal species, species that surveyed as there was no specialist live in holes or crevices in the reef or available. However, a new species of under the sand, small cryptic plants and John Huisman is a contract seaweed sea star was discovered at South Scott animals and wary pelagic species will specialist at the WA Herbarium and a Reef. The limited results indicate that not have been observed. Whole groups, research fellow at Murdoch University. sea cucumber populations at Scott such as the worms and soft corals, were He is an international expert on seaweeds, having studied WA’s marine and Seringapatam reefs may have not recorded due to the unavailability of plants for more than 20 years and suffered from habitat degradation (after specialists during the field work. Even written several books on marine plants severe cyclones and possibly ongoing some clearly visible species will have in various parts of the world. global warming) and fishing pressures been missed because it was impossible Sue Morrison of the WA Museum (they are a favoured food in parts to survey a sufficient number of sites has coauthored the DEC books The of Asia) from Indonesian fishers. This Marine Life of Ningaloo Marine Park to be sure of documenting all species degradation could detrimentally affect and Coral Bay, Wonders of Western in the time available. It must also be the reef ecology. Waters, Beneath Busselton Jetty and remembered that all such surveys are The Turquoise Coast. She is a regular just a ‘snapshot’ in time—there are contributor to LANDSCOPE and can be Habitat descriptions contacted on (08) 9212 3743. A video method devised by AIMS often seasonal variations in numbers and species possibly related to breeding The authors would like to thank their was used to document the habitat at many co-expeditioners, who are named each site. Video recordings were taken times and movement, variations due in the text, and Woodside Energy by Peter Morrison and later analysed to to currents, storms and cyclones, plus Limited for its financial support. determine the percentage cover of each the effects of human impacts through

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