16 A Q U A T I C E X R I B I T S

been completed. the decorative rockwork and corals having already been installed, and about 80% of the entire exhibit complex had also been built. A tank that would not hold water and windows that were not only aesthetically unpleasing but also posed a potential safety hazard were considered serious enough problems for the opening date to be abandoned so that the necessary repairs could be made. With this began the long process of research, redesign and repair which eventually took four years to complete at a cost of USS300 000; the cost of the original building work had been US$200 000.

The exhibit design for the reef tank was extensively modified. The concept of using curved lexan for the windows was discarded and three of the overhead tanks in the viewing tunnel that had been glazed with lexan were removed. The life- support system and window frames were redesigned and the method of construction for the island rockwork support was considerably changed. The following repairs were made: ( I ) corals and coral rockwork removed; (2) wall and

floor inspected and repaired; ( 3 ) tank surface ground and sandblasted; (4) tank divider walls removed; (5) low wall installed to separate the tank into two sections; (6) window frames modified to accept glass; (7) windows installed; (8) tank resealed and repainted; (9) tank tested for leakage; (10) corals and coral rockwork reinstalled. The tank was leached and the pH adjusted with hydrochloric acid for several months before fish were introduced on 15 October 1985; a month later the exhibit complex was officially opened.

PRODUCTS M t N I l O N E D Ih T H E TEXT

Enka-mat mesh: manufactured by American Excelsior Company, 609 South Front Street. Yakima. WA 98901. USA. Lexan MR4000: manufactured by General Electric Corporation. Plastic Sales Division. I Plastics Ave. Pittsfield. MA 01201. USA. Silicone rubber RTV 732: manufactured by General Electric Corporation. Silicone Products Division, 260 River Road, Waterford, NY 12188, USA.

Manuscript submitted 17 November 1086; revised January 1987

Ill( L~~~~ i t l (19x7) 26: 2 6 19 &)The Zoological Society of London

The Atoll Reef exhibit at Ocean Park in Hong Kong J . CHIN O c e m Parh , Wong Chi& Hang R o d , Aherdeen, Hong Kong

Coral reefs are the most richly populated habitats in the ocean. with hundreds of species of fish and invertebrates living together in a single relatively isolated community. There are three basic reef types, the coastal, barrier and ring-shaped atoll reefs. At Ocean Park in Hong Kong a simulation of the third of these types is displayed in the Atoll Reef tank. one of the most spectacular attractions in the oceanarium.

Built in 1976, the reef tank is oval in shape. 22 m wide, 38 m long and contained in its own oval building situated on Brick Hill 125 m above sea level. The tank contains two million litres of water which varies in depth from just under 2 m at one end to 7 m at the other. A downwardly sloping pathway follows the curve of the glass-panelled tank wall, passing through four galleries set at progressively lower levels to give views of

A Q U A T I C E X H I B I T S 27

Plate 1. The first gallery of the Atoll Reef exhibit at Ocean Park in Hong Kong showing the artificial coral island in the centre of the tank and graphics panels mounted on the outer walls.

the interior from the top edge to the deepest point. The first gallery starts at the shallowest end of the oval, where visitors look at the exhibit from its edge to receive the impression of a lagoon with a plant-covered coral island surrounded by a sandy beach rising from its centre (Plate 1). The artificial island is oval in shape and made of fibreglass covered with living as well as artificial plants. Large graphic panels, some of them lit from behind, provide information on the reefs and their inhabitants.

Passing through the next gallery the visitor receives a view through glass panels of a sloping fringed reef with rocks and colourful corals through which swim schools of beautiful shallow-water- inhabiting fish. Species include the Emperor angelfish Pomacanthus impera- tor, butterflyfish (Chaetodontidae) and surgeonfish (Acanthuridae). The coral structures are either artificial, made of fibreglass, or natural coral skeletons

which have been painted; the main types shown are staghorn, table, lettuce, brain, finger, star and pillar. All provide homes for a large variety of marine invertebrates such as Starfish Astropecten scoparius, Sea anemonies Radianthus macrodactylus, Sea urchins Echinothrix diadoma, Sea cucumbers Holothuria leucospilota and Tube or Bristle worms Sabellusturte indica. All plants which appear under the water are artificial. The third and fourth galleries become progressively deeper to show Moray eels (Muraenidae), groupers and sharks, the biggest of which is the 2.5 m long Leopard shark Stegostoma fasciatum which swims along the bottom of the tank. Giant marine turtles, two Green turtles Chelonia mydas and two Hawksbill turtles Eretmochelys imbricata, can also be seen foraging for food. Each gallery presents a unique scene showing different aspects of a coral reef community. Backlit graphics above the glass panels provide illustrations and

28 A Q U A T I C E X H l B l T S

Plate 2. View of the Atoll Reef tank from one of the lower galleries showing the location of the illuminated graphics.

information on the types of fish which are likely to be seen at each level of the exhibit as well as on more general marine biology (Plate 2).

Lighting has presented a number of unique problems because of the size and depth of the tank. Apart from natural light which enters through the glass roof of the building illumination is provided by a system of 15 halogen lamps, eacq 4OOW, which hang from the ceiling 3 m above the water, set at an angle which is perpendicular to the water's surface. In addition I 1 low-voltage (direct current) underwater spotlights have been mounted under the island to ensure that visitors see iis much of the tank interior as possible.

The Atoll Reef tank is of course an exhibit dealing with a specific theme, and the presentation of educational material is seen as an integral part of the display. Exhibitions, each dealing with a particular topic, are mounted in all the galleries to introduce the public to some

of the mysteries of the coral world. The topic is corals and coral reefs in the entrance foyer and first gallery, the coral reef community in the second gallery, marine fish biology in the third gallery and the identification of common marine fish in the fourth gallery. A new exhibition hall, which will form part of the entrance to the building, is due to be opened to the public at the end of 1986 and will provide information on the many aspects of reef natural history.

At present there are c.3000 fishes of 300 species displayed together in the Atoll Reef tank, together with sea turtles and large numbers of invertebrates. In order to ensure that this vast array of marine life can live in relative harmony the tank has been designed as a series of carefully arranged habitat types, each suitable for particular species groups. Each day divers provide regular amounts of appropriate food to each region, so most species remain in fairly discrete areas of the tank.

A Q U A T I C E X H I B I T S 29

Any particularly voracious feeders, such as sharks or groupers, are usually found in the deeper parts of the tank and are kept well supplied with food. In any event, the artificial reef structures contain many hiding places for vulnerable species should a hungry shark happen to pass by.

Natural reef communities are extremely delicate and survive only if the water is clear and clean. Since the reef tank is designed specifically to maintain these fragile species it has a well equipped life- support system which ensures a highly sterilised and stable environment. Basically, the circulation system is fully closed and the water content of the tank is recirculated through sand-pressure filters. Sterilisation is by ultraviolet light and vortex-induced sprays, and a stilling chamber ensures the removal of air bubbles before the water is returned to the tank. Boilers and chillers maintain the water temperature at 2625°C throughout the year. Sea water, pumped from the ocean and chlorinated then dechlorinated and stored in a reservoir, is used to replenish losses caused by evaporation; in addition about 5% of the water is renewed daily so as to minimise the accumulation of dissolved toxic materials. The quality of the water is monitored regularly in a laboratory situated adjacent to the tank. Divers inspect the inside of the tank every day, removing debris and brushing algae off all structures including the insides of the windows. Such manual cleaning is essential to control the build- up of algae, since this cannot be done safely by chemical means.

Restocking of invertebrates in the tank is carried out every five or six months and

fish are replaced as necessary. Most of the fish and turtles have been living in the tank since it opened. Any newly acquired animals will not be introduced into the tank until they have completed three weeks’ quarantine in special holding tanks. The tanks are also used for any fish which appear to show signs of illness; these fish are collected by the divers and kept separately until they have been treated and are healthy enough to be returned to the exhibit. Research into practical husbandry problems, such as the formulation of feeds, fish disease, artificial propagation, the cultivation system and display techniques, is conducted in the laboratory by members of the diving staff. The most commonly occurring disease in the tank is white-spot disease, caused by Cryptocaryon irritans, which affects Blue tangs Paracanthurus hepatus.

Although none of the fish in the tank has bred successfully, eggs have been hatched artificially for a number of species including the Blue damsel Amblyglyhidodan xanthurus, Brown- spotted cat shark Chiloscyllium puncta- tum, Blue spotted grouper Epinephelus hoedtii, Red grouper E. akaara and Black sea bream Sparus macrocephalus.

The building and maintenance of the Atoll Reef exhibit has provided us with a challenge both in terms of engineering and animal management. After ten years of operation it has proved to be a great success, not only with the public but also as a habitat system.

Manuscript submitted 30 September 1986; revised January 1987