Into The Deep

Coral lagoon

My visit was to see a new reef tank located in the ‘Coral Realm’ gallery of the aquarium. I met up with Curator, Dr David Gibson and his Senior Aquarist, Andrew McLeod, who is responsible for the tank.

On our way to the display I couldn’t resist taking a look at another exhibit, the Coral Lagoon tank.

This seriously awesome 200m3 live exhibit is a circular open-topped tank enclosed within perspex walls measuring 15m in diameter and a metre or so in depth and it houses brightly coloured shoals of Yellow tangs, along with a whole array of other surgeonfish species, like Achilles, Regal and Sailfin tangs and countless other coral water species including Bonnethead sharks, Blue spotted stingrays and lots of the more familiar marine aquarium species.

There are over 1200 fish in this exhibit, which includes over 60 species. I was amazed how healthy and colourful the fish appeared to be and, as it was feeding time, how eager they were to feed.

David explained that good water quality was the answer and managing the tank properly necessitated a weekly water change of around 10% of the tank’s contents (20m3) to allow them to maintain a target concentration of no more than 50ppm nitrates.

This may seem high by hobbyist aquarium standards but for large public aquarium fish exhibits it’s exceptionally low, bearing in mind the large bioload imposed on the tank’s filtration system.

Perhaps the most stunning feature of this tank is that a quarter of its circumference drops down in depth to form a reef face some 4m in depth which can be viewed through a flat 3m tall x 5m long window on the floor below.

There are no live corals in this exhibit but the fibreglass replicas moulded by a Danish company, are convincingly lifelike and just watching the continuing procession of fish spilling over the top edge of the reef face from the shallow lagoon above into the depths is a pleasant reminder of some of the dives I have enjoyed on the top edge of the reef face of natural reefs in the Red Sea and Indian Ocean, appearing so close as it does to the real thing.

Coral realm

The Coral Realm live coral reef tank is a fine replica of a slice of a true coral reef and quite spectacular with a 4m x 1.1m/13.1′ x 3.5′ flat viewing window revealing a live coral wall, bristling with hard and soft corals and bold dashes of vivid colours from the accompanying fishes and invertebrates.

It didn’t seem possible that a tank matured for four months could look so well established. Although there were gaps, thriving corals and encrusting forms of colonial anemones were busy colonising all of the living rock surfaces.

Andrew explained that the tank had formerly been a working display illustrating wave surge patterns, hence the shape of the tank which, in fact, is 6m long x 1m or so tall, with a metre of its length either end hidden behind the fascia panelling where wave dump tanks were originally installed.

In its original form the width of the tank for this exhibit had only been 70cm/27” but Andrew has now extended the back wall of the tank to form a shallow shelf 50cm/20” deep which doubles the overall width of its former dimensions.

This also provides a shallow area for SPS (small polyped stony) corals which will be added when the aquarium has had time to fully mature.

A brightly coloured shoal of Anthias produces an instant dramatic effect, their intense coloration contrasting vividly with the other Indo Pacific fish like brilliant Yellow tangs, Red Sea blue tangs and various blennies, wrasse and damsels.

Good environmental conditions and live and frozen foods supplemented with multi-vitamins make these fishes a pleasure to maintain.

The tank carries only a light load of fish following the policy of ‘The Deep’ to not overcrowd subjects. Stocking levels in this tank are far more natural than cramming large numbers of fish into a system.

Fish are less stressed when they have ample room to behave naturally. Anthias species in particular, which don’t always succeed in small systems, prefer lots of free swimming space.

Behind the scenes

Taking a look behind the scenes I was not surprised to find a pretty conventional form of commercial filtration system – a large skimmer, wet and dry trickle tower and fluidised bed found commonly in these kind of systems. But
I noticed there was no CO2 calcium reactor.

Andrew has found that by increasing the movement of water through the fluidised sand tower the coral sand media produces sufficient natural calcium to maintain acceptable levels in the tank without the inconveniences associated with CO2 reactors.

“The effectiveness of the fluidised bed as a filter diminishes slightly, but the ease of calcium management is a bonus”, he told me.

Rather than employ intense skimming methods Andrew believes in a gentle skimming action which leaves more of the elements like plankton, calcium and essential minerals intact. The stability of the system and the water quality owes a lot to the massive quantity of first grade Fiji living rock in the tank.

The Deep uses salt mix and RO water in all their live exhibits. The Coral Realm live coral tank has its own dedicated RO system for topping up water and water changes, but all the other exhibits are serviced from a central facility.

It is a surprisingly small installation, but capable of producing swimming pool sized quantities of water daily.

David is very keen to have accurate data on water conditions and the tanks are monitored using electronic probe systems or lab grade spectrophotometers, so that any anomalies can be revealed and dealt with promptly.

Conservation and research

The Deep was established as a conservation and education charity. Andrew took me along to the research facility to see some of the initiatives they are undertaking.

The projects all aim to conserve the World’s oceans and raise public awareness of the threats faced by marine animals. They work in collaboration with many institutions, universities, conservation organisations and aquariums.

One area of his current research could lead to a highly sustainable means of propagating hard corals. He showed me fist-sized colonies of Acropora tenuis produced from settled planula larvae they had received from an aquarium in Holland.

The colonies were just over a year old and a similar initiative conducted commercially could produce colonies of fast growing corals like Acropora for the aquarium market which would be sustainable and non-damaging to the environment and existing natural reefs.

As only a tiny proportion of planula larvae in the wild manage to find a suitable substrate and survive to form new colonies, any collected for a coral farming project from the huge mass spawnings which regularly occur would have little impact – merely a further use of Nature’s bounty.

Switched-on science like this is a massive advantage today’s public aquariums can offer towards conserving and protecting the world’s oceans and marine life forms.

Factfile

Tank vital statistics
The display tank is a recently modified rectangular tank which was originally 6m x 70cm x 110cm/234” x 27” x 43” deep. A shelf has been added to the back wall of the tank extending the width to 140cm/55” with a depth of 50cm/20” forming the tank into a ‘D’ shape. The capacity is around 4000 l./880 gal. before displacement.
A small sump with a capacity of 500 l./110 gal. plus the water in the filtration system gives a total volume before displacement of around 5500 l./1210 gal.

Biological filtration
A commercially developed system incorporating a trickle filter and fluidised sand filter supplemented Berlin style by approximately two tonnes of living rock, which occupies around 20% of the display area in volume terms.

Chemical filtration
None used

Skimming
A skimming tower measuring 60cm/24” dia. x 1.2 m/4′ tall provides a gentle skimming action processing approximately 7m3 of water per hour.

Calcium/carbonate hardness management
Calcium replenishment is made by passing tank water through the fluidised sand filter bed at a higher rate than is usually used when operating the bed purely for biological filtration. The sand bed in this filter contains around 25kg of coral sand.

Water circulation
Water circulation is delivered by two 14m3/h pumps, one of which also services the filtration system, the other is completely dedicated to water circulation in the main display area. The total water movement of 28m3/h in terms of litres is 28,000 lph, which is equivalent to a turnover of around 6-7 times per hour based upon the displaced volume of water in the display area.

Cooling
Water cooling is by means of a 2kW counter current titanium heat exchanger.

Lighting
2 x 400w Azmet metal halide Osram 10000K flood lights
2 x 250w Azmet metal halide Osram 10000k flood lights
3 x Arcadia lighting units each fitted with 2 x 250w metal halide 10000k lamps plus 2 x 36w Actinic tube fluorescents
This provides around the 350w per sq. m. essential with a tank of this depth.

Photo period
0800-2000 with lighting up and closing down staggered over 5 minute intervals, by each set of units. The large floodlights are fitted 40cm/16” above the surface of the display tank, the Arcadia units 25cm/10”.

Water parameters
Temperature 26C
pH 8.15-8.25
Salinity 33g/l 1.020 sg
Nitrite –
Nitrate 5ppm
Phosphate 0.15-0.20
Calcium 400ppm
ORP 280-300

Quick reference
Filtration – Berlin plus trickle filter and fluidised bed
Skimming – Constant and gentle skimming
Kalkwasser delivery – None
Water circulation – 6-7 times per hour
Light intensity – 330w/m3
Water change – 5-10% per week using Tropic Marin
Phosphate remover – None
Additives – None

What’s in the Coral Realm reef tank?

The tank is dominated by soft corals with a small number of hard corals, mainly large polyped species.

Hard corals
Mainly colonies of Euphyllia, Plerogyra and Lobophyllia species.

Soft corals
Anthella, Briareum and Xenia plus large numbers of Sinularia, Sarcophyton and Capnella sp. Gorgonians are also included.

Sessile invertebrates
Heteractis crispa anemone plus colonial Actinodiscus, Discosoma and Zoanthid sp.

Mobile invertebrates
Various echinoderms e.g. Long spined Diadema urchin, Linckia, brittlestars and the Knobbed seastar (Protoreaster sp.); Crustaceans e.g. Cleaner shrimps, Peppermint shrimps, various hermits (Red legs and Blue legs) plus Tridacnid clams, Turbo snails etc.

Fishes
A group of Pseudanthias (15); Salarius blennies (4); Yellow tangs, Tomato clowns, Pyjama and Silver bellied wrasse, Bicolor blennies, Yellow-tailed damsel, plus a Copperband butterflyfish and a Purple tang.

Feeding
Fish are fed a diet mainly of live and frozen brine and Gamma shrimp, non-live foods supplemented with Zoovet International Liquidvits multi vitamins, and occasional feeds of another ZIL product, Reef gel, formulated for herbivores.

This article was first published in the December 2005 issue of Practical Fishkeeping magazine.