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Conference Papers

Marine Aquaria - The Balanced Community Technique

Tony Isaacson

Science /Marine Studies Teacher
Hallett Cove School
Gledsdale Rd
Hallett Cove
South Australia 5158

Hallett Cove School is located near a beach and a wave cut platform 20 kilometres south of Adelaide, South Australia. With an enrolment of 1500 students it is the largest single campus school in the State educating children from reception to year 12. Tony Isaacson has fostered an awareness of marine ecology for 20 years and as a Sydney based high school student in 1969 he was a foundation member of the Marine Aquarium Research Institute of Australia (MARIA). Returning to South Australia to complete his Bachelor of Science degree and Diploma of Education, Tony established the South Australian branch of MARIA at Flinders University.

In 1978, his first attempts to bring marine life to the classroom were pioneered with priority project funding in the biology laboratory at Port Augusta High School. MARIA evolved to become the Marine Life Society of South Australia (MLSSA). Tony's workshop will rely on a booklet written by members of MARIA and MLSSA. It is focused on the care of temperate water marine life and is related to the development of a 2000 litre refrigerated sea water system at Hallett Cove School.

Getting Started

The session begins with a video image of leafy and weedy seadragons believed to be from home ranges near Victor Harbor in South Australia. A quotation based on an ancient Tibetan saying appears on screen….

"In the end we will conserve only what we love.
We will love only what we understand.
We will understand only one week can learn."

These thoughts underlie the approach to marine education at Hallett Cove School and it is the reason for promoting the unique bio-diversity of southern temperate species in five interdependent marine habitats adjacent to a tropical coral reef community from Darwin Harbour.

The video cuts into the noise of primary school children at the viewing wall during Seaweek - an annual event at Hallett Cove School. Seadragons on the TV monitor are largely ignored as students busy themselves with marine life in the aquaria. There is a sense of excitement as they spot things previously unseen and unknown from local waters.

A debriefing of the Seaweek experience gives children the opportunity to reflect on the significance of the seadragons. In a single generation over 50% of seagrasses along the metropolitan coast of Adelaide have disappeared. Photographs of Hallett Cove taken in the early 70’s show a white sandy beach and an unbroken field of seagrass at low tide.

In the 90’s, a littoral assortment of wave rounded rock and glacial erratics sit on an ancient clay base. The seagrasses have receded and with them the sand and a diverse community of marine life including the leafy seadragon - the unofficial state fish of South Australia.

Windows on an Unseen World

The balanced community technique is a best practice tool to showcase marine life from a range of habitats and to arouse an interest and enthusiasm in students to find out more. The emotional bond that develops as a child witnesses the in vitro development of a Port Jackson shark or the kaleidoscopic behaviour of a cuttlefish as it feeds cannot be matched by a book, a photograph, a video or an interactive CD ROM. The technique is a microcosm of the real world and it is contingent on a balance that is the hallmark of any sustainable endeavour.

Bacteria and Slime

Marine studies students gather first hand data of chemical changes in natural seawater during an experiment that investigates the role of nitrifying bacteria. Students learn that lethal concentrations of ammonia can very quickly develop as plankton die and other organic matter decomposes. They observe that it can take up to 6 weeks before lethal concentrations of ammonia are replaced by less toxic peaks of nitrites and a steady increase of relatively harmless nitrates (a plant food).

Experimental aquaria filled with natural seawater can be very different when tested for total ammonia, nitrite and nitrate levels. Seawater systems isolated from the natural environment can have nil readings for ammonia and nitrite while recording near lethal concentrations of nitrate.

A key factor in the survival of captive marine life is the metabolism of toxic wastes into simple compounds that can be recycled by animals and plants living in that environment. Bacteria like Nitrosommonas and Nitrobacter, unseen and unloved, become the organisms that overshadow the magnificence of a seadragon as students come to terms with the dynamics of a marine community isolated from the real world.

Green slime and algae of various species respond to increasing levels of nitrate and grow on every available space including the viewing windows. A healthy growth of green algae is a good sign. Molluscs, like warreners and abalone, leave mosaic reminders of their grazing habits on the glass to delight teachers of ecological processes and to the angst of those who like clean fish tanks.

Devices known as "scrubbers" use algae to reduce nitrate levels and other metabolites but most aquarists rely on periodical water changes for this purpose. About 10% replacement per week is good practice and at Hallett Cove water change is the equivalent of an annual replacement of 2000 litres. Increasing proportions of brown and red algae indicate that oxidation levels are low and the mix of species, feeding habits and daily routines could need some review. If in doubt, change some water.

Glass, Cement Blocks and Plastic

The marine store is annexed to a larger than usual biology laboratory designed for year 11 and year 12 students in 1995. The Department of Education and Training Employment (DETE, formerly DECS) provided the physical space following a consultation process with teaching staff. Students and staff using readily available items like stormwater pipe and irrigation fittings did the installation of the seawater system.

While the video shows how the parts go together, it does not explain how the system evolved from a behind the scenes look at the Niagara Falls Aquarium in 1973. For example, Sydney Aquarium inspired the idea of supporting aquaria on corrosion free cement blocks and fibre-cement board behind a one sided stud wall as illustrated in figure 1.

The basic under-gravel filtration system observed at the Niagara Falls Aquarium was essentially the same as the one described by Geoffrey Mower in the booklet printed for this workshop. However, under-gravel filtration systems have their limits and some lateral thinking was needed for the installation at Hallett Cove School.

Click tp enlarge
Figure 1 - click to enlarge

Lessons Learned

Hallett Cove is a dormitory suburb with non essential industry and emergency services. As with other areas of Adelaide, power can be cut on the hottest days of summer during periods of peak electricity demand. The school transformer was another source of intermittent power and it caused a disaster during the combined AAEE and MESA Conference held in Cairns, 1994.

Whist the teacher was at the World Heritage Conference, students experienced the unmistakable smell of hydrogen sulfide (rotten egg gas) after the under-gravel filters of several aquaria failed. What might have looked like the doomed bycatch from a prawn trawler included favorites like 'Lochie', the brown moray eel, and Jackie, the in vitro Port Jackson shark. It was a tragedy that touched the whole school community, particularly the junior school students who had watched Jackie grow from a 3cm long embryo.

Gravity and Oxygen

The basic under-gravel filter relies on gravity to draw water, oxygen and other organic debris through coarse shell grit and a bottom plate before returning "cleaned" water to the viewing space. When power cuts stop the aeration, aerobic bacteria (including Nitrosommonas and Nitrobacter) die by the millions having used whatever dissolved oxygen is in the water.

Most macro-organisms including fish, molluscs and crustaceans suffocate and within hours they contribute to an organic pollution load that only swamp hardy anaerobic bacteria can thrive in. Organisms that survived on decreasing levels of dissolved oxygen are killed by rapid increases of ammonia, hydrogen sulfide and other toxins. Sea anemones and corals from Darwin Harbour did survive against the odds.

For several years a concept marketed as "bio balls" or trickle filters have replaced under-gravel filters. They also rely on gravity to let water flow over a large surface area of plastic (or any other suitable material) in an atmospheric, and therefore oxygen rich, environment. The activity of nitrifying bacteria and other aerobic microbes is less likely to be affected by a cut to the power supply as most of the decomposing organic matter is out of the main volume of water and it remains in contact with atmospheric oxygen when electricity is off.

Aquaria with trickle filters tend to have only a light sprinkling of "sand" on the bottom for aesthetic reasons and an overflow device which doubles as a surface skimmer and delivery system to an external (trickle) filter.

Keeping it Simple at Hallett Cove School

On the basis that it is easier to maintain one volume of water than six or more separate marine aquaria, the 2000 litre installation at Hallett Cove School relies on gravity and an Onga swimming pool pump. Six 200 litre drums carry water from SARDI-aquatic sciences at West Beach, about 15 kms north of the school. Water is pumped from the trailer into large plastic header tanks at the ceiling level where titanium cooling coils chill it to about 15 degrees Celsius.

A PVC manifold delivers cooled water to six aquaria set up to represent five South Australian marine habitats and one as a multipurpose holding space. Two additional valves on the manifold allow for the future inclusion of an algae "scrubber" and plumbing that provides water for temporary "touch pools" in the laboratory.

Gravity delivers water below the viewing space of each aquarium via irrigation fittings and a false bottom. Water flows upwards through coarse shell grit into the viewing space and out of the aquarium via an overflow hole cut into the glass before assembly. The central aquarium containing mangrove and rock pool species has a small self starting siphon which can be adjusted to give the effect of a rise and fall in tide levels.

Storm water pipe collects the overflow and delivers it to "trickle" filters before draining into plastic sump tanks located below the aquariums. When the sumps are full the pump is activated to return water to the header tanks at about 10,000 litres per hour. In the absence of a generator that would keep the system going during power failures, water simply drains through the system into containers set up to catch the overflow when the pump is not activated. The system self starts when power is restored and the "tell tale" water in the overflow containers is either returned to the system or replaced with water stored in the bank of 200 litre bottles.


The purpose built seawater system built at Hallett Cove School is maintained by students under the supervision of a teacher. No student has a complete understanding of the system and a trouble shooting chart would be an excellent project for 1998. Two biology teachers replace staff who have taught marine studies since its development in 1995.

Time will tell if a specialist facility like the one described here can endure as a resource to inspire a generation to save the planet. A first prize for the BHP Science Teachers Award in 1997 recognised a commitment to develop the system for Seaweek, junior science lessons and the marine studies course for year 11 students.

The facility has generated a lifestyle. It is not a computer that can be turned off at the end of the day nor a busy desk that can be walked away from between school terms. It is a community of organisms that collectively represent the workings of a natural world, a community which, at the end of the day, is dependent on human intervention if it is going to survive.

Southern temperate waters of Australia can boast over 85% endemism (Dalgetty 1996). There is an argument in favour of showing this unique heritage to the generation that might save it from extinction.

"In the end, we will only conserve only what we love.
We will only love what we understand.
We will only understand what we can learn."


Dalgetty, A. 1996, Southern Fisheries, Volume 4, Number 4, PISA Fisheries, Adelaide, South Australia.