describing the Seafriends marine aquariums
By Dr J Floor Anthoni (2005)
|Introduction to the ideas and principles behind these aquariums: self-circulation, constant volume, cooling, oxygen supply, isolated habitats, tidal tanks and more.|
|Design of the circulation system, aquariums, dimensions and other considerations. Where improvements can be made.|
|The main habitats around Leigh: estuarine habitats, reef habitats and the 'sin bin' with predators.|
|Methods of quality control and maintenance|
|What went wrong and why flushing with new sea water did not help.|
|By keeping track of water quality with the DDA method, the health of the aquariums improves gradually. At the same time new animals and plants are introduced to stock the aquariums such that they maintain ecosystem health.|
|major improvement||In May 2008 the amount of incident sunlight was more than doubled by a simple modification to the roof and hoods. A new era began.|
|A timeline of progress in progradation, symptoms and new species introduced, with photos. (in progress)|
|An annotated species list by habitat type. A separate document (9 pages)|
One of the first things built for the Seafriends Field Centre were the aquariums because we knew that they needed quite some time to settle in. Indeed the first six months gave many problems. There was only little money available (NZ$16,000 from own savings) such that we had to achieve the most for the least expense. Temperate aquarium ecosystems are not common around the world and when we enquired around, the firm advice we were given was: "Don't do it!". But what is a marine education centre without aquariums?
We decided we would need one tank for each habitat or habitat zone and we were not certain about estuarine tanks. These mainly show sandy and muddy bottom and would be less interesting than the others. But then we realised that we were doing all this based on ignorance, meaning that they should be there because we could not predict their role in the whole. All habitats were to be interconnected by their shared outlets and inlets.
So the tidal tanks were built. As it turned out, children find these the most fascinating with their hermit crabs, cushion stars and other creatures. We simulated the tide on a strict twelve hour cycle, the mud flats inundated for only four hours (because they are higher up the estuary) and the sand flats for eight hours every twelve hours (later this became 6/6). The creatures didn't seem to mind that the moon cycle was not simulated fully. The tidal movement was achieved with two circulation pumps in each tank, pumping the water out to the other, controlled by an electrical time clock.
As we aimed for a fully operational ecosystem, we had to let sunlight
in from above. Fortunately the roof of the lean-to shed where once sheep
were dried overnight before being shorn, was low and covered in corrugated
iron which could easily be removed and replaced with transparent corrugated
Lexan (polycarbonate). The shape of the roof forced us to align the tanks
east to west rather than north to south which would have allowed for more
light. With the knowledge we have today, this was a mistake as the density
of life in these tanks is entirely determined by the amount of sunlight
We chose not to have powerful lights as these run up quite a high electricity bill, and the heat they produce must be compensated for by a more powerful cooling system, also a financial liability. It so happens that sunlight is the coolest light available, and is (still) entirely free of charge. All aquariums have lights but these are operated with a PIR (passive infra-red) presence switch whenever people enter.
The tanks were designed such that the water could circulate in a natural way, entering from below as cool water and exiting over a weir (dam of glass). Proteins from wastes would collect at the surface and be skimmed over the weir towards the shared bacterial 'filter'. The other function of the weir is to keep the volume of the aquariums at a constant level, such that we would know precisely up to where to replenish evaporated water with fresh. It also provides a safety against tanks draining in case of an accident.
The bacterial filter contains hollow Siporax beads (expensive but lasting) over which the water flows. It is cooled by a cheap (second-hand) air conditioner which also cools the room. Part of the air blows downward with the flowing water over the Siporax beads which oxygenates and cools the water within seconds but also contributes to evaporation. In winter the air conditioner is turned off and air circulation over the filter is maintained by the flow of water. The bacterial filter does not 'filter' anything. A large load of bacteria inside the filter converts what it is able to in an environment rich in oxygen but kept entirely in darkness. (Later an in-line water cooler was installed)
From the filter, the water ends up in the sump from where it is pumped
up by a spa (jacuzi) pump. The pump forces water at high pressure through
the pipes, thereby keeping the inlet pipes free from marine fouling, a
serious problem in marine aquarium systems. The returning water flows under
low pressure, thereby fouling the outlet pipes in a matter of months. Thus
a third set of pipes is kept fallow and sealed such that all life inside
dies and decomposes to a stinking mess. When this pipe is needed, the black
putrid water is pumped out to a wastewater tank and pipes are swapped by
means of flexible radiator hoses.
Seafriends aquariums are run as an 'open' ecosystem because some feeding
occurs as the aquarium cannot sustain predator species. But adding food
to the ecosystem will eventually result in very high nutrient loads and
eutrophy the system. Thus excess nutrients need to be removed. In commercial
aquarium systems this happens by pumping new seawater through, something
we can't do, located 1.5km away from the sea and 150m high. The diagram
shows how we solved this. Above the separating line a normal aquarium or
tanks with fish as we call it. Fish are fed and soil their water, but the
water is pumped out, often at the rate of eight refreshments per day.
In our ecosystem aquaria we have bacteria inside the bacterial filter but at least as much outside on the glass and in the sand. These bacteria convert feces and urine and dead matter into nutrients. By admitting light, the nutrients cause phytoplankton to grow, which is consumed by filterfeeding clams and sponges. The nutrients also make stringy algae grow on every object in the aquariums, and these are grazed by grazing snails. When the aquarium is healthy, it also produces some zooplankton.
The Seafriends aquariums are unique in their kind as a fully functional open ecosystem that uses the phenomenal growth of plankton to remove wastes.
We keep a pulse on the aquariums by monitoring the levels of the most poisonous intermediary products: ammonia, nitrite and nitrate. Once the aquariums have reached stability, the ecosystem has also become very sturdy, surviving pump failures and prolonged power breaks. But even though seemingly stable, the aquariums can become sick. We are watching the marine creatures carefully as they exhibit the first signs of stress.
The ecosystem can become unstable because of overfeeding or by an accident such as a pump failure. When necessary, new seawater is obtained in a 600 litre black polythene tank on a trailer and old seawater returned to the sea. Until recently, this solved most of the unexpected problems. However, in 2004 when the aquariums became really sick and even sea cucumbers died, the refresh cycle no longer delivered. What was wrong?
The Dark Decay Assay method invented by Dr Anthoni to measure the health of natural water, came just in time and it showed us not only that the aquariums were at a level of health comparable to the worst found along our coasts, but also that the sea around Leigh has become too sick to be of any use for refreshing aquariums with. Then the idea arose to nurse the aquariums back to health (progradation) using the new-found knowledge with the DDA method. It should be possible to end up with sea water healthier than that found inside the Goat Island marine reserve. Thus the Seafriends aquariums have become a scientific tool for studying marine degradation by the reverse process of progradation. It is a very exciting prospect.
The aquarium system was designed for utmost simplicity using materials that are easy to obtain, so that maintenance can be done locally. The tanks, measuring 120 x 60 x 60 cm were placed on sturdy wooden tables, connected by a hood to the roof. One corrugated iron roof sheet was removed and replaced with a transparent Lexan corrugated sheet. The pipes were placed underground in a sand matrix covered by garden tiles. The tops of the aquariums were enclosed in a plywood hood whose inside was covered with silvered building paper. The aquariums could be reached through flap doors of 30cm high between the glass and the hood. This is enough to place one's head inside, to reach the bottom everywhere and to pass small buckets through. The flap doors are covered in information sheets.
|The aquariums are all at the same level, about 120cm above the floor and the sump tank is located about 40cm below ground level, such that water flows swiftly back to the sump. There exists ample head of water to remove bubbles and air locks. A spa pump sucks water out of the sump and pumps it under high pressure through a non-return valve to all tanks. Here it enters close to the bottom and exits over a glass weir along the surface. The small triangular basin behind the weir fills and empties as the pump works intermittently, affording enough pressure to overcome any air locks. Above the sump is a dark box filled with SIPORAX glass beads that have very fine tunnels for bacteria to settle on but their open cores allow the water to flow through swiftly. A standard air conditioner blows cool air into the aquarium room and this flow is tapped to also flow through the box. By allowing air to enter, the water is oxygenated almost instantaneously. Since August 2008 when the roof was opened up further to let more light in, an in-line Haylea water cooler of 1kW has been installed.|
The whole idea behind the Seafriends aquariums is to afford visitors a look at the local sea in miniature. So all habitats and habitat zones needed to be represented.
Where the estuary encounters wind, small waves are produced and these winnow the mud from the sand, allowing it to be transported out to sea. So the bottom is sandy. One can find eelgrass in the upper reaches of the estuary and various clams in the lower reaches. A number of crabs, hermit crabs, snails and cushion stars are found here. The tide clock and small pumps pump the water in for eight hours out of twelve.
The deep estuary is marked by current channels. It never falls dry during spring tides. Because of its shelter against ocean waves, currents and rich waters, it is rather distinctive with various seaweeds, filter feeders, shellfish and starfish.
The sheltered reef is not very common, as it is connected to the open sea but sheltered from the brunt of ocean waves by a promontory, inlet or similar feature. It is an area rich in variety, particularly of fragile species. One finds a large number of fine seaweeds there and many representatives of all phyla. Unfortunately people like to live near such places, reason that this habitat is threatened everywhere.
The exposed reef covers the sun-lit zone of the rocky reefs around New Zealand. Around Leigh it is bordered by stringy bladder kelps on top and the stalked kelp forest lower down. In between one finds a barren zone grazed by sea urchins. This habitat zone is rich in species. In our aquariums we cannot simulate the wave action and bright sunlight, and this limits what the tank can show.
The deep reef extends below the photic (sunlit) zone such that plants can no longer grow for lack of light. One finds a variety of filterfeeders here such as various clams, sponges and seasquirts. Also detritus feeders are found. We placed the deep reef under dim light to simulate the light situation.
The Sin Bin is not a habitat found in nature but a tank that allows us to keep animals that are particularly destructive in the habitat where they belong. The large anemones are fierce predators, catching snails, crabs, sea horses and so on. The dwarf scorpionfish is also quite destructive, and predating starfish such as the eleven-armed star and the ambush star. Even so, we had to ban the most destructive of all, the predating conchs and the seven-armed star. Some crabs are very destructive like the paddle crab of the sand flats and also the spiny lobster (crayfish) and the octopus. They practically need a tank for themselves with a few animals that they leave alone (but crayfish eat everything).
The quarantine tank is placed above the sump, connected in a side loop. It serves as a temporary holding tank for sick or stressed animals and it also serves as a learning place for slow feeding fish that have to adapt to our food. It also allows new fishes to adapt to the four walls and that there is no escape. Dubious predators such as some conchs and crabs are placed here to observe what damage they can cause.
The quarantine tank also serves to monitor water flow as it is filled by the sump pump but emptied by a constant flow. A flow switch sits in the outlet pipe. When the flow is too low, a resettable timer expires, ringing the circulation alarm and an alarm monitoring service.
In nature predation is not well defined, as we discovered. Basically any larger fish eats any smaller one. So we have to keep a watchful eye out for size. Fortunately our aquariums are too small to accommodate large fish (say larger than 20cm), and these are returned to the sea as soon as they become a menace to others or when they require too much food.
Aquariums require maintenance because they are such small environments and are usually overstocked. Services provided by nature such as circulation, oxygenation, warming, cooling, wave action and waste removal must be provided artificially. In order to understand this better, we'll discuss the five basic kinds of aquarium system.
|Public marine aquariums
Public marine aquariums want to show the public a large collection of remarkable species with the least amount of problems or risks. They are usually located at the sea side where water can be pumped in from the sea and out again. An underground sand bed helps to filter the incoming water. It is then sterilised by ultraviolet light to kill all bacteria. The refreshment rate is high, about eight times per day.
Such aquariums often have Perspex transparent tunnels which are easily scratched while cleaning. So the rate of fouling is kept to a minimum by dim lighting. These aquariums are not self-sustaining ecosystems and are unsuitable for plants and lower organisms such as sponges.
|Commercial marine fish tanks
For holding and transporting live fish, commercial tanks have the minimum in life-support. Most commercial fish species are rather hardy, able to survive a few weeks in very poor conditions. Life support consists essentially of oxygenation, cooling and circulation. No bacterial filtering is applied. Sometimes an ultraviolet light steriliser is provided. Freshwater fish like carp and tilapia are hardier still.
|Tropical fresh water aquariums
Keeping a tropical freshwater aquarium is very popular because it is not difficult. The only things needed are warming, circulation and filtering for waste removal. Most freshwater fish species are very hardy and lazy, requiring the least amounts of food. Many fish also adapt to the poor quality water, being able to survive for years. Maintenance also consists of replacing the water periodically and this could be a problem since drinking water is often chlorinated and fluoridated. However, every dwelling can collect enough rain water. But when an unknown limit is exceeded, things can go wrong rapidly. Also diseases can be introduced from various fish vendours.
|Tropical marine aquariums
The tropical marine aquarium is popular because of the sheer variety of beautiful and weird species that can be kept, from corals to anemones, crabs and snails to starfish and many gaudily coloured fish species. But marine species are not as hardy as freshwater ones, and this brings problems. Because the tropical water is warmer than the ambient temperature, only warming is required, which is much easier than cooling. These aquariums must provide for heating, circulation and filtering for wastes. Often very strong lights are provided to enable corals to grow. Some ultraviolet-A light can accentuate fluorescent colours. An ultraviolet-C steriliser is strongly recommended to remove bacteria from the water. At times the water must be replaced to remove liquid wastes, and this can be done by dissolving sea salt in clean fresh water.
|Temperate marine aquariums
Temperate marine aquariums are more difficult than tropical ones, not only because a form of cooling must be provided but also because temperate species are rather energetic, requiring a high food intake. Apart from this, they can be managed like tropical marine aquariums.
|Temperate marine ecosystem
The most difficult to keep are marine ecosystems. An ecosystem is essentially self-sustaining, requiring neither feeding nor waste disposal. All minerals, nutrients, oxygen and carbondioxide are circulated within. It can essentially be capped and live forever, as long as circulation and cooling are provided. However, such complete ecosystems are rather boring for the public since they need to be very large to accommodate predator fish species. Their density of life is much less than that along the coast because they do not have an extra supply of plankton. For this reason, the Seafriends 'open' marine ecosystem is supplied with food for interesting species, and their wastes are converted to phytoplankton which is partly removed by filters.
Circulation and oxygenation
Degradation in the sea happens invisibly and slowly, alternating with the El Niño cycle, such that most people remain unaware. In the aquarium ecosystem it happens when feeding exceeds waste removal. Conversely, progradation can be achieved by removing more wastes than that caused by feeding. Most marine aquariums are somewhat stressed, and we have run our aquariums in a rather stressed mode in order to show more interesting creatures like an octopus. As a result, bacterial levels remained too high for certain organisms, but without DDA one does not know this. A large and active bacterial component is absolutely necessary for any ecosystem, but the decomposers need to be locked up inside the sand, a filter and so on, and should not be allowed to roam free in the water.
Doomsday came in the year 2004 when problems in our aquariums could no longer be cured by replacing the water with new sea water. We had not noticed two main causes:
We removed all large animals, including octopus and crayfish and all stressed animals since their deaths would contribute to the problems. Then we discovered that cushion stars were impervious to cyanobacterial poisons, and we let many of these clean up the mess. It worked, as we also at the same time aggressively removed wastes (in the presence of sunlight, nutrients convert to phytoplankton which is caught on standard aquarium sponge filters and removed weekly).
As more and more nutrients were removed, paradoxically, the algae grew faster and faster, and so did the wastes we removed. Then we discovered the DDA and applied it to the aquarium water. How had we been able to run this aquarium with such poor quality water for so long, and without DDA? And why did this not show up in the levels of ammonia, nitrite and nitrate? Obviously the DDA is a far better quality test.
We have never been able to grow marine macroalgae like the brown, green and red seaweeds, but never found an acceptable explanation. We tried all possibilities such as more or less sunlight, trying sea weeds from various depths, making strong currents and even wave action, but nothing seemed to help. Now we know that seaweeds are rather sensitive to bacterial attack.
|Progradation, the way forward
Armed with new knowledge about how the marine ecosystem really works, we are now prograding the aquariums by a different approach. In the past we focussed on healthy bacteria to decompose all wastes but now we have changed our priority.
Our first priority is now to create an environment where plants are happy (forget about fish for a moment). Once they grow, they will remove nutrients from the water and create a bacterial medium in their slime that helps decomposition while at the same time helping other plants grow and trapping free roaming bacteria. We expect that this will make an enormous difference as also phytoplankton are plants.
We are now (June 2005) at a stage that filter feeders like mussels, cockles and even seasquirts and sponges are growing. They too remove wastes from the water. Once growth is sufficiently fast, we will stock larger numbers of these and try other varieties.
By now the aquariums look quite different from what they were before, as more and more organisms take over from the waste filter as the waste filters are already becoming less effective. We expect that their combined synergy leads to the final phase, as we hope to be able to also nurse the plankton ecosystem to optimal health.
Within this plant- and filterfeeder- dominated environment, we then plan to stock a tolerable number of fish and perhaps some energetic ones like trevally.
The process of progradation will enable us to learn more about degradation
and how the various species react. The Seafriends marine aquariums have
thus become an important link in our research.
graphs show how the aquariums are prograding. In black the total biodensity
(slush + decomposable biodensity), in green the decomposable biodensity
and in red the bacterial rate of attack. After very high values before
April 2005, bacterial activity (ROA) gradually decreased from 30-40 hion
to below 10 hion. Above 15 hion, most seaweeds are not able to survive.
In December the water was so clean that mussels could not find enough food.
In March-April 2006 excessive stocking allowed the water to degrade to
a peak level during which young snapper died. Progradation was applied
aggressively in May and June 2006, with ultra clean water as result.
The ROA peak in September was due to mussels dying. They have since been
shifted to the tidal habitats where plankton densities are kept higher.
Also some filter pumps have been disabled. Note how the black curves of
total biodensity remain high due to high slush content, but as seaweeds
establish themselves, it is expected that this source of nutrients will
be utilised. In October 2006 various green, brown and red seaweeds were
growing happily, as also a large variety of sponges did.
Ideally the green line should stay on or above 100 hion and the red line below 10, in order to simulate a healthy coastal sea. Ideally, the various tanks should be managed in three groups: estuarine (dense plankton), near-coastal and far-coastal (cleanest water). Please note that very little is known about these aspects of the sea and how the DDA measurements vary seasonally.
|A major improvement
It has always been clear that the amount of sunlight was the aquarium's main limiting factor, and possibly also the main reason why brown seaweeds could not be kept. In order to fix this, the whole aquarium room needed to be re-built from scratch, with wider tanks lined up in a north-south direction and this would cost $120,000 if we did the work ourselves. With Seafriends in a state of near bankruptcy, this was not an option.
Suddenly seaweeds began to grow spontaneously, of which two red seaweeds that we never placed in these tanks. Still, the brown seaweeds did not take. We had discovered that by their symbiotic association with bacteria, seaweeds decompose wastes more effectively than bacteria on their own (symbiotic decomposition). Thereby also the free-floating bacteria become less numerous (losing out in competition), and with it the chance of infection and disease. In other words, as seaweeds take over, the aquariums also become healthier, until one day also brown seaweeds may grow successfully. The first has indeed happened, and very few mortalities have been recorded, and none in the past 6 months, as also sick sponges recovered.
It deserves mentioning that there are four major limitations to our aquariums and for that matter any other marine aquarium:
Terrestrial plants have 'pumps' to pump their liquids around. Their main mechanisms are uplift by capillary action in thin pipes, and evaporation from leaves, which sucks the liquids up. Downward movement is performed mainly by gravity. By contrast, sea plants have none of these mechanisms. Their transport of liquids is done mainly by external water movement which flexes the plant's tissues, thereby 'pumping' liquids around inside (like the human lymph system). Thus for seaweeds to grow, there must be wave action. (not entirely true)
One can think of many ways to make waves, but if the cost of electricity
is also taken into account, few solutions remain that are simple, invisible,
cheap and reliable. Our solution was a tipping bucket made from half of
a 20 litre chlorine container, cut diagonally. The triangular bucket is
hinged critically, so that when it is filled by a small pump, will eventually
tip to discarge its content completely, thereby creating a surge of water
resembling wave action. This tipping bucket is placed above the tanks,
and thus remains invisible. This method has proved to be reliable, even
though a few times each year, the algae inside need to be removed.