Native marine aquaria are pretty scarce. Little information exists on how to be successful in maintaining healthy coldwater marine systems in domestic aquaria.

Hopefully this record of my failures, triumphs and ideas will assist others interested in keeping some of our fascinating, beautiful and often little known sea denizens in aquariums.

Saturday, 13 August 2011

Biological Balance

I'm not entirely sure that the title of this post is really right, but I'll plough on regardless and hope that all becomes clear. Those of us who have kept tropical marines will be familiar with the basic nuts and bolts of the Nitrogen Cycle and will be obviously tempted to assume that the same principles apply equally to native/temperate systems. However, it occurs to me that there may be some differences that might be worth exploring.
This is purely hypothesis, I would welcome discussion, either backing this up or refuting it. As such I may well ramble, I may be entirely wrong, but whatever the case I believe its worthy of discussion.
Firstly there are fundamental differences in the nutrient levels of tropical and temperate enviroments. Speaking extremely broadly it seems to be an established principle that tropical reefs are nutrient poor. I've never been entirely sure what this actually means! However, it also seems equally established that cold water ecosystems are nutrient rich. I understood this to mean that cold currents upwelling from the deep carried minerals and nutrients to the surface providing food for massive plankton growth which fuels some of the largest bioloads on the planet. Wherever these currents rise to the surface - the West Coast of South Africa, the East Coast of South America, the West Coast of North America vast numbers of fish, birds, whales etc benefit. I dont know what these nutrients are - organic or mineral? Whether the term 'nutrient' is accurate or not it is a term often heard on Nature Programmes on the television when describing the rich food chains of the places mentioned above.
Anyway - what does this have to do with native marine aquaria?
Tropical marine aquaria are geared towards nutrient export, to approach the conditions found on tropical reef crests it is obviously necessary to do so. As tropical aquaria in the UK and North America are almost certainly required to use synthetic seawater, inert coral sand and 'live' rock that has been cured (ie all dead and decaying organic matter removed) they start off with only the hardiest bacteria and microfauna to carry out the biological processes of nitrification and denitrification, phosphate reduction, detritus mineralisation and everything else. In many cases this seems to be adequate, successful tropical reefs are attainable and well documented. All seem to employ live rock and nutrient export.
Deep sand beds, filters, mineral additions, 'miracle mud', refugiums, skimming, water changes, water movement, detritus removal, careful husbandry and lighting in a myriad combinations and variations all play a part in successful tropical reefkeeping.
Temperate reefs do not have the benefit of live coral rock, many of the rocks found around our coast are impermeable, essentially inert with no buffering capability and provide no habitat for bacteria other than the surface. Likewise the sands and gravels found around our coast are often silica based, in a tropical aquarium such rock and sand would be deemed utterly useless as a substrate for carrying out the nitrogen cycle. Yet the mineralisation of organic waste still occurs effectively. It seems possible that other processes are at work here. This is where I get on to very shaky ground!
My tentative theory is that effective mineralisation is carried out in captive native systems by multi-celled organisms as well as bacterias. We dont have the vast surface areas utilised in tropical aquaria using coral sands and rocks. Whilst Nirobacter and Nitrosomas bacterias are undoubtably present in significant amounts there is simply not the same surface area for them to colonise. I notice that the sand bed of my tank, collected at low water and transported directly to the aquarium was dark just an inch or so under the surface. As it has settled and matured there are myriads of tiny tunnels throughout. Vast numbers of worms, too small to be visible to the naked eye are present. What other creatures also live in this sand? What do they eat? What processes are being carried out? Are similar organisms present in tropical aquaria? I believe that these organisms may not survive prolonged exposure to travel and collection trauma. In a native reef we are fortunate to be able to transport them alive and well by rapid transit. I believe that the presence of microfauna of many different species in a native captive reef are in some way facilitating all the biological processes necessary to effect mineralisation of organic waste to end products suitable for plant take-up.
Therefore, it seems that a fundamental difference in 'nutrient' utilisation is apparent between tropical and temperate systems. Temperate systems may well need nutrient retention within the food chain. Tropical systems are geared towards nutrient removal from the system.
Thats probably enough to be thinking about for now. I'll have more to say on such fascinating topics as detritus later.
Its low tide at Osmington Mills in 90 minutes and the family are ready to go rockpooling. More topshells are needed!

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