SEAWEED NUTRITION

Reproduced, with permission, from "Keeping Marines", 1972, by Gerald Jennings, FIMSS. Published by the then International Marine Study Society. Second Edition.
 

In a system employing sub-sand or sub-gravel filtration, the majority of waste products produced by the inhabitants of your biosystem will be converted to nitrates. Initially the bacterial activity in the bed will be low, but if a good throughput of air and water is maintained, then an active aerobic bacterial bed will result in a short space of time and will need no further attention.

The nitrates produced by the bacterial bed will be metabolised by the seaweeds present for growth. Seaweeds also require supplies of potassium, phosphate, vitamins of the B complex and other minor trace elements, all of which are present in natural waters, but some of which, notably phosphate, do not seem to be present in many artificial seawaters. If you are not too sure whether all these essential components are in fact present in the water being used, there are now tests available to determine the presence in seawaters of both nitrates & phosphates. If the reading obtained on a kit proves negative, appropriate quantities of the missing component will have to be added, but added in such a way that the chemical balance of the water itself is not greatly disturbed. Potassium you will not have to check for if a reputable brand of seawater substitute is used. It is present in quite large amounts (by comparison) in natural water If the water being used is found to be lacking in phosphate, the addition, per 100 litres (or approximately 22 English gallons) of 1 gram of tri-Potassium orthophosphate will remedy the deficiency. If the water is found to be lacking in nitrate, which may happen if seaweed beds establish themselves well, the the addition of 1 gram of hydrated Calcium nitrate per 100 litres will be found to remedy this deficiency. No substitutes should be used for the salts mentioned above, neither should they at any time be mixed or added together to the tank. Both should be dissolved in a small amount of fresh water before being added.

Where all readings on the above food compounds are showing positive, and the light intensity and duration are as stated in the chapter on lighting, but your seaweeds do not seem to be doing as well as they should, a vitamin deficiency is probably the answer. If a lack of vitamin B12 is suspected, then this, if proven, could well affect far more than the seaweeds. It is simply remedied, either by purchasing a vitamin solution, (one which is added directly to the water) or by following the details given below on making a B12 vitamin solution:

PREPARATION OF A VITAMIN B12 SOLUTION Add 0.1 gram of chemically pure Vitamin B12 to 100 cc. of pure water. Take l cc. of this stock solution (which should be corked firmly & stored in a cool dark place) and add this to one litre of distilled water. Use one drop of this litre to each gallon of water in your biosystem. Discard the remainder. Make fresh stocks from 99 cc. of stock solution left.

ADDENDUM:  A comprehensive study of the nutrition and metabolism of marine bacteria (which is directly related to seaweed growth in marine aquaria under the system stated above) was undertaken by MacLeod & his co-workers over a period from 1954 to 1960. These authors investigated the requirements of marine bacteria and the compounds needed for maximum growth. They also studied the effect of amino acids (by-products of fish metabolism - excretion ) as sources of nitrogen and carbon. It appears that the saprophytic marine bacteria do not differ markedly from terrigenous strains in their requirements.