Marine Invertebrates
It is very tempting to try to reproduce in the aquarium a living reef inhabited by a cross-section of all the
available forms of life. This can be done, but in practice it is difficult — for a variety of reasons.
Living coral is available from dealers, complete with the flower-like polyps which emerge at night to feed on plankton. Many very large Sea anemones also feed on plankton, and these are frequently offered for sale. Yet another form of plankton-eater is the Tube-worm; this produces a horny tube, growing vertically up from the sand, from which the head of the worm emerges like brightly coloured flower to sieve plankton from the water. All of these organisms are beautiful, and can be kept successfully in the aquarium. Yet it is not possible to provide the huge amounts of living plankton they require: the filtration system does an excellent job of removing plankton. They can only be fed by switching ofthe filters while stirring ground clam or shrimp into the water, and then switching the filters on again a little while later. However, in such conditions sooner or later water fouling is inevitable. The only truly successful way to keep these creatures is in a separate invertebrate tank, with only minimal filtration, and where there’re no fish to attack the vulnerable invertebrates. Corals are an exception, and many types subsist on nutrients produced by algae living within their tissues. All they demand is very strong light, sufficient to keep the algae healthy.
A few large anemones are available which feed on chunks of meat or fish, just as do those in our rock pools. These are generally tougher and easy to feed, and, since they have stinging cells on their tentacles, most fish leave them well alone.
Mollusks of several types are available. Scallops and their relatives are bivalves (they have two shells joined by a hinge), endmost swim by clapping their two shells together, lying on the sure-face of the gravel most of the time. They are filter-feeders, and areas difficult to feed as the other creatures.
Various other mollusks, such as Sea snails and Sea slugs, are similar to their terrestrial relatives but often very beautifully coloured. Some can be kept easily, feeding on lettuce or on pieces of fish, but most have very specialized diets. The Octopus is also mollusk, but is very delicate and difficult to establish, and has an astonishing ability to climb out of the most tightly covered tank. Even a large Octopus can force itself through a 1 cm gap!
The Crustacean is the most practical invertebrates for the aquarium; they include Shrimps, Lobsters and Crabs. Some are quite tough enough to live in a tank with fish — some will eat the fish! Most interesting of all are the Cleaner shrimps, which are of various brilliant colors and are highly territorial. They establish a shop’, which fish visit to have the Shrimps clean parasites and dead tissue from their surfaces, and even from the insides of their mouths and gills. Cleaner shrimps are seldom eaten — even by very large fish which normally eat other Shrimps and their relatives.
Hermit crabs are amusing and bold invertebrates for the tank. They need a good supply of spare shells into which they can climbs they grow.
Yet another class of invertebrates is the Echinoderms, include-ding Sea urchins, Sea cucumbers, and Brittle stars. All are scavengers, and all are difficult to keep for any length of time. They share with other invertebrates a tendency to disintegrate: they foul the tank very rapidly should they die.
Probably the biggest difficulty with invertebrates is their sensitivity to compounds containing copper, the basis of many drugs used to treat the most common infections of fish. This poses problem if disease breaks out in a tank where invertebrates and fishier being kept together.
Algae grow copiously in marine aquaria. Most are encrusting types, forming a film over the glass and coral, and these are grazed eagerly by the fish. The larger tropical algae, popularly known as seaweed, can also be kept in the marine aquarium, but are not easy to maintain. There are several attractive types, notably Penicillusor Merman’s shaving brush, which is called Ulva, which grows in lettuce-like sheets; and Caulerpa,which resembles British seaweed in shape. All are dark green incisor, although there are also some red algae. The main problem with algae is that they do not survive chilling or even being lifted out of the water. This is because they have no solid framework, and their cells are easily ruptured. If a damaged alga is placed in the tank the ruptured cells decay very rapidly. If you can obtain algae in good condition, and give them sufficient light, they will grow very rapidly, spreading by means of runners across the gravel surface. They perform a very useful function in using up the waste products of the fish, but are something of a time bomb, waiting Togo off as soon as something goes wrong with water conditions in the tank, and decaying with frightening speed. They are best avoided, except by the expert who has spare tanks available in case of emergency.