Marine aquariums always contain large quantities of ornamental rocks. What is the reason for it? Are the rocks only used for aesthetic purposes, or do they also have biological value? Because of the often high cost of a living rock environment, many beginners or aquariofiles who wish to change from freshwater to marine wonder if it is not possible to do without. In freshwater aquariums often only floor material and plants are used. Is it not possible to set up like this a marine aquarium too, without ornamental rocks? In a few words, it wouldn’t make much sense. The freshwater aquarium reproduces mainly the biotope of a river or of a similar environment. Here water plants take root in the floor, which is reproduced in the aquarium. In a marine tank, however, we try to reproduce a snippet of a coral reef, and in this case limestone is prevalent. In fact, the whole reef, with all its inhabitants, exists on a base of calcareous rock. However, these reefs have grown over the remains of organisms such as shellfish, snail shells, hard corals and other organisms. The skeletons and remains of these creatures have been “welded” together in a compact mass by calcareous algae. These relatively light and often porous calcareous rocks are the base for all the reef’s corals. Therefore, to set up a marine reef aquarium, we cannot do without calcareous rocks.

A dry but very porous calcareous rock of marine origin, ideal to be turned into living rock.

Which type of rock is the best?

Which material then is the most appropriate? To this question too is easy to answer: the best is without a doubt the marine “living” rock, just the one that has formed in the reef itself. It is much more than a simple calcareous material, as it is rich of life inside. Micro organisms, countless worms and many other animals colonize it densely. We will never see many of these organisms, but their hidden life contributes all the same to increase the species variety, biologically stabilizing the aquarium. Many of the worms, shrimp, crabs, slugs and other organisms are detritivores, mainly active during the night, when they leave their hiding place and feeding even of dead fish before it can pollute the water. Deeper in the rocks live the bacteria that uses nitrates for their breathing, helping limiting the increase of this substance in the water of the aquarium. For these reasons, natural marine rock is the best solution for every reef aquarium. Very thick and heavy rocks, offered on the aquariological market as “dolomitic perforated rock” or something similar, are in the best scenario only a second choice. They are surely suitable, because of their shape, for invertebrates to insert themselves in their recesses, but the porous structure that is vital to many small organisms is missing. The thicker these rocks are, the less suitable they are to set up a well functioning reef aquarium. If an aquarium is set up with only these rocks, later it will only be possible to avoid the increase of nitrates only by using alternative means (nitrate filter, etc.). In any case, the rocks should be calcareous, if anything for aesthetic reasons. A reef aquarium would certainly not have a natural appearance with other materials. One should be careful with colored veins, especially brown ones. They are often compounds that can later bring complications related to heavy metals. In this way it can be easy to complicate things, making the growth of bothersome algae uncontrollable, or facing inexplicable coral deterioration symptoms. While this risk has to be considered for all of these kinds of rocks, it is almost absent in the case of living rock.

Part 2 will follow