Up till now we’ve discussed biotopes in their literal sense — systems built around a specific geographical or spatial location, and systems centered on a specific niche within that location. In this hobby though, there are no hard and fast rules, and the limits of what can be considered a ‘biotope’ are only capped by your imagination.
If you’ve decided that you want to set up a biotope but aren’t sold on the traditional avenues, here is a sampling of systems that are becoming more and more popular.
Single-species systems are exactly what they sound like: the bioload is dominated by a single species, genus or perhaps family. Systems like these can take many forms; a systems designed around a Fu Manchu Lionfish, complete with a central cave for perching, is an example. Or perhaps a 40 Breeder with six inches of sand and a plethora of Upside-down Jellyfish.
Rhinopias sp., perfect for a single-species tank.
The goal with a single-species tank is to choose an organism and then build the system around it. That lionfish is going to need a strong skimmer to clean up after its messy eating, and those jellyfish would benefit from gentle flow and a sump packed full of live rock. People often create systems for a specific species due to their sensitive nature or difficult feeding habits, such as with dwarf seahorses or pipefish. Make sure you understand the needs of your chosen livestock, and meet those needs through your system.
Marine Planted Tanks
Macrolagaes occur on all the world’s reefs. In fact, in some reefs macros are the dominant calcifying organism. That means that instead of the reef being built by corals, it’s built by algae. No biotopic presentation can be called complete without the addition of some form of macro algae. The more popular macros in the hobby can be fairly drab, but there are plenty of species out there that would contribute to a spectacular algae-dominated planted tank.
A system centered on macroalgaes does have a few specific considerations though, the first being pH. Just like terrestrial plants, macros take in carbon dioxide during the day and release it at night. This lights-out release of carbon dioxide can cause pH fluctuations; the more algae in the tank, the higher the probability of the pH changing dramatically, which can cause stress or even death for other inhabitants of the system.
Halymenia sp. macroalgae, a popular and beautiful species.
The simplest way to combat this is to have a refugium plumbed to the main tank, containing an algae such as chaetomorpha. Set up the light cycles so they oppose each other — when the main tank lights are on, the refugium lights are off, and when the main tank lights are off, the refugium is on. In this way the cycle of carbon dioxide release is offset and the system will remain more stable.
Another problem that can be encountered is algae going sexual. When this happens, the algae turns translucent and releases spores in an attempt to repopulate a different location. This spore release is generally accompanied by a nutrient spike, but for a planted marine tank this is of little concern. Simple remove the dead portions of algae and the other macros in the tank will utilize the nutrients released. If you have other livestock in the system, such as fish or corals, and you notice them having an adverse reaction to the algae going sexual, do a waterchange and run some carbon.
The algaes most likely to go sexual in home aquaria are Caulerpa sp, although all macros have the potential. Halimeda sp also go through the process fairly often, although it is usually just a few ‘pads’ that go and not the whole colony. Algaes go sexual for many reasons, though usually it is caused by being overgrown or not receiving enough nutrients. Basically, the algae does not think it has a good chance of survival where it is, and is trying to move somewhere more suitable. Some algaes will go sexual for no apparent reason however, and because of this there’s really no way of preventing the problem completely. I’ve never heard of a tank crashing specifically due to algae going sexual, so it’s one of those ‘deal with it as it comes’ scenarios. Don’t let it scare you off though, algae-dominated tanks are a beautiful sight!