A Biotope-Specific Refugium
Plants Can Add to the Health of Your Saltwater Aquarium
A simple Red Mangrove and Shoal Grass refugium can improve the overall health and stability of your marine system and make you a more educated and informed aquarist.
A biotope-specific refugium is an excellent idea for the inquisitive marine aquarist. In particular, experimenting with a planted refugium allows the hobbyist to simulate the connectivity found in an expansive reef ecosystem, while also contributing to the health of the overall system.
The reef tanks maintained by many hobbyists are diverse and rely heavily on that diversity to control basic needs (e.g. clean-up crews, substrate-dwelling bacteria, live rock, and algae grazing fish). Even the most self-sufficient tank, however, tends to ignore the expansiveness of the reef ecosystem—an ecosystem which is intrinsically tied to other biotopes such as seagrass beds and mangrove fringed shorelines. While it’s true most home-sized refugia cannot export enough nutrients to make other filtration redundant, it is still an excellent means of removing some excessive nutrients from the system while at the same time providing a source of live food for your animals.
Consider, for example, you have a 30-gallon near-shore, Indo-Pacific reef display tank. By connecting a 15-gallon refugium populated with red mangroves, shoal grass, pods, macroalgae, and a few beneficial invertebrates, you can recreate interesting aspects of the reef ecosystem while increasing the overall volume and health of your system.
To plumb such a system, you might have the display tank’s overflow drain into the sump and the refugium in a 70/30 split (use a ball valve to control the flow to the refugium). The refugium’s overflow then drains into the sump where it is pumped directly to the main display tank through the sump’s return pump.
Since you are planting shoal grass in this refugium, thirteen centimeters of mud is sufficient. In addition to requiring less substrate than other grasses, shoal grass also requires less water depth—as little as 15 cm is all that is needed. Although shoal grass is eurythermal, it does best in water temperatures between 20- and 30-degrees C, which is consitent with the temperature of a reef tank.
Three red mangroves are planted in this refugium because they are both readily available and considered the most aquatic. Propagules can either be planted directly in the substrate, or they can be grown hydroponically. The latter technique achieves more aesthetically pleasing and natural looking effects as the mangrove roots stretch out and extend. This can be accomplished by attaching the propagules to a rod suspended above the refugium and keeping as much as two-thirds of the propagule above water.
The refugium requires its own light since, like terrestrial plants, seagrasses make their own food through photosynthesis. A high-intensity purified daylight fluorescent light over the refugium with light intensity in the range of 0.215278208- 0.484375969 centimeter-candles is optimal, and the mangroves do fine with this as well. This light is run on an opposite cycle from the display tank’s lights in order to stabilize pH.
The refugium requires flow which is created by the water draining from the display tank. Estimates of optimal current velocity for seagrasses range from less than 50 cm/sec up to 100 cm/sec. For the refugium, make sure the velocity is low enough to keep sediment from blowing up into suspension, yet high enough that water moves through the system and keeps it from becoming stagnant.
Experimenting with plants in a biotope-specific refugium connected to a complementary display tank simulates aspects of an expansive reef ecosystem often overlooked by the marine aquarists. In addition to improving the health and stability of the system, such a set-up provides an excellent educational opportunity for the inquisitive aquarist.
