Mangroves are way cool. They are under appreciated and lacking in attention for nearly all circuits of the aquarium hobby. Historically mangroves only made an appearance in the reef hobby as a source of filtration, often growing in sumps as a way to remove nitrogen compounds. Oddly enough as the years have gone by a general consensus has formed believing that mangroves in general are a very poor choice for filtration. They grow slow, and they appear to remove little nutrient from the water, especially when compared to many species of fast growing macro algae.
Mangroves are a family of trees classified as Rhizophoraceae. They are found circumtropical and grow where the land meets the sea. They can live in freshwater, brackish, marine, and even very highly saline areas. They form a solid structure supporting coastal integrity preventing erosion by dissipating the energy from waves. From a coastal management point of view…. they are indispensable. However, very little of this pertains to aquariums.
Mangroves for Filtration
As was mentioned before, mangroves have had a place (albeit small) in the hobby as a source of filtration. They do incorporate nitrogen compounds and trace metals into their tissue which does pull it from the system. However over the years the actual effectiveness of mangroves has been questioned and current thinking is that the filtration ability of mangroves is negligible.
Mangroves for Habitat
This has been a growing part of the hobby, and has potential for blossoming. Mangrove displays and habitats have been part of public aquaria for years, but still very rare in the hobby. As a trend for natural systems and biotopes has grown, so has an interest in mangrove displays. Mangroves can be used in displays as part of the aesthetics, or even as a central theme for the biotope called a mangal.
Obtaining Mangroves
There are a hundred of species of mangroves but in hobby terms there are Red Mangroves, White Mangroves, and Black Mangroves, all named for the color of their tissue under the outer dermis. Red Mangroves are the most common because they are common to find and easy to obtain. I recommend a simple search on ebay and you’ll be all set. As someone who studies biological oddities I find the Red Mangroves to be completely fascinating. They are actually viviparous! The seeds actually germinate and grow into a propagule while still attached to the parent tree! Very cool.
Planting and Transplanting
Planting mangrove propagules is easy. They are torpedo shaped, fat end goes does and will develop the root system, the thin point is the apical meristem and will grow into branches and leaves. These are true plants with vascular systems. The bottom ends need to be placed into the sandy or muddy substrate. At first, they do indeed grow fine for quite some time while simply suspended in the water. But ideally they grow in sandy/muddy areas and their root system will provide a lot of support, not just nutrient uptake. The substrate itself is debatable. I've planted them in all sorts of muds and sands, and even buried fertilizer sticks in the sand to feed them. However, at this point I can't see they grew any better than when I simply planted them in clean crushed coral of a running aquarium. The water from the tank was certainly carrying enough organics for them to do quite well in multiple systems.
The upper end of the propagule must remain above the water line. For this reason a small container or specimen cup is often used for planning mangroves, keeping them up high enough for them stay above the water level.
If you are transporting mangroves from one system to another then be forewarned of some challenges. While Mangroves can live in a wide range of salinity, they don’t often do well moving from one to the other. Meaning if you are growing mangroves in your freshwater aquarium, they may stress and die from moving them to your reef aquarium. Make slow changes to salinity. Also, once uprooted the mangrove will go into a stress situation. Often times after moving mangroves their leaves turn black, curl up, and fall off. You may think you’ve killed them. Don’t give up on them yet, this stress response will pass and in a few weeks they will start producing leaves once again. If I were moving mangroves from one area to another I would dip the roots in a nutrient dip. While I don’t have much experience to go on, I’d still try something like Ecological Laboratories Microbial Root Dip. It’s a small cost for what could be a great benefit.
Light and Heat
They do best in light around 6500 K. I’ve never found a single article that had PAR levels or recommendations for mangroves. My testing of mangrove systems shows that they will grow in light as low as 20 micromoles, and will also grow in light of 200 micromoles. While I’m quite confident they’ll grow in light up into high hundreds and even thousands of micromoles I would say this is rare in aquarium conditions because they reach the actual bulbs and physically get burned. So if you can hit them with a lot of light, but not burn them, I’d expect to see fabulous growth from the mangroves.
Mangroves however, do like warmth. Not exactly heat, but warmth. A warm humid area (like your sump) is ideal. Having mangroves in exposed display aquariums can be a challenge for cool or dry climates. Mangroves will take in salt through their roots, and expel it as salt crystals on their leaves. The leaves need to be sprayed frequently (maybe daily) as a way to wash off the salt. This also help in creating the humid environment if you are misting the plants.
Mangrove Care
Mangroves need very little care. They can takes weeks to establish but once rooted and growing they are pretty much as a "set it and forget it" type of plant. Mangroves take in saltwater via their roots and they excrete salt from their leaves. In natural conditions this salty film or salt crystals are washed off by frequent rains. In aquariums it is advised to spray the leaves daily to rinse off the excreted salt. Although not advisable I can testify to seeing mangroves growing quite well in some of my system with never being washed.
Conclusion
While mangroves remain a side little oddity in the hobby, they are of great importance to natural systems. They may never become commonplace in the hobby but there is certainly a need to study them, keep them, and to develop aquariums around them. Mangroves systems are unique and intriguing. Great developments in the hobby are owed to those who study niche ecosystems and mangals are no exception.
Reef Addicts Message