Mangroves as a natural method of filtration and means of NNR (Natural Nitrate Reduction) in saltwater aquariums

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Mangroves as a natural method of filtration and means of NNR (Natural Nitrate Reduction) in saltwater aquariums

Post  saltz on 25th October 2013, 11:36 am

The use of mangroves plants for filtration in a saltwater aquarium, particularly for helping to reduce and control nitrates is not a new concept. It has been around for quite some time, but few aquarists have really known much about it. However, this is changing because more and more aquarists are looking for a "natural" method of filtration for their aquariums, so mangroves are drawing more attention all the time.

During my recent visit to Bangkok, I had the opportunity to visit Chingchai's massive 1200 gallons SPS system that apart from the massive Bubble King skimmer, Phosphate Reduction Reactor, Carbon Reactor, Ozone Reactor, also incorporates a refugium with 30-40 mangrove pods growing in it. I had a little discussion with him regarding the decision to replace the Chaeto that was previously in the refugium with mangrove pods and how much difference it made to the system, in brief, he reckons that mangroves are much better at nitrate reduction than Chaeto, and maintenance is easier and less messy. With chaeto, he'll have to remove the excess Chaeto every couple of days, ensure that enough water flow goes through them, etc. With mangroves, he only needs to mist the mangroves every day to remove the salt from the leaves that burns the leaves if left alone.

He also mentioned that most of the successful large systems (over 1000 gallons) he knew of uses mangroves, some of the more notable ones include Reef Central's "NineBall", Julian Sprung and Anthony Calfo. That conversation sparked my interest in mangroves, and while I don't see myself growing mangroves as a means of filtration for my current setup (mainly because of space constrains), I'll definitely consider it for future setups. Now, for those interested, here's a little information I've gathered from the internet.

Mangroves as a means of NNR (Natural Nitrate Reduction)

While Mangroves normally grow in mud in the wild, it is not required to grow mangroves. They can be grown very efficiently in a sump, refugium or directly in an aquarium. They are fed by absorbing nutrients and organics from the water, which in turn creates a natural filter for cleaning water. Mangroves not only have the ability to absorb nitrates, but phosphates and other organics as well. In fact, they remove organics so well from the water that they act as a replacement for a protein skimmer. When using mangroves you will notice your protein skimmer working less and less all the time. The more the mangroves grow and mature, the more they absorb the excess organics in your water, and the skimmer has nothing to remove and becomes obsolete. If you are a naturalist and don't want to have to use chemical additives or compounds to reduce and control nitrates in your aquarium, this is a very effective filtration method to consider.

Advantages Of Having Mangroves In A Reef Tank

Mangroves take the nutrients necessary for their growth from the aquarium water. This means that we have a means of exporting phosphates and nitrates. Macro algae do the same, but they easily set those nutrients free when they are eaten by fish or die and dissolve. With mangroves this is different, at least if the aquarist succeeds in preventing the mangrove leaves from falling into the water and dissolving there. While many mangrove species export excess salt by depositing it on the surface of their leaves for the rain to wash away, some mangrove species deposit excess salt inside of their oldest leaves, which then will turn yellow and drop down. This is a natural process, but in the reef tank we just have to make sure that the leaves will not dissolve in the aquarium water and release nutrients back into the aquarium water.

But, on the other hand, regarding the nutrient export capacity of some mangrove plants living on the upper zone of our reef tank, we should not expect miracles. They are slow-growing plants, and their nutrient uptake is limited. To say it clearly: if we have the problem of exporting phosphates and/or nitrates from our tank, due to over-feeding, insufficient foam fractionation, etc, we will certainly not be able to solve it by planting mangroves. Having mangroves in the tank just helps to make the man-made biotope a little more natural, in function and appearance. If we try to create something we call a "mini reef," we should take every opportunity to employ natural mechanisms. Even though their functional contribution to the system is relatively small, it makes our "mini reef" a bit more natural.

Types of Mangroves

The word 'Mangroves'' refers to a group of plants which may actually belong to several families (species that distinctly belong to their own evolutionary group). The term therefore indicates an ecological rather than a taxonomical (scientific classification) grouping - the species are not related. They are unique plants because of their ability to grow in unstable tough environments.

Mangroves are unique because they are able to thrive in areas where the water is poor in oxygen content, in salt water, in fresh water and in brackish water (a mixture of salt and fresh water). Mangroves are fast-growing trees taking several years to reach up to 25 meters when they are fully grown. There are 39 species of mangroves in Queensland alone, including the Red Mangrove, that has been found to be the most suitable for use in the saltwater aquarium.

Red Mangrove


This is a common species of the Rhizophoraceae family. Its range extends across coastal northern Australia from the Richmond River in New South Wales to Shark Bay in Western Australia.  Red mangrove forms extensive, often pure stands around the shores of shallow protected bays, estuaries and inlets. It prefers soft, well drained muddy soils. It also establishes on rock or coral-based sandy soils and is a dominant species of lower tidal mangrove forests. It is commonly seen along the lower tidal reaches of rivers and immediately behind the seaward fringe of mangroves, sometimes with grey and yellow mangroves.

Red mangroves in North Queensland may grow to 20 m high, though trees of 4 to 5 m are more common elsewhere. The main trunk is erect and covered by rough, reddish-brown bark.

Stout, large arching prop roots are characteristic of the species, which support the main trunk and contain numerous lenticels (air pores) on their surfaces. The lenticels are air-filled spaces that connect with underground root structures. Aerial roots growing from the tree´s limbs also help the plant breathe. These do not take root even after reaching the soil and are produced by lower branches.

Leaves are oval-shaped, thick and leathery, and may reach 15 cm in length and 6 cm in width. They are dark green with numerous small, reddish-brown dots on the lower surface and a small deciduous pointed tip. Small, creamy-white flowers occur in branching pairs while the leaves are arranged in opposite pairs on the stem.

Flowering occurs in winter, with the production of a single-seeded, brown, oval-shaped fleshy fruit during summer.

Seeds germinate on the tree (vivipary), which results in the appearance of a long, green, rounded propagule (seedling) about 30 cm long. The propagule protrudes through the wall of the fruit to hang vertically beneath it. This buoyant germinated seed is the first stage of the root system.

Buying Mangroves

Some suppliers cultivate and harvest mangroves from the wild, while others aquaculture them in closed systems.

There are four basic stages of mangrove seed growth:

 The seed with no roots or leaves.
 The seed with knobby root starts beginning to form, but no root sprouts yet.
 The seed with some roots started and a leaf sprout formed.
 The seed with a full root system and fully grown leaves.

If you get seeds in the first or second stages, it will take a while for them to mature. Mangroves in the third stage have a good root start and will grow to maturity faster. In the fourth stage you already have mangroves with an advanced root system, and generally you can see results in a very short period of time after introduction into the aquarium.

How to Acclimate Mangroves

The biggest mistake that one can make is immediately slam the mangroves into some water, expose them to intense lighting, such as metal halides, and then hope for the best. This is a sure fire course to failure.

Mangrove plants received by mail order will more than likely have been in transit for several days without light, water and CO2. The plants can literally be in "shock" when you open the package. Therefore, they should be slowly and carefully acclimated and introduced to their new environment. After shipping, sometimes they may even go through a dormant stage, but if cared for properly they will awaken from this dormant stage and continue to grown and mature.

Hopefully the plants you receive will have been well prepared for shipping. To us this is best done when the leaves and roots are wrapped in a damp water absorbent material (paper towels/newspaper) and sealed in a plastic bag. Remove the plants from the shipping material and gently rinse them in room temperature fresh or tank water. This will remove any extraneous contaminants, and allows the plants to "breathe" and adapt the their surroundings, before placing them into their new home.

How many should I get?
You will need one mangrove per 10 gals of water, each mangrove will need at least a 3inch diameter of surface area. You can get away with less space if size is a concern, but it is not recommended. Mangroves are slow growing plants, so don't expect them to be miracle solution to your tank's nitrate issues. The take time to get establish and grow, but given the right conditions and time, they have been known to improve the quality of the tank's water and slowly replacing many of the other chemical, mechanical, and biological filtration in the system.

Mangrove Placement & Care

The method most often used for keeping mangroves is to place them in a sump, or a refugium can be used. Mangroves do grow in a range of substrates from fine to coarse, but seem to strongly favor fine sand or muddy substrates.

Be warned, though, their very elaborate and extensive root systems must be given due regard in the aquarium. Even a seedling mangrove can develop a formidable root system that can stress or damage glass or acrylic aquariums in as little as three years. Do not underestimate these roots by judging their modest leaf and branch growth above! Mangroves should be planted in containers that are as large as possible (removable pots), thereby reducing future disturbances of the tree without making it overly difficult to service for transplantation in the future. Rest assured, though, that growth overall is so slow and easily managed that these fascinating angiosperms can be enjoyed perhaps indefinitely in most aquarium systems.

Mangroves can also be kept without planting them in any substrate, they can be kept by suspending them in mid-water.  The seeds are inserted into pieces of styrofoam and floated with the roots in the water, then provided with a plant light source, and some aquarists suggest an iron supplement.

Illuminating Mangroves

The simplest illumination for the mangroves is the light emitted at the side of a halide lamp. But you need to make sure that the plants don't grow directly under the lamps because of the strong heat emitted there. Also, the plants would shade corals when growing directly under the lamps. The stronger your halide lamp, the greater the distance you need to plant the mangrove from it. But, if necessary, you can cut the plant in shape at a later time when it grows branches too near to the lamp. Also the color temperature of the lamps is of importance for the mangroves. The best light for mangroves is, of course, a daylight lamp at 6,000 Kelvin, since they are land plants. With a lamp of 10,000 Kelvin it may also be possible to grow mangroves, but a 20,000 Kelvin lamp will probably make it harder to satisfy the physiological needs of mangrove plants.  If the aquarium is placed under a window, we can also use the natural daylight to grow mangroves. An alternative to the natural daylight or the halide lamp would be a special plant lamp hanging on top of the mangrove. That helps placing the lamp a greater distance from the mangrove, and also permits putting it right on top of the plant, resulting in a more natural looking growth form.

Maintaining Mangrove Plants

Mangrove plants don't need much care. Mangroves export salt by producing a thin layer of salt crystals on top of their leaves. This should be washed away daily - or at least two to three times per week - by spraying fresh water on top of the mangroves. Be very careful when spraying water on to the mangroves on top of the aquarium if there are lamps and electrical outlets! That is about all you have to do other than cutting some branches occasionally or even the growth tip of the plant if it comes too near to the lamp.

Examples of Saltwater tanks incorporating Mangrove Filtration

In the recent MACNA, Julian Sprung's Two Little Fishies booth, displayed several display refugia, each full of huge mangrove trees. Unlike traditional refugia, these didn’t have a chaotic look. Instead, they actually looked very well kept with a modern minimalist feel.

Display refugia are no new thing. People have been doing them for many years. Mangrove setups aren’t new either, but the way that Julian displayed them at the conference just felt so fresh.  The biggest issues with growing mangroves have always been those of height limitation when they were in a traditional style sump. With these setups, which are nothing more than Nuvo nano aquariums full of sand, the intricate root systems can be viewed in all of their splendor and the tops of the trees can grow as high as they want.

Below are some pictures of Mangroves systems gathered from the web:

Obtaining Mangroves for your Aquarium

Now, after reading this thread, you may be tempted to start going out to the beaches and start pulling out mangrove plants to start planting them in your sump, refugium or tank, but first you need to know the regulations and legislation regarding the collecting of mangrove plants in your area. The regulations and legislation on collecting marine plants may be different in each state in Australia, so please find out more from the fisheries department in your state before you carry out any collecting.  

For example, here in Queensland, all marine plants (including mangroves, saltmarsh vegetation, seagrasses, marine algae, dead marine wood) are protected under the Queensland Fisheries Act 1994. Section 123 of the Fisheries Act 1994 applies to all marine plants and penalties apply to unlawful removal, destruction or damage.
"Section 123 Protection of marine plants
A person must not unlawfully—
(a) remove, destroy or damage a marine plant; or
(b) cause a marine plant to be removed, destroyed or damaged.
Maximum penalty — 3000 penalty units."

However, certain permitted collection activities can be authorised through compliance with self assessable codes which apply to operational work that is for the removal, destruction or damage of marine plants if the removal, destruction or damage is necessary for minor impact works as defined in the code.

Limited collection of marine plants is permitted under Self Assessable Code MP06, specifically for:

Table 1 Code standards (maximum allowable disturbance and method of disturbance) for minor impact works for private purposes

Table 1 Work type 1.3 (page 10) of the Code – Removal and/or possession of algae for private use in aquaria

Table 1 Work type 1.6 (page 10) of the Code – Removal and use of mangrove seeds and propagules for private use for mangrove rehabilitation within or immediately adjacent to the developers property (owned or leased)

Table 2 Maximum allowable disturbance and method of disturbance for minor impact works for public purposes

Table 2 Work type 2.11 (page 17) Fish habitat rehabilitation or restoration works (including not-for-profit marine plant nursery establishment)

Alternatively, you may choose to purchase your mangrove seedlings instead. Once again, there are specific regulations and legislation for the sale of mangrove plants. In Queensland, legislation pertaining to buying and selling fisheries resources (including marine plants) is found in the Fisheries Regulation 2008.

Specifically Section 632 outlines arrangements and exceptions are listed under subsection 632 (2):
Section 632 Selling Queensland fisheries resources before second point of sale
(1)A person (a seller) may sell fisheries resources taken from Queensland waters only if the seller—
(a)holds an authority that authorises the sale; and
(b)gives the person buying the fisheries resources the number of the authority.
(2)However, subsection (1) does not apply if—
(a)the sale is authorised under chapter 7 or a management plan; or
(b)the seller cultivated the fisheries resources in a way that was authorised under the Planning Act; or
(c)the seller sells the fisheries resources after the resources have been sold by another person under subsection (1); or
(d)the seller sells the fisheries resources after the resources have been bought from another person who cultivated the fisheries resources in a way that was authorised under the Planning Act.


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