Several years ago reef enthusiasts started to
take a fancy to mangroves. To my knowledge this was something "made in the USA,"
because Julian Sprung was the one who got it started, which was not surprising for someone
who lives in Miami Beach, Florida. He planted a mangrove in his 15 gallon reef tank, and
to everyone’s surprise - maybe even to his own surprise - it started to grow
wonderfully and still does to this day. This was copied by many reefkeepers, and after
Julian had published an article about mangroves in a German aquarium magazine, even German
reefkeepers got keen to plant those little trees into their tank.
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Growing mangroves enables
one to decorate a tank to look like a fringing reef that surrounds an island, as seen from
the ocean. In fact, this is what I tried to do with my 1500 gallon tank with the help of
40 mangroves. A viewer that sits in front of the tank faces the "wall" of a
"fringing reef," and if he looks over the water surface, he can see a
"beach area" behind it, planted with mangroves. When standing behind the tank,
one feels like a giant looking at a little mangrove forest over the beach area into the
coral reef. Sometimes you can even see corals and other sessile inverts growing on the
submerged parts of the mangrove’s trunks. I remember a Pavona venosa fully
surrounding one of my mangroves, covering the complete submerged trunk - a little unusual
because Pavona cannot be considered a typical coral genus growing in the mangrove
area. But, in fact, those mangroves growing near the lagoonal area where their roots are
permanently submerged even during ebb tide often have lots of sponges, mussels and even
corals growing on them. Pocillopora damicornis grows in this area, and occasionally
we can also find corals typical for a lagoon. If we plant mangroves in our aquaria and we
want to create a coral community that has some similarity to the low and submerged parts
of a natural mangrove zone, we can use Catalaphyllia, Goniopora, Pachyseris,
Leptoseris, Herpolitha, Euphyllia, and many others. Even small polyped scleractinians
like Porites, Montipora, Pavona, Pocillopora and even some Acropora species
can occasionally be found there, aside from zoanthid polyps, disc anemones and soft corals
like Sarcophyton or Sinularia.
What is the advantage 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.
For which types of reef tanks are
mangroves suitable?
Of course, a tank where we want to plant
mangroves needs to be open on the top, so the plants have space to grow. Theoretically, we
can also cut an opening into the light hood of a closed tank, but from an aesthetically
point of view this can hardly be satisfying, at least if one tries to copy a natural beach
area. The most fascinating thing with mangroves in a reef tank is - at least to my opinion
- the view from the top in front of the tank on the little "coral reef" that
extends from the "deep ocean" to the "shallow lagoonal area," ending
in the mangrove-populated "coastal zone." With a light hood this does not work.
Another type of tank for mangroves is a
special mangrove-aquarium. This can even be done with a filter tank and is very simple.
Julian Sprung has a tank of this type connected to his "famous" little reef
tank. All you have to do is to take a few mangroves that root on some porous lime rocks,
place it in the center of this tank and surround it with some corals typical of the
lagoonal zone. A weak water current is sufficient for the mangroves (but obviously you
should also ask the corals for their opinion). This mangrove tank can be connected to your
main reef tank, for example by placing it a little higher and pumping a small amount of
water from the reef tank into the mangrove tank, so it will flow back into the reef tank
via gravity. With the help of a timer you can even add a second pump which will pump at
certain intervals and transport more water into the mangrove tank, resulting in a higher
water level. By doing so you will imitate the natural high and ebb tides. If you create
the decoration of your mangrove tank in a way that lets some areas fall dry during ebb
tide, you can even add animal life typical for this mangrove zone, a fascinating thing.
Mangrove propagules or mangrove
seeds?
Mangrove species have developed different
strategies for propagating. Those species growing on the more elevated areas near the land
which falls dry during ebb tide develop propagules instead of seeds, e. g. Bruguiera-
and Rhizophora-species (mostly R. mangle). A propagule is a sprouting young
plant that looks a bit like a candle. When it falls down from the mangrove tree at ebb
tide, it can bore itself deeply into the muddy ground. This helps to prevent it from being
washed away when the sea water returns during high tide. One must know that once those
mangrove propagules have been washed away from the shore area reaching the open sea, the
chances of their survival by finding another shoreline of an island is very limited and
the long term survival of those propagules would be very questionable, though they can
survive even three months floating around. Other mangrove species inhabiting other areas
of the shoreline develop other strategies of propagation and form seeds, mostly in the
size of a hazelnut.
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The propagules as well as the
seeds can be used in a reef tank. The seeds grow into a plant with a thin stem that can
perfectly adjust its growth form to the light conditions on top of the aquarium, but they
seem to be a bit more sensitive if the halide lamps emit too much heat. Propagules seem to
be hardier, but they are also larger and in a very small reef tank they might look
unsuitably large, while a mangrove plant that has grown from a seed may have a more
natural tree-shape, giving the scene a more natural appearance. A few years ago I was able
to get mangrove propagules and seeds from Florida and the Philippines. In my experience it
was much more difficult to keep the seeds in place. Even when it was securely fixed
between the rocks, some fish came nibbling around on the seeds. In contrast to this,
propagules can easily be put between some lime rocks. In my case, the propagules and seeds
grew nicely during the first few weeks, but then about one half of the mangroves grown
from seeds died. This may have been caused by planting them too near to the 1000 watt
halide lamps, which emit a lot of heat. All in all, the survival rate has been much better
among the mangroves grown from propagules, though today I still have some mangroves grown
from seeds.
Planting mangroves in a tank is
simple
Under natural conditions, mangroves do not
only root in mud, but also in lime rock. Consequently, we can offer them some porous lime
rocks placed in the upper area of the tank. The simplest way is if you push the propagules
between two or three porous rocks, allowing their roots to grow into the pores. If the
propagule already has developed fine roots when you get it, you can also lay those roots
around a porous lime rock and carefully fix it with a rubber band, waiting for the roots
to hold tightly to the rock This way it is easy to change the plant’s location at a
later time, though this should be avoided as far as possible because the plants strongly
adjust to their environment, especially to the illumination.
But a single mangrove has little similarity
to a mangrove forest. If you want to have a "real mangrove forest," you may need
to employ a different way of fixing the plant in the water. For this purpose, I have
embedded the propagules into rock wool and placed the whole thing in a small grid basket
formed of plastic commonly used for freshwater aquarium plants. The roots grow through the
rock wool and the holes in the basket, holding the plant tight. This basket makes it easy
to connect several mangroves to each other by using nylon cable ties. That way I have
created groups of mangroves that stabilize each other in their position.
If you want to create a "beach
zone" with fine white sand and mangroves on top of your tank, you can go one step
further and connect those plastic baskets to a perforated plastic sheet (PVC or acrylic).
This sheet with mangroves then gets placed in the upper area of your tank, where you can
cover it with coral sand, coarse grain size on the bottom of the sheet, and covered with
fine white coral sand.
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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 (though I have not tried it).
Mangroves and daylight
If the aquarium is placed under a window, we
can also use the natural daylight to grow mangroves. In this case, we can even illuminate
the tank with fluorescent tube lamps, even with a closed lamp hood having a hole for the
mangrove. 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.
The most frequently traded mangroves are Rhizophora mangle, which exports 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. We use distilled water for this purpose. 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.
A
view on the mangrove zone of the authors’ 1500 gallon reef tank with a "floating
coral nursery". Photo: Daniel Knop
Occasional
cleaning of the mangroves from salt is helpful. Photo: Daniel Knop
Sometimes
mangroves in aquaria even develop the typical roots. Photo: Stefan Albat, Germany
The
mangrove grown out of a seed (center bottom) develops a different and probably more
interesting growth form than the specimen grown out of propagules seen at the back.
Photo: Daniel Knop
Nylon
cable ties help to connect mangroves that are placed individually in plastic grid baskets.
Photo: Daniel Knop
When mangroves propagules
are placed in plastic grid baskets it is easy to attach it to a perforated sheet with the
help of nylon cable ties. Diagram: Daniel Knop
Zonation of a natural mangrove
forest:
The zonation of a natural mangrove forest
starts with very salt-resistenrt species of the genus Sonneratia (1) on the sea
side that are capable of tolerating a permanent submersion of their roots. Moving more
near to the shore at the upper end of the intertidal zone we mostly find Rhizophora
species (3), which is the most commonly offered mangrove species in the aquarium trade.
Here they are submersed only for a limited period of time. Species of the genus Bruguiera
(4) have more sensitive roots that are not capable of living unter the rough conditions we
find in the intertidal zone. Therefore they mostly grow over the intertidal zone in the
mud collecting here.
Tipps for buying and keeping
mangroves:
- Prefer propagules instead of seeds, if
available
- Try to get the species Rhizophora mangle,
because it is very hardy and adjustable
- Buy a propagule with some roots and some
leafes
- Make sure that the roots are not hurt. It
is best if the roots have grown into rock wool, covered by a pot.
- Chose a propagule with healthy green
leafes. yellow or dried leafes can be something natural, but as well it can be a sign of
transport damage.
- Some mangrove species - especially Bruguiera
sp., react very sensitive to infections with molds fungi, which sometimes develop in the
humid conditions near an open aquarium. Try to avoid the development of molds on the walls
and ceiling if you want to keep mangroves.
Storch, V. & Welsch, U. (1997): Systematische
Zoologie, 5. printing. Gustav Fischer-Verlag, Stuttgart
Knop, D. (2001): mangroven im natürlichen
Lebensraum. KORALLE 9, June 2001
Knop, D. (2001): mangroven im Riffaquarium.
KORALLE 10, August 2001
Web Links:
[There are some excellent hyperlinks to mangrove biology available on the
web,
the first (especially) and the third are excellent resources. The
fourth gives the three species of mangrove found in South Eastern US. Craig Bingman, Science editor.]
