Red mangroves (Rhizophora mangle) are attractive
and utilitarian additions to the natural marine aquarium
system. A unique Atlantics biotope refugium has been
created here for the display of Upside-down jellyfish
with mangroves. Photo by Anthony Calfo.
have become increasingly familiar additions to marine displays
and refugia. Yet despite their presence and improved availability
in the hobby, they are still largely misunderstood and less
than optimally kept. I have enjoyed keeping these uniquely
coastal plants for many years in my own personal aquariums
and have grown out several thousand specimens from seed in
my greenhouse through the years. I hope to share some useful
tips and observations here to help you succeed with one of
the few, true marine plants for marine aquaria.
Let's first consider a bit of an overview on the plants called
"mangroves." Much has been written about their enormous
ecological importance in the tropical marine environment.
They provide habitat for countless life forms above and below
the surface and at the water's very edge. Birds, reptiles,
mammals, fishes and invertebrates exploit mangrove communities
for food, shelter and reproduction. The utilization of these
communities as a nursery environment by larvae has extraordinary
ramifications far up the web of life, on both sides of the
shoreline. The very structure of these strategically tangled
trees is crucial to coastlines for protection from erosion
and in the stabilization of sediments from run-off that could
otherwise pollute the offshore reef communities and subsequently
affect the fish and invertebrates dependent upon them. The
protection of mangrove habitats is crucial for the survival
of coral reef ecosystems and economies, from the fisherman
to the fished-for and so much more in between.
There are, in fact, over fifty families of plants claiming
a species called "mangrove." Only three genera of
mangrove, however, are commonly recognized, and aquarists
are principally only interested in the most saline aquatic
variety: the Red Mangrove (Rhizophora mangle).
A brief mention of the other two genera first:
The Black Mangrove (Aviccenia germinans) can be found
coastally as a partial immerse or fully terrestrial resident.
Although they are more tolerant of pruning (and cooler temperatures)
than the Red Mangrove, their preference for decidedly less
saline waters and a significant soil/mud component to their
substrate makes them less attractive to marine aquarists.
The White Mangrove (Laguncularia racemosa) does not
tolerate full submersion in seawater very well, if at all,
and really is best kept as a fully terrestrial plant. Aside
from uncommon, but interesting, "land and sea" style
biotope displays, the white mangrove has almost no appeal
The key to healthy and vigorous growth in cultured
Red Mangroves is the daily spraying of leaves
with clean, fresh water to help the plant export
salt crystals. Photo by Robert Fenner.
For marine hobby purposes, we seek the Red Mangrove specifically.
Indeed, it is the first species likely to be encountered by
aquarists. It is the most commonly photographed for its magnificent
aerial prop roots (the arched and exposed knobby knees plunging
into the coastline and shallows). And it is by far the most
important species of this family to marine environments as
mentioned above. They are the most hardy and adaptable species
for aquarium use if given some very simple maintenance. The
one thing you should remember from this article above all
is that red mangrove leaves need to be sprayed with clean,
freshwater almost daily for optimal health and growth.
The reasons for this are explained further below, but first
- a summary for the species:
Red mangroves occur in all saline gradients, but cannot
typically move between salinities rapidly. When buying mangroves,
it is very important to learn the salinity of the water from
where the seedlings (propagules) sprouted, and insure the
same at home. While propagules sprout roots and leaves readily
in fresh-, brackish-, or full seawater just the same, they
should not be moved quickly between them, but instead acclimated
over a period of many weeks. You can imagine that the salinity
of even nearshore environments is, by and large, quite stable
by virtue of the volume of the sea. 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! I recommend mangroves 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.
The wild collection of mangrove trees is forbidden
in many areas, but the harvest of their abundant seeds (propagules)
is fairly unrestricted. Un-sprouted propagules look like long
green cigars with a narrowly tapered end from where leaves
sprout, and a thickened, blunt, often brownish, end where
the roots grow from. The propagule's larger end has evolved
by design to increase the likelihood of it finding its way
into a substrate when cast or carried adrift, provided it
does not have the good fortune of finding itself plunged into
the sand after a straight drop from the parent canopy. Un-sprouted
seedlings may survive out of water in temperate conditions
for up to a year.
Aquarists are strongly advised to seek only un-sprouted seedlings.
If any roots or leaves are evident upon arrival, you really
must learn the salinity level in which the propagules were
sprouted. Without such information, salinity shock is a very
real concern and may be evidenced by a "desiccation"
and demise within weeks as the propagule takes on a wrinkled
appearance from the osmotic shock.
Next, you must give serious thought to how and where to plant
your mangroves. Some folks nestle them precariously in overflows
or plant them in small refugiums. Others make a concerted
effort to build an inline vessel or display around the young
trees for a dramatic aesthetic impact and unique biotope display
in its own right. The matter really boils down to a long-term
veiw versus short-term one. Some folks do not plant the seedlings
at all, but rather suspend them in mid-water ("Book of
Coral Propagation, Vol. 1", pp 30-32) for the purpose
of encouraging magnificent aerial prop roots. For aesthetic
and utilitarian (biotope) purposes, the cultivation of arched
prop roots on mangroves is very easy to finesse, despite the
lack of tidal cycles in the aquarium.
The placement of seedlings in overflows and small refugiums
is a temporary solution at best. While they may grow
slowly with limited stimulation of the roots, it is
not ideal for long term keeping and vigor. Photo courtesy
of Doug Wojtczak.
To encourage elaborate, aerial root systems, begin seedlings
tied gently to a post (PVC pipe, rigid airline tubing, etc.)
with flexible gardener's tape - available at a landscape
or garden center. Be sure to use flexible tape, as rigid ties
will cut into the plant as it grows. Immerse the tethered
seedling to a depth where only the lower 1/3 of the propagule
is submerged in water. Roots will sprout before leaves. As
roots begin to grow and develop, you only need to gradually
move the "body" of the plant upwards on the stake.
In this teasing manner, strong roots will grow thickened and
extensively to support the weight of the tree above the water
as if the tide was going out. It will take many months before
the propagule's body can be lifted completely out of the water
with an arched and anchored root system, but what a magnificent
and natural sight to see! If, instead, you choose to simply
stick a propagule into a bed of sand like a dart, substrata
root development will occur quickly and profusely, but aerial
prop roots are unlikely, if possible at all, without a replication
of tides and the exposure of some roots to air over time.
Attractive aerial prop roots can be encouraged without
simulating intertidal cycles by gently tying your mangrove
to a stake with soft, flexible gardener's tape. Over
time, gradually raise the barely immersed roots further
and further out of the water for them to form handsomely.
Photos by Anthony Calfo.
Fertilizing the substrate may be helpful in new or dry sand
beds, but unnecessary or dangerous in aged aquariums where
levels of dissolved organics are typically high. One notable
exception may be magnesium as mangroves have been implicated
as a measurable draw on the element. Of course, so many other
things in a thriving reef aquarium are also a burden to magnesium
levels, which may require being supplemented, so don't let
that stop you from keeping mangroves!
Mangroves will not develop exaggerated aerial prop roots unless
they are suspended or exposed at times to simulate intertidal
exposure. Nonetheless, planted directly in the sand or mud,
they develop strong root systems fast. Photo by Kevin Pockell.
Regular partial water changes, however, may be the simplest
means to improve overall water quality and support vigorous
mangrove growth. If protein skimming is not your principal
means of nutrient export beyond water changes, a mangrove
feature (refugium, sump, in-line vessel) should be fed raw
overflow water from the display to give them the opportunity
to utilize dissolved and particulate matter. It would be both
counter-intuitive and counter-productive to feed mangroves
clean, filtered water, given their natural habitat and needs.
Photo courtesy of Margarita Man.
For all my love for keeping these plants, however, I must
admit that they truly are not comparatively efficient nutrient
export mechanisms. It's a very simple matter. Growth overall
is slow, and leaf drop is often concurrent with new leaf growth.
The net gain of mass from these plants is, in fact, dismally
slow, and leaf drop alone (as a vehicle for nutrient export)
cannot compare to a vigorous Chaetomorpha or Gracilaria
based vegetable filter.
Lighting is a simple matter with mangroves. They are quite
adaptable to a wide range of light but prefer bright illumination.
Expensive reef aquarium fixtures are not necessary. Common
warm, daylight-spectrum bulbs from the local hardware or DIY
garden center store work very well. Many aquarists have grown
fine mangroves under incandescent (including mercury vapor
and metal halide) plant-growth spectrum floodlights or spotlights.
More than lighting, though, regular spraying of the healthy
leaves with freshwater is a bigger influence on plant vigor
and growth. On humid and often rainy coastal shores, it's
no trouble for these plants to purge the daily influx of salt.
But in dry homes without "rain" (spraying of the
leaves), mangroves suffer noticeably in short while!
Pruning red mangroves is a sensitive matter, though, and
a rather moot point for most aquarists. Even under the best
conditions, mangroves really are slow growing for most folks
taking three or more years to even get 2-3 feet tall. If you
must trim your tree, be sure to delay any pruning until after
the axial tip has branched. Damage to the growing tip before
it has split can be fatal to young specimens.
Follow these simple rules and you can enjoy an attractive
feature to your marine aquarium. Dedicated aquarists can enjoy
natural biotope displays with mangroves and Diadema
urchins hosting baby cardinalfishes
or Upside down jellyfish
littering the sandy floor of a special display. Look deeper
into coastal habitats and niches and you may find many, truly
unique and rewarding new ways to enjoy your hobby with mangroves!
If you have any questions about this article, please visit
my author forum
on Reef Central.