With the launch of our brackish-water specialty line, Estuary by Tannin Aquatics, we're starting to see an increasing interest in mangroves and mangrove habitats. This is great, because it's not just an interest in the aesthetics of mangroves (they do look cool!); rather, it's an interest in understanding the habitats from which they come, and the ecology of these environments.
The most diverse and rich mangrove communities occur in tropical regions, where water temperatures are typically 74 degrees F/24 degrees C or greater year 'round. The roots of mangroves help in stabilizing and binding the soils in the areas in which they occur, and help with the establishment of microorganisms which further help stabilize soils. Mangroves not only help to prevent soil erosion- they also help to reclaim land from ocean!
Mangrove estuaries are well-known as breeding and nursery grounds for a number of marine organisms including shrimp, crab and fish species in marine habitats, and for facilitating the growth and development of numerous specialized brackish-water species.
The most interesting zone to replicate for our aquarium purposes is subject to regular tidal effect where the effects of soil accumulation and inundation is a continuous process. The mangrove species in this zone are specially adapted with stilt roots, prop roots for stability and anchorage. This is where our personal fave, Rhizophora mangle, the "Red Mangrove" occurs.
Rhizophora species have prop roots which descend from their trunks and branches, providing a very stable support system. They also posses what are known as "stilt roots", which, in addition to anchoring the plants, serve to facilitate aeration, as the mud in which mangroves grow tends to be quite anaerobic!
These estuary habitats are subject to tidal action, which plays a determinant role in the creation and distribution of seeds or propagules. And of course, tides also influence the salinity in an estuary. Mangroves live in rather hostile environmental conditions, like high salinity, hypoxic (oxygen deficient) waterlogged soil strata, tidal pressures, strong winds and, depending upon location, even wave action. To cope with such hostile environmental conditions, mangroves exhibit highly evolved morphological and physiological adaptations to extreme conditions.
One of the most common questions we receive is whether or not mangroves need salt, and the answer, in short is no! Mangroves are what botanists call "facultative halophytes", which means that the presence of salt in their environment is not necessary for their growth...In fact, they can grow very well in freshwater. We've even been sprouting and growing them in our office tank- in some pretty serious blackwater conditions! There are many natural habitats of mangroves which bare an uncanny resemblance to the blackwater inundated Amazonian forests that we love so much around here...
Now, one distinct advantage of growing in a salty environment is the lack of competition from other plants! Only a very limited number of plants have adapted to intertidal conditions. By contrast, in the optimum conditions of a tropical rainforest, diversity is great and the competition quite fierce, so it's little wonder why mangroves are dominant in their habitats! Interesting fact- some mangrove species have significant levels of tannins in their bark...so one need only think about the implications for our "brackish water/botanical "tinted" tanks!
Mangroves are equipped to deal with the salty habitats where they flourish in multiple ways. First, they can prevent much of the salt from the water from entering their tissues by filtering it out from their roots. R. mangle is so good at this, that it can exclude more than 90 percent of salt from the water it's growing in at the root level! Some mangrove species are also equipped with specialized salt-secreting systems in their leaves and tissues. Still others will concentrate salt in bark or in older leaves, which carry it with them when they drop. Leaf drop in mangroves also serves to enrich the environment via microorganism and fungal growth, forming the basis of a rich food chain. And of course, this is a fascinating aspect to recreate in the aquarium!
Hundreds of species of crustaceans and shellfish have been recorded in mangrove habitats, and this density and diversity is an indicator of the richness of this habitat. The significant deposits of silt and detritus in the mangrove environment are important to the many life forms which live there. The leaves shed by mangrove trees, along with the rich sediments brought in by rivers contribute greatly to the organic constituents of mangrove soil. As a result, a tremendous source of food is created, utilized by all sorts of detritovorous organisms, such as crustaceans and molluscs.
As you might suspect, there is a significant zooplankton population in mangrove areas, which interestingly includes lots of crustacean larvae, which feed on the numerous suspended solids which accumulate in mangrove root systems.
The mature crustaceans which reside in these habitats create burrows which are used for feeding, shelter and reproduction. Many species filter water through these burrows, and feed on suspended plankton, nutrients, and other materials in the water. All of these interesting burrows are very important to the overall mangrove habitat, as they facilitate draining, aeration, and turnover in the very dense soil layers. Oysters will often grow on the roots of mangroves, filtering sediments out of the water, and becoming exposed at lower tide intervals, creating an interesting aesthetic!
All of these organisms and their activities are very beneficial to the mangroves, which in turn provide them shelter- a very interesting interdependent relationship! The implications for creating unique displays are many!
If you're looking to recreate the function and look of a rich mangrove estuary, you'd be advised to include an assortment of shells and other materials to represent the diverse community of animals which live there. One of our favorite shells to use for this purpose is Telescopium telescopium, a snail that is strongly associated with mangrove environment! In eluding a few of these scattered about the substrate is a realistic touch to your mangrove aquarium!
We could go on and on about the incredible diversity, complexity, and interest that is found in the unique mangrove habitats, but I hope that this admittedly superficial review of them has piqued your interest in recreating, on a functional and aesthetic level, some aspects of them in your brackish water aquarium! So many angles, such replicating the root/substrate interface using mangrove roots and leaf litter.
Or, you might want to totally "build from scratch", and actually sprout and grow live mangroves and the associated life forms in a more comprehensive representation of this habitat!
There is so much to learn, and so much to experiment with when looking beyond the "straight" aesthetics and considering the fascinating interactions between the plants, animals, and the overall environment.
Get a bit salty and join us on this compelling journey.
Stay engaged. Stay creative. Stay curious. Stay (a little) salty...
And Stay Wet.