On any tropical shoreline where there are shallow, flat stretches of soft sediment that is not subject to heavy wave action you will most likely find extensive beds of sea grass comprised of single or multiple species, often closely intermixed seeking to gain their share of sunlight and nutrients from the near mud like substrate. Seagrass communities are among the most productive communities in nature providing habitat for large populations of invertebrates and fish, and acting as some of the richest nursery and feeding grounds to be found anywhere on earth.

 Seagrass sediments - A place of complex nutrient dynamics and home to many species.

  The seagrasses are considered to be ecosystem engineers since they partially create their own environment simply by growing and living in most soft, sandy sediments. Once established by the pioneer species, their extensive root systems take up nutrients which are then transported to the leaves.Upon the leaves’ death and detachment, they will settle on the surface of the sediment and through decomposition not only return a portion of its sequestered nutrients to the sediment, but will also create the acidic conditions through decomposition that releases even more adsorbed nutrients from the sediment in which it grows. All of the nutrient exchange is also utilized by the multitudes of infauna that through their own actions within the sediment contribute to the distribution of nutrients and thus the growth of the seagrasses. 
 

   Algae are not the only organisms that quickly take advantage of any substrate that affords them a position in the sunlight or water currents much to the detriment of the smothered individual leaf.  The sacrifice of individual leaves creates a much greater benefit to the seagrass meadow as a whole and is responsible in large part for the high rate of productivity which in turn fuels the complex ecosystem and nutrient food web that extends far beyond the confines of the seagrass meadows.  
  Epiphytic growth while seemingly detrimental to the seagrass may also benefit those plants that grow in areas that tidal movement exposes them to the air.  With a coating of epiphytic life forms, moisture retention is enhanced and may allow the seagrass to avoid desiccation (Bell 1997).

    As each leaf is covered in epiphytes, the ability of the leaf to perform photosynthesis is reduced and reaches a point where the leaf is of no use to the plant anymore. The leaf is cast off, along with any epiphytes unlucky enough to have settled on what seemed a permanent home.  The cast off leaf now further enriched with other life becomes part of the leaf litter mat and is acted upon by bacterial and fungi creating the detrital matter that so many other organisms find of use.  Having lost a leaf, the plant then pulls even more nutrients out of the sediment to create a new leaf to regain its photosynthesis capacity and makes sediment bound nutrients available once again. In turn, yet another new surface area arises for the epiphytes to colonize, and so the circle begins again.  With individual leaf life spans having been estimated to be anywhere from 3 to 10 days, there is a vast amount of organic material that a seagrass meadow is producing in a single week.

  Ulva follows a reproductive pattern called alternation of generations, in which it takes two generations to complete its life cycle, one that reproduces sexually and one that reproduces asexually. Although mature members of both generations look the same to the naked eye, microscopic chromosomal differences distinguish one from the other. The first generation, which has two complete sets of chromosomes (2n), the second generation has only one set of chromosomes (n). The first generation, called the sporophyte, undergoes asexual reproduction to form spores, tiny reproductive cells that develop into mature individuals called gametophytes. Gametophytes produce gametes, male and female reproductive cells that fuse together during fertilization to produce a zygote, an organism with two complete sets of chromosomes that matures into a sporophyte, thus completing the life cycle.
  Ulva spp.are relatively simple when compared to more advanced algae and vascular plants. They do not differentiate into tissue layers or show much specialization among cells, making them a colony of like cells forming new cells perpendicular to the surface which gives this species their distinctive thin "tissue paper" appearance.  Since each cell, including the reproductive cells, are capable of photosynthesis, the uptake of nutrients and adjustments to light intensity is very rapid.
   Due to their high nitrogen requirements and their limited ability to store nitrogen, Ulva distribution is nitrogen limited and explains their seemingly quick appearance and subsequent disappearance after heavy rainfalls. Such occurrences make Ulva spp. good bioindicators of local water quality pertaining to its level of nitrogen enrichment. In such areas of constant enrichment, Ulva spp. become a permanent feature and can easily smother all benthic organisms found below it.   
  It is worth noting that there are no local Ulva populations here that could account for the sudden growth observed during periods of eutrophication after heavy rainfalls. This leads me to conclude that their zygotes are being carried in from distant locations that do contain permanent populations due to year round nitrogen enrichment as found near sewage discharges or river inlets.
  Once nutrient conditions favor local growth, these algae can make a very sudden appearance near the shoreline.  As they grow they will begin to settle on top of the bare sand and rubble substrate nearshore to the seagrass meadow and remains near shore. I at first attributed the shallow water propensity of Ulva to one of light intensity but have since learned that its appearance in near shore shallow water is simply a matter of available nitrogen through terrestrial runoff and only remains near shore due to a lack of sufficient wave disturbance.  A study of U. lactuca (Hansen 1992) has shown that this macroalgae can compensate for reduced light intensity by its ability to rapidly increase its cellular chlorophyll content and has its highest rate of growth with a mere 10% of available ambient light.  These facts do not bode well for the marine habitats as the only limiting factor of U. lactuca appears to be the availability of nitrogen, making any relatively shallow habitat vulnerable to being smothered by its rapid growth should nitrogen eutrophication occur over extended periods of time.
   With their appearance and having reached a sufficient size to present enough surface area to be uplifted by storm driven waves the algae is then carried offshore by tidal action where they become entangled with the seagrass leaves.  I have not noted any detrimental affects to the seagrasses other than the localized loss of single leaves due to shading by these macroalgae. Upon the loss of the leaves, the attached Ulva are either dropped down into the leaf litter where local grazers consume it or if left uneaten, will in a matter of days die as any available dissolved nitrogen is quickly consumed. Upon decomposition its limited nitrogen content does not appear to have any long term consequences as I have observed this local seasonal phenomenon since 2004 with no apparent loss of seagrass cover to date.  
  

  Having explored a natural seagrass meadow we now turn our attention to the keeping of seagrass within an aquarium. Given the conditions and the nutrient dynamics discussed pertaining to natural meadows we now have a greater understanding of their needs and what they can bring to a reef aquarium system.  When used as a refugium plumbed into a reef display aquarium the nutrient processing and production of an aquarium reef system is enhanced and negates the need to use equipment and other products that attempt to do what nature does best, if allowed to. 

   Sediments -  The seagrass refugium's sediment is vital to the health and long term survival of the seagrass just as it is in natural meadows.  How you construct the sandbed is going to determine its functionality in providing a nutrient rich environment for the seagrasses rhizomes and root structures.  Seagrasses are plants that depend upon their roots for the uptake of nutrients, roots that require extremely fine grain sizes, it will be imperative that a calcium carbonate substrate with grain sizes ranging from 0.2 - 1.02mm be used with a depth of no less than six inches, deeper if possible.  Incorporating a live mud into the sediment during the sand beds construction will ensure a suitable number of infauna are introduced.  Just as in nature the infauna are critical to the functionality of any sandbed to process nutrients and prevent the formation of sand clumps by their movement through the sediment (Shimek 2001).

  Patience -  With the refugium plumbed inline with the rest of the aquarium system now comes the most difficult part of it all. The wait. It will take at least six months to one year for the sediments to have become enriched enough to support the requirements of the seagrasses (Calfo 2005).  To rush the introduction of the plants will most likely ensure their loss.  Having been uprooted, transported and their root systems likely damaged, the plants will need everything to be in their favor to get off to a good start.

 Indo-Pacific Plant Selection -  With the construction of the sandbed having been completed you now have at least six months to determine which species are available to you and study their husbandry.  My experience with any of the seagrasses is limited to the indo-pacific species yet through my study and recent attempts at keeping indo-pacific seagrasses it appears they all share some basic needs and care requirements, evident by their all being found within the same seagrass meadow.  

    Halophila ovalis appear to be the most tolerant of less than ideal handling and capable of surviving being shipped with bare roots and wrapped in moist paper towels for a number of days (Borneman 2008).  Being a pioneer species may account for this hardiness as they are frequently the first species to grow into uncolonized soft substrates. This apparent ability to go where no plant has gone before would in my opinion make them the best candidate for establishing a seagrass habitat with the later introduction of other seagrass species. Their very short growth and relatively low lighting needs in comparison to other seagrasses make them ideal for placement in coral reef aquariums as there is no danger of this seagrass shading or becoming abrasive to the corals and will tolerate the lowered light intensity found at the aquarium's sediment level.

    Thalassia hemprichii  -  While not as common as T. testudinum (shown in the photo), the two species share very similar morphology and husbandry requirements. Given such similar morphology, I doubt many hobbyists can distinguish between the two other than by knowing where they were collected. With T. testudinum being an Atlantic species it is most likely that those hobbyists in the United States will use this species as their first seagrass keeping attempt(s) as it would be the most readily available of the species.  While not impossible to maintain, this species does appear to be sensitive to uprooting and the subsequent exposure to air.
 
    Syringodium isoetifolium  -  Second only to the Halophila sp. in its ability to colonize.  I have found S. isoetifolium to be hardy and fast growing.  It transplants much easier than the Thalassia sp. with a high rate of survival.  This species would make a good addition to either a newly established or mature seagrass aquarium, able to colonize rapidly while making a suitable companion species with established Thalassia spp. Normally not growing as tall as the Thalassia, it is not affected by partial shading and with their very thin, tubular leaves they pose no risk of shading the wider bladed Thalassia spp. either.  These traits between the two genera may explain their combination being the dominant structures in natural seagrass meadows here in the Philippines.

    Enhalus acoroides  -  With leaves averaging a length of 130cm and 3cm wide with root systems that can extend well beyond 30cm deep, this species is not a realistic choice for home aquarium systems.  For scale, the floor tiles shown in the photo are each a square foot with the plant being so long that I had to stand on a chair to get the entire plant into the frame. However, if one were to set up a suitable aquarium for this species it would make for a very unique display.  The affect of such a planted aquarium would be reminiscent of a kelp forest.  

Lighting the Seagrass Aquarium -   Given the environment the seagrasses are found in as discussed previously it should be obvious that they require high light intensity to thrive. Estimates from various studies (Kenworthy 1996) done on the minimum lighting requirements of seagrass species have shown that their lower toleration limit to be in a range from 24% to 37% of the light just beneath the water surface which equates to photosynthetically active radiation (PAR) levels of between 200 to 600 PAR at wavelengths between 400nm and 700nm.  Levels below these minimums result in the seagrasses producing shorter and fewer leaves, obvious indicators that more light intensity is needed over the aquarium. Extended periods of light levels below their minimum requirement places a stress on the seagrasses that some species are unable to recover from.  Halophila spp. are the exception and have much lower lighting requirements.
  Since most hobbyists have their own preferences in the lighting systems that they use, I am not going to suggest any particular type of lighting and instead stress again the importance of  light intensity to the seagrasses.  How that intensity is provided is irrelevant unless it has an impact on animals being kept within the same system due to heating of the water.

Water Flow & Temperature -  Tropical seagrasses have a high thermal tolerance averaging 90 degrees fahrenheit and live close to their thermal limits in the shallow, protected environments they are found in.  An aquarium that maintains the average Indo-Pacific coral reef water temperature of 82F is well within the temperature range that tropical seagrasses are adapted for, those aquariums that maintain lower than normal coral reef temperatures may encounter slower seagrass growth and their failure to thrive. Temperature is second only to light intensity pertaining to tropical seagrasses primary needs.
  Water flow through the seagrass aquarium should not include the use of powerheads or other high flow pumps and instead simply allow the overflow volume from the rest of the system to provide bulk water movement that will not suspend the leaf litter and detritus and encourage diversity of fauna and infauna.

 Water Parameters -  Being a plant, the seagrasses utilize the same common nutrients as terrestrial plants.   Nitrogen, phosphorus, iron and carbon dioxide, most of which is absorbed by the roots from the sediment with the exception of carbon. Phosphorus will not normally be a limiting factor in an aquarium system due to the input the system receives through the addition of food.  Nitrogen and iron is more likely to be utilized first by algae and bacteria and may become limiting to the seagrasses.  These limitations can be overcome by the use of plant food sticks or tablets (Borneman 2008) pushed down into the sediment near the plant's roots.  It is unlikely that nutrients provided in this manner will have any affect on the system unless the sediment is disturbed allowing the release of the nutrients into the circulating water.
 
Planting the Aquarium -  Now that the long wait is over with the sediment having been given time to sequester nutrients and the plant species selected for planting, its time to break out the gardening tools and... actually you will need nothing more than your gloved hand to accomplish the delicate task of placing your seagrasses into the sediment.

    The roots of seagrasses are fragile with any damage done being the biggest factor in losing purchased plants.  This is unavoidable when purchasing seagrasses from commercial sources as the roots are usually stripped of any sediment to lessen the shipping costs involved with heavy sediments (Calfo 2005).  A good reason to start out with the hardier species that are known to have a relatively high survival rate when transported in such a manner.  If seagrasses are being shared or purchased from a local established seagrass aquarium then you have the opportunity to collect individual plants with less damage or disturbance to the roots by gently moving the sediments to expose the rhizome and cutting the rhizome with scissors in six inch lengths.  Once cut, gently lift the plant so as to keep as much of the root attached sediments intact and place the plant in a suitable container while being held under water (Borneman 2008).
  Having collected seagrasses from the local meadows, I have found that it is much easier to properly plant such lengths of the seaweed by simply making a trench in the aquarium's sandbed and gently place the rhizome and its roots into the trench and cover with sediment.  Do not force or push the rhizomes into the sediment as it will only break the rhizome and cause further damage.  Again, having access to the local seagrass meadows means that I can take extra measures to tip the plants survival rate in my favor.  A shallow, wide tupperware container and a spatula allows me to lift entire sod sections containing the rhizomes, roots and all of its surrounding sediment gently into a tupperware container (all done underwater) for easy transport back to my aquarium.  Digging a suitably sized pit into the sandbed I can then lower the tupperware onto the sediment and gently slide the entire sod section into the pit and cover with a centimeter or two of sand.
  Once planted, it is not uncommon for the seagrasses to drop all of their leaves due to the shock of having been disturbed.  With their relatively fast rate of leaf production, new leaves should begin to emerge within a week or two at most.  You can help ensure the plant has additional nutrients to replace its lost leaves and to recover more quickly by following a tip from Eric Borneman who has had increased success with newly planted seagrasses by purchasing freshwater plant food tablets that are broken in half and pushed down into the sediment close to the plant's root structures.


    As with any available lighted surface, microalgae will grow upon the seagrasses leaves and shorten the leaves usefulness to the plant by blocking the available light.  With Astralium spp. being the most commonly found snail consuming the microalgae on seagrass blades in natural meadows and being the most commonly sold species, they would make the best choice for keeping your seagrasses clean of epiphytic microalgae. A good stocking number to start out with would be one snail per plant, increasing their numbers if you find that the snails are unable to keep up with microalgae growth.  I feel I should point out that these species are most often sold to the reef aquarium hobby not because they are suitable for our rocky coral displays, they are not, but simply because they are found in great numbers in the seagrass meadows and with the meadows being nearshore and easily accessed they are collected by simply wading through the meadow and picking them off the seagrasses without any need for scuba gear as is required to collect the snail species that are found in coral reef areas.