Seagrasses, until recently, had earned only an obscure place in marine aquaria as occasional, short lived accents in full blown reef tanks or as nutrient export plants in refugiums. With a little attention to their needs, however, it is possible to grow and maintain beautiful stands of seagrasses as the focus of a marine planted or lagoon style aquarium. This article attempts to assemble information on seagrass husbandry to serve as a guide for interested aquarists to set up seagrass dominated systems. It also briefly covers the natural ecology of seagrass beds and the current state of this natural resource. Much of the information represents results and observations from several projects, experiments and versions of tank design I have attempted over the last few years in which I have focused on marine plants.

The term "seagrass" is actually somewhat ambiguous, and hobbyists sometimes apply it to anything green from the ocean. Seagrasses are not a true species of grass (which are in the family Poaceae), and the common name reflects only their similar appearance to land grasses with long, strap-shaped leaves. Further confusion is sometimes added when aquarists refer to "seaweeds" or "marine plants," both of which serve as a catchall phrase for seagrass and macroalgae. As with other aquaria inhabitants, it usually is best to avoid these muddy terms by referring to the plants by their Latin species names.

Seagrasses are a diverse group of true vascular angiosperms (or flowering plants). They are distinct from the red, green and brown macroalgae species by the presence of vascular tissue, true roots, underwater flowers and submarine pollination of those flowers. Currently, taxonomists recognize approximately 60 species of seagrass, though this number is debated, as is their placement in the taxonomy. Most biologists recognize four major families of seagrasses: the Zosteraceae, including Zostera and Phyllospadix genera; the Hydrocharitaceae, notably with Thalassia and Halophila; the Cymodoceae, encompassing the familiar Halodule and Syringodium; and the Posidoniaceae, which hosts only Posidonia genus plants.^1,2,3 Additionally a fifth family, Ruppiaceae is sometimes accepted as a family of seagrass, though they are typically more common to brackish water. Ruppia species are, however, very important as seagrass in parts of the Mediterranean region, particularly in the Black, Aral and Caspian Seas.^2,3

The Hydrocharitaceae is unique among the four families as it hosts genera of freshwater, brackish and marine aquatic plants. This placement in the taxonomy hints at seagrasses' evolutionary development and at their relationships to freshwater plants such as water lilies and lotuses. Flowering plants are the most recent major addition to the plant fossil record, and seagrasses are some of the younger forms of angiosperms, evolving approximately 100 million years ago.⁴ Flowering plants can be found in a nearly limitless array of forms and in many different habitats, including lines of plants that have recolonized the water. Seagrasses as a group represent several evolutionary lines of flowering plants returning to the oceanic biome.⁵

These plants are found in nearly every temperate and tropical shallow coastal environment in the world. Each ocean and continent hosts its own diverse population of seagrasses though the diversity is highest in the tropical waters of Papua New Guinea, the Philippines and India.² Many genera have pandemic distribution, and this is particularly true of species within the Halophila genus such as H. decipiens (paddle grass). Other species within this same genus are highly endemic and have their distribution limited to a few hundred square miles, such as southeastern Florida's Halophila johnsonii (Johnson's seagrass) or Hawaii's Halophila hawaiiensis. The Zostera genus is also widespread through temperate waters along North America's east and west coasts, parts of Africa's Atlantic and Red Sea coasts, the British Isles and France, as well as populations spanning the Pacific in Japan and Vietnam.² The Zostera genus is also widespread through temperate waters with species occurring along North America's east and west coasts, parts of South Africa and southern Australia, the British Isles, France, and Chile, as well as populations crossing the Pacific in Japan.²

Of the 60 seagrasses, four currently available forms are suitable for use in tropical marine aquaria. All four hail from the Caribbean basin. It is likely they appear in the trade because they can survive the short transit times from collector to the local shops here in the U.S. They are: turtle grass - Thalassia testudinum, manatee grass - Syringodium filiforme, shoal grass - Halodule wrightii and star grass - Halophila engelmannii. Two baygrasses, Ruppia maritima and Vallisneria americana (tape grass), are also found in the hobby, but are most suited to brackish water aquaria whose salinity does not exceed 20ppt. Likewise, eelgrass - Zostera marina, is an unusual find among hobbyist sustained systems as it is a candidate only for temperate aquaria not exceeding an average of 68°F (20°C).

New species from other regions are bound to find their way into the U.S. marine hobby once source material can be imported and the plants are aquacultured. Collection permits vary considerably by national and local governments, and it is prudent to thoroughly research the topic before attempting to collect any species. Typically, phytosanitary certificates must be obtained to send plant life, including seagrasses, across national borders. There are two species of seagrass that are very unlikely to become a part of the aquarium trade, Halophila johnsonii (Johnson's seagrass) and Phyllospadix serrulatus, a member of the surf grass genus. Halophila johnsonii has been included since 1998 by the U.S. Fish and Wildlife Service on the federal threatened list under the provisions of the Endangered Species Act (1973).^6,7 Ultimately, our desire for new species must be tempered by the need to respect and protect this natural resource.

The Seagrass Habitat

Relative to coral reefs with which we are most familiar, seagrasses inhabit high nutrient, clear to fairly turbid water in areas of soft sand and mud substrates. Aquarists who have had the pleasure of roaming marshes, estuaries and seagrass beds are sure to recall the characteristic fragrance of such substrates. Besides often being anoxic within the first few millimeters, these soils often release hydrogen sulfide when disturbed. Seagrasses can be found within bays, lagoons, and estuaries as well as offshore and within yards of patch reefs in coastal areas. Seagrass beds can consist of single species stands that stretch for hundreds of yards or they can exist as patchy multi-species beds covering only a few hundred square feet of bottom. There are shallow water long lived beds of seagrasses that tend to exist for decades, if not centuries, and there are deep water ephemeral beds of seagrasses out on the coastal shelf that exist for only a few months of the year.

Substrate fauna is diverse and includes annelids, polychaete worms, bivalves such as oysters and scallops and burrowing snails. Even the seagrass leaves create a microhabitat that supports an amazing array of life including encrusting bryozoans, sponges, epiphytic macroalgae and micro-algae, mussels and other fauna. One study reported, after combining surveys from several regions, that there are 450 species of epiphytic algal that coat seagrass blades, and that's just the algae!⁸

Juvenile lemon sharks, Negaprion brevirostris, are common in flooded mangrove forests and patrol the periphery of seagrass beds, as seen here, waiting for potential prey. Photo: Sarah Lardizabal, Warderick Wells, Exuma, Bahamas.

A large number of reef-associated species also inhabit seagrass beds and other shallow coastal habitats such as oyster reefs and mangrove swamps during their juvenile stages. Some representative species from around the world that inhabit grass beds during this phase include trumpetfish (Aulostomids), goatfishes, rabbitfishes, a number of wrasses and parrotfish, as well as game fish including grunts, snappers, grouper, drums and spadefish. Year-round and lifelong residents vary by region and include, as a limited sampling, urchins hosting cardinal fish (such as Banggai cardinals), sea anemones and their resident clownfishes in the Pacific, pipefishes, ghostpipefishes, seahorses, sheepshead minnows, sargeant majors (Abudefduf sp.) and similar Chromis and Dascyllus sp. fishes. In more temperate areas sheepshead minnows, Fundulus killifish, grass shrimp (Palaemonetes sp.) and the economically important Callinectes sapidus (blue crab) are common. Nassarius sp. snails, whelk, Strombus sp. conchs and a multitude of other invertebrates are also found within seagrasses in the western Atlantic. Predators such as nurse sharks, juvenile lemon sharks, juvenile moray eels and groupers, stingrays and barracuda often patrol the edges of seagrass beds searching for prey among the sandflat infauna. Great barracuda often chase shoals of prey toward the shore through the beds. The particular species diversity associated with a seagrass bed depends heavily upon where in the world it is located. Just as fish and corals are not the same from a Caribbean to an Indopacific reef, seagrasses and their associated species change as we move through oceans, zones and seas.

Several families of fishes and invertebrates not only live within the meadows of seagrass but also consume the plants themselves. Urchins, abalones and angelfish have been known to visit seagrass beds for plant buffets. In reef aquaria the popular rabbitfishes, surgeonfishes (excluding the bristletooth tangs such as the Kole and Chevron - Ctenochaetus sp.) and many angelfishes (in particular the larger Caribbean grays and French, Pomacanthus arcuata and P. paru) also occasionally graze on seagrasses. In addition to these fish and invertebrate browsers there are mammalian and reptilian foragers of seagrass. Worldwide, manatees, sea cows and dugongs (Trichechus, Dugong and Hydrodamalis sp.) are known to consume mostly seagrass in their diets. Sea turtles, such as the Caribbean native green (Chelonia mydas) and loggerhead (Caretta caretta), also are prime examples of seagrass consumers in the wild.

In terms of coral populations, both hard and soft corals are found in this environment and, like the fish, vary by the seagrass bed's location. These include but are not limited to: star corals - Montastraea, brain coral - Diploria labryinthiformis, fire coral - Millepora alcicornis, Gorgonia, Fungia, Porites, Heliopora, Sarcophyton, Sinularia and Nehpthea. Cnidarians such as tube anemones, flower anemones and even Cassiopeia jellyfish may be appropriate, though require more specialized tanks. It should be mentioned that, in the wild, most corals would be found within a climax species dominated bed, such as near Thalassia in the Caribbean.

Seagrasses are also crucial habitat for a number of threatened, vulnerable or endangered species including the aforementioned green sea turtles, manatees, dugongs and sea cows. The entire seahorse genus Hippocampus is listed by IUCN⁶ and several species inhabit seagrass beds through their life cycle in several regions. Seagrass meadows also serve as nursery and breeding grounds for three listed species of grouper: the gag (Mycteroperca microlepsis), Venezuelan (Mycteroperca cidi) and the endangered Nassau (Epinephelus striatus).

The Status of Seagrasses

Like coral reefs, seagrasses are a valuable natural resource that are under direct and indirect human impacts that have led to their decline in several areas of the world. Increasing coastal populations contribute to pollution of seagrass habitat via nutrient-laden runoff. Freshwater drainage of wetlands and rivers can also contribute overly rich water to seagrass beds. An imbalance of nutrients typically drives algal blooms that smother seagrasses either by overgrowth of the leaves or by limiting the amount of light reaching the plants. While these marine plants thrive in nutrient rich areas, the wrong mix of nutrients can be lethal if conditions persist long enough. Direct human impacts are seen in areas where seagrass beds are dredged for piers, channels and other coastal development.² Additionally, localized seagrass death can occur where anchors are dropped. Unaware or careless marine vessel operators contribute to the decline of intact beds by propeller scarring, carving deep white scars into the beds that can be seen from aerial vantage points.

In the U.S., Florida's seagrasses show some of the largest declines, particularly in Tampa Bay, which lost over 80% of seagrass coverage from 1879 to 1981.^2,9 Disease has played a major role in the decline of the beds due to a slime mold, Labyrinthula sp. in these areas, particularly in the Chesapeake and north Atlantic in the 1930s.^2,10,11 There are signs that the loss of seagrass habitat can be reversed with good management and through bed restoration activities. Over the last twenty years Chesapeake beds have made a recovery, increasing over 30% throughout the Bay.² In Tampa Bay the seagrass had recovered to 35% of historic levels by 1997 and current survey projects continue to show progress in its recovery.¹²

The decline of grass beds is extremely costly to our economy in the U.S. and in the world. The beds stabilize sediment and help to maintain high water quality by filtering out nutrients from terrestrial inputs, trapping sediment, recycling nutrients within the ecosystem, and sequestering carbon.² They also serve as enormous nurseries for hundreds of species of commercially important fish and crustaceans. In Monroe County, Florida the value of five commercial fisheries based on species that depend on seagrasses in their lifecycle is estimated to be $48.7 million annually.² This figure does not include revenue from industries such as ecotourism that are also indirectly associated with the area's seagrass beds. In fact, the global value of all known seagrass and algal beds for their single role of "nutrient cycling" is estimated at $3.8 trillion each year.² Add to this the associated value of global commercial fisheries support, ecotourism and coastline protection, and we begin to grasp just what we stand to lose if seagrass beds disappear.

Seagrass Species

Presented here are the profiles of four species of seagrass that are available to marine aquarists today. Since they are all from the Caribbean basin they share similar ranges including the east coast of the U.S. in Florida starting at Cape Canaveral, along the Gulf of Mexico coasts from Florida to Texas and along the full stretch of Mexico's coasts to the Yucatan. They are also found distributed along the coasts and near the reefs of several Caribbean countries including Bermuda, the Bahamas, Puerto Rico and Cuba. In deeper water a few species can be patchily distributed between larger islands. Most of the seagrasses are usually found within the protected lagoons created by barrier islands within the Gulf and along Florida's Atlantic coast. Around the island countries and in the Florida Keys the seagrasses stretch out immediately from shore onto the coastal shelf and extend seaward.

Turtle grass - Thalassia testudinum

According to most taxonomists Thalassia belongs to the Hydrochartiaceae family and is a genus containing species across several different continents. The most often seen species is the Caribbean and Western tropical Atlantic T. testudinum, or turtle grass. As the name suggests this species is a popular item in the diet of sea turtles. Turtle grass is a climax species in a seagrass bed, typical of areas that have long supported seagrass and other aquatic life. They are relatively large plants with strap-shaped leaves that grow 10-16" in length and have varying leaf widths ranging from a slim ¼" to ¾" across. Collected fragments of these plants tend to come from outside the U.S. and into the trade via private small sales.

Thalassia is the only seagrass species I have attempted to culture that can be transplanted as a single plant without an attached rhizome. This species has a very large root system that can extend well beyond the 6" DSB often recommended for these plants. Turtle grass is common in shallow water as little as 3' deep and often extends down to 30 - 40' in coastal areas where they form extensive monospecific underwater meadows measuring several football fields in length.² Turtle grass grows well only in areas of consistently high salinity (28 ppt and higher) and is usually found at the inlets of lagoons and bays. They can also be found farther out on the shelf near coral heads and between spur and groove reefs where water quality allows light to reach the plants on the seafloor.

Manatee grass - Syringodium filiforme

The Syringodium genus belongs to the Cymodoceae family and is also a subtropical to tropical zone seagrass genera. Syringodium filiforme is the most common seagrass found in the hobby, and is found naturally as small populations within larger turtle grass beds or at the periphery of turtle grass beds. It is also found mixed in with Halodule wrightii in shallow areas from 5 - 20' in depth. Manatee grass, like turtle grass, gains its name from one of its consumers, the manatee in the Caribbean. Like other species of seagrass, floating disturbed fragments of these plants continually wash ashore on the lagoonal beaches and mangrove swamps close to submerged beds. Manatee grass can grow to considerable heights in tall aquaria, up to 24", and produce thin (1 - 2mm) tubular positively-buoyant leaves. In shorter tanks the leaves tend to break off at the water line. This does not seem to be detrimental, so far, to the few plants of this species that I currently culture.

Manatee grass is often hard to distinguish from shoal grass, but their tubular leaves, appearing circular in cross-section, distinguish it from the flattened leaves of shoal grass. The two species can also be distinguished if you have reproducing populations of both. Manatee grass produces new plants by extending the rhizome under the surface and pushing daughter plants through the substrate whereas shoal grass produces new plants and rhizome material in the water column and anchors them by roots which tap into the substrate and drag the new plant down.

Shoal grass - Halodule wrightii

The Halodule genus is another temperate to tropical zone genera belonging to the Cymodoceae family and includes several Caribbean natives as well as species in many other oceans. Halodule wrightii is the dominant species of the Halodules and has the largest range of the four seagrasses in the trade. Including the range mentioned through the Gulf of Mexico and Florida's coasts, this species pushes north along the U.S. all the way to North Carolina where it shares turf with Zostera marina.² This species is typically the first to colonize disturbed seagrass beds and propeller scarred areas, and grows prolifically just a few feet below the low tide line in very shallow water as little as 6" deep and can extend out to the edges of deeper manatee and turtle grass dominated beds in several feet of water. There is a small complex of closely-related species spread out across the Caribbean, but H. wrightii does not currently belong to this taxonomic grouping.² Halodule wrightii is currently the most common Halodule species in the trade and is, like manatee grass, typically available from Florida collectors.

This plant exhibits very thin, 1mm wide leaves that are flat and grow from 3 - 14" in height, though 6-8" is far more common. Interestingly, this species and manatee grass both respond to increasing water flow velocities by growing taller and faster. Shoal grass roots penetrate an average of four inches into the substrate and are much shorter than those of turtle or manatee grass. It also takes far less time to recover from transplant shock and, in good conditions, should be sprouting new plants in aquaria inside of two weeks.

Star grass - Halophila engelmannii

The Halophilas are a very diverse group of small seagrasses that display shapes and growth patterns very different from typical seagrasses. They are a tropical species and belong to the Hydrocharitaceae alongside Thalassia and Enhalus genera. As a group they are very small in size in comparison to the other seagrasses and range from a diminutive 0.5 to 4". Their leaves are also quite different and vary by species from a basic oval leaf shape to elongated pinnate forms. Leaves can be arranged into various patterns, as pairs, palm-tree-like pseudowhorls, fern-like presentations and in more basic groups of three or four.

Several species are from the Caribbean but only one, H. engelmannii, has so far made it into culture and from there into the trade via a small group of hobbyists. Star grass, so named for its delightful arrangement of 6-8 leaves in a pseudowhorl around the plant's stem, is a small (1-3" tall) plant with a tenacious growth rate in aquaria. This species, like another Caribbean native, H. decipiens (paddle grass) is reported to occur in deeper water farther out on the coastal shelf around Florida up to 60'.² However, I have found small populations of this seagrass growing alongside manatee and shoal grasses in much shallower water from 5-10'. In aquaria it grows well in a range of light (90 - 280 micromoles/m²/sec) and salinity (20 - 36 ppt) regimes and is quite unaffected by temperature, happily growing in 65 - 85°F aquaria. When aquaria temperatures rise a few degrees from cool periods (generally above 72°F) the plants are stimulated to produce female flowers. Male flowers have only been produced in one event in my aquaria, following the start of a dinoflagellate bloom that ultimately smothered the star grass.

When conditions are optimal this species, like shoal grass, grows quickly enough to be considered weedy in aquaria. Over 500 plants were produced in one six-week period from an initial eighteen plants in one particular system. With growth rates like this fragments can be harvested from the parent frequently without the need to produce and germinate seeds and seedlings for the trade. Since this species is the least demanding of the four available, I predict it will also soon be the most common of the four within the trade.

Tank Husbandry

The idea to setup seagrass dedicated aquaria has gained a bit of momentum in the past two years, particularly following the recent publication of Julian Sprung's¹³ and Steven Pro's¹⁴ articles touching on seagrass aquariums. Anthony Calfo¹⁵ has also penned an article concerning these plants, and hints from Eric Borneman can be found in a few places on the web. Many questions, however, remain unanswered as this relatively new aspect of our hobby grows.

There are many ways to integrate seagrasses into aquariums, but there are two general categories for seagrass tanks: 1) lagoon style setups where seagrasses are included as small percentages of the total biomass, and 2) setups where seagrasses (and sometimes macroalgae) are kept as the system's dominant biomass, called seagrass dominated or marine planted aquariums.

In both systems the physical aspects of the tank design - particularly light and substrate requirements - are the most important. The approach that best fits an individual aquarist depends solely on the goals for the display in question. In lagoon style tanks the emphasis is on corals, and the seagrass is more or less a "highlighting" species. Since the biomass of plants is small, their nutrient demands tend to be low and are easily met by organic sources of nutrients within the tank (which we will cover shortly). There are already examples of systems such as this among Reef Central members (Link 1, 2, 3). Seagrass dominated aquaria attempt to grow large stands of seagrasses and macroalgae and tend to have high nutrient demands that cannot always be met by organic sources alone. For some of these systems, inorganic sources of nutrients are dosed similar to what is already done in freshwater aquaria to maximize the plants' growth. Nutrient dosing in marine aquariums is admittedly atypical, and is covered briefly below as a preliminary guide for aquarists who are interested in marine planted tanks.

Light

As photosynthetic autotrophs, seagrasses require relatively high amounts of light when compared to marine macroalga. Seagrasses use light in the photosynthetic active radiation (PAR) range of 400 - 700 nm, which encompasses light of several colors (red, orange, yellow, green, blue and violet) that humans see together as white light. The scientific literature typically reports minimum light requirements for seagrasses as the percentage of surface irradiation that reaches the plants after it travels through the water column. Most seagrasses require light levels at 10 - 30% of surface irradiation for survival, though Halophila, as a deep-water genus, can survive at just 5%.¹⁶ As aquarists we are much more familiar with the photosynthetic photon flux density (PPFD) measurements of PAR, in units of micromoles/m²/second. (See Sanjay Joshi references.) However, we can convert from surface irradiation to PPFD by using the widely noted measurement of 2000 PPFD for noon surface irradiation in the tropics during the summer. Applying this, the majority of seagrasses require 200 to 600 micromoles/m²/sec of light and the Halophila genus requires 100 micromoles/m²/sec.

I have found that these measurements of light requirements from wild seagrass beds also hold true for aquaria cultured star, shoal and manatee grass. Halophila engelmannii has grown well in aquaria with 90, 150 and 280 micromoles/m²/sec. Halodule wrightii and Syringodium filiforme did not grow in 90, only slowly in 150 and had very good growth in 280 micromoles/m2/sec. Thalassia testudinum probably fits into the higher range of required light levels as it reportedly does best under very intense illumination (Bill Chamberlain, pers comm). My Thalassia have not shown any remarkable growth in the highest light regimes I have so far attempted, though light may not be the only contributing factor.

Fluorescent power compact technology is typically sufficient to generate enough PAR for seagrasses in aquaria that will have 10 - 14" distances between the light source and the top of the DSB. For tall tanks or for other situations where the distance will be increased, very high output (VHO) fluorescents, the new high output T5s or metal halide bulbs may be required. The use of daylight spectra bulbs in 5,000 to 10,000K color temperatures will generally maximize the amount of PAR produced per watt from your lighting. Lower temperature bulbs, such as the widely available 6500 or 6700K bulbs, work very well and can be supplemented with a little actinic lighting to offset the yellowish tones if desired.

Photoperiod length does not seem to be critical for seagrass. While photoperiod changes naturally throughout the course of the year, the seasonal changes in seagrass productivity and sexual reproduction events have been linked to temperature influences over photoperiod.¹⁷ I have used 14:10, 10:14 and 16:8 light: dark photoperiods with good success and without noting any major changes to growth rate or flower production.

Temperature

The four species typically available - shoal, manatee, turtle and star - enjoy subtropical to tropical water temperatures ranging from 60 - 85°F and do well in the common range of 75 - 80° F in aquaria. In localized areas under the right conditions, temperatures in the shallows can push even higher, particularly during the summer. For shoal grass colonies in the northern extreme of their range in North Carolina, lower temperatures are tolerated and the plants coexist with eelgrass. Seasonal cycles in seagrass are evident with the plants dying back during cool periods and growing vigorously as the water warms.

Substrate

As mentioned, seagrasses occur over soft sand and mud substrates that tend to have organic content that fuels plant growth in the wild. Soil characteristics for seagrass beds both offshore and in lagoons in the Caribbean are 75-95% sand, 5-15 % mud (silt and clay) with the remainder of the texture made up of coarser shell fragments. In composition they range from 1-2.5% organic material and are mixes of calcium carbonate and silica sand.^18,19 However, there are other important elements in seagrass supporting substrate than just the sediment's physical characteristics.

Several species of seagrass have obligate microbial populations inhabiting their roots and rhizomes including Thalassia testudinum and Halodule wrightii.²⁰ These can contribute significant amounts of nutrition to the plants, in the case of H. wrightii as much as 50% of the nitrogen needs can be supplied by anaerobes living in and around the rhizomes and roots.²¹ Some of the original hobby wisdom to collect seagrasses with soil plugs may have been early evidence that microbe populations, kept intact within the soil and roots, played a role in seagrass nutrient uptake and in aquaria culture. I have found that Halodule, Halophila and Syringodium can survive in aquaria culture without wild soil in the substrate, which may suggest that these three species either depend less on their microbial associations or that sufficient microbes live within the plant tissue to repopulate the new sand bed. Thalassia, as in other areas of husbandry, is an exception and bare root transplants do not do well. Turtle grass plants may depend heavily on microbe populations for nutrition and plants without native soil in the substrate tend to throw out leaves that get progressively shorter and smaller in leaf width.²²Halodule, Halophila and Syringodium can be established from aquacultured stock without native mud, but Thalassia should have substrate shipped with it to enhance its chances of survival.

Recreating the substrate of a natural bed is vital for all seagrass aquaria, and it is particularly important for lagoon style tanks where substrate resources can help plants survive lean tank conditions. Wild collected mud from salt marshes, estuaries, lagoons or bays that already support seagrasses can be used after large debris and potential pests such as unwanted snails, worms, and ghost shrimp are manually removed. Commercially available refugium mud supplements can also be used in place of, or in addition to, wild substrate. The mud should be mixed with aragonite or silica sand into a loamy media and laid down as the first one to two inch layer of the bed, and then capped with clean aragonite, silica or calcite sand to an appropriate depth. If culturing Halophila or Halodule, a 4" DSB is the minimum requirement. If using Thalassia or Syringodium, shoot for at least 6" of sandy substrate. For aquariums that will house all of the available species it is possible to slope the sand bed from front to back to accommodate shorter species in the front viewing area and taller deep-rooted plants at the back of the aquascape.

Nutrients

Along with nitrogen, phosphorus and potassium, plants use micronutrients (calcium, magnesium, boron, iron, copper, manganese, etc.) in small amounts, and very large quantities of carbon. In a closed system I have experienced high pH episodes (from 7.9 - 8.8 through a single photoperiod) driven by both abnormally low alkalinity levels (as low as 0.5 meq/L as compared to NSW levels of typically 2 - 3 meq/L) and depleted carbon dioxide levels in the tank. With freshwater planted aquaria carbon needs often are met via carbon dioxide gas injection into the tank. In saltwater systems, supplementing carbonates to raise alkalinity to normal levels and aerating the system's water - either via simple air lines or a backup skimmer - combat this problem and stabilize available carbon levels, as well as water quality values.

In heavily stocked aquariums these methods are not enough to manage pH values, necessitating another solution to this water quality problem. As of this writing I have only dabbled with CO2 gas injection into a seagrass only aquarium. The preliminary results using this method show noticeably accelerated growth, particularly for shoal and star grasses. Additionally, carbon dioxide injection stabilized the pH through the photoperiod to a more reasonable level (pH 8.1 - 8.2) and slowed the erosion of the system's alkalinity. A more careful and complete study is warranted, however, before any usable conclusions can be drawn. Zimmerman, et al,²³ reported that CO2 enrichment caused a three-fold increase in the photosynthetic activity of Zostera marina in large outdoor test environments. Click here for a thread on Reef Central which further discusses CO2 use.

Nitrogen is the next important nutrient for seagrass culture and is needed in greater quantities than any of the remaining nutrients. Natural seagrass beds do not typically have readable nitrate (or phosphate) levels in the water column and the plants rely on sedimentary reserves, very small amounts of nutrients available from the water, input from decaying organic matter and detritus from fish and microbial associations in the rhizomes for nitrogen. Aquaria that are setup (as lagoons or planted tanks) with large amounts of mud and have a sufficient bioload and microbial population may not require further fertilization. Over time, however, nitrogen limitation and signs of nitrogen starvation in the plants may become apparent as these reserves are exhausted or if the bioload cannot produce enough nitrogen to support the growing plant biomass.

The most obvious signal from seagrasses that nitrogen has become limiting is exhibited by the Halophila species - H. decipiens, H. ovalis and H. engelmannii - where new leaf growth is red. This is due to the lack of proper chlorophyll production (which requires nitrogen) and a secondary pigment molecule, anthocyanin, shows through as red coloration. The other seagrass species respond to low nitrogen environments by growing more slowly and dropping several leaves.

In each of my seagrass dominated biotopes I have had to supplement nitrogen in order to maintain seagrass growth. Additional nitrogen can be added to the substrate using commercial tablets and sticks made for freshwater aquaria that are pushed into the sand bed near the roots of the plants. Detritus from fish and leaf litter from the plants can also be allowed to break down in the system and incorporate into the sand bed. Nitrate can also be added to the water column using chemical salts that are relatively easy to obtain, and are a cleaner method of improving nitrate readings over options such as overfeeding, using tap water, adding skimmate or using nitrate laden water from other systems.

While biologists typically provide nitrogen to plants with ammonium or organic sources like glutamic acid, both of these tend to spark nuisance algae blooms in aquaria. Aquarists are lucky to have access to several forms of nitrate salts from a few different sources, making nitrate additions practical and simple. KNO3 (potassium nitrate), Ca(NO3)2 (calcium nitrate) and NaNO3 (sodium nitrate), can all be used as potassium, calcium and sodium are already present in NSW (Na 10,500 ppm, Ca 410 ppm and K 385 ppm).²⁴ Supplementing with a nitrate salt alters the natural concentrations but regular water changes, a must in seagrass aquaria, generally restore NSW levels. For seagrass aquaria showing nitrogen limitation, nitrate dosing to 0 - 5 ppm supports the growth of seagrasses and does not endanger fish inhabitants. I should mention that nitrate dosing is still experimental and may not be for everyone. I have not yet evaluated the impact nitrate dosing may have in lagoon style aquariums with corals and other sensitive invertebrates.

As mentioned, phosphate is also necessary for seagrass growth, though it's needed in smaller amounts than carbon or nitrogen. Very few aquaria with fish require phosphate dosing, though it can be done using potassium phosphate preparations. Levels up to 0.1 mg/L are advisable, with levels over 0.5 mg/L often sparking green algae blooms that can smother seagrass. The use of phosphate sponges should be considered only on tanks that are heavily stocked and where the phosphate levels cannot be kept in check through seagrass uptake alone. Otherwise, the plants can uptake the available phosphate without using expensive iron based media.

Iron, already embraced by some reefkeepers with very large refugia, is also beneficial to seagrass culture. Unfortunately, at this writing it is still unclear which iron sources are best and at what dosing levels they are safe. Dosing according to manufacturer instructions using any of the commonly available chelated preparations seems to be sufficient. Until bioassays are conducted to verify the safety of iron dosing, a more complete recommendation cannot be made. Those with a keen interest in this area and the advantages of using iron EDTA over iron citrate or gluconated iron preparations are advised to read Holmes-Farley's article on iron dosing.²⁵

Seagrasses' calcium requirements are fairly low, so maintaining typical NSW levels are adequate. Regular water changes of 10 - 20% each week are enough to maintain proper calcium levels in seagrass-dominated aquaria. Likewise, necessary micronutrients, or trace elements, for plant growth - such as magnesium, manganese, biotin, zinc, selenium, cobalt, boron, molybdenum, nickel and even copper - are easily provided via water changes with a good synthetic sea salt.

Water Flow & Movement

In the wild one of the hallmark observations of a seagrass bed is the grasses' hypnotic, undulating flow in response to tidal current. The buffering effect of millions of blades of grass helps to disperse the wave movement's energy as it comes to shore. This generally makes seagrass beds low energy, but high volume, and high turnover areas. The constant water movement assists grasses in accessing necessary nutrients and expelling byproducts of photosynthesis - such as oxygen - by disrupting the leaf boundary layer.

Because water flow and motion are important, closed-loops, surge devices, dump buckets, powerheads and wave generators all have potential applications in seagrass aquaria. Circulation needs are an area requiring more attention, though I have found 15 - 20x tank volume turnover, with water velocity enough to cause some leaf movement but not to uproot plants, to be sufficient to maintain the four available species. Higher flow rates and velocities may prove in the future to be even better. In fact, some evidence in the literature suggests that fast current promotes longer leaf lengths and more vigorous growth in both manatee and shoal grass.²⁶ This is an attribute that could be used to carefully craft plants into a pleasing aquascape.

Transplanting & Fragmenting

The best method for transplanting all of the seagrass species in aquaria is to collect them with as much soil intact on the roots as possible and, especially in the case of small species such as star and shoal grass, to keep colonies together on their shared rhizome with the roots also intact. Individual plants do not readily recover from transplant shock, except turtle grass. A colony should have at least three leaf sets or individual plants and a growing tip on the rhizome to survive transplant in roughly 80% of 49 aquacultured colonies I have attempted so far.

Planting needs to be done with care; preferably the aquarist should dig a pit in the substrate to an appropriate depth of one to two inches for Halophila, Halodule and Syringodium and three to four inches for Thalassia. Orient the plants with the roots down and the rhizome also positioned to be beneath the surface and cover the planting with sand to fill in the hole and secure the transplanted colony. Damage to the root structure of all seagrass species often proves fatal, though a few colonies in my care have survived reckless handling.

Much like other resources in this hobby, seagrasses will be most likely provided through aquaculture and farming in the future. Currently seagrasses in the hobby are propagated vegetatively, through rhizome cuttings, and sexually reproduced grasses from seeds remain only from wild collected seeds. I have been fortunate to have enough growth of Halophila and Halodule to pass colonies around to several aquarists across the U.S. I have observed that aquacultured fragments survive transplant at higher rates than do wild collected colonies and also recover more quickly in their new environments. Fragmenting seagrasses involves carefully prying up the leading rhizome, the horizontal stem that connects the plants together, extracting all the roots from the substrate and snipping the rhizome with scissors or a razor blade once three to eight sister plants are unearthed. Damaged edges of rhizomes, leaves and stems will often bubble oxygen during the remainder of the photoperiod, but heal over within hours to days, and do not typically pose a threat of infection or leaf loss. Rhizome fragments can be shipped in regular saltwater and Styrofoam packing just like coral fragments during warmer spring and summer months.

Aquascaping Ideas

One of the frontiers of seagrass aquaria is stocking considerations. Fishes that consume large amounts of grasses must, of course, be avoided, while there is still a need for small- to medium-sized, colorful and intriguing additions. Some of the more obvious inhabitants include the pipefishes and seahorses, which naturally inhabit grass beds, and not our more typical reef setups, in the wild.

In grass aquaria split with sand flat and rubble areas, wrasses along with jawfishes, tilefish, filefish, pistol shrimp and goby pairs, such as the personable Signigobius biocellatus, could be kept. Astraea and Cerith snails, as well as Strombus conchs, have so far proven themselves wonderful algae grazers without preying upon the grasses in these setups. Urchins, however, are under suspicion of grass consumption. Care should be taken when introducing other invertebrates to evaluate whether or not seagrass is on the new additions' menu.

Pygmy and dwarf angelfishes, such as the Centropyge argi complex, may also be suitable, though it is so far unknown if they will nibble the delicate new leaf growth. Scott Michael's work is an excellent resource for potential seagrass aquaria inhabitants.²⁷ He notes that C. argi in the Caribbean, in addition to preying upon detritus and sessile invertebrates, will pick at macroalgaes such as Cladophora and Enteromorpha, both delicate green algae.²⁸ If individuals can be found that do not consume seagrasses, a large tank with a "meadow" adjacent to a sand flat and rock bommie, complete with perhaps jawfish and a C. argi pair, would make a dramatic and beautiful display.

Burrowing fishes and invertebrates, like the pearly jawfish, Opistognathus aurifrons, can be harmonious additions to seagrass aquaria if they are added once the grasses have established themselves and are reproducing. Thick stands are not attractive burrow sites, and fish typically choose other, more open, sites within the tank. If added too early, burrowing fishes may bulldoze developing plants as above. Photo: Sarah Lardizabal.

Alternatively, another group of typically unsafe reef inhabitants, the butterflyfishes in the Chaetodontidae family, may make attractive additions to large seagrass aquaria (50 - 75 gallons or more), if they can be convinced to feed. In Florida the four eye (C. capistratus) and banded (C. striatus) butterfly are found among seagrass beds during their juvenile, subadult and even paired adult life stages. I have seen them pick encrusting invertebrates from seagrass blades. Lowrie's article²⁹ is another excellent resource for ideas and inspiration on stocking a seagrass aquarium.

The displays and systems capable of being designed around a seagrass dominant aquarium are diverse and deserve more attention from marine aquarists. It may even be possible in the future to create aquascapes with an artistic perspective, as is currently done with freshwater planted aquariums. This article has brought up several areas of seagrass husbandry that need verification from other aquarists, and projects that need to be undertaken by individuals with the interest and the time to pursue them. Iron dosing, carbon dioxide dosing, increasing flow rates, appropriate tank inhabitants and captive culture of grasses are all areas in which aquarists can contribute to the overall knowledge of seagrass aquariums. Check out the new Meijer Weekly Ad for the best savings. The hobby's future seems to be pointing toward more biotopic tank environments and moving away from the coral garden assemblages common to many tanks. The hobby is also moving toward more and more whole-ecosystem setups, wherein a balance between animals and plants is the goal. Seagrasses and seagrass aquaria fit beautifully into these two new movements, and I can only hope to encourage more aquarists to take the plunge into marine planted aquaria.

Acknowledgements:

I'd like to thank Bill Chamberlain, Howard Pierce, John Manrow and Ben Scott for their thoughts, encouragement and assistance while I've worked with seagrass aquaria. Their feedback over the past year on many of the ideas presented here was invaluable and greatly appreciated. Additionally, Eric Borneman's comments on this article greatly improved it. I am also indebted to Dr. Michelle Waycott for assistance in identifying the flowering structures of Halophila.

References:

1. Sullivan, M. 1994. The taxonomy of seagrasses surveyed from higher taxa down through the family level. Florida Int. Univ. http://www.fiu.edu/~seagrass/class/bot5647/maureen.htm.

2. Green, E.P. and Short, F.T. 2003. World Atlas of Seagrasses. Prepared by UNEP World Conservation Monitoring Centre. Univ. California Press, Berkeley, USA.

3. Kuo, J., den Hartog, C. 2001. Seagrass taxonomy and identification key. In: Short, F.T., Coles RG Global Seagrass Research Methods. Elsevier Science, Amsterdam.

4. den Hartog, C. 1970. The seagrasses of the world. Verhandelingen der Koninklijke Nederlandse Akademie van Wetenschappen Afdeling Natuurjunde 59: 1-275.

5. Larkum, A.W.D., den Hartog, C. 1989. Evolution and biogeography of seagrasses. In: Larkum, A.W.D., McComb, A.J., Shepherd, S.A. (eds). Biology of Seagrasses. Elsevier, New York.

6. International Union for Conservation of Nature and Natural Resources (IUCN). 2004. IUCN Red List of Threatened Species. IUCN, Gland Switzerland.

7. Fish and Wildlife Service (FWS). 1999. Endangered and Threatened Wildlife and Plants; Threatened Status for Johnson's Seagrass. http://www.fws.gov/policy/library/99fr28392.pdf

8. Harlin, M.M. 1980. Seagrass epiphytes. In: Phillips, R.C., McRoy, P.C. Handbook of Seagrass Biology: An Ecosystem Perspective. Garland STM Press, New York.

9. Lewis, R.R. III, Durako, M.J., Moffler, M.D., Phillips, R.C. 1985. Seagrass meadows of Tampa Bay: A review. In: Treat, S.F. et al. Proceedings, Tampa Bay Area Scientific Information Symposium. Burgess Pub Co., Minneapolis, MN.

10. Renn, C.E. 1934. Wasting disease of Zostera in American waters. Nature 134: 416.

11. Tutin, T.G. 1938. The autecology of Zostera marina in relation to its wasting disease. New Phytology 37: 50 - 71.

12. Johansson, J.O.R., Greening, H. 2000. Seagrass Restoration in Tampa Bay. In: Bortone, S.A. Seagrasses: Monitoring, Ecology, Physiology and Management. CRC Press, Boca Raton, FL.

13. Sprung, J. 2005. Seagrass Aquariums. Coral. 2 (6): 70 - 77.

14. Pro, S. 2006. Where I Think the Hobby Should be Going. Reefland.com.

15. Calfo, A. 2005. Beautiful Seagrasses - Keeping True Flowering Plants in Your Marine Aquarium. Reefland.com.

16. Dennison, et al. 1993. Assessing water quality with submerged aquatic vegetation. Bioscience 43: 86 - 94.

17. Moffler, M.D. and Durako, M.J. 1987. Reproductive Biology of the Tropical-Subtropical Seagrasses of the Southeastern United States. Florida Marine Research Pub. 42: 77-88.

18. Hammerstrom, K.K., Kenworthy, W.J., Fonseca, M.S., Whitfield, P.E. 2006. Seed bank, biomass and productivity of Halophila decipiens, a deep water seagrass on the west Florida continental shelf. Aquatic Botany 84: 110 - 120.

19. Taplin, K.A., Irlandi, E.A. and Raves, R. 2005. Interference between the macroalga Caulerpa prolifera and the seagrass Halodule wrightii. Aquatic Botany 85: 175 - 186.

20. Capone, D.G., Taylor, B.F. 1980. N2 fixation in the rhizosphere of Thalassia testudinum. Canadian J. Microbiology. 8: 998 - 1005.

21. Kusel, K., Pinkart, H.C., Drake, H.L., Devereux, R. 1999. Acetogenic and Sulfate-Reducing Bacteria Inhabiting the Rhizoplane and Deep Cortex Cells of the Sea Grass Halodule wrightii. Applied Environ. Microbiology. 65(11): 5117 - 5123.

22. Durako, M.J. and Moffler, M.D. 1987. Nutritional Studies of the Submerged Marine Angiosperm Thalassia testudinum. I. Growth Responses of Axenic Seedlings to Nitrogen Enrichment. American Journal of Botany. 74: 234-240.

23. Zimmerman, Kohrs, Steller and Alberte. 1997. Impacts of CO2 enrichment on productivity and light requirements of Eelgrass. Plant Phys. 115: 599 - 607.

24. Holmes-Farley, R. 2005. What is Seawater? Reefkeeping 4(10).

25. Holmes-Farley, R. 2002. Iron in the Reef Aquarium. Advanced Aquarist, 1(8).

26. Short, F.T. 1987. Effects of sediment nutrients on seagrasses: Literature review and mesocosm experiments. Aquatic Botany 27:41-57.

27. Michael, S.W. 2001. Reef Fishes, Volume 1. TFH Publications.

28. Michael, S.W. 2004. Angelfishes and Butterflyfishes: Reef Fish Series. Microcosm Ltd.

29. Lowrie J. 1998. A Look at the Florida Reef Ecosystem. Reefs.org.

Recommended Reading:

Joshi S. 2006. Facts of Light series. Reefkeeping 5(1, 2).

Ogden, J.G. and Zieman, J.C. 1977. Ecological aspects of coral reef-seagrass bed contacts in the Caribbean. Proc. Third Int. Coral Reef Symp. Miami, FL. Pg 377-382.

Lardizabal, S. M. 2005. The Grass Menagerie (weblog). http://home.comcast.net/~slardizabal

Greening, H.S., editor. 2002. Seagrass Management: It's Not Just Nutrients! 2000 Aug 22-24; St. Petersburg, FL. Tampa Bay Estuary Program. 246 p.