A different kind of "Green"- Sea Grasses!

As a traveling fish geek, I’m lucky enough to talk to lots of hobbyists on a monthly basis. It’s a good life, with good times (“If this is Saturday, I must be in Akron, right? Or was it Detroit…?). I see a lot of cool aquariums and neat people. I see aquariums chock full of corals, rare cichlids, Plecos, exotic plants, etc. Some aquariums feature amazing aquascaping or ingenious plumbing systems. I see crazy fish rooms and the occasional basement fish-breeding operation.

Rarely, however,  do I encounter aquariums dedicated to-or at least featuring-seagrasses. That’s right- seagrasses!


Okay, we all have probably seen or heard about these saltwater plants at one time or another, but rarely do we find ourselves actually playing with them! They are not at all rare in the wild- In fact, they are found all over the world, and there are more than 60 species known to science. Seagrass beds provide amazing benefits to coral reef ecosystems, such as protection from sedimentation, a “nursery” for larval fishes,  and a feeding ground for many adult fishes.. In the aquarium, they can perform many of the same functions. So why are we not seeing more of them in the hobby?

I believe there are three main reasons why we don’t: 1) They suffer from what I call the “Caulerpa Syndrome”- a bad rep ascribed to just about anything green in the marine side of the hobby- “They will smother your corals”, or “They can crash and kill everything in the tank”, or even,  “They give off toxic byproducts that inhibit coral growth”.  2) There simply aren’t enough people working with them to get them out to the hobby in marketable quantities. 3) They are finicky and hard to grow. 4) More planted freshwater enthusiasts need to get on board with these!

Let’s beat up  Number 1 first: Seagrasses are true vascular plants, not macroalgae, and they  do not creep over rocks, go “sexual” and crash, or exude chemicals that will stifle the growth of your corals.  In fact, they are mild-mannered, grow  at a relatively modest rate, and are compatible with just about everything we keep in a reef tank. And no, they will not smother your corals or grow over rockwork.  They grow in soils and sandbeds, and need to put down root systems, so converts from freshwater planted tanks have a great leg up on the rest of us with their skill set. You can keep them nicely confined to just the places that you want them. Dedicate a section of sandbed that you’d like them to grow, plant them, give them good conditions, and you’ll be singing their praises in no time!

Reason Number 2 is probably caused in part by #1, but in actuality, is the most probable reason why we don’t see them everywhere: Until very recently, they were the sole domain of dedicated specialty hobbyists, who delighted in growing plants and taking on other challenges.  The hobby as a whole simply never sees them in quantity, helping spur the (false) image that they are rare, dangerous, or difficult to work with.  Someone (hey- that can be YOU) needs to step up and produce/distribute them in quantity!

Reason Number 3 has a bit of truth to it. Some of the seagrasses can be a bit finicky at first, and don’t always take initially when transplanted. Like any plant, they go through an adjustment period, after which they will begin to grow and thrive if conditions are to their liking. It has also been discovered in recent years that there are microbial associations in the soils/sediments that they are found in which enable them to settle in better and adapt to new conditions. So in short, if you are obtaining  seagrasses, you can never hurt your cause if they come with some of the substrate that they grew in.

If you can provide a mature, rich sand bed (say 3”-6”), good quality lighting (daylight spectrum or 10k work well), decent water quality, some iron fertilizer, and no large populations of harsh herbivorous fishes, like Tangs or Rabbitfishes), you can almost guarantee some success. And the other key ingredient is patience. You need to leave them alone, let them acclimate, and allow them to grow on their own.

By the way, you can use a variety of  commercially-available substrate materials in addition to your fish-waste-filled sand, such as products made by Kent Marine, Seachem and Carib Sea, that are designed just for this purpose! How ironic- products exist to help  grow seagrasses, and so few people are actually taking advantage of them!

There are three main species that we find in the hobby: Halodule, or “Shoal Grass”, Halophilia , knows as “Stargrass”, “Paddle Grass”, or “Oar Grass”, and Thalassia, known commonly as “Turtle Grass”.  I call them “The Big Three”. Each one has slightly different requirements, and I will briefly cover them here.

Halodule looks a lot like the freshwater plant Sagittaria, or “Micro Sword”, in my opinion- and grows like it, too. Plant it  in a modestly deep (3”), rich substrate, and it will put down a dense system of runners as it establishes itself.  Once it establishes itself, it’s about as easy to grow as an aquatic plant can be, IMO.  I think it’s the best candidate for extensive captive propagation, so those of you with greenhouses should devote a tray or two to this stuff.  I envision this being grown in “pony packs” like you see  with groundcover plants at your local nursery, so that a hobbyists can purchase a “flat” of Halodule and simply plop it into their tank.. Think of the commercial possibilities here, folks!

Halophila is a very attractive plant, which, although slightly more delicate and challenging than Halodule, is still relatively easy to grow, and is really pretty, too! I’ve grown this plant in substrates as shallow as 2.5”, but you probably want 3” or more for good solid growth.  This seagrass definitely “shocks out” when you transplant it, and you will lose some leaves straight away. However, with patience, good conditions, and a little time, it will come back into its own and form a beautiful addition to your reef tank. And man, it would be a nice sight to see at your next club auction- I’ll bet you could get a choice Bucephalandra in trade for a few Halophila!


 Thalassia is “THE” seagrass to most people- the one we envision when we hear the term “Seagrass”. It’s called “Turtle Grass”, and it is one of the larger varieties, growing up to 24” in height if space permits. Its thick leaves create a beautiful contrast to rockwork, and it can create an interesting area for fishes to forage when you can get a thick growth of it. It does grow VERY slowly, and you will typically have to start with a quite a few plants if you are trying to fill in a designated space in your tank. It requires a pretty deep sandbed, too-  5 to 6 inches  or more is ideal.  Because of  it’s slow growth rate and height requirements, it’s the least attractive candidate for captive propagation, IMO. However, it is still a lovely plant with much to offer.

Seagrasses offer just another interesting diversion and an opportunity  for the hobbyists to try something altogether new in the aquarium. Not only will you be growing something cool and exciting, you’ll have a chance to get in on the ground floor of a new area of the marine aquarium hobby. With a background in freshwater planted aquariums, you'd be the PERFECT hobbyist to try this! By unlocking the secrets of seagrasses, you will be further contributing to the body of knowledge of the husbandry of these plants. Obviously, I just scratched the uppermost surface of the topic here, but I’m hopeful that I have piqued your interest enough to give the seagrasses a try!

Till next time…

Stay Wet.

Scott Fellman

Scott Fellman
Scott Fellman


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