Caribbean Biotope Seagrass Tank

[Michael Hoaster]

I resumed nitrate dosing today. I think the grasses got less yellow. That points to nitrogen limitation. I will continue dosing the water, and I'll consider substrate dosing. I want the seagrasses to get the first shot at the goodies.

[Xeniaamore]

Hello,

I have been growing seagrasses for about six months now. I am using the grasses for scientific research. I have been searching the web for two specific species: Halophila ovalis and Halophila minor. I have doubts anyone of this forum would have Halophila minor, but if you have either H. ovalis or H. minor, please contact me. I will pay you to ship a small frag of your grasses or will trade you for the grass I have (please PM if you are interested). If you choose to send the grasses free of charge, your name will be included in a special 'thank you' if any research becomes published. Thank you for reading.

[Michael Hoaster]

I don't have those species. You might check with Florida Pets: http://floridapets.tripod.com/marineplants.html

Just out of curiosity, what are you researching? I'd love to hear about it.

I have kept manatee and turtle grass for a year now. I'd be happy to share anything I've learned, if it would help.

Good luck with your research!

[Xeniaamore]

Thanks for your response.

Most of the details have to remain private for now. What I can tell you is that getting the seagrass to grow vigorously has been a journey. We are now using carbon dioxide, which has contributed greatly to the success of the plants. This also causes our pH to be somewhat low, which has been frustrating. We are planning on comparing C02 injection with a liquid carbon project to see if that resolves the problem satisfactorily.

[Michael Hoaster]

I too have been injecting CO2, with some success. One other source of carbon (and nitrogen) I have considered is ammonium bicarbonate. I forget where I got the idea. I am dosing potassium nitrate currently, with some success. My manatee grass has grown nice and tall, but I'm not getting rhizome growth/new shoots, which I desperately want. Since my grasses are competing with macro algae, I'm looking into substrate fertilization to give them an edge.

Anything else you can share would be great! Thanks!

[Xeniaamore]

Thanks, that's a great suggestion. What we have found so far is that our initial concept of allowing the water column to be depleted of nutrients (using macroalgae) and using substrate fertilizers for the grass is ineffective. While this method did reduce diatoms and cyanobacteria to low levels, growth of the seagrass remained very slow until nutrients in the water column were raised. We still use macroalgae to compete with the microalgaes, but we are hoping to remove these once a sufficient amount of seagrass has spread. Water flow seems to be a key variable in keeping both diatoms and cyanobacteria low. The next step in our project will be to move everything to a bare bottom tank in individual pots.

[Michael Hoaster]

Good to know about the substrate dosing, thanks.

Why would you put them in pots? The only reason I can think of, is to sell them this way, along with their own 'personalized' soil. It would be great to be able to buy them this way.

[Xeniaamore]

Keeping the tank bare bottom will allow us to scrub for algae more thoroughly as well as have more individualized specimens rather than one late lump of grass.

[Michael Hoaster]

I see. I have to remember that what you are doing is for research, not display.

I'd love to hear more. Please drop by and give us an update anytime.

[Michael Hoaster]

My caulerpa is overtaking the tank again. The growth rate seems exponential. I'm not making it from one weekend to the next, without having to crop. I need to do a big export, and get ahead of it. Surely the seagrasses are getting some of the nutrients I'm dosing. It's just hard to tell, in comparison. Dosed a little iron today, along with the nitrate.

My magnesium chloride arrived today, so I'll make some up and give it a go. I kind of doubt magnesium is a problem, but you never know. My wife can use it in her tub if I don't.

I still think the grasses are nitrogen limited. I think the caulerpa absorbs it quicker. I think the key is to reduce its biomass, in relation to the grasses. I think a lot…

[saltwater sam]

Caulpera is as competitive as it gets. Time for a culling!

[karimwassef]

So.. here's an interesting observation from my summer dive and snorkeling in Cancun.

There are zones where each kind of algae has dominance. Where the sea grasses are, there is no caulerpa. Where there is turtle grass, there's no branchy coralline, etc...

The zones can all be within 100ft of each other, but they don't overlap.

I don't really know why that is - just an observation of algae dominance.

[McPuff]

You may need to put a tang in there... it'll go after the caulerpa first as it's the most tender. It would likely go through it pretty quickly though. Would be the easiest way to get rid of it. I'm not sure you can have that with the other macros... it's too fast-growing. Besides, you don't want it to get to a reproductive phase.

[Michael Hoaster]

Very interesting, Karim. You really got a lot out of that trip! Man, I need a snorkeling trip!

Could you tell whether the different zones were divided by depth (light), or water movement velocity?

[Michael Hoaster]

Thanks, McPuff. A few pages back, there was much discussion on the possibility of adding an Atlantic Blue Tang. That was my concern, that it would go through it quickly. But, that was also before I began dosing nitrate and iron. Now I have explosive growth, and I could use some help cropping it back. So I'm definitely leaning towards getting one. Keeping the macros cropped back might be the key to getting my seagrasses to take off. My biggest fear is that a tang might go after the grasses, once the macros are exhausted. But I think they'd be more interested any algae growing on the seagrasses, rather then the seagrasses themselves.

One other concern I have is order of introduction. My original plan was to add a tang last. Adding one now, second only to the Barnacle Blennies, could be problematic. But since it would be the only herbivorous fish, it might work just fine. A possible plus of adding it so early, would be its effect on later additions of schooling fish. Having a bigger fish in the tank will encourage schooling fish to 'stay in school'.

[karimwassef]

Originally Posted by Michael Hoaster

Very interesting, Karim. You really got a lot out of that trip! Man, I need a snorkeling trip!

Could you tell whether the different zones were divided by depth (light), or water movement velocity?

Good question... light and depth were a big deal as were flow and nutrient content and sediment type.

The sea grasses and turtle grasses were never in the shallow or fast zone. They were always deep with relatively gentle flow. Doesn't look like they need a lot of direct light. The sediment mattered though. It was a little like densely compacted sand? Not loose, soft sand, not rock or rubble.

The caulerpa and other macros were in the more tidal zones. Much shallower and very very fast flow. Dangerous to snorkel in fast. They also seemed to be closer to the shore and the water was generally warmer too. I'm thinking higher nutrient. They liked rubble or rock. Didn't go for sand.

[karimwassef]

The branchy coralline zone was almost always just a little inland of the grasses. So much that I almost thought they were related in some way. They don't share territory, but if you find the grasses, swim a little in and there's the coralline. Might mean that calcium and magnesium matter?

these were shallower and brighter zones, cleared water too. mix of sand and rubble. No big rocks. Water was calm, but not as calm as the grass region.

The encrusting coralline was only with big rocks and really tracked where the coral was.

[andycook]

You seem to be dosing the water column. I didn't think sea grasses pulled from the water column. I think somewhere there was a mention of some kind of substrate fert. Are you mostly feeding the caulerpa?

[Michael Hoaster]

Welcome, andycook! Yes, I am mostly feeding the macros, right now, but I expect the seagrasses to benefit as well. Seagrasses take in nutrients through their roots as well as their leaves. I am experimenting with water column and substrate fertilizing. Everything I've read supports dosing the water, but I'm still I wondering if substrate fertilization could help. Just a few posts back I was told that water column dosing was more effective, so I'm hedging my bets, so to speak. On 9/27/15 I pushed a small plant tab into the DSB, next to some manatee grass. In a previous experiment, I saw results in two weeks. So we'll see!

[Michael Hoaster]

Welcome to the ghetto…


Fall foliage in the lagoon.


A look at the current-sculpted substrate on the high velocity end of the tank.



A tidal wave of caulerpa.

[sam.basye]

Would the tang also go after your multi-colored macro's as well? It might not discern against the different varieties you have and next thing you know, bam! Your blue and red macro's are now a brown carbon source. Lol

[Michael Hoaster]

Yes, Sam, that's likely. It wouldn't go after all of them, but the grasilaria would likely take a big hit. The more calcerous reds will be fine. I don't know about the blues. If I want help cropping the caulerpa, I have to be ready to accept the indiscriminate feeding style of the fish. Bottom line, I think it will help the seagrasses if I reduce all the macros' biomass.

[Michael Hoaster]

Hello. I'm a Panamic Barnacle Blenny. What are you?

Big caulerpa export yesterday. Pulled out more red macros too. I've still got a ton of little red fragments. The turtles grass is still outpacing the manatee grass, growth wise. Putting out daughter plants frequently, but not getting much more than a foot tall. The manatee grass grows sloooooooow. But it does get tall, the tallest almost 3 feet.

I wonder if my manatee grass is a victim of succession. In the wild they move in first, then the turtle grass follows, eventually crowding out the manatee grass. Within the limited confines of my DSB, the effects could be exaggerated, even though they don't look crowded yet. Hmm…

[saltwater sam]

I believe competition would be more accurate since the manatee grass was never the established species. It looks great! I almost went and bought some seagrass the other night but I decided I must be patient for the new tank

[Michael Hoaster]

Thanks, Sam. I suppose I should be happy with the turtle grass doing well. It's just that it was the manatee grass that I was hoping to cultivate. When I was just starting up this tank, I bought the turtle grass last minute, because they were short on manatee grass. Now, with it doing so well, I may have to shift focus. If I could figure out what works for the manatee grass, I'd love to have too much of both!