Gravel substrates for seagrass?

[piercho]

I've been using silica and calcerous substrates of less than 0.1 mm size to grow seagrass. This is very fine sand. For Tank2 I'm considering much courser substrate, nothing smaller than 0.5 mm and up to 6 mm, with the majority of the substrate in the 2-3 mm size. I may also put granular laterite or other iron-rich, pH-nuetral gravel substrate at the bottom of the bed, using Enkamat to keep large diggers from disturbing it.

The only grass I'm very familiar with in nature is Zostera. It grows in very fine and highly sedimented silica sand, as well as gravel with the interstices filled in with fine silica/sediment. In my case there would be no fine sand, but I would expect the instertices to fill in with sediment to a certain extent.

There are two reasons for course substrate. The first is that there are fish and shrimp I'd like to keep that need course substrate to build long, stable burrows. The second is that as you approach marginally strong flow rates, fine sand will blow around. I want Tank2 to be able to take much higher flow rates than Tank1. The bed would be 6" deep, with a 1" Jaubert plenum. The last inch of substate over the plenum would be laterite in Enkamat.

So...can seagrass (Star grass, Shoal grass) grow well in gravel? Can seagrass make use of iron-rich substate in the hypoxic/anoxic areas of the substate? How long do you think it will take before the bed would be filthy enough to plant?

 

[Samala]

Can it grow in gravel? Observations from the wild would suggest that yes, it can grow in fairly large sized substrate, though the deeper reaches tend to be more finely sedimented soil. For example, silica sand with various organics at the bottom of a plug, but increasingly large grains as we approach the surface layers. I have seen Thalassia and Syringodium over oyster shell hash, Zostera as well.

I have not seen Halophila in the wild over larger sizes, but it grew just dandy in a substrate that is popular with the freshwater crowd, Soilmaster Pro Select in nifty Charcoal color. Talk about contrast with bright green plants. I'd call it gravel, if not just a bit smaller. The original purpose of this is for infields in baseball or soil amendment as I understand it, much like Schultz Aquatic plant soil (which can be found in most Home Depot's). Both are inert so far as I know. Soilmaster thread on APC.com I wanted to try Seachem's Onyx, but havent gotten 'round to it. I also want to try EcoComplete's gravel for african cichild tanks, but again, no time.

And dont forget I use medium (ish) grained sand in my current setup. Its definitely not sugar sand or very fine.

Honestly I'm at a loss to say whether or not the plants will use iron rich substrates as used in freshwater. The FW plants that seem to do the best with these substrates tend to be riverine species which would, I suspect, be subsisting in fairly high clay content soils in the wild. Seagrass beds dont seem to contain much clay or even organic content from the literature.

Maybe I need to go digging in the literature once again..

>Sarah

 

[Samala]

I am really not sure how long it might be before the bed is truly mature enough, but you could always start with fairly sterile substrate and fertilize the bed and/or water column to get things going. That is.. if you're willing.

I take it there are no plans for eelgrass bed mud since burrowing critters are going to disturb the lower reaches and give you little cloudy water/ cyano outbreaks (the jawfish did in mine at least)?

And then there is that whole root microbe association thing to consider. I wouldnt anticipate a problem in gravel substrate (which would be more likely to stay aerobic over anaerobic, but microbes from Thalassia and Halodule were reported to survive being exposed to oxygen rich environments) for the microbes but I just wonder how much the microbes contribute and if it is they or lots of organics in the bed that decides whether or not you have good seagrass growth.

PS: Whats a Enkamat? Anything like a flexible fiberglass insect screen? Thats what I was thinking might help to keep iron rich particles from getting stirred up but will allow roots to move through.

>Sarah

 

[dalbrecht]

My concern with the Eco Complete for african cichlids is that the chemical properties of the rift lakes are significantly different than those of marine environment. Although Alkalinity is high and Carbonate hardness are both high. Many of the less common minerals exist in significantly different proportion. Most notable is probably the high concentration of magnesium. I'm not sure that it would be detrimental in an isolated tank, but it could cause problems in a setup containing corals.

 

[algaeguy]

Have you considered a mix of varying size substrates, such as some of the damp "mud" products on the bottom (like Walt Smith's stuff), mixed in with some of the Carib-Sea or Kent "refugium substrates" (dry products, I believe)? Then, you could go with progressively more coarse substrate material (like Seachem "Aragamax" oolthic, then "Sea Floor Special grade" for the top layers. Seems like a lot of work, yes, but maybe it's the best of both worlds? I'm considering this type of substrate arrangement for my new Seagrass system.

I'll bet that the microbial association that Sarah has mentioned is more important than we might think, too. I'm sure this is a very good reason to use the "plugs" of mud material that the plants come in, covered by a more coarse substrate.

Seems like the most exciting part of this is that so little has been done in this area (with the exception of the fine work by you guys!) that almost every new Seagrass tank is breaking new ground.

Please do post after you decide how you're gonna go with the substrate! Looking forward to more inspiration!

Good luck!

Scott

 

[piercho]

Thanks for taking the time to reply. Using a Jaubert plenum is a radical shift for me, and I'm trying to start off within the basic constructs of that method. The bulk of the substrate should be 2-3 mm, with no fine sand, mud, or mulm. Coral, unless they naturally occur on a gravel/sand bottom, go on the walls. This leaves the whole bottom an open bed of gravel. Enkamat is a pad of stranded polyester or nylon. The ââ"šÂ¬Ã…"œweaveââ"šÂ¬Ã‚ of the strands is open enough to allow sand, soil, or small gravel to penetrate and fill it. I think it was engineered as a topsoil reinforcement to prevent erosion along drainage ditches. It has found several uses in aquaculture (see the AES catalog), such as for spawning mats. Julian Sprung has called it a good way to prevent diggers from exposing the plenum in Jaubert systems.

I've considered another DSB with more gravel and shell thrown into the mix to allow burrowing animals to do their thing without having their burrows collapse. If I wanted to use a laterite-like substrate in that case, I could just lay it on the bottom with a fiberglass screen over top. In a mixed substrate, smaller particles tend to work down, so a mix of gravel, sand, and shell above the screen would tend to naturally zone itself as Scott describes I think. But for now Iââ"šÂ¬Ã¢"žÂ¢m leaning towards a Jaubert, because they have been proven to ââ"šÂ¬Ã…"œworkââ"šÂ¬Ã‚ for years and decades with gravel substrate bottoms.

Sarah, I used 100% eelgrass bed sand/sediment to start Tank1, and it stayed in there 4 years until Tank1 got moved last summer. When I moved I shoved three 6" diameter pipe sections down through the sand, then removed the rest of the sand. This allowed me to get the weight of the tank down enough to move it, but preserved whole cross sections of the sand community and sea grass roots. I refilled the removed sand with clean aragonite. I like the aragonite because itââ"šÂ¬Ã¢"žÂ¢s whiter and reflects up more light than the grey silica did. The star grass and shoal grass survived, the manatee grass did not. The original silica sand, removed from the top 3 inches of an eelgrass bed, was highly sedimented. The sand appeared to become less sedimented over the 4 years, not more sedimented.

I think that the interstices of the gravel, especially in the Enkamat, with fill in with baterial floc and other nutrient sources for the sea grass. So I think I can maintain sea grass without a fine, sedimented substrate. Thatââ"šÂ¬Ã¢"žÂ¢s my notion anyway.

 

[Samala]

I think its a great notion, and something I cant wait to see in action. I agree that the bottom reaches of my mud tanks seem to be lighter in color and less sedimented as it approaches a year's worth of use and doesn't appear to be more sedimented. I do not have much for fish load in the tank though.. but its an interesting observation.

Your manatee grass failure was, and still is, a mystery. My fragment still refuses to throw new plants, more than a year after its collection. I honestly think its related to that rhizome bacteria association, though I did collect manatee bed mud along with shoal for the intial tank. Perhaps it doesnt survive a little freshwater abuse well though. Live and learn! Sprung has manatee growing in leaps and bounds last I heard, so perhaps we should be testing his soil for the proper microbes.

I would be happy to send you fresh mud to seed the tank with some potential bacteria in a few months if that's something you'd like to try. I've been thinking about how to test, in a hobbyists' tank, whether or not bacteria are really important. Hard to really think up workable stuff though, there are so many variables. Add to this that I do not think Halophila is a good lab rat for this study since it does well in most transplant situations so we'd have to try larger 'grasses that also take longer to reproduce, longer transplant recovery times, etc.

So.. is this going to be a herbivore free tank, did you decide? I have some really fun species to send to you if you're not going to be keeping any Halophila munchers!

Scott - its so nice to see you around here again. I completely agree with you, every new seagrass tank breaks ground in some way. And boy do I have some puzzles for you to help answer once your tank gets under way.

>Sarah

 

[piercho]

Sarah, thanks for the tip on Schultz Aquatic Plant Soil and Soilmaster. I've read the link you provided and tried to track down a little more info (MSDS).

 

[Samala]

I believe they are just fired clay, dont remember the specific types. The Aquatic plant soil did seem to leach a little orange color, but this was no where near as bad as the Flourite. Soilmaster in the dark color (basically the same as the Aquatic plant soil just a different color from a different mined vein I believe..) did not leach at all. You may get more hits on this if you use the name Turface for the Schultz soil.

You might want to see Thekrib.com's Substrate page and Turface page for a little more info.

>Sarah

 

[piercho]

Iââ"šÂ¬Ã¢"žÂ¢m catching up on my own threadââ"šÂ¬Ã‚¦could not find the Schultz Aquatic Plant Soil today at Lowes, will try a garden center specializing in aquatic features soon. I just want to see what it looks like size-wise. Iââ"šÂ¬Ã¢"žÂ¢m still wrestling with some basic design parameters for Tank2, but Iââ"šÂ¬Ã¢"žÂ¢d like to get Tank2 at least up on a stand with the gravel in and water running by the middle of August. Iââ"šÂ¬Ã¢"žÂ¢m trying to parlay out a trip East for a couple months work in the late summer of fall into a Florida collecting trip, and Iââ"šÂ¬Ã¢"žÂ¢d like to have Tank2 ready to receive.

No fish grazers? No gold-rim tangs (sob!!) or rabbitfish if I want to keep Halophila. The shoal grass seems less palatable and if I stick with just that specie I may by able to negotiate an A. japonicus pair. A Kole tang actually seemed to encourage the Halophila to grow by keeping the blades clean.

I think I just missed a good root section on the manatee grass when I moved the tank. It did like the deeper sand in the stiller corners of the tank where detritus settled and advection of O2 was likely low. Anyway, I definitely got more mass of blades from manatee grass than shoal grass or star grass combined; it is the one grass Iââ"šÂ¬Ã¢"žÂ¢ve had to crop back. But it took it the better part of a year to take off. The star grass was off and running the day I planted it, and I could even cultivate it in a shallow tray (1ââ"šÂ¬Ã‚) in the sump while I still had the rabbitfish.

If Sprung is growing Mantee like crazy, its probably in a Jaubert (gravel over plenum) system. He seems to have a real boner for the Jaubert system, and IMO is quick to defend it against claims that a DSB/no-plenum system functions as reliably for NNR.

And now Iââ"šÂ¬Ã¢"žÂ¢m off to follow Sarahââ"šÂ¬Ã¢"žÂ¢s linkââ"šÂ¬Ã¢"žÂ¢s on Turfaceââ"šÂ¬Ã‚¦

 

[piercho]

Those linked articles from the Krib are leaping out of the computer and boring into my brain. I just learned what CEC is, Sarah must be keeping all these soil-engineering details to herself. Vermiculite as a nitrate retaining surface, hmmmmm.... Now I'm probably REALLY going sideways.

 

[graveyardworm]

Sarahs been holding out big time, those links are awesome.

 

[Samala]

Sorry guys, I coulda sworn I had posted those links to my website ages and ages ago. Besides, doesn't everyone suffer through soil science and plant-soil interface classes in college???? :lol:

Any thoughts/discussion after reading the posts?

>Sarah

 

[piercho]

No thoughts, yet, but some observations:
In a short test, vermiculite floats in salt water and appears hydrophobic. I'll give it a couple days to see if it will fill up with water and sink. I always thought it was a water-retainer and would soak up water.
The local fancy nursery with pond stuff sells something called PondCare Aquatic Planting Media . The parent company is Aquarium Pharmaceuticals, Inc. It is a mix of "all natural Zeolite and Arcillite". I know about zeolites through some SPS nutbags, its a broad term. First time I'd heard of Arcillite . It was $11 for 0.24 ft3. Could not find Turface or Soilmaster locally, at least not without calling the distributors.
Well, one thought: why would a fired clay substrate be preferable to a calcium carbonate substrate? The benefit of fired clay seems to be a porous structure. The clay has a low CEC so its not binding nutrients like a high-CEC substrate would, is it? Crushed coral or aragonite should be pretty dern porous, I'd think. Since crushed coral is lighter by volume than clay gravel, rationally I'd think its more porous.

 

[dalbrecht]

vermiculite will float in freshwater too. I believe it to be the (or one of the) bouyant force(s) in miracle mud. Amano recommends a mixture of heavy clay soil and vermiculite in his tanks. I can't remember which issue of tropical fish hobbyist he outlines his recipe but it's roughly: 1 part high clay soil, 1 part vermiculite. The vermiculite is mixed with water by hand to break it up into the finest possible particles, this mix is then combined with the clay topsoil. If it's mixed well and kept wet it doesn't seperate when you add it back to the water. I'm thinking of doing a recipe like this for my tank, adding fertilizer tabs, and then covering it with an inch or so of southdown.

 

[piercho]

OK, Iââ"šÂ¬Ã¢"žÂ¢ve read Jim Kellyââ"šÂ¬Ã¢"žÂ¢s articles dealing with CEC and the effects of pH on cation exchange. First observation, since most of the discussion of cation exchange is for pH values in the range of 7 and less, Iââ"šÂ¬Ã¢"žÂ¢m not sure how applicable much of his discussion is to cation exchange in SW substrates. 2nd observation, there is a whole lot of calcium and other positively charged ions floating around in SW, which I expect would have a big effect on how a high CEC substrate (like vermiculite) would perform in SW.

Something I didnââ"šÂ¬Ã¢"žÂ¢t really know: some plant roots can release H+ and O2 into the substrate. Iââ"šÂ¬Ã¢"žÂ¢m beginning to get an idea how a plant can control the environment in the substrate local to its roots, and how it can root into substrate zones normally very low in O2, and how it can get the substrate to give up bound nutrients. This gives me some additional notions why manatee grass dominated the back corners of my tank with lower water flow, deeper sand, and more detritus accumulation, while shoal grass seeks the front and sides of the tank where flow is highest and the sand is shallowest.

Iââ"šÂ¬Ã¢"žÂ¢m going to play with vermiculite and the fired clay gravel in containers in the sump soon. I promised some folks some grass, anyway, and need to get some grass out of the tank and rooted for shipping as the cheap shipping season is almost upon us. Iââ"šÂ¬Ã¢"žÂ¢m also going to take a chance and use some of the big pond-plant sized fertilizer pellets just loaded with phosphate in these trial containers. The next photos of my tank may feature a shag carpet of brown fuzz...

 

[piercho]

Updated thoughts and notions.

Updated thoughts and notions.

1st, results of trial run using clay gravel, shoal grass and star grass, and a great big pond plant fertilizer tab: Not so good. Star grass poked along, shoal grass did nothing.

As a side note to the above, I'm currently having problems growing star grass at all...and I've been claiming it to be a really easy grass. Star grass seems to lose out to shoal grass in competition to claim the sand bed. At this point I may have lost my entire stock.

2nd, the result of my mental cud-chewing about iron-rich gravels is that I won't use them. CaCO3 gravels are more porous I think, and I think I'll get adequate iron liberation from nutrient recycling in the bottom of the bed. And if I don't, I've got a 1 gallon bottle of iron chelate just sitting around waiting to get used.

3rd, I've about 5/6th dumped the idea of using a Jaubert construct (plenum) for Tank2. It's a conflict with having a suitable environment for a colony of jawfish. I want to give the jawfish 4 or more inches of substrate to burrow through, a Jaubert is only 4" deep at most, and the lower 2" should be protected from burrowing animals. Plus, a Jaubert is supposed to be a homogenous (2-5mm) gravel substrate, and all the pearly jawfish photos I've seen show them in a rubble/gravel/sand mixture with a lot of rubble (3 cm and bigger) present.

4rth, Tank2 will have a Ca reactor. I haven't been able to keep at least a 2.0 meq/L TA level with just limewater for the last 2 years. Originally I thought I'd drop the nutrient rich low-pH reactor return into the veg filter/sump to feed the weeds. After reading those FW planted threads and articles I've got a different notion. I'd like to PUSH the reactor output into the bottom of the sand bed using a peristaltic pump. I'm thinking something like this: a CPVC pipe network at the bottom of the tank with slits cut in it (like an UGF). The peristaltic pump pulls water through the reactor at a constant rate (1-4 liter/hour) and pushes the output into the pipe network. Around the pipe Ill put a little vermiculite; over the pipe network I'll put a sheet of Enkamat to keep the fish from digging all the way down to the pipe network.

This should give the grass the first crack at the available CO2 and nutrients from the reactor. It should also promote cation exchange in the sediments by forcing a low-pH zone at the lowest level. It may improve the O2 gradients in the lower reaches of the bed (less of the bed approaches anoxic levels). And if the Ca reactor screws up, the whole sand bed might act as a "secondary chamber" (buffer to absorb excess CO2 by dissolution).

The main functional problem could be with CaCO3 (from the reactor) precipitating out in the bed, potentially to the extent that that the bed starts to fuse. I've got to query the chemist-heads about that.

5th. I bought a tank, stand, and sump! It’s a 140G Oceanic tank with 2 overflows (48L X 24W X 30T), a matching cherry Oceanic stand, and a 40G acrylic sump. A local reefer switched his priorities (kids) and I was the benefactor. The best thing about this is that I'm no longer flopping and twitching over the basic tank parameters - they are now set in stone (or at least glass and acrylic). So, I'm making progress towards Tank2. However, given the current state of my summer remodeling projects, I don't think I'll get water moving in it before the end of August like I had hoped.