Macroalgae vs. Seagrass Nutrient Uptake

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Anonymous

Guest
Eric,

We were discussing nutrient uptake tonite on #maco and I posed the question on the relative nutrient uptake of macroalgaes compared to seagrasses. As I have not yet read that section of EIS pt II and have no experience with seagrasses I really don't know the difference between macroalgaes and seagrasses but I have to assume that there is a difference since a distinction has been made in the literature. Would you mind explaining the relative difference between seagrasses and macroalgaes and also focus on their relative nutrient uptake and the pros/cons of their use in nutrient export?

Thanks!

Shane Graber
(aka Liquid)
 
A

Anonymous

Guest
Glad you posted - Thankfully, I remembered, too.

Seagrasses are true grasses that grow completely submerged or tidally exposed in marine water. They are vascular plants. Algae are barely plants <gg> and do not have the "advanced" features (sea that chapter for description).

Your question is a good one. As far as I know, there are no data to compare uptake, and relatively few on uptake of the sort that aquarists are interested. The ecology of seagrasses is fairly well studied, but lots to go. In the wild, where there are seagrasses near reefs, the communties are capable of removing all the excess production of the reef...and absorb all the terrestrial inputs, too - at least normally (they may be buried where activities on land have caused above average deposits to flood the coastal areas). As a community, they appear, like reefs, to be nutrient limited. Conversely, the higher than average plankton in seagrass areas and the amount of detritus they produce feeds the reefs. A sort of mutual backscratch. But, it is not just the seagrasses. Also, like the reef, its the whole community, and the blades of seagrasses trap particulate matter and allow it to settle in their dense rhizome network. here, with all that "food" are a myriad of organisms - from very high sponge and mollusc population, to predators, brooderies, etc. Because there is so much nutrient waste trapped, it is well broken down and mixed and sediments are usually silty to mucky - and they stink!! Why? because there is a very very high level of microbial (bacterial and other) action going on - and it is probably this aspect that allows for the nutrient efficiency, rather than the seagrasses, per se. However, without those grasses and the communtiies they foster, you have a regular sandy bottom that is, by comparison, rather useless.

Algae may also grow across sandy bottoms or directly on hard substrate. They do not form the intricate ecological communities to the same degree (exceptions occur, like kelp forests, etc.). More more often than not when on reefs , macroalgae often are symptomatic of a reef receiving too much nutrient and this is called eutrophication. They react very quickly, too. Now, of the algae, the turf species that grow intertidally seem to be the most efficient. They are highly grazed and have the fastest growth rate increase. Among these are aquarists undesirable filmaentous species, as well as very attractive astroturf-like types. The macroalgae, in general, are probably much less efficient at nutrient uptake roles in the wild. Phytoplankton and bacteria just respond so much quicker and usually deal with the problem unless it is chronic...and then the slower macroalgae respond. i have seen some references suggesting that corals, sponges maybe too, are more efficient than certain macroalgae at nutrient uptake. Makes sense, too.

So, if I were to wager a semi-educated guess, seagrasses probably have among the slower growth rates, followed my macroalgae, then filamentous then other turfs....and this would be a decent measure of their nutrient uptake ability, too. However, as a community, seagrasses and associated microbes are probably the greatest. They also are normal with healthy coral reefs and have that "symbiotic community" aspect that I think is desirable.

So, if you plant a few seagrasses around your refugium, are you going to "filter" your water? No. Same with mangroves....same with macroalgae, I suspect. But, they will all help. If you have a seagrass community with good sediments and of good size, it will probably contribute significantly to nutrient processing.

How's that?

Eric
 
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Anonymous

Guest
Heh, yeah that pretty much summed it up!
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Well, I'm *almost* done with the reading assignments for this week so I may have time this weekend to hit Chapter 18 "Seagrasses" in a little more detail as I'm interested in reading up on them. I'm suprised the EIS did not cover macroalgaes in a chapter like they did with seagrasses. Any idea why?

Also, from what I understand both you and James have seagrass tanks setup connected to your main systems. Any reason why you went with a seagrass tank over a macroalgae tank? Also, you wouldn't by any chance have a website where you have some pix of your system would you?

Thanks!
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Shane (aka Liquid)
 
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Anonymous

Guest
Shane,

We collected the seagrasses together in Florida after MACNA. Probably the reason we both have seagrass tanks...:)

My grasses died WAY back during the winter. The mangroves I collected didn't sprout right away either. THey just started growing a few weeks ago. I guess they are "semi-anual" Hopefully the seagrasses will start growing too. They are pretty much "crawling" right now.

Cheers
James

------------------
Reefs.org Channel Operator
 
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Anonymous

Guest
Hi Shane:

Inosofar as my various grass plantings:

First couple of times, i collected poorly, bare-root, and/or were sent to me in bad conditions. The losses were considerable. Time before last, i collected and planted with care, and they thrived for a couple years. Major tank problems last year, and I lost them 9along with just about everything but the fish) while on extended travels. James and I collected fairly well, but flight problems and transfer probelms and poor planting on my part in a rush to get them in the tank resulted in a lot of loss again. Of course, i think they should be seasonal like other plants in terms of transplant and growth, and it has been winter. Also, IME, quite a bit of acclimation time. Fortunately, mine have started tos prout after losing the blades on most plants, and some never lost the baldes and are doing well. rhizomes apparently are viable for years without sprouting. They don't grow fast in tanks, don't know why yet. Lots of work to be done here, lotsof trials. Best scenario I have had prior to the tank tumult was collecting large sediments around plants , planting well and deeply with a little pelletized fertilizer, and things thrived. I had to keep that tank unconnected for awhile while things stabilized and the muck settled or it would have been a disaster. After things settled, it went back inline and things went very very well. Yes, i can upload some pictures later - too busy right now.

Why did I go with seagrass and not macroalgae? Not sure I did. I try to have it all. I think a blanced community is ideal, and so try to grow macroalgae, too - at leastt the ones which i think are desirable to keep (not Caulerpas or Dictyotas, for example)...However, conditions favorable to coral growth usually don't favor macroalgae growth, and most macros do poorly or fall apart for me over time. Not so with the grasses (or Halimeda so much, for that matter, now that I think of it), or so it seemed when it was full and lush. I'll let you know as this batch fills in again.

Eric
 
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Anonymous

Guest
Eric wrote:

<BLOCKQUOTE><font size="1" face="Verdana, Arial">quote
try to grow macroalgae, too - at leastt the ones which i think are desirable to keep (not Caulerpas or Dictyotas, for example)...

Why not caulerpa and dictyota? I can guess that you would not recommend caulerpa becaues it tends to go "sexual" but why not dictyota?

Shane
(aka Liquid)
 
A

Anonymous

Guest
its VERY hard to get rid of - pretty, but a nightmare. When you try and manually remove it, it doesn't come off easily, the blades break and start new colonies, and its even hard to scrub it off.

Eric
 


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