Parrotfish and coral

[Hank49]

Actually the parrot fish, beach sand theory is backed up by leading scientists and ichthyologists. Sim, you are correct howver in that not all sand is made this way. But on calm South Pacific islands without major pounding surf, this is the theory. Ever watch parrot fish when you startle them? ththththtpppp. Out comes the sand, or crunched coral they injested. Millions of years of this.....unless you're a creationist but that's another thread.....

 

[simbrooks]

Split this discussion off the long hose thread as it was getting way off topic...

Now how do we prepare the parrotfish?

How much damage do they really do to the reefs?

 

[Rick Murchison]

Only some parrotfish munching is done on living coral. A lot of their feeding is scraping algae off dead coral and rock.

Indeed, the vast majority of parrotfish grazing is on dead coral.
As for sand, coral sand is pretty well restricted to the tropics - the sands in the rest of the world are from various rock. The most beautiful I've ever seen are the snow-white quartz sands of the Redneck Riviera (roughly Fort Morgan to Port St. Joe).
S

 

[Charlie99]

all the sand of the world in fact comes from the crumbs of coral falling out of the mouths of parrotfish -.

It's not falling out of their mouths ..... swim behind a parrotfish and pretty soon you will see where that ground up coral comes from.

On a more serious note, a large portion of the sand is from halimeda algae and other calciferous plants.

 

[H2Andy]

actually, i read somewhere (can't find it now) that lack of parrotfish hurts the
coral reef.

apparently, the parrotfish eat algae that grows on coral, and if they stop, the
coral weakens and can die

i wish i could find this article, but no luck so far

this one isn't it, but it does touch on the subject:

http://www.scidev.net/news/index.cfm?fuseaction=readnews&itemid=1448&language=1:

By removing dead coral and feeding on algae, these fish play a central role in reef
maintenance and regeneration. And they help reefs resist change towards seaweeds
dominating over corals...

 

[Corigan]

TriggerFish are also coral munchers.

Matt

 

[Hank49]

Great idea. Let's all stand on the reef, bring some sledge hammers, and create some beach sand.

Brilliant.

Detroit, no need for that. The large and sledge hammer head "hump head parrot fish" already do it. I saw 100 lb (guessing) ones off Sipadan and you can hear them slamming the coral. they bust off chunks and chew it up. I'm thinking of bringing some over to Belize because it may be cheaper than trucking in the sand to make a beach in front of my house. Do you think they'll stick around until my lot's filled?

 

[MXGratefulDiver]

Hmmm ... with all the parrot fish around Bonaire, it makes one wonder why there are no sand beaches there ...

... Bob (Grateful Diver)

 

[Dan Gibson]

I was going on the assumption that sand would weight as little as 90 lb/cft dry. That's way far back in college for me to really remember numbers from my geotechnical classes. Dirt didn't interest me, so I have pretty much ignored it since those early days. Since 3 tons is 6000 lbs, it only takes a volume of 67 cft to hit that weight. That's a cube that's around 4 ft on each side. It really didn't seem all that great considering how often these fish take a dump in front of you while on a dive.

To put some kind of science to this - but with some assumptions (specific gravity (G)~1, moisture content (w) ~30%, saturation (S) =100%) - hopefully not too far off with these:
Vs (solid volume) = Wt/(G*Unit Wt water) = 6000#/(1x64pcf) = 93.75 CF
Vt (total volume) = Vs*(1+w*G/S) = 93.75*(1+0.3*1/1) ~ 122 CF
122CF/365 days = 1/3 CF/day

Now lets consider the fish itself - that is might be only about 24" long (i read adult size ranges between 18" and 4-ft long - that is one huge parrotfish) as an example, maybe being 12" in height (seemed to be ~ 1/2 length) and about 4" wide (guesstimate from proportions i have observed UW) = 2/3 CF total volume (assume its a box of that size), it has to devour, digest and expel almost half its body volume every day!

 

[simbrooks]

I was going on the assumption that sand would weight as little as 90 lb/cft dry. That's way far back in college for me to really remember numbers from my geotechnical classes. Dirt didn't interest me, so I have pretty much ignored it since those early days. Since 3 tons is 6000 lbs, it only takes a volume of 67 cft to hit that weight. That's a cube that's around 4 ft on each side. It really didn't seem all that great considering how often these fish take a dump in front of you while on a dive.

Sorry dirt is my job, every day, i did take interest in my geotech classes and made a career out of it

But that stuff wont be dry, hence my 30% moisture content [WW/(WDS+WW)] which will bulk it up a bit. Also 90pcf is going to give you a G=1.4 (i would give that for organic matter like peat maybe) which would mean this stuff would sink like a stone (although not literally as sand/stone is in the G=2.6+ range) and seeing as we see this stuff kind of "floats" for a while when they do what they do when nature calls, i went with G~1, although its probably a bit higher than that as it eventually sinks) - even so its roughly in the ballpark between my number and yours (which would become 95CF when you factor in the moisture content @30% again). Even so 95cuft would still be just about 1/4 CF/day which is still about 3/8 of the parrotfishes total volume every day.

I really havent followed parrotfish around to see quite how much they excrete every day, but that sure sounds like a high proportion to me! Your parrotfish's regularity may vary