Coral Reef Ecology mini-forum

[galleon]

My Holiday gift to Thereeftank.com.

I just thought it ouwld be neat to start a mini-forum thread for Coral Reef Ecology... anyone with a question or comment re: the topic, feel free to post! Relate it to aquaria or ask about wild reefs, it doesn't matter, just go for it!

[nickg]

When it rains alot in the tropics, doesn't that cause a salinity change? if so does it cause problems with the wild coral? I was wondering in relation to evoporation from the sump.

[MontanaRocknReefer]

Hey Chris! When we do skimming in our reef tanks to rid our mini-reef of bad stuff, is there any relationship with the waves in the oceans of the world. When the waves wash up on shore, are they in a way cleaning the ocean waters as welll. Johnny

[galleon]

Hi Nick!

doesn't that cause a salinity change?

Yes, and there are several variables here, the largest being tidal sequence. Some others are depth and morphometrics.

Re: tidal sequence. If its pouring down raining, and you're at a slack tide, you may get indeed get a considerable shift in salinity.

Depth; well, depth relates to a volume ratio of the freshwater being added over the reefscape to the amount of saltwater it is diluting. If your wave energies are even average, your going to get a mix of the fresh and saltwater very quickly... and with a large depth (read: reservoir of saltwater) the freshwater is being mixed into, the salinity is not going to change much.

With morphometrics you factor in exchange factors for saltwater, ie, if you're in a lagoonal environment where the salinity is being affected by downpour, blocked in by shallow (inches) microatolls, you aren't going to exchange much of the water via wave energies with the norm salinity water being brought towards the lagoon by currents/tides/energies.

if so does it cause problems with the wild coral?

No, as exposure times to water of low salinity are often low, and the shift usually isn't all that fast. Don't forget, reef flat scleractinia deal with (by mucus) complete exposure to freshwater rains if they have been exposed to air tidally.

HTH,
Chris

[nickg]

Thanx Chris, that was very informative. Have a happy new year!!

[galleon]

Hi Johnny! Hope you're feeling better!

When the waves wash up on shore, are they in a way cleaning the ocean waters as welll.

Well, technically yes. Turbulance from breaking ocean swells often causes fractionation of any hydrophobic/hyrdophyllic proteins local to the water being carried by the swells (technically a wierd combination of longitudinal and transverse mechanical waves caused by winds). This usually only involves the already pretty oligotrophic waters of beaches, as waves only break when the depth is less than half the wavelength. So waves don't start to break (and thereforre fractionate) until they reach shallow water, which can be reef structure or beach zones. The only time the fractionated foam is collected though is on beach zones. So only the water column local to the beach becomes fractionated. Any organic nutrients in the water column on the reef (few and far between) may be carried into beach zones, but they will likely be uptaken by algae or seagrass beds or plankton prior to being fractionated (not that some aren't fractionated on the beach, though). The intensity of the breaking wave fractionation also depends on the mechanics (fetch, wind velocity, wind time) of the wave (the average swell passing over a near-equatorial reef averages about 500,000 horsepower), but in general, while yes it happens technically, no, it isn't a major component of reef (or even beach zone) ologigotrophicism, as it just isn't that intense. Its just one of the most convenient ways for aquarists to try to maintain an oligotrophic environment in their systems.


HTH,
Chris

[GaryG]

Re: Salinity

We have observed (non-scientifically) that the salinity in the oceans differs from place to place.

For example: When we scuba dive in Cozumel we need to wear more weight than when we dive in the Bahamas. Some say it is because the currents are stronger in Cozumel but I think the water is saltier.

Now that you have made me think about this I think I will bring my hydrometer with me on the next few trips and check it out!

[galleon]

Now that you have made me think about this I think I will bring my hydrometer with me on the next few trips and check it out!

Definitely keep a log of this! Not only of the specific gravities you measure, but water temperature, lat/long, and weather (ie, how many inches of rain the reefs got on which days), seasons (date and time will have bearing on salinity/temp altering currents and exchangin tides), winds... should be a neat project! But very involved if you want to be intensive about it

[Drew]

Hey Chris, thanks for doing this, it's really great of you. Now I got a question for you.
Why are there so many corals which in the wild, extend their polyps only at night, but while in captivity they extend during the daytime and also at night. Is this because of the greater chance of being fed in an aqurium during the day time? (I.E. the corals "learn" when the food comes) Or is it because of something else? TIA

Drew

[galleon]

Hey Drew!

You are dead on... the corals which you speak become encouraged to feed in the day as well as night in aquaria. In the wild they are active night predators.

[Drew]

OK good, that makes sense. But how do they "know" to open their polyps? They don't have brains, so I was under the impression that pretty much everything they do is based on their genetics. Meaning it is pre-programed for them to grow into a certain shape, just like it is pre-programed for them to open up at night. Am I wrong here? (yes)

Drew

[galleon]

Drew,
It is instinctual adaptivity behavior, you have a set pattern of behavior that in general, doesn't change from wild colonies being imported... Instinctual triggers from chemical pathways (nitrogen present) extend polyps at night. However, corals react to nitrogen stimuli, especially polyp extensions, and "food reactions" (a set pattern of behavior generally qualified in the presence/capture of food), which are being brought about by not only feeding during the day but the nitrogen present in captive water, thus the coral adapts to a continue provocation of a food reaction. Its all about conserving energy/metabolic expense.

[Drew]

Thanks Chris, I learn something new everyday!

[Brooke]

Chris-
I'd be happy/honored/thrilled to give you a whole forum for coral reef ecology.

Ok my turn. In Cozumel we visited Columbia lagoon...which is saltwater and surrounded by mangroves. The water is normally blood red because of the mangroves. What causes that? (the water was yellowish because of the recent hurricane..and not red. That would have been cool to see).

Brooke

[galleon]

What causes that?

Wow... the water was a really intense red? Must be a real low tidal exchange zone.
The cause is the leaching of tannin into the water via degradation of mangrove litter and mangrove bark. Tannin contents are highly elevated in Rhizophoraceae as to increase resistance to herbivores.