An article on temperature on reefs is featured, by DBW, and then all the OZ REEF Marine Park news.

Editorial

Hello there again. Hope all your reefs are going well, as OZ REEF seems to be cruising along nicely currently. Things are not as dynamic as they have been in the past, and I suspect it may have to do with the fact it is starting to mature a bit. It is also a possibility that something is 'missing', such as a trace element or an excess of a waste product or pollutant. But even saying that, I am happy, and it appears that most of the residents are happy too.

At the start of this month I finally connected up the calcium reactor. And it appears to work very well indeed, a fact that I am very happy with. To start with the yeast technique was being used as the carbon dioxide source, and yes it did work quite well. Although it was a little difficult to keep a constant supply going at just the right amount. I am sure with a bit of experimentation this could very easily replace the more expensive bottles supply. Anyway, I got a little fed up with the yeast, and went out and got a carbon dioxide flow valve, regulator and bottle. All up it cost around A$180, which is the cheapest I could get it. And guess what? I had to get a 6 kg bottle! and I didn't have much of a option on this one, as it is the smallest and cheapest cylinder available. That size bottle is usually used for carbonating soft drinks in small restuarants and such I believe. Now I am sure that will last for quite a few years, considering the small amount of CO₂ that is used per day. The only other hassle has been the bubble counter, it leaks :-( I just found out today the reason why too .... the silicone airline tubing that I was using cannot be stuck to by any adhesive that has been developed. That is a little surprising, but that is the way it is.

OK, so what are the results that the reactor is achieving? Well, I cannot really tell you the calcium levels as I have one of those wonderful Seachem Calcium test kits. I am yet to be able to get some consistant results out of it, no matter how many times I have tried. Tighter cotton packing, very gentle inversion of the precipitation vial, you name it, I have tried it. So, based on this, I would stay away from this guy. But I must say that I am happy with all the other Seachem test kits I have, including the magnesium which I have just got, and all give consistant results. What I do know though, is that the effluent gets down to a pH of around 7.2 and has an alkalinity of 9.0 meq/l. I will have to wait and see if that is attaing enough calcium in it, but from the tank alkalinity, increasing to 5.5 meq/l over a couple of days from 3.5 meq/l, then it seems to be doing OK. Additionally, the pH seems to be riding a bit higher too, up to 8.2-8.3 compared to 8.0-8.1. Although this may just be the test kit, *shrug*, it is a hard thing to know when using a thing that is rather inaccurate and is only good to give trends. So that is how I am using my kits, to get trends and relative values.

This month has been my lucky month too :-) At our society meetins, of the MASOV, we now have a door prize. And I WON!!!!! Wahoo. It was something that I can use too, which is always good. Anyway, it was a Rio2100 powerhead. It is now located at the left-hand, rear, top end of the enclosure, providing much needed additional current. This will tie me over until I get enough money, and it becomes a priority, to get another external pump such as an Ehiem 1060. This on top of the fact that I cleaned the circulaton pump lines out, has vastly increased the water circulaton within and around the reef stucture.

And it is getting to that time of year that most reef keeper dread, summer! So far the temperature is keeping to underneth 27^oC, without any supplimentary cooling. But this weekend I am putting together the thermostat for the ventilation fans and chiller. The chiller is not finished yet, and it is the next on the list of things to do with my spare time ;-) I am sure though that the fans will do a great job of keeping the temperature down, and the chiller should only be required on the long hot streches that we get in Melbourne during later January and early February.

Well thats it for this month,
Catch ya, DBW

Welcome OZ REEF's New Residents

The rate of new residents moving has really slowed down now. The main reason for this is to leave things as they are currently, and make sure that everything within the Park is OK. The only two new residents to move in this month were two Acropora sp. fragments given to The Caretaker.

• 1 x Acropora sp., Staghorn Coral. A very different shaped yellow colony, with a very fine structure and low density of polyps.
• 1 x Acropora sp., Staghorn Coral. Short fragment of a brown with purple tip colony. The purple is a deep colour and has come out slightly more since put into the tank.

Resident of the Month

Dear Marther ReefKeeper

Dear Marther,

I have noticed that many of the sensile residents [corals] of OZ REEF Marine Park have a large vaiety of shapes that they form and vastly different colours. This includes throughout the entire phylum and even within the same family and species. What are the reasons for this, and do they have an advantage, or is it all just a coincidence or evolution?

From,
Curious Chromis

Dear Curious,

Well, believe it or not, but the majority of physical and psychological features of organisms are there for a very good reason. In the case of corals, from the phylum Cniardia this is no exception. The shape that a colony or solitary polyp takes on depends on the environment it is living in. Depth is a good example for hermatypic: at shallow depth, almost all sides of the colony get exposed to light directly from above or via reflections. Therefore it is advantageous to become spherically or dome shaped in order to expose as much surface to the light. As the depth increases then the source of light starts to become limited to directly up, and to maximise exposure the coral then spreads out in a plate like structure.

Current also has a similar effect. When the colony is in a high current zone, then it has to take a form that will give good strength so the form can be stubby and fat. If the current is very slight then it can take on a more delicate structure, forming more fingered and thin forms.

You can also take other environment factors, such as light intensity, exposure to air at low tide, preditation etc., and apply then to the shape that a coral colony will take. So there is means in all this apparent chaos.

From,
Marther ReefKeeper

Tom's Bit

by Thomas S. Heo

Well, what can I say. Tom seems to be very busy with his new advertising/WWW type job, so I am really unsure if he will be writting anything for OZ REEF Press again. If you really want him to, as I certainly do, then drop him an email and tell him to get his act together ;-).

Special Feature

Temperature on a Reef

by

Firstly lets look at the temperature found around a natural reef, as this is where the organisms have evolve, and are collect from before they are placed within a reef aquarium. The water temperature within a reef environment is not as 'stable' as many marine aquaria authors lead you to believe. Variations of up to around 10^oC have been recorded without corals being killed. The reason that the corals are not killed by such an alteration is the time frame over which the temperature change occurs. It will typically be in the order of months for the time it takes the temperature to change over this entire range.

Seasonal Temperature Variation

The dominant temperature changes that occur around a reef are directly related to, and caused, by various effects of the change of season: winter, spring, summer and autumn. The temperature changes, put simply, are caused by the following variations:

• Solar radiation received by the ocean water, which is particularly important for the immediate surface temperatures and long term effect of long distance ocean currents.
• Ocean current variations, with these effecting the entire depth cross-section of the ocean and the type, or origin, of water entering a region.
• Trade winds, effecting the mixing of the water body and influencing ocean currents.
• Rain fall, which is important for surface waters and water bodies located close to river mouths.

The seasonal variations can be linked to three location parameters to give general trends:

• The further the reef is located from the equator the greater the temperature variation. This effect is cause by the variation in the amount of solar radiation received over the year, with a more consistent supply receive in the equatorial region.
• The further inshore the reef is located on the continental shelf, i.e. the close to land, the greater the temperature variation. Water is more easily effected by run off from the land via rivers when close to land, and is located further, and more isolated, from the temperature stablising effect of deep ocean currents. Seasonal variations in inner shelf regions can be up to 11.5^oC.
• And the shallower the water around the reef the greater the temperature variation. Shallow water receives the same amount of solar radiation, but has a small volume through which to distribute it. At the extreme, shallow water heated by the sun can reach a sufficiently high temperature to inhibit coral growth. This phenomenon has been observed close to shore of Mer Island (Torres Strait, Great Barrier Reef), in the shallow water around Arno Atoll (Marshall Islands), and the beach rock at Heron Island (Great Barrier Reef).

The largest temperature series that has been published (Wolanski, 1994) spans 2.5 years from 1980 to 1982. This was obtained from data collect at Green Island, Great Barrier Reef. Green Island is located on the mid-inner shelf ... This data is presented below in Figure 1, along with data from further measurements taken during the same time interval for several other locations, Linnet Reef (mid-shelf), Lizard Island (mid-shelf), Euston Reef (outer-shelf), and Cape Upstart (inner-shelf). These sampling site are spread over a 600km stretch of the Great Barrier Reef, so it can be seen that conditions are relatively along this region, with similar trends occurring at all locations.

Figure 1: Temperature variation of seawater for 5 locations on the Great Barrier Reef (Wolanski, 1994).

The dominant feature that can be seen from Figure 1 is the seasonal variation, which is following a nice cyclical variation. The variation is in the region of 9^oC, from a maximum in late February-early March of 29^oC (late summer-early autumn) to a minimum in July of 21^oC (mid winter). This study found that temperature variations due to tidal changes are very small. The large short-term fluctuations, of up to 1.2^oC, that occur over around a week are due upwelling of continental shelf slope water onto the shelf. This cooler water rapidly lowers the shelf water temperature, and then when the upwelling stops the shelf water returns back to a similar temperature within a similar time frame of one week. (Wolanski, 1994)

Along the Great Barrier Reef, the average minimum water temperature is well with the limits recognised for coral growth. Coral flourish best in a temperature range of 25^oC to 29^oC, but they can withstand limited exposures to lows of 16-17^oC. At the tip of Cape York, the north most reaches of Australia and the Great Barrier Reef, Booby Island has an average surface temperature from 28.6^oC to 25.3C. The average minimum temperature is 24.2^oC in August, and then in December the average maximum is 29.5^oC. At the other extreme is Lady Elliot Island, located below Rockhampton, and it is not considered part of the Great Barrier Reef system. Here the minimum average winter temperature falls below 20^oC, and moving further south the temperature begins to limit coral growth. The average surface temperature varies from 26.5^oC in summer to 19.0^oC in winter. As can be seen from this data, the seasonal variation in the average surface temperature is from 3.3^oC at the northern reaches, up to 7.5^oC in the south. (Brandon, 1973) The temperature over the entire length of the Great Barrier Reef actually works out to be roughly linear with distance.

It has been reported that corals can in fact adapt to a larger temperature variation than that normally encountered by corals. An example is Kingsman (1964) has reported flourishing coral reefs on the Oman coast (near Saudi Arabia) in waters having a seasonal variation of 16^oC to 40^oC, a seasonal change of 24^oC! Now these are some remarkable corals. This is a good example of organisms evolving or adjusting to environmental conditions that are outside the range they typically live in.

Daily Temperature Variation

Daily variations are cause by the complex currents, mixing of currents and water bodies, and localised heating/cooling around a reef. These variations would be more pronounced when the reef is located in a region where the mixing of two different water bodies is occurring, or in the eddies of a large land mass.

A source of data showing the daily variation within a reef environment has yet to be found. But as noted about from information published by Wolanski (1994), the tidal variation was noted to be insignificant. A couple of possibilities are in the pipeline, but if such data is known of then please contact the author.

Depth Temperature Variation

The temperature of the seawater around a reef also depends on the depth. The temperature profile with depth depends on the region and takes three basic shapes. The most common profile on the Great Barrier Reef is essentially straight, with an almost constant temperature. This results from the good mixing of the water at all levels, which eliminates and temperature differences. This is typically due to mixing by strong tidal currents and trade winds. When the trade winds are operating there can be typically only a temperature increase in the upper meters of the water column of a few tenths of a degree. During the summer season the trade winds shut down over the Great Barrier Reef and more pronounce temperature profiles can develop. This creates the second type of profile, also existing in deeper waters with less mixing. A maximum of around 30^oC exists at the surface, which then decreases with an asymptotic curve to around 25^o at 60m of depth. Beyond this there is only very minor temperature changes until well beyond the range of corals. Rainfall can also have a pronounced effect during the period when the trade winds are not operating. The rainwater tends to stay at the surface as it is less dense than seawater, and has its temperature increased by solar radiation. This then again decreases the density, generating a feedback cycle creating a stratifying effect. This stratifying effect is quite easily broken down again by a short period of strong winds. The final profile type is that found close to the shore and river mouths. Here the temperature at the surface is greatly decreased due to the cold water input from the river, lowered to around the 20^o mark. As 5-10m depth is reached, then the temperature increases rapidly up to around 30^o. Beyond that depends on whether is shallow, well mixed waters or deeper, stagnant as discussed previously.

Bibliography:
Brandon Dale E., Waters of the Great Barrier Reef province from Biology and geology of coral reefs: geology 1,.vol. 1, Academic Press:New York, 1973, (edited by Jones O.A., and Endean R.).
Kingsman D.J.J., Nature, 202, (1964), 1280.
Raven P.H., and Johnson G.B., Biology, 2^nd ed., Times Mirror/Morsby College:St. Louis, 1989.
Wolanski E., Physical oceanographic processes of the Great Barrier Reef, CRC Press:Boca Raton, 1994.

You Wouldn't Believe It!

..... that some species of nudibranch have the ability to store living cells from their prey, as well as their toxins. When these nudibranchs eat an anemone or hydroid, the stinging cells are captured, preserved and transferred through their digestive tract to the tips of their cerata. The stinging cells are kept alive to defend their adopted host. When harassed, they simply wave their cerata about in a display of warning, and when touched the stinging cells are discharged, driving toxins into the predator.

..... since ascidians (sea squirts) are filtration feeders they can be used as effective indicators of pollutants in the ocean environment. Microcosmus sulcata has demonstrated the ability to concentrate heavy metals cobalt, zinc, chromium and selenium, and Ciona intestinalis is an effective indicator of iro build-up in water. Other species have been found to accumulate scandium, antimony and some other harmful pollutants.

Bereavement Notices

Gonipora sp.
Well, I suppose it had to happen eventually, the large colony has finally succumed. The strange thing is that it occured in two stages. About 2 months ago several patches of the colony died off, leaving some of the skeleton exposed. The remaining polyps didn't seem to react to this at all, continuing to fully expand during the day time. And then about 2 weeks ago the remaining polyps started to receed and detatch from the skeleton. It was not the best thing to watch at all. I hope that someone out there soon discovers the correct conditions to maintain this beautiful coral. Mainly because I don't see its collection being stopped because of how spectacular it is, and that is a bit disturbing.

Acropora sp.
This is one of the nice tan/skin and green coloured colony. I fragmented the colony into three pieces, and now only one of the pieces has survived. I think that the reason that they have not survived has something to do with the water conditions, and not the current or lighting. This is deduced from the fact that the three colonies were placed in three differnt locations that give varied conditions. And all three have died off at least partially. One part of one of the colonies has survived and is looking like it should pull through.

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