Information and data on the daily temperature variation on a reef are featured, the finally part of the temperature article, and Martha discusses why crustaceans molt.

Editorial

I hope you all had a wonderful Christmas and New Year. It is a period that I really enjoy, and I get heaps of time to spend at home and play with OZ REEF ;-) It just gave me some extra time to do the things that are not quite a high priority, but still have to be done sooner or later.

Anyway, it ended up that I redid some rock work in the center and to the left of the Park. The reason for this is that a particularly large rock decided that it did not like its position, and prefered the sand. Luckily the two of sand dwelling corals that I have were not underneth it at the time, but one was and got slightly damaged. The Trachyphyllia geoffrey is recovering well, but is also suffering a bit of tissue damage from being buried deeply in the sand for several days as well. The resulf of the rearrangement of the rock work is a much flatter section in the middle, with larger holes through the structure. I prefer as it is now, as give much more room for light loving corals to be fully exposed to the lighting.

And now onto the exciting bit, the breeding pair of Valenciennea puellaris. These two have been very active over the last month, and have decided to move burrow to the opposite end of the Park, the left hand side. And this of course entailed a huge amount of sand moving and is a much better for viewing of their behaviour. I am also very glad that I have placed a layer of eggcrate half way into the sand be, as this is stopping them from moving the entire sand bed around and disturbing the denitrification that is occuring there. One morning I was able to watch them both emerge from the burrow, it was such a cool site with the sand moving in the entrance of the burrow, then a goby head poping out. I wish I had my camera handy then. A day after the burrow was finished, the female remained sealed inside the burrow for 3 days and the male slept at the other end of the tank in their old burrow. On the 4^th day she emerged. I am unable to see into the burrow at all to see if there are any eggs lining the walls or roof. No further such 'breeding' activity has been noted since then, with both of them returing to their usual behaviour. They do not appear to be guarding the burrow, and several days after she emerged they redid some of the sand around the burrow. This seems a little odd to me, especially if there are any eggs inside the burrow. I am not really sure yet what they are doing, if there are any eggs inside the burrow, or if I have missed the hatching. All I can do is keep on observing them as much as I can, and keep an eye out for more signs. I hope I work out their breeding behaviour eventually ;-).

I have also managed to set up a larvea tank, mainly for the V. puellaris fry but I might also use it to try the Lysmata ambionensis, cleaner shrimp, larvea if I happen to catch them after release. The tank consists of a 60cm tank with 15cm of one end partitioned off with a sheet of glass. This is to act as the sump for the tank, and has a simple air driven skimmer for filtration and a Rio 600 pump in it for a return. Over the top of the overflow is a piece of eggcrate and filter floss. The idea of the floss is to further reduce the local water velocity to such a point that the fry will not be taken over into the overflow. The tank has a thin covering of fine coral sand over the bottom, including a seed of sand from the main Park, and a couple of pieces of live rock. The live rock is now begining to develop an incredible colouring of coralline algae, even though it is only underneth a 20W fluorescent daylight globe. And that is all that is too the tank, oh yeah, and it has a 50W water heater to keep the temperature up. It is a very simple tank. To keep things stable with the water in respect to the main tank, 30 litres of water per week are currently being change with water for OZ REEF. In such a time that there is larvae in the tank, this will be increased to at least every two days to keep the water quality up.

I have also finally got organised and tried the re-charging my Tap Water Purifier Deionisation columns. And I must say this is a great cheap and simple way to get heaps more life out of your column, it bets buying a new one everytime it is exhausted. All it requires is hydrochloric acid, use for washing down bricks, and soduim hydroxide, or caustic soda is used for unblocking drains and pH adjustment in swimming pools. Both chemicals are obtainable from the local hardware store, and purchasing even the largest container of each, which will last a hundred odd recharges, costs significantly less than a new DI column. As for the technique, you can find it currently on the #reefs site, at www.reefs.org, in the Library section. The first time I did it took a little longer that anticipated, but that was because I was just being extra careful and making sure that I followed the instructions to a T. The instructions also have some great other ideas of uses for the TWP unit, including the one that I am going to do eventually. The idea is to separate out the resins and activated carbon from three columns, then put each one in its own column, and get a separate mixed bed column. Then link them in the following order, activated carbon, cationic resin, anionic resin, mixed bed. Now it is much easier and more efficient to recharge the columns, a longer service life is available for the resins as the last column protects against leak through of impurities when the end of the life of the other columns are approaching, and a very pure deionised water is attained. Much more cost effective and wasteless technique than reverse osmosis units I think.

And another finally is the DIY thermostat for the two 12V DC ventilation fans on the tank canopy has been finished. It has been set to activate the fans at about 27^oC. Until now on a hot day I have just left the canopy door open and placed a desk fan on a near by table and aimed it at the open door. This has worked surprisingly well, with the temperature staying down to a maximum of 28^oC on very hot days. The new fans have yet to be tested out on a really hot day, but I suspect they will be more than able to handle it. It was also going to have a thermostat for the chiller, but I ran into a couple of problems with that and have amended that idea. Because of the great cooling effect of the fans, it is highly likely that the chiller will only be required on the hottest days and periods of extended hot weather. Therefore it simplier just to connect up the unit when the days are exceptionally hot, instead of having it connected constantly. If this does not work out, then I will just make another thermostat for it.

Thats it for another issue, enjoy the rest, til next month. I just walked past OZ REEF Marine Park and thought to myself, "God I love this hobby", thought I would let you know that.
Catch ya, DBW

Welcome OZ REEF's New Residents

• 1 x Temnopleura sp., Sea urchin. This is a very nice small sea urchin that lacks any real large spins, they are all very short and fine. And so far he has not turned into a bulldozer, and should not be any real problem because of his small size, 30mm.
• 1 x Zebrasoma veliferum, Sailfin Tang. I have finally got a bit sick of having to trim back all the macro algae. To start with it was rather interesting and whatever, but I got over that ;-). So this guy to control it, and he is getting very fat too.
• 2 x Ciliopagurus strigatus, Orange hermit. These are the same ones that are already in the Park. They are doing such a great job, don't hassle anything at all, and are such brilliantly coloured that just had to have some more move in.

Resident of the Month

Dear Marther ReefKeeper

Dear Marther,

I was wondering why myself and other shrimp have to molt?

From,
Curious Crusacea

Dear Curious Crustacea,

The reason that shrimps, and all other crustaceans, molt is so that they grow. They have evolved such that they are covered by a hard exoskeleton. And the only way they can grow and increase their body size is by shedding or molting the hard exoskeleton, and growing a new one that is a bit larger.

The time between each molting is dependent on a lot of factors, such as: age, food availability, nutrient availability etc. As they grow older the interval between molting increases. This is due to the fact they are approaching their full grown size, and the growth rate slows. Additionally, the more food they eat, the faster they can grow which then results in more molting.

It is easy to identify when the molting time for a cleaner shrimp, Lysmata amboinensis. The exoskeleton starts to appear very dirty, with small dark marks all over it, particularly on the abdomen.

A cleaner shrimp's reproduction cycle is actually directly coupled with their molting, if they have a mate present. Just after molting they spawn and carry the fertilised eggs under the tail. When the eggs reach maturity and are ready to hatch, the shrimp then release the larvae, and molt the old exoskeleton. There are then two ways to see when they are about to molt: the condition of the exoskeleton, and the maturity of the eggs.

Just before the shrimp molt, they start to reabsorb some of the existing exoskeleton, and then use this to help rebuild a new one. Just after they have molted they are typically very shy, as they have to wait for the new exoskeleton to harden. In this condition they make very easy prey. Also there can actually be a high fatality with shrimp when they molt, because they have to molt the entire external skeleton, including the lining that goes into the gills. So they need all the help they can get, i.e. stressless environment, good food supply and the desired nutrients, of which iodide is thought to be one.

From,
Marther ReefKeeper

Special Feature

This is the 'final' instalment of the Temperature article, and the full article can be found in the Reference Material section of OZ REEF Marine Park.

Daily Variation Of Temperature On A Reef

by

Daily temperature variations are cause by a large variety of complex factors, but basically they fall into either complex currents involving the mixing of ocean currents and water bodies, or localised heating or cooling. The temperature variations that occur on a reef, both the magnitude and type of variation, are highly dependent on the location of the reef, whether inner shelf, mid shelf, outer shelf, or deep ocean. The temperature variation is larger the further the reef is from the open ocean and closer to the shore. The variations are also 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.

Daily variation in temperature depends on:

• Location on the continental shelf, deep ocean, outer shelf, mid shelf, or inner shelf.
• Distance from the equator, which determines the total amount of solar radition that the water surface will recieve and the ocean currents recieved.
• Cloud cover, particularly important in shallow water as is has an effect on the solar radiation.
• Season, (summer, autumn, winter, spring) with this determining the available solar energy, prevailing winds and ocean currents.
• Depth, with increasing reef depth the temperature becomes more stable.
• Proximity to a river mouth, and the degree and efficiency of mixing of the water.
• Ocean currents, which cause a stablising or destablising effect on the reef temperature depending on its temperature and the degree and efficiency of mixing of the water bodies.
• Continental shelf upwellings, these can temporarily cause a large temperature change which then returns to normal after the upwelling ceases.

The following data is a selection from data obtained by Great Barrier Reef Marine Park Authority, which has a large number of temperature loggers located along the entire length of the Great Barrier Reef. The particular data sets used are to help illustrate some of the general trends that can been seen in the water temperatures on a reef, both with season and location. The first data set, Figure 2, is for the period of the 1^st to the 8^th of July 1995, winter, and the second data set, Figure 3, 20^th to the 25^th of February 1995, summer. The three locations featured are Magnetic Island (inner shelf, green), Myrmidon Reef (mid shelf, red), and Kelso Reef (outer shelf, blue). The pure coloured lines are for the temperature logger located on the reef flat, and the shaded for the reef slope. The reef flat loggers are typically at a depth of # to #m, while the reef slope ones are # to #m. The major gridlines are in 1^oC graduations for the vertical axis, and 6 hour graduations for the horizonatal axis.

Figure 2: Daily temperature variation in Winter, for 3 locations on the Great Barrier Reef.

Figure 3: Daily temperature variation in Summer, for 3 locations on the Great Barrier Reef.

The most obvious feature of these figures is the cyclical form of the temperature data, particularly with the inner and mid shelf reefs, Magnetic Island and Myrmidon Reef respectively. The day begins with the temperature slowly on the way down, with a minimum being reached around 7am in the morning. After this the temperature rises steeply to a maximum around 4pm in mid afternoon, followed by an equally rapid fall to around midnight, 12am. The temperature then continues to decrease into the early morning at a slower rate. The rapid increase from early morning to late afternoon illustrates the effect of solar energy input into the water having a large influence on the temparture. This effect is most dramatic with shallow water locations, the reef flat and when the reef is located on the mid to inner shelf.

The difference between the reef flat and reef slope data is also quite distinct, with the exception of the Kelso Reef data. The largest temperature variation is found on the reef flat, with the same period of variation occuring on the reef slope, but the magnitude has just been reduced. This is mainly due to the closer proximity to the surface, and the solar energy recieved from the sun causing more heating of the water body because it is distributed over a smaller water volume. In the case of Kelso Reef, located on the outer continental shelf, there is very little difference between the reef flat and reef slope temperatures and the cycle each follows. The localised heating of the water in the shallow water at Kelso Reef is off set by the input , displacement by, and mixing of deep ocean water, so that very little difference appears.

Seasonal variations in the daily temperature variation also is evident. During summer the highest temperature difference is higher than winter, 2.2^oC to 2.5^oC for Magnetic Island, 1.4^oC to 1.2^oC for Myrmidon Reef, and 0.6^oC to 0.5^oC for Kelso Reef. The seasonal variation in average temperature, as previously discussed, can also be see for all of the reefs.

You Wouldn't Believe It!

..... a complete new starfish can grow from a small fragment. With some species one of the arms will literally pull itself away from the body and regenerate. Regenerating starfish can be recognised by their lopsided appearance.

..... sponges can typical pump water equal to 4-5 times its own volume every minute. For a sponge about the size of a football, this equates to several thousand liters each day.

..... the venom of a sea snake is highly potent. A fatal dose of venom from the Beaked sea snake, for an adult human, is only 1.5 mg. An average sized sea snake can produc 10-15 mg of venom.

Bereavement Notices

No-one
I am pleased to say that no resident has died in the last month :-).

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