Heat and Temperature

[coralite]

I thought that for my first write up, I would cover how temperature and heat affects our corals and aquaria from a physical, chemical, and biological point of view to give you a better understanding of how critical the readout on your thermometer can be. Ideally, the format for this inaugural write up will be similar to what I will try to follow in future write ups so that readers can get a good sense of what to expect from me. When I feel that I have covered a semi-comprehensive overview of the various effects of heat and temperature, I will open the thread.

Physical effects
-heat vs temperature
Before I can go into a serious discussion of how temperature and heat affect our coral's world, it is important to differentiate between the two. Temperature is a measure of the average kinetic energy that is contained within a substance. Kinetic energy is in reference to the movement of the molecules that make up a substance so at a higher temperature, you have more movement of the particles that make up molecules and you have a higher temperature. In essence, temperature is a relative measure of the energy contained in a substance. Heat is a direct measure of energy. The basic unit of thermal energy is the calorie which is equal to the amount of energy required to raise 1gram of water 1C. We dont talk about calories much in our aquaria so I'll stop there.
To give you an idea of how we are trumped by our perception of temperature and heat, imagine a piece of steel and a piece of wood sitting in a room, right next to each other. They've been sitting there for quite a while so that both items are at thermal equilibrium. If we touch the steel, we will believe it to be colder than the wood but in fact, they both have the same temperature. So what accounts for this difference in perceived temperature? The answer is specific heat.

-specific heat
Specific heat is a measure of the amount of heat a substance can absorb. An object with a high specific heat, like water, can absorb a lot of thermal energy(heat) before it changes temperature. The reason a piece of steel feels cold to the touch is because of its capacity to absorb heat faster than something like foam or wood. That is precisely why we use foam to ship our livestock, to slow the absorption or loss of heat by our container. The point to take away from this is that since animals and plants are mostly water, the organism will experience the same temperature as the surrounding water.

-density
I think most of us know that density is inversely proportional with temperature meaning that a higher temperature water will be less dense than lower temperature water. This is the mechanism that a standard thermometer uses. The expansion of the fluid within a thermometer has been calibrated to a specific temperature. So why is it important to think about density in terms of corals? Well the most obvious answer is that most of us use swingarm and floating hydrometers to measure salinity and so colder saltwater will give us a higher salinity reading than warmer saltwater. The other thought I want you to take away from this is that since less dense water will float on top of colder, denser water, oceanic habitats can have a thermal stratification called thermoclines.

-thermocline
The further you go out to sea, the deeper the thermal stratification called thermoclines. The reason for the deeper thermocline in offshore habitats is that there is a lot more water to absorb heat and there is more currents to mix the stratified water. The closer to shore you go, the more pronounced and shallow are the thermoclines. All of our photosynthetic corals come from habitats that are shallow enough to allow for sufficient iradiance to drive photosynthesis meaning that many of our corals come from habitats that are subject to sharp thermoclines which may be more than 3C over a few meters.

-wrap up
Popular aquarium dogma will lead you to believe that our corals live in habitats that are the equivalent of thermal humidors, but all snorkelers and divers can attest to the fact that its warm at the surface and cold at depth, no matter how tropical your reef is. The key thing to consider when applying scientific principles to aquarium logic is the rate and scale at which temperature changes occur.

[coralite]

Chemical Effects

In a way, it is logical to begin with the physical properties of heat as it is the single greatest influence on the rate at which almost all chemical reactions will occur. In terms of heat, chemical reactions are classified into exothermic and endothermic reactions. Exothermic reactions put out heat (give off energy) and endothermic absorb heat (require energy). The addition of dry calcium additives containing Calcium Chloride to a dilution of water will produce a lot of heat in a small container. Water that is warm will have a poor calcium solubility.

-calcium solubility
Since the dissolution of calcium into water is an exothermic reaction, it will dissolve at a faster rate and more completely in cold water than in warm water. Because of this property of calcium, there is a depth of pressure and temperature at an avg of 4000m where no calcium carbonate exists because the water is so cold. Fill up your kalkwasser jug with cold water! Along a similar note, true coral built reefs occur only in areas experiencing an average temperature of 69F because below this temperature the calcification rate of corals is so low that the erosion of waves and currents out paces the growth of the reef structure. Conversely, in warm water calcium tends to precipitate faster which is why so-called super quiet pumps like the Quiet One and Silent Seas/Velocity series pumps tend to precipitate a lot of calcium in reef aquarium situations. In the same note that computer enthusiasts add extra cooling mechanisms to their overclocked cases, I believe the next step in the evolution of the Calcium Reactor is in the design of cooler running units with low heat pumps, thermoelectric microchillers and of course, the very sexy backlit, digital temperature (and pH) readout on the dial.

-rate of reactions
Depending on wether a reaction requires or releases heat, your temperature will either enhance or inhibit the rate of reaction. I will discuss a whole lot more reactions that I thnk of more as biochemical ones in the following post.

The biological effects of heat and temperature coming soon in the next installment.

[coralite]

Most of us are aware that our photosynthetic corals occur only at tropical latitudes but have you ever asked yourself why? Why can't my acropora coral grow off the coast of New Jersey? Many of us can intuitively deduce that this it is difficult for a tropical animal to grow in temperate waters (although thats not stopping lionfish) and in this segment I will try to bring together the physical and chemical effects of the thermal environment and how it affects the thermal biology of corals.

The temperature limit for true photosynthetic coral reef formation is an average of 69F (20C) because below this temperature, corals grow so slowly that the rate of erosion by waves and biofouling organisms is greater than the rate at which coral reefs form.
Corals have evolved in tropical seas and therefore, their biological requirements have adapted to be able to cope with a narrow range of temperatures. The ideal temperature range for coral growth appears to be between 74F (23C) and 81F (27C) but at the the geographic limits of where corals grow they can experience temperatures anywhere from a minimum of 52F (11C) to a maximum of 97F (36C) (Coles and Fadlallah 1991). This equates to a temperature range of 44F (25C) but this is certainly at the extremes of where coral reefs occur and it gives you an idea of what corals can cope with when they are adapted to it. As long as the rate of change is gradual, our corals could easily cope with a range of 10F (18C) over the year and in fact, this is precisely the seasonality of temperature that conditions corals for sexual reproduction. It is common knowledge that many benthic organisms are triggered to spawn according to lunar cues but the phases of the moon occur throughout the year and most corals that are broadcast spawners do so only when the water gets above a certain temperature.

Since corals are at the same temperature as the water they are in, they are not at liberty to put on a coat to stay warm or strip to stay cool. However, they can regulate their biochemistry to a certain degree, either to enhance their fitness in a changing environment or to negate the impact of thermal stressors under adverse conditions.

For all organisms, a higher temperature means a higher metabolic rate. If the metabolic rate for our corals increases, so does the metabolic and photosynthetic rate of the zooxanthellae within the corals. At very high temperatures, the production of oxygen by the zoox. is so high that the coral cannot get rid of it at the same rate as it produced so there is a build up of oxygen in coral tissues. The shedding of excess O2 is largely regulated by the amount of water motion around the coral colony. Since corals cannot actively breathe, they rely on water motion to rid themselves of metabolic and photosynthetic byproducts by maintaining a high diffusion gradient, that is, a large difference between the concentrations inside and outside the coral. If the coral cannot rid itself of excess O2, this will produce free oxygen radicals which are toxic. The production of free O2 radicals is believed to be the reason why corals expel their zooxanthellae during periods of very high temperature. Since the coral cannot control the photosynthetic rate of its symbionts it simply expels them but then it will severely limit its capacity to acquire energy. The critical temperature for the onset of coral bleaching seems to be around 86F (30C). The scientific literature cites many examples of mass bleaching but for any given bleaching area there is usually some reports of enclaves of healthy corals that have cheated death and these generally occured in locations of high water flow.

One of the main biological features that allows organisms to survive in varying thermal regimes is enzymes. Let me quickly explain what an enzyme is and then I will cover how they are important.

-an enzyme is a chemical catalyst that brings two compounds together to facilitate a chemical reaction. Enzymes work by having a shape that conforms to the reactive sites of two molecules. By bringing these two compounds in close enough proximity, the two molecules can react and once they do, they leave the enzyme. The enzyme is left unchanged and since this reaction required no energy to begin it is said to be passive. Enzymes are designed with flexibility in mind and at warmer temperatures they are looser and at cooler temperatures they are more rigid. Enzyme catalyzed chemical reactions can only function in a certain range of enzyme rigidity so if the temperature is too cold the enzyme is too stiff and if the temperature is too warm, the enzyme will be too loose to function. If a coral (or any other organism) is going to adapt to live and grow properly it will have two options regarding its enzyme properties but this will come at an energetic cost.

The seasonal effect on tropical temperatures is slight so throughout the year, the optimum average ideal temperature of the enzymatic suite changes only a little. That is, in the summer months, the corals' enzymes function best at warmer temperatures and in the winter they function better at cooler temperatures. The second option of enzyme production is restricted to organisms living on the edge of tropical and sub-tropical conditions and they produce isoenzymes that function at a wide range of temperatures. Iso-enzymes are a kind of one-size-fits-all for enzymes and they are more common in inshore and lagoonal corals as these environments experience a greater range of temperatures on a daily time scale.

If our corals are kept in a narrow temperature range they only have to invest in the production of a few enzymes and they will have more energy left over for growth and reproduction. If our coral has to invest in energetically expensive iso-enzymes that will function in a range of temperatures they will have less energy left over for growth but they will be able to resist large temperature changes. The bottom line is that there is a trade off between having an enzyme system that will give you the most function for your energy while still allowing you to deal with changes in temperature.


So what does all this temperature business mean for our reef tanks anyway? Well first of all, for the love of God reefers, get yourselves a real thermometer and make sure to have some back ups. Digital thermometers are precise but they can become inaccurate so you need a good reference with which you can calibrate them. Secondly, if your reef has a very strict temperature control system, your corals will grow faster but if you ever have a thermal stress event, your corals will be more likely to suffer and perish. On the other hand, if your tank has a daily 1-2 degree temperature swing, your corals may grow a little bit slower than if they were in a very narrow temperature regime but if your AC goes out and the tank gets really hot, your corals will be more likely to survive. Also, since most reefers try to keep a constant temperature regime in their tanks, we are not likely to start experiencing more coral spawnings unless we allow our systems to an annual range of temperatures.

This is by far not a comprehensive review of the effects of temperature but its a start, an overview of how temperature affects our corals and how heat affects their environments. There is so much more material out there but I tried to focus on the topics that would be most obviously applicable to our aquaria. In the next session I will round up a few articles and give an aquarist point of view abstract of the implications the research results has for our reef tanks and for our corals. I hope you liked the write-up, that you found it informative and that you are inspired to take another look at your reef tank and reevaluate what kind of temperature conditions your corals are experiencing.

I implore all inquiring minds to ask questions and the more effort you put into forming your question, the more precise I can be in answering it.

References

Coles, S.L. & Y.H. Fadlallah (1991) Reef coral survival and mortalityat low temperatures in the Arabian Gulf. New species-specific lower temperature limits. Coral Reefs 9 (4): 231-237.

[Bad Motor Finger]

Hey Jake -

Jake here. We must be the Two Jakes in this thread.

You've given an extraordinary explanation; I really appreciate this.

My plan for my new system, which will have a large sump in an outdoor shed, is to run MH lighting at night to help moderate temp. I live where the avg temp is in the 50s (almost never below 40F even nights in winter), though it can get near 100 periodically.

I know corals and fish especially can handle some swings, but you detailed some interesting points.

My thought: trigger heaters near the lower end, fans and ultimately a chiller at the higher end of temps, and provide a range of maybe 10F.

Would this range be suitable for healthy corals? Or should I dial in 74 and 81? I see with your points about a slightly wider range of variance than just 1 single degree A wider range allows more seasonal variance and electricity conservation.

Sorry if this is an obvious question, especially after reading your thorough research. I'd just like your thoughts on my specifics, if you have a moment to respond. Thanks again for your research.

PS my thought is I'd rather have stronger corals than fast growing ones. If I had no temp variance, the power bill would kill me and a chance event would kill my tank. I've lost corals to temp changes and I don't like it. I'll take a small, strong frag over a big fragile colony.

Maybe the range of 7-10F swing is too large though?

[Aged Salt]

Jake[BMF] that degree of temp swings do not bode well for SPS. Maybe the other Jake[coralite] can discuss temp variances on coral physiology & viability more in detail? thnx. Bob

[coralite]

If you want to incorporate some kind of temperature swing in your system you need to consider at which scale you are trying to have an effect. Temperature change on daily time scale will toughen coral and symbiont physiology and an annual temperature range will stimulate will also stimulate spawning mechanisms.
the difference between 74 and 81 degrees is way too much swing and this is not a suitable range of temperature on a daily basis. In most cases, if you dial in a specific temperature with a heater/chiller that is appropriately sized for your tank, you are likely to get a 3 degree temperature swing on a daily basis anyway. In my experience, aquariums have different avg temperatures in the winter and the summer and this yearly change alone is enough to toughen the enzymatic systems of our corals.
If you were going to try to replicate or allow some level of temperature change I would suggest doing a gradual change of 74-77 in the winter, 76-79 spring and fall and 78-81 in the summer. If our various controllers allowed for this range of seasonal tamperature shifts, it would single handedly increase our reports of captive coral spawning by at least one order of magnitude.

It is very important to consider that the rate at which you affect and change temperature is going to be critical in the delivery of your temperature regime. As long as the change is gradual, you will not have any problems. There is a big difference between experiencing a temperature swing over the entire day and having the temperature drop 3 degrees right when the lights go off. Fortunately, the heat carrying capicity of water is very great so most temperature changes do not occur that fast.

I hope this helps and do not hesitate to ask if you have further questions.
:smoker:

[Chad W]

The Neptune AQII's have a seasonal temp. function were it does exactly what Coralite is describing. Hope the Aquatronica will do the same
Great info in this thread, Thank you.
Take Care,
Chad

[Bad Motor Finger]

Great points.

One of many, many, many upgrades on my System 2.0 is going with a controller. That should more closely control the heat spikes.

I'm also planning to run a less intense lighting regimen in terms of hours, and run it starting at sunset.

I'm going to need to continually dial-in a range.

I'm got a dedicated older laptop to running the system, and plan to set the fans to go on towards the higher end... maybe 79, then the chiller at 80 or 81 to lock that down.

But instead of having my heaters set lower, I'll probably try to keep them at 75+ so the tank doesn't experience a chill.

My two extremes are winter nights in the low 40s and a couple late summer/early fall late afternoons where the temp can get to 90-100.

In addition to the shed sump (Rubbermaid stock tank) helping keep a larger body of water overall, the display is on the ground floor and out of the sunlight, in the coolest part of the house.

I've been blown away at how much I've had to use the chiller even when it's been seemingly cool outside. The temp in the top floor of the house, in a sunny window, with MH on, gets plenty hot.

That problem will be going away.

This is going to take some careful dialing. The great thing is, all 3 tanks (old reef, FOWLR, new reef) can be up at the same time so I can slowly acclimate corals, properly zeo-start the new system, and control temp. I can get the new system 100% locked in before anything living touches the water other than my hands.

I was going to start measuring temps in and out of the house until then, but it really won't matter until I have it plumbed, pumping, and full so I can see how it goes. I'm also thinking of putting a thick styro sheet on the surface of the sump during the winter to help insulate, and keeping my entire maintenance gear, as well as a fuge, inside a nearby closet.

I'm hoping the heat of a big pump can help mitigate temps that otherwise want to run cooler. If there's an outage, the display will stay room temp and only the sump will get cool.

Any recommendations? Where can I improve this design? I know my logic can't be spot-on.

[mesocosm]

Bump! ...