Temperature and Salinity in Maintaining Coral Reef Aquarium Animals.


Ronald L. Shimek, Ph. D.


There are a few basic “rules of thumb” that have to be learned when trying keep living things in the best of health. Probably the first and the foremost of these rules is that these organisms need to be provided with a mimic or analogue of the natural physical environment where the organisms do best. Sometimes this is easy to do, sometimes it isn't. However, in all cases, any captive living thing has the best chance of thriving when kept under conditions that are most like those in the natural world where individuals of that species do the best. For aquarists discussing marine animals, this raises the question, “Where does the animal do the best?” To determine this, we need to do a bit of detective work. Natural selection has given every species to a specific set of physiological tolerances, and without exception. Consequently, the most suitable range for any environmental factor is that range of conditions for that factor where the organism evolved. Basically, organisms do best under the conditions where the species first evolved. This may seem trite and obvious, but for a great many aquarists, it seems to be a point that is simply overlooked.

To determine what conditions are optimal, it then becomes necessary to establish where either the animals evolved or where they do best under natural conditions. Determining where any animal or group of animals originated may seem to be a difficult proposition, after all, many species are widespread, it would seem that locating where they evolved and hence will do best might be nearly impossible. Additionally, most species living today evolved long ago, often in world where conditions were much different, such as Earth during the last Ice Age. However, determining where the animals do best is often much easier, and with many tropical marine species, it may be relatively easy. All organisms have a geographical distribution and this means that they must have spread out from either their place of origin or where they do best. This spreading is referred to as a species' radiation, with the analogy that the spreading occurs something like light radiating from a light bulb.

Determination Of Optimal Conditions

Widespread species often exist over a considerable geographic area, and may encounter many different sets of habitat conditions in that range. It should be obvious, and it must be remembered, that they don't do equally well everywhere within that range. The evolution of a species from some ancestor may occur relatively rapidly, however once a species has evolved any further changes are incremental and small, and the descendents continue to maintain many ancestral characteristics (See Gould and Eldredge, 1993, for a discussion of these processes). Often the conserved properties include tolerances for physical conditions. Particularly in marine environments, organism distributions tend to spread to the edges of these physical tolerances. For example, if a given coral species has a temperature optimum of 84 ° F, but can tolerate temperatures from 75 ° F to 93 ° F, that species will spread through out the contiguous environment to occupy all survivable habitats within that temperature range. It is worth remembering that organisms near the edges of their distributional ranges are generally stressed and the conditions near the edges of distributions are not going to be even near to optimal. Instead, near the edges of their species' range organisms generally just “hanging on.” These sorts of conditions are not what you want to use in trying to keep organism in the best of health. In contrast to the lack of growth and reproduction at the edges of the distribution, in the center of the range there is a surplus of energy. Because they are not counteracting the problems of low or high temperatures, the organisms in these areas can expend more energy in other biological processes such as competition, defense, and reproduction. Because they can produce many more gametes than those in less benign environments, they are more likely to produce variations that are successful in occupying specific new microhabitats within the center of the range. Eventually a pattern develops within a group where more species are found in the area at center of the distributions where the physical conditions are best, and progressively fewer species found as the distance from the center increases. This pattern of an ancestral species and its group of descendent species is called the “adaptive radiation” of that specific group.

Figure 1. A hypothetical species distribution. The red dots represent populations spread evenly over an radial environmental gradient of conditions, with the best conditions at the center of the distribution and progressively less favorable conditions at increasing distances from the center.

It is often easiest to see these sorts of radiation patterns if whole communities or assemblages of organisms are examined. Often many groups of organisms have coevolved for similar conditions, particularly if they live together in a specific type of ecological assemblage such as a coral reef. It turns out that corals provide one of the easiest assemblages to see these sorts of patterns. If one looks at the pattern of distribution of corals found in the Indo-Pacific, a striking pattern is apparent. The number of species and species groups of corals is highest in the Malay Peninsula-Indonesia-New Guinea region and drops dramatically and steadily in all directions from that center of distribution. It is not coincidental that virtually all coral reef organisms show the same pattern.

Figure 2. The pattern of adaptive radiation represented by living tridacnid clams. See Figure 4 to compare with the adaptive radiation of corals. Note that the center of radiation is in the New Guinea-Philippines-Indonesia area. Data from Rosewater, 1965.

It is relatively easy to determine the centers of these distributional patterns. In widespread species, the center of radiation may be often be simply determined by scanning a map of the distribution and simply “eyeballing” the center of the distribution. After this is done, it is a simple proposition to go to some source of climatic or physical conditions and find the conditions around that center and use those as the model of the conditions for the organism's care. Alternatively, the species' distributions may be examined for any peculiar or specific climatic or geographical conditions, such as ocean currents, or upwelling areas (often with cooler water, for example). These may be factored into the determination of the range and tolerances. The physical extremes can be examined and the midpoint of those extremes may be chosen as a first estimate of the various physiological optima.

Working with a specific single species, it may be somewhat difficult to find the optimal conditions, particularly if the organism is widespread. However, if data are available about reproduction and growth rates, these problems tend to disappear. Organisms grow fastest, and produce more offspring under optimal conditions than they do elsewhere and often those differences are dramatic.

Why Is Temperature So Important?

The importance of having the optimal physical environmental conditions in the care of any coral reef organism is probably most evident when considering the effects of temperature. Most coral reef animals have no way of adjusting their internal temperature. They must live at the temperature of the environment around them. This ambient temperature regulates the reaction rates of ALL of their internal chemical processes or, put another way, their metabolic rates are governed by the external temperature.

The metabolic rate of such organisms is really determined by the rate of the slowest essential internal chemical reaction. Temperature is a measure of molecular agitation and as the temperature changes, the rate of all chemical reactions changes. Discussions of changes in reaction rates of chemical reactions may seem dry and uninteresting to aquarists, but all life is based on the balance and “coupling” of large numbers of chemical reactions. The term “coupling” is used to describe any chemical reactions where the products of a first reaction are necessary for a second reaction to occur. At any given time in any cell, upwards of 20,000 chemical reactions are occurring. It is vitally important for the survival of the cell that these reactions occur in the proper sequence. Any improper sequencing results in a build up of metabolites which can and often will cause adverse consequences. Such consequences may include a build of toxic materials, or a lack of necessary ones. As result of such potentially adverse affects, natural selection has favored the development of enzymes and reactions that function optimally at one temperature. Reactions that may be fine-tuned to be complementary at one temperature will deviate from that fine tuning with any temperature changes. Evolution works to fully “tailor” organisms to their environments; consequently, after not so many generations, the internal cellular chemistry of these animals is fully attuned to the temperature range found in their environment. This means that slight changes in this temperature range are tolerated, but major changes are often disastrous.

The rate of change of these reactions with temperature is significant (Prosser, 1991). One method of determining temperature changes effect reaction rates is called the Q 10 term, the formula for which is given in the box below.


Q 10 =


  • k 1 and k 2 are the chemical reaction rate at temperature 1 and 2, respectively, and
  • t 1 and t 2 are temperature 1 and 2, measured in degrees Celsius


The Q 10 term is the factor by which reaction rates are increased by a rise of 10°C (18°F) in temperature. The Q 10 term is not a constant over normal temperature ranges and is typically larger at lower temperatures. Consequently, the temperature range for which it is calculated must be specified. This is because physical properties of solutions are less affected by temperature changes than are biologically catalyzed reactions. Generally, most biological reactions within the temperature range of coral reefs have a Q 10 of about 2.5. A Q 10 of 2.5 means a change of 9.6% in the rate of the reaction per 1°C (or 1.8°F). In other words, if the animal is maintained at a temperature about 5°C (or 9°F) above or below its optimal temperature, its metabolic rate will be 48% higher or lower. As an exercise, the reader is encouraged to calculate what the metabolic rate of the organism might be at a temperature 10°C (18°F) below the optimum.

At 10°C below the optimal temperature, the metabolic rate would be reduced by about 96%, or put another way, it would only be 4% of normal. Under these sorts of conditions most animals die. In fact, most organisms will die if maintained for extended periods under conditions that constrain their metabolic rate to one half of normal. Even metabolic rate reductions to about 75% of optimal may cause significant problems or death (Withers, 1992). A reduction of this magnitude will be caused by keeping an animal with an optimum of about 82 ° F at a temperature of about 77 ° F.

The most rapid growth of most corals is generally around 27°C to 29°C (80.6°F to 84.2°F) (Barnes et al., 1995; Clausen and Roth, 1975; Weber and White 1976; Coles and Jokiel, 1977, 1978; Highsmith, 1979a, b; Highsmith, et al., 1983). Subtracting 10°C from this range gives a temperature range of 17°C to 19°C (62.6°F to 66.2°F). The lower temperature that is typically considered to be acceptable for coral reef formation is 20°C or 68°F, which is close to the value that would be expected by using the Q 10 value. In essence, the Q 10 value may be used to approximate the lower limit of most coral reef distributions; however, in reality relatively few coral species persist at temperatures much below 24°C (75.2°F). Certainly, there are coral reefs found at these cooler temperatures, but they contain a much reduced array of cold tolerant (for a coral reef) animals compared to warmer reefs.

Interestingly, while the lower limit of most corals may be determined by examination of the Q 10 term, the converse is not true. Natural selection seems to have shaped corals, and many other coral reef organisms, to have an optimal temperature near the upper end of their normal acceptable range. This makes biological sense in that the evolutionary process works on the production of offspring. As far as the evolutionary process is concerned, the organism that produces the most viable descendents wins the evolutionary lottery. At the higher metabolic rates generated under higher temperatures, more eggs and sperm can be produced and the more potential offspring can be generated. But these are organisms are on the edge, at temperatures only a few degrees above the optimal for most coral reef animals, enzymatic reactions begin to uncouple and the organisms start to show signs of severe distress. So, while one might expect from the Q 10 values that the upper limits for most coral reef animals would be in the range of 40°C (104°F), it appears that the natural upper limit for reef organisms appears to be prolonged exposure to temperatures above 33 ° C (92 ° F), and is naturally reached in some areas in the Persian Gulf, or in shallow water areas in atoll lagoons (Brandon 1973; Glynn and D'Croz, 1990; Fitt and Warner, 1995; Lesser, 1996).

Natural Coral Reef Temperature Conditions


In 1999, Kleypas, and her coworkers, published data on coral reef temperatures (Table 1) (Kleypas, et al, 1999). They examined and summarized published data taken from separate measurements on over 1000 different coral reefs. It is worth remembering that these data were gathered prior to the recent increase in temperatures attributable to global warming and probably reflect more-or-less “normal” conditions for the last couple of centuries. The data in the average column are probably the most pertinent. The average temperature calculated for all 1000 + coral reefs was 81.7°F. Over all reefs, the average lowest temperature observed was 76.4°F, and the average highest temperature was 86.4°F. One way that these data could be interpreted would be to say that for most corals and coral reef animals, the best conditions would be between 76°F and 86°F, with the average being about 82°F.

Table 1. Coral Reef Temperatures From Kleypas, et al., 1999. All Converted to Degrees Fahrenheit.

















Effects Caused By Variations From Optimal Conditions .

Some reef organisms, particularly fish and the structurally complex invertebrates such as mollusks and crustaceans, are often physiologically tolerant of a wide range of temperature and salinity. Nevertheless, if these animals are kept in an environment near the limits of their physiological range they are stressed and their survival is poor. There is a very simple reason for this poor survival. It is so simple that it is almost invariably overlooked by reef aquarists. That reason is that the amount of energy that any given animal can process is limited.

An organism may be thought of as a living machine. All of its moving parts are really the chemical processes occurring within it, and its speed of operation is its basal metabolic rate. The fuel is the food that it eats. The throttle on such machines is set externally by the temperature of the surrounding environment and the organism really can't vary it much. In the marine environment, only marine mammals, birds, and a few large fishes can significantly alter their internal environmental temperature away from that of their surroundings. For all other animals, when conditions start to shift much from the normal conditions, a lot of food energy must be maintaining its internal conditions. This results in less energy being available for other necessary needs, such as growth and other normal metabolic functions, to say nothing of finding yet more food and fighting infection.

When the external environmental conditions become severe, and severe may be defined as a temperature difference of only a couple of degrees Fahrenheit, there is simply not enough energy available for the organism to kept its internal environment stable and do all the other necessary things it must do to survive, and that organism dies. Consequently, physical factors generally put the absolute limits on the marine organism distributions. In marine systems, the basic physical parameters are those of temperature and salinity. Acceptable management of these factors is the first step in the successful maintenance of a mini-reef aquarium. Forcing animals to "live on the edge" of physiological disaster is doubtless the cause of many unnecessary deaths.

As the environmental temperature varies from the optimal, the organisms must spend more of their limited energy to compensate for the differences. In practical terms, this means that near the extremes of species' ranges, where the temperatures are different from the center of the distribution, if only by a few degrees, the organisms must spend more and more of their metabolic energy ameliorating, or altering, their internal environment to withstand the effects of the temperature extremes. As the species spreads further and further into the extreme areas, the individuals have relatively less and less energy to spend on other aspects of their lives, such as growth and reproduction. Finally at the edges of the temperature distributions, the organisms may survive, but they grow slowly and reproduce poorly, if at all.

Cold Temperatures Are A Problem

Although aquarists are often concerned with the effects of high temperatures, the effects of low temperatures are equally deadly. A recent study shows how differences of only a couple of degrees Celsius determine the distribution of Montastrea annularis populations in the Gulf of Mexico and in the Caribbean Sea, proper ( Carricart-Ganivet, 2004 ). In this case, the no growth lower limit of zero calcification occurred at 23.7°C (74.7°F) in corals from the Gulf of Mexico and at 25.5°C (77.9°F) in corals from the Caribbean Sea. It is worth noting that prior to recent bleaching events that some of the richest coral reefs, often dominated by Montastrea annularis , in the Caribbean were found near Belize. In the mid-1970s, these areas' average monthly temperatures were generally above 29 ° C, (84.1 ° F) and the monthly maximum temperature may reach 33 ° C (91.4 ° F) (Highsmith, 1979a. b; Highsmith, et al., 1983). Montastrea annularis appears to have a center of radiation in the Belize area, as do most other Caribbean corals.

An area's average annual temperature does not tell the whole story of course, as there fluctuations around this average. These fluctuations may vary from month to month as illustrated in some data from Belize (Table 2). It is worth noting that some of the richest coral reefs in the Caribbean have been historically found near Belize, and in these areas average monthly temperatures are generally above 84.1 ° F (29 ° C), and the monthly maximum temperature may reach 91.4 ° F (33 ° C) (Highsmith, 1979). These are temperatures slightly cooler than the Indo-Pacific areas of highest coral diversity, but the Belize area is significantly further north.

Table 2. Surface Water Temperatures for Belize City, Belize, 1964-1971. Data from Highsmith, 1979a.





° F

° C

° F

° C





























































Coral Reef Organism Adaptive Radiation

In contrast to the lack of growth and reproduction at the edges of the distribution, in the center of the range there is often a net surplus of useable energy. Animals in these areas are not counteracting the problems of low or high temperatures and they can expend more energy in other biological processes such as competition, defense, and reproduction. As they can produce many more gametes than those in less benign environments, they are more likely to produce variations that are successful in occupying specific new microhabitats near the center of their range. Eventually a pattern develops within a group where more species are found in the area at center of the distributions where the physical conditions are best, and progressively fewer species found as the distance from the center increases. This is the pattern of adaptive radiation.

In the tropical Indo-Pacific, many animal groups are most diverse and abundant in the Malay Peninsula-Indonesia-New Guinea area. Here as well, the physical conditions are closest to being optimal for virtually all of these animals. Even for those species, such as the widespread coral species Pocillopora damicornis , that are able to tolerate the extreme conditions, the best conditions are those found in the center of the distributional pattern. The sheer numerical abundance of species that follow this pattern is reflected in the overall pattern of coral reefs and coral reef diversity throughout the region. The most diverse coral reefs are found in a band running from New Guinea and Northern Australia in the west to Palau in the Western Caroline Islands up through the Philippines and Indonesia in the east (Veron, 1986). In this area, prior to the recent period of global warming, the atoll water temperature averaged around 84 ° F and probably never got as low as 80 ° F.

Figure 3. Average annual sea surface temperature; 1981-1999. Contour lines are plotted in Celsius degrees, but there is a conversion chart to the right of the map. Note that the temperature of the richest coral reef areas is generally in excess of 27 ° C (80.6 ° F). Modified from NOAA/JPL satellite imagery available here .

Figure 4. Top. Average sea surface temperature in a normal, or non-el Niño, year prior to 1990 (modified from satellite imagery). The temperatures over 80.6 ° F (27 ° C) are shown in shades of red to yellow. Bottom. The number of coral genera found in the Indo-Pacific (from Veron, 1986). Note the close positive correlation between the sea surface temperature and the number of coral genera. Sea surface temperatures in the Indo-Pacific typically extend down to depths of about 165-330 feet (50-100m).

Salinity Conditions

The concentration of dissolved sodium and chloride ions, often referred to as salinity, is the major factor that determines the ionic concentration of sea water. Salinity has been measured for more than a century and its values typically reported as parts per thousand by weight (ppt). Normal sea water varies from about 2.6 ppt to over 40 ppt depending upon precipitation, runoff and evaporation. Most marine animals cannot survive over the complete salinity range, and, in fact, the range of acceptable salinities is really very small.

If you go to the oceanographic literature to examine salinities, you may find that it is expressed in a variety of ways, particularly in the recent literature. There are problems with the calculation and measurement of dissolved materials in sea water, primarily in that the chemical composition of sea water varies from place to place and under differing conditions of pressure and temperature. Consequently, there has been a movement by chemical oceanographers to define a measure of salinity in a manner that is less variable. Since about 1980, the salinity of seawater is frequently defined as a dimensionless unit, referred to as S, PS or PSS for various combinations of the words “Practical Salinity Scale.” Salinity is now defined as the ratio of the seawater's conductivity to that of a specified potassium chloride solution. Thus, in the recent oceanographic literature salinity may be expressed as S, PS, PSS, or, by traditionalists, as ppt (Pilson, 1998).

Salinity, at least as aquarists refer to it, may be measured by any number of devices. Some measuring instruments such as hydrometers are indirect. Hydrometers measure the specific gravity of the solution, not the salinity. If the solution has a composition that closely approximates the distribution of ions found in sea water, then the salinity may be calculated from the specific gravity. Unfortunately, as the temperature changes, so does the specific gravity of sea water and volume of the hydrometer. This means that either the hydrometer must be used at a specific calibrated temperature or tables must be used account for how their readings will vary. Additionally, the hydrometers available and commonly used within the aquarium hobby are, in some cases, poorly made. Electronic measuring devices may also be used to measure conductivity. A printed table may be used to convert those values to salinity. These devices require calibration and care in their use. Probably the cheapest, simplest, and most accurate devices to measure salinity are refractometers. Those commonly available through aquarium suppliers measure salinity directly. They also require occasional calibration, but this is easy to do.

Even though the concentrations of sodium and chloride constitute most of the dissolved material in sea water, other dissolved materials also contribute to the total sea water ionic concentration, which is referred to as the osmolarity of the solution. Many marine animals have an epidermis that is at least partially permeable to sea water and to some of the ions found dissolved it. These animals are often able to metabolically maintain or regulate the ionic balances inside their cells. However, such regulation takes energy, and specialized metabolic processes. Most animals are able to regulate either salinity or other ions only over a short range, and are referred to as "osmoconformers." Their total internal ionic concentrations are very close to those of the medium they are bathed in. If the concentration of dissolved material differs from their physiological optimum, they may suffer damaging effects. The further the conditions differ from their various optima, the more likely the organisms will suffer irreparable damage.

Animals such as corals, sea anemones, sea stars, and some worms, are osmoconformers and have very limited capabilities for internal regulation of balance of either sodium, chloride, as well as other ions. Even though they do not have much capability to alter their internal environment away from that of the surrounding medium, such osmoconforming animals will spend up to 80% of their metabolic energy maintaining internal cellular ionic balances. This relatively large amount of energy being spent to shuffle ions back and forth across cell boundaries under NORMAL conditions means that these animals simply do not have much latitude to adjust to variations of salinity in the water surrounding them.

The lower salinity limit that most reef animals can tolerate at for at least a few hours is about 30 ppt. This represents the salinity normally found in estuaries, or around river mouths or, periodically, in some lagoons after substantial rainfall. Coral reefs are generally located in areas that have salinities in the range of 35 ppt to 38 ppt. Most of our corals, and the associated fauna including fishes, will live best at those conditions (Weber and White 1976). Most organisms, even osmoconformers, can survive for brief periods in salinities well outside their normal range. But if maintained for longer period outside of that range they will be stressed and eventually will become so damaged that they will die even if returned to their normal salinity. Higher salinity is slightly more tolerable to these animals than is lower salinity, and adult animals are more able to withstand the extremes than are the juveniles or larvae.

Incidentally, the Red Sea is a noteworthy exception to the above generalization regarding salinity in reef situations. The southern Red Sea averages about 38-40ppt, the central Red Sea averages about 40-41 ppt, and the northern Red Sea has salinities up to 41-42 ppt (Kleypas, et al., 1999). These salinities approach the upper survivability limit of salinity which is about 42 ppt, which is reached in some hypersaline lagoons.

The bottom line for salinities is simple. There is simply no reason at all to maintain the salinities of our systems below normal reef conditions. All reef inhabitants will suffer damage from prolonged exposure to lowered salinities. Invertebrates kept at low salinities often die within a few days to a few months. Given that corals, sea anemones, sponges and some other invertebrates have no old age or senescence (or to put it another way, they are immortal), low salinities result in a quick death. Some mollusks, crustaceans, and most fish kept at low salinities die of kidney failure; it just takes them longer. A fish which dies in a couple of years in a hyposaline aquarium may have had the potential to live more than 20 years had the salinity been appropriate.

Aquarium Considerations

Many reef aquaria are set up and maintained in a manner that continually stresses the organisms in them. In general, these stresses are not enough to kill the animals outright, but often the environment is sufficiently unhealthy that the organisms are continually on the edge of disaster. This is probably the reason that many reef animals are considered to be delicate. Most animals, including reef organisms, if maintained with proper basic care and conditions are very resilient and actually are rather hard to kill. This is particularly true of sponges, sea anemones, corals, and most other invertebrates. Nonetheless these groups have the unjustified reputation of being hard to keep.

Unfortunately, it is the poor practices of aquarists that are to blame for the substantial mortality witnessed in many systems. For many years, research scientists have maintained and grown many of these so-called delicate organisms in aquaria, sometimes in flow-through systems, but much more often in closed systems similar or identical to those used by most hobbyists. These scientists are often quite successful at getting the animals to grown, spawn, and reproduce. Yet, in the reef aquarium community, those same animals have the reputation for being difficult to maintain. What is the reason for the difference between research and hobby situations that allows more success for the researcher?

The primary reason for the laboratory success is that researchers tend to set the conditions of their systems as near as possible to the physiological optima of the organisms they are raising. Having raised and kept invertebrates for over 20 years in research systems that were more-or-less typical, I can vouch for the fact that scientists are just as sloppy and lazy as everybody else. They want to spend their time doing just about anything except working to culture animals, so they often arrange their systems to minimize maintenance. The major basic rule of thumb in keeping animals easily is: "Find out what the animal's physiological optimum temperature and salinity ranges are, and adjust conditions to match those optima." While this rule should seem obvious, it is violated by many reef aquarists. Both the temperature and salinity of many reef aquaria are kept near or even somewhat below the lower normal survival limit of physiological tolerance for many of the common animals. This results in substantial and unnecessary mortality. In effect, these mini-reef systems keep the animals just healthy enough that they die slowly.

Some Final Thoughts

The array of new and different organisms becoming available for the mini-reef hobby is due to the biological mining of the areas near the centers of distribution. This is, after all, where the diversity of organisms is greatest. In most cases, we do not know the specific physiological tolerances of these animals. Successful conditions for maintenance, however, can be determined by finding the conditions at the center of the species' distribution. Additionally, there is another rule of thumb that can be applied here. Fresh water is less dense than sea water, and as water stratifies by density, rainfall and diluted sea water tend to float on sea water, and with relatively little mixing at the boundary. Consequently, reef animals from shallower areas (less than 33 ft (10m)) have to be tolerant of lower salinities and can withstand them much better than those from deeper waters. Unfortunately, many common corals or coral reef animals offered in the hobby are now being collected from depths in excess of 100 ft (30 m) and these animals are far less tolerant of inappropriate salinities.

Figure 5. A storm in Chuuk (Truk) Lagoon, September, 1984. Many coral reef areas receive more than 2.5 m (100 inches) of rainfall annually. This means surface waters, down to 10 m (33 ft) or more often have significant and fluctuations in salinity. Most shallow water coral reef organisms are tolerant of transitory and minor changes in salinity.

We often try to maintain a constant environment in mini-reef systems and trust that such an environment will provide the appropriate conditions for organism survival and growth. Constancy of conditions, however, is not particularly important if those constant conditions are wrong. Additionally, fluctuations in the reef system environment are of no concern as long as the fluctuations are not so extreme as to exceed the animals' tolerances. Temperature in lagoonal environments often varies as much as ± 18 ° F (10 ° C) per day around an average value. That average value, however, is often close to the physiological optimum of the species present. While hobbyists should try to maintain the average conditions in their captive environments near the physiological optimum for the organisms involved, fluctuations in temperature and salinity will not cause problems as long as they are within the tolerances of the species involved.

Maintenance of the reef system at optimal conditions is not without problems. Invertebrates maintained near the lower limits of their physiological ranges metabolize and live very slowly compared to normal. This can have its advantages; a dying animal will look good for several weeks or months, and still be effectively dead. It is metabolizing very slowly and, in effect, is almost in a state of suspended animation. Corals, particularly, under these conditions seldom need to feed, and may not even have enough energy to feed. They subsist on their stored energy reserves and byproducts of their endosymbiotic algae, which under normal situations provide nowhere near enough nutrition for adequate growth. Additionally at these low temperatures, the zooxanthellae are also producing significantly less nutrition than they would be doing at higher temperatures (Coles and Jokiel. 1977; Goiran, et al., 1996; Leletkin, et al., 1996;). Coral growth is effectively minimal, and will be hard to detect (Goreau and Goreau, 1959; Goreau, 1961; Goreau, 1977ab; Houck et al., 1977; Highsmith 1979). Additionally, the animals may repair injuries too slowly to prevent infection. After they use the last of their stored reserves, they will die slowly. Of course, they will still be around to enjoy for a period of a few weeks.

Animals maintained near their physiological optimum will need to be fed regularly and adequately for growth. As an example, I maintained a small Heliofungia for an 11 month period during which time it almost tripled in diameter. It was fed the equivalent of 1 to 2 feeder goldfish per day. It eventually succumbed to damage from a predator inadvertently placed in my tank, but was growing and thriving prior to that time.

At normal (for the organism, not the aquarist) temperatures and light conditions, to assume that corals and other animals can get full nutrition from their endosymbionts is to insure that they will not survive (Sorokin, 1990a,b; 1991; For an excellent in-depth and fully referenced treatment of foods and feeding see: Borneman, 2002 -2003 = 1 , 2 , 3 , 4 , 5 , 6 , 7 ). They will need to be fed or the light intensity increased well beyond the normal range for the organisms. Unfortunately, few of these animals are generalist feeders and their survival will depend upon finding an adequate and appropriate diet. Other reef inhabitants will need to be fed more frequently as well. This provides a continuing challenge, but the variety of foods on the market today generally makes finding an acceptable food not too difficult.

Finally, there is the very real problem of the mixed fauna and flora found in many of our systems. Aquarists tend to mix animals from different geographical areas with joyous abandon. This results in a tank full of animals with a variety of ranges of tolerance depending on whether the animal was from the very warm waters of Indonesia or the cool subtropical waters of the northern Gulf of Mexico. A modification an old saying would apply here. As a "Jack of all trades is a master of none," generalized conditions are not good for any tank inhabitant. Maintaining a tank in upper 70 degree F range (24-26 degrees C), will stress any reef inhabitants from the central Indo-Pacific as it is too cold, and as this is near the upper limits for subtropical organisms it will stress them as well. It would be better for all concerned, if aquarists concentrated their efforts in maintaining separate systems for organisms from geographically disparate areas.

To examine the sea surface temperatures (and remember, for the tropics, these temperatures extend downward in the water up to 165 ft (50 m) or more), follow this link . There are several menus allowing the examination of average temperatures back to 1981, as well as to specify and examine specific areas in high resolution and detail, temperatures from about 1984 to the present. Similar data for salinity will be found by following this link , and going to the appropriate submenu.


References Cited:

Barnes, D. J., B. B. Taylor, and J. M. Lough. 1995: On the inclusion of trace materials into massive coral skeletons: Part II: Distortions in skeletal records of annual climate cycles due to growth processes. Journal of Experimental Marine Biology and Ecology. 194:251-275.

Borneman, E. H. 2002. Reef Food. Reefkeeping. July, 2002. www.reefkeeping.com

Borneman, E. H. 2002. From The Food of Reefs To The Food Of Corals, Reefkeeping. August, 2002. www.reefkeeping.com

Borneman, E. H. 2002. The Food of Reefs, Part. 3. Phytoplankton, Reefkeeping. October, 2002. www.reefkeeping.com

Borneman, E. H. 2002. The Food of Reefs, Part. 4. Zooplankton, Reefkeeping. December, 2002. www.reefkeeping.com

Borneman, E. H. 2003. The Food of Reefs, Part. 5. Bacteria, Reefkeeping. January, 2003. www.reefkeeping.com

Borneman, E. H. 2003. The Food of Reefs, Part. 6. Particulate Organic Matter, Reefkeeping. March, 2003. www.reefkeeping.com

Borneman, E. H. 2003. The Food of Reefs, Part. 7. Dissolved Nutrients, Reefkeeping. April, 2003. www.reefkeeping.com

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Ron Shimek