Temperate and Coldwater Biotopes

Most of the earth’s reefs are centered in the tropics, a narrow band on either side of the equator. Conditions in this band are relatively constant: long days filled with sun and predictably warm water temperatures have led corals and their relatives to evolve into light worshipers. But the further north or south of the equator you get, the more the oceans change. Days become shorter, water temperatures drop, and water clarity decreases. Benthic animals along temperate shorelines evolved to meet their needs without the sun, mainly by capturing foods that float by.

A temperate seahorse hitching to Zostera marina, a seagrass.

This difference in behavior is the main factor separating tropical biotopes from temperate biotopes. But even though their setup, feeding and maintenance requirements differ, both still rely on the Elements of Reefing.

Water

Almost all of the water parameters of temperate tanks are the same as for tropical tanks. The main thing that sets temperate tanks apart is the water temperature. The temperature range in the wild can be astounding – from close to freezing at areas of arctic upwelling, to isolated pools approaching tropical temperatures while waiting for the tides to return. The average temperature along most temperate shorelines is 50–60°F. Shooting for a temperature in this range is ideal; which end of the range is right for you depends on livestock, which we’ll discuss later.

In order to cool the water to the desired temperature, you’ll need (appropriately) a chiller. The name may be a misnomer however. A chiller does not create cold, but actually removes heat. The ability of a chiller to remove heat is measured in BTUs (British Thermal Units). One BTU will raise one pound of water (approximately one pint) 1°F. A unit with a higher BTU is more efficient and will remove heat faster than one with a lower BTU. A chiller operates similar to a refrigerator or air conditioner. The refrigerant gas picks up heat from the aquarium water and then delivers it to the radiator as the gas pressure is dropped. A fan then dispels heat from the radiator.

In order to choose a chiller, you will first need to calculate the amount of “pull-down” you will need. To do this, subtract the temperature at which you want your aquarium to be from the maximum temperature you think will be produced in the aquarium. Here is an example on how to determine pull-down:

So, let’s say you have a 20g tank that normally sits at 75°F. For your temperate tank you need the temperature to be at 55°F:

Now that you know you have a required pull-down of 20°F, you can work on finding the correct chiller size. Remember earlier when I mentioned that chillers were rated in BTUs? Well, that rating will help determine which chiller you need. One BTU will raise the temperature of a pound of water by one degree. A gallon of salt water weighs roughly 8.5lbs., so for our example, 20g of salt water weighs in at 170lbs. Since you need to pull the water temperature down by 20°F:

There you have it, you now know that you need a chiller rated at least 3400BTUs to get your tank to the required temperature and keep it there. Now, you will most likely have to settle for a chiller with a BTU rating slightly above or below your measurement. If that’s the case, always go for the more powerful unit. The less the chiller has to work, the less electricity it will consume, and the less often you will hear it running.

Since water temperature is so critical to the health and success of a temperate reef tank, this is an area in which you should not skimp. A quality chiller is necessary to bring the temperature down and keep it there. Chillers are generally expensive, but since other costs associated with temperate tanks are much lower than their tropical counterparts, it all evens out.

Filtration

In tropical tanks, the majority of the filtration duties generally fall on live rock and on water changes, with supplemental filtration systems such as protein skimmers and refugiums added as needed. A temperate system has to be approached a little differently, however.

The rock found in temperate zones is smooth and incredibly dense, like large pebbles or river stones. Unlike tropical rock with its porous surface, temperate rock has no nooks and crevices in which beneficial bacteria can reside. Add to that with the slower metabolic processes caused by lower temperatures and the heavy feedings that are required with the largely non-photosynthetic livestock, and you’re left with a biological filtration system that just can’t cope.

For this reason, temperate tanks must rely heavily on mechanical filtration to maintain water quality. No matter how small the system, a quality protein skimmer is a must for a heavily stocked and heavily fed tank. While most temperate livestock is incredibly hardy and can tolerate excess nutrients in the water column, without strong filtration nuisance algaes will begin to capitalize on the higher nitrate and phosphate levels. A well-skimmed tank is a happy tank.

Flow

In the wild, anemones and other intertidal temperate species are subjected to the constant pounding of waves and tidal surges. While they are more than capable of withstanding the same unrelenting flow in a home aquarium, they will not open to their fullest. Random and chaotic flow is still important in a temperate system, but a medium flow level suitable for tropical soft corals and LPS is about what should be aimed for. With this medium flow level, anemones will expand and become more full.

Light

There are two approaches to take when lighting a temperate aquarium. If the system is just to house corals, most anemones, fish and other non-photosynthetic livestock, then simple low-wattage lighting is sufficient, say a single PC bulb.

If, however, the system will contain macro algae,  Anthopleura sp. anemones and other photosynthetic livestock, then more traditional reef-type lighting is appropriate. The sky is the limit here depending on your preferences, although high levels of light (such as from metal halide or T5HO fixtures) are generally unnecessary.

Livestock

Corynactus californica.

Corals – Temperate corals are not only hard to find, but can be very challenging to keep alive. Be aware that by having these on your wish list you’re committing yourself to a high current environment and to providing an ongoing supply of zooplankton. One notable exception to this is the so-called strawberry anemone, Corynactus californica. This corallimorph is beautiful, relatively hardy and has been known to reproduce in aquaria.

Anemones — You should avoid getting “lots of anemones”. Generally speaking, anemones get poor grades in ‘gets along well with others’ and, depending on species, may employ a number of means to discourage competition. In some cases anemones sting each other as a way to prevent encroachment. That’s probably no big deal so long as you keep them sufficiently separated and take advantage of their individual lifestyles to avoid having two species migrating into each other. I’ve personally witnessed that various Urticina sp seem to go into decline if put into a crowded situation, this in spite of the fact that the facility uses a flow through system that changes the water a the rate of several hundred percent per day.

Anthopleura elegantissima in the shallows.

Your best bet with anemones, and other cnidarians as well, is to start small and add animals very slowly. Pick one or two species and resist the urge to expand until you’re sure that they are thriving. Keep in mind that many anemones are incredibly long lived; Urticina sp are thought to live for 500 years or more, and Anthopleura elegantissima is essentially immortal!

Macroalgae — The main consideration here is probably one of scale and that the species of macro which will stay small enough for a home aquarium are generally found in surging intertidal areas. Keep these requirements in mind when choosing from available species.

Fish — Temperate fish occasionally come into the trade unawares – Catalina gobies (Lathrypnus dalii) are one notorious example. Australian boxfish are also occasionally available, but are costly, sensitive and large. Another option would be to catch your own fish, if you are close to a temperate shore and your local laws allow it. I highly recommend adding FishBase.org to your favorites/bookmarks. Once you get used to it, FishBase can give you all sorts of information about a given species. Another good resource is the book Coastal Fishes of the Pacific Northwest by Andy Lamb & Phil Edgell, if you can find it.

Nudibranchs — Most people recommend against nudibranchs for several reasons. First, they tend to have very specialized diets and if you can’t supply exactly the right thing they will starve. This is complicated by the fact that in many cases “exactly the right thing” is either unknown or is misreported. For example, if you look at most books on Pacific Northwest marine life you’ll be told that the White Lined Nudibranch (Dirona albolineata) eats small snails in addition to other things. Yet according to Dave Behrens, D. alolineata exclusively eats Bryozoans. Second, they’re pretty short lived even if you can feed them correctly; most nudibranchs seem to have a life expectancy of about a year. Finally, visibility can be a problem. For all their beauty most nudibranchs are quite cryptic on their preferred prey. It’s entirely possible that the only sign that you have a nudibranch will be that its food item is being munched.

There are a couple of exceptions though. The Opalescent nudibranch (Hermissenda crassicornis) has quite a wide diet including hydroids, anemones, and even carrion (if the books are to be believed). Another possibility would be to consider the sacoglossan sea slugs Placida dendritica or Elysia hedgpethi. Strictly speaking, these aren’t nudibranchs but herbivorous slugs that specialize on Codium fragile and Bryopsis corticulans algae. Elysia is especially interesting since some of the chloroplasts that it eats continue to photosynthesize and provide the animal with nutrition. These are sometimes referred to as “solar powered sea slugs”.

Sponges — Sometimes sponges do well in aquaria but, since they’re filter feeders on very small phytoplankton and bacteria, I wouldn’t try collecting any until your tank has been operating for quite a while and the sand bed is well established. When you reach that point you’ll need to be careful in your collecting technique. Many species of sponge are extremely sensitive to being exposed to air; even a brief exposure can start a chain reaction that is ultimately fatal to the entire colony. An exception to this is the Purple Encrusting Sponge (Haliclona permollis) which is intertidal and seems able to handle exposure with impunity. If your aquarium turns out to be sponge friendly there’s a pretty good chance that you’ll find out by seeing sponges ‘magically’ appear in the tank — I suspect that it’s virtually impossible to collect other stuff without also collecting some sponge or sponge larvae.

Tropical reefkeepers generally recommend that an aquarium be developed slowly. For a coldwater reef you should probably go even more slowly just because the lower temps tend to make most other processes slower. Besides, by going slowly you can wait to find the best possible specimen of a given animal.

The Tank

Lastly, we come to the tank itself. In humid environments, standard glass tanks will tend to ‘sweat’ and form condensation when holding water at lower temperatures. The simplest solution to avoid condensation is to use an acrylic tank, the thicker the better. Acrylic insulates better than glass does, which helps to cut back on condensation. The extra insulation also means your chiller doesn’t have to work quite as hard to keep the water temperature stable.