Can Corals Be Exposed To Air? in Reef Tanks or in Nature

This is an article about how much and under what conditions corals in a reef tank can be exposed to air. Which species will survive exposure, and which marine types should not be exposed at all.

Most corals can be exposed to air without problems. Reefs occasionally peek out of the water at low tide and survive a few hours. They secrete a protective mucus that prevents drying out. It’s better not to unnecessarily stress the coral though. Try not to exceed 5 to 7 minutes time limit.

The duration of a harmless exposure to air is directly related to the amount of mucus coral produces. But that’s not the only factor… Keep reading to find out what other aspects my biologist friend named.

Difference in Air Exposure Depending on Reef Tank Species

Alcyonacea, or soft corals. Structure and habitat features make this species unfriendly to external stimulation. A typical air-timer is about 10 minutes with carnation coral as a bright example. There are two main reasons:

1. Instead of the skeleton, they are supported by wood-like protective elements and fleshy layers full of fluids.
2. With more nutrients and less sunlight in the middle part of the reef, their secretion and photosynthesis functions are less developed. 

Although there are resistant species like finger leather corals. The surface of polyps is almost always sticky because they release a lot of protective mucus. So they can be exposed to air for 2-3 hours without problems.

This is important information to understand if you’re for example going to propagate your corals through fragging. I’ve written an in-depth guide on how to propagate corals that you can read if you like.

Scleractinia, or stony corals. The group may be narrowed down to:

• LPS — large polyp stony. They are poorly adapted to the tidal impact, which means that LPS don’t deal with air exposure very well. As long as you keep the duration of exposure to air below 20 minutes, the LPS coral will be fine. This applies to the popular sun polyps. In general, this type reigns in the middle depths, close to the coast, but the tides are less likely to affect its life. In addition, they have a small skeleton and most of the hard-filled tissues growing on top. It takes a lot of fluids to keep in shape, so when it is not enough, LPS suffer more than other representatives. But there are exceptions. For example, some mushroom corals have a high mucus secretion capacity which helps to cope with air exposure longer. 

• SPS — small polyp has a more stony structure compared to LPS. This means that they have more solid tissues that are virtually independent of fluids. For SPS that live closer to shore, the optimum air impact time would be under 1 hour. Of course, they can withstand more, but that’s a risk you’re probably not willing to take. 

Vase corals live at the top of the reef to receive as much light as possible, so they are sometimes exposed to air. For deep-water species, the time they can withstand being exposed to air is slightly less: about 20 to 30 minutes. For example, acroporid coral from “20,000 Leagues Under the Sea”.

Coral Acclimatization Without the Air Exposure Risk

Your corals may be exposed to air during transportation, partial water changes, or cleaning. To protect your coral and other marine animals, you can follow these instructions::

1. Although it may be a hassle, dim the light in the room and turn it off completely in the aquarium. This way you eliminate unnecessary stress. Let those inside to accommodate.
2. Prepare a separate non-metallic container and fill it up with tap water. Not too cold or warm.
3. Place the transporting bag under the waterline and put the marines inside. Use separate bags for every creature as they may damage each other. For instance, some mushroom polyps act aggressively trying to latch the neighbor with poisonous tentacles. Seal the plastic and slowly pull it to the surface.
4. Let it float in the prepared container for 20 minutes (don’t open). This way you maintain inside-outside temperature balance and keep oxygen ration the same.
5. Use the scissors to cut the top of the polyethylene (which is near the сlip or knot). Roll up the edge 1-2 inches down for convenience. Now, make sure that bag’s contents don’t mix with the container immediately. You can put a plastic cup underneath the bag.
6. Add a third of a cup of container’s water to the inside of the bag every 5 minutes until the bag is full.
7. Drain half(into the sink) and repeat the previous step. 
8. Release the marines. Submerge sponges and gorgonians underwater.

For up to an hour periods it is sufficient to moisten the surface of the coral (make it damp, not wet) Also take care that the room is humid and the temperature is the same as in the tank.

Carry out scheduled activities. Periodically check the condition of the animal. The light should be kept dimmed for the entire process.

Eventually, repeat the reverse procedure. If you filled the glass with liquid from a container, scoop it from the tank when relocating marines back to home. 

The Possible Effects Of Air On The Rest Of Your Reef Tank 

To understand how to treat the rest of the inhabitants, let’s study their features.

Rocky intertidal organisms such as anemones, tunicates, barnacles have to withstand harsh nature-like conditions. In the process of evolution, they have developed a shell that increases resistance to drying. And the tissues are resistant to changes in humidity and salinity levels. They can withstand up to 6 hours out of the reservoir at 54 to 59 °F / 12 to 15 °C without problems. The only exception is the bryozoans family. Since they live in a colony, their viability in a dehydrated environment varies (1 to 24 hour period depending on species and colony size).

For deep-sea invertebrates and some filter-feeders leaving the aquatic environment will be unaccustomed. For example, tubeworms, which live in symbiosis with the millions of bacteria that feed them. The invertebrate is protected by a dense shell of chitin, which has some liquid in it to keep the bacteria from dehydrating for a couple of hours. Prolonging it will reduce the chances of survival.

Some species of gorgonians are able to withstand harsh environments (e.g. Eunicea flexuosa survives 8 hours in the tropics in the blazing sun and breeze). But for most representatives, a time limit of 5-10 minutes is recommended.

Sponges have no tissues or organs, instead, they consist of two layers and fluid full of bacteria between them. The inner layer is covered with tufts that allow a large volume of fluid to pass through the tissues. This way, the sponges get rid of toxins and receive nutrients. Now imagine that you take this finely tuned system out of the tank… Nourishment stops, toxins are deposited deep inside the invertebrate, and air penetrates into the smallest pores, reducing the total volume of internal cavities (meaning it can take in less fluid). It is categorically not recommended to remove the sponges from the reservoir when cleaning. As even a slight jolt disturbs the inner equilibrium.

Related Questions

1. How other parameters affect maximum air exposure time?

Polyps are incredibly sensitive to environmental changes. Factors that can increase a polyp’s ability to hold water: (it may be exposed to air longer)

1. Room about 75°F / 24°C.
2. Minimum of 5 watts per gallon of lightning.
3. Humidity up to 55% depending on the season. In summer up to 65%, in winter up to 45%

Normal level for salinity and acidity vary with specific samples. Specify that upon purchasing, or use search to find out.

2. What to do if the coral is affected by air for a long period?

Place them in a familiar environment and observe the organisms closely for the next 14 days. If specimens become stained or blackened, consider removing the infected tissue (not more than 70% of the volume). In other cases, watch out for clarity, salinity, temperature of the water, and lightning.

3. Do corals resist air better than sponges? 

Corals maintain integrity through intercellular interaction, while sponges maintain integrity through self-regulation within a single cell. External stress damages cell function, which is why sponges have a hard time with it, unlike corals. Healthy cells perform the functions of damaged ones, which increases the organism’s resistance.