Leather corals are a popular soft coral species, known for their tough, leather-like texture, overall hardiness, and ease of care. While they can not be as colorful as other corals, they are still very attractive and have very interesting personalities.
A leather coral’s behavior can be alarming for newbie hobbyists, because they occasionally retract their polyps at night, and are known to develop a waxy mucus coating over their tissues, which they remove in a process called ‘shedding’.
Both these behaviors are normal, despite them looking sick or even dying to the uninitiated reefer. However, their quirks shouldn’t cause you concern if you have a well-maintained aquarium.
Do Leather Corals Close Up At Night?
Most leather corals will close during the night, unless you provide them with nutrition, such as directly feeding them. In the wild, leather corals feed during the night because of the availability of their food source; the highest density of zooplankton and phytoplankton is during the night.
However, in captivity, corals get most of their nutrition (around 80%) from the zooxanthellae that live inside your coral’s tissues. This makes leather corals (and most corals in fact) photosynthetic, therefore opening during the night when aquarium lights are switched off would be pointless.
Why Do Leather Corals Close Up?
If you are worried about your leather coral closing up, first, rule out water quality issues like spikes in ammonia, nitrate, and phosphate. When these three water parameters skyrocket, they can be very toxic to corals and fish.
Once you have ruled out those three water conditions, you can start to dive deeper into why your leather coral has closed up.
Unstable Water Conditions
In addition to the three main water chemistry issues (ammonia, nitrate, and phosphate), fluctuations with other parameters may also be the issue.
Even though leather corals are known to adapt to a broad range of aquarium conditions, they do not cope well with rapid changes.
It is vital to keep your aquarium water’s temperature, pH, calcium, alkalinity, and other water parameters stable. To maintain the following parameters, remember to frequently test the water and make adjustments as needed – a dosing pump is a great way to maintain stability!
Ideal water parameters for leather corals:
- Temperature: 76-82°F
- pH: 8.0-8.4
- Salinity: 1.025
- Calcium: 350-450 PPM
- Magnesium: 1250-1350 PPM
- Nitrate: <10 PPM
- Phosphate: <0.10 PPM
Photo Shock From Lighting
Your leather coral requires lighting for both nutrition and growth, but if you give it too much, then it is likely to close up from photo shock.
A sudden increase in your aquarium’s lighting intensity or upgrading your lamps to a higher-output lighting fixture can be very stressful for your leather coral. An increase in stress may cause your leather coral to contract its polyps until the lighting conditions are back to ‘normal’.
Normal for your leather coral is low to moderate lighting with a PAR of 50-150, however, some leather corals can tolerate levels up to 250, so always check the lighting requirements for your specific leather coral. If you are unsure, speak to your local fish store (LFS).
If you are upgrading your lighting fixture, you should:
- Place the lighting fixture higher than normal, lowering it over a few days to allow your leather coral to acclimate to the new bulbs.
- Reduce the photoperiod before slowly increasing it to your aquarium’s normal cycle.
Insufficient Water Flow
Because of where your leather coral originates from, it requires a moderate water flow which is non-linear. Turbulent water flow helps them naturally shed, and it also prevents the build-up of detritus on their precious polyps.
If your leather coral is placed in an area where there is not enough flow (known as dead zones), or you expose your leather to direct flow, they will close up to protect themselves from waste smothering their polyps and risk of tearing their tissues.
Poor Supplementation Maintenance
Now, do not get me wrong, supplementation does promote coral health, but often hobbyists, particularly beginner reefers, get a little ‘over-excited’ and before you know it, your aquarium water quality is all over the place.
If your leather coral has closed up, you may need to remove non-essential supplements one by one, to determine which one(s) are causing the issue. Once you have gone through the process of elimination, and have resolved the issue, remember to always follow the instructions on the manufacturer’s directions or speak to your LFS about how much they dose their aquariums with.
Sometimes your leather coral will also close because they are being disturbed by other organisms in your aquarium. As your leather coral has relatively tough tissues, invertebrates on the move will happily climb over them and fish may even try to take a nip at their polyps. If this frequently happens, your leather coral will get rather irritated, and they may temporarily close or remain contracted.
We can’t just blame the mobile organisms in your aquarium, as other corals may also be the issue. Neighboring corals that start attacking your leather coral’s personal space may start chemical warfare, stinging your leather coral in the process.
Leather corals release toxins into the water if threatened so always allow adequate space between competing corals, try adding some chemical filtration systems such as activated carbon, and remember to keep on top of those partial water changes. These steps will be your best allies in a coral battle!
Do Leather Corals Shrink At Night?
When leather corals close at night, you may also notice them shrinking. This is normal behavior for leathers, and do not worry, if they are happy and healthy, they will expand again once the lights come on.
As leather corals get most of their nutrition from zooxanthellae, opening during the night when aquarium lights are switched off would be pointless.
Leather corals will also close if the water chemistry, lighting, and water flow are not to their liking. In addition to a poorly-maintained aquarium, pesky neighbors can also irritate your leather coral, making them remain contracted.
If you wish to encourage your leather coral to open during the night, you can target feed them and add moon-lighting, but closing at night is no cause for concern, as corals are nocturnal organisms in aquariums.