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Related Articles: True or Stony Corals, Order Scleractinia, Growing Reef Corals


Stress in LPS (Large Polyp Stony) Corals
Definition, Recognition & Avoidance


By Bob Fenner  


Querying most folks, aquarists and not, finds that they consider stress something to be avoided. Know thn that some stress is good… without it our aquarium reefs will suffer akin to the “Boy in a bubble”; not developing immunity from sudden to prolonged changes in the environment; a large danger. Still, too much stress is definitely to be avoided. Too much, too soon can result in loss of Zooxanthellae; bleaching. It can lead to tissue loss and mortality outright. Here we’ll delve into the nature of stress in Large Polyp Stony Scleractinians, what you can and should to avoid it, and what ameliorative steps one might take if their corals show signs of excessive stress.


To Start; Some Definitions: Stress and LPS

            Please forgive my past background as a High School science instructor here; but defining terms up front helps to clarify a subject, assure we’re all “talking” about the same things.

First off the term “stress”; this is any phenomenon that challenges or induces a negative reaction… in our case from a living organism. As with considerations of kinds of aquarium filtration; it’s easy to discuss stress divided into inputs that are physical, chemical and biological in origin. We’ll do so in a bit.

Secondly the label of “LPS”, Large Polyp Stony corals: This convenient term has become established to include member genera, species of Scleractinians that are comprised of large, fleshy polyps. Folks in the know realize that this is an artificial assemblage; that several families of true stony corals possess both LPS and SPS species. Daniel Knop sets the difference in size here at smaller than 4 cm. or larger than 4 cm. (about an inch and a half) to discern large as opposed to small polyp size species.

Some LPS families are unmistakable in their being large polyped; like this Trachyphyllia geoffroyi (family Trachyphylliidae)


Other families possess both SPS and LPS genera, species. Here is Porites porites on the left, an SPS found in the Atlantic; and below right a Flower Pot Coral, genus Goniopora of the Indo-Pacific ; both of the family Poritidae.




Be this as it may, this distinction of large versus small/er polyp size is of use to us as aquarists. In captivity, by and large SPS are more “touchy”; requiring cleaner (less nutrient concentrations…) settings; more light by and large, and greater attention to meeting nutritional needs than LPS. This does strike me as strange in some ways, as the principal Families of hermatypic (reef building) corals, the Acroporidae, Poritidae and Pocilloporidae comprise the corals most often exposed at extreme low tides, experience the greatest wave and current exposure, and are entirely Small Polyp Stony species.


Types of Stress: MANY

Too much or little light, excess and a paucity of nutrients, allelopathy/pests/predation and much more are common stressors.

Physical Stressors: Include too hot or cold water, or just too much change in temperature in too short a period of time. This is the likely single largest factor in natural coral bleaching; resulting in the expelling, loss of Dinoflagellate species labeled Zooxanthellae, living in tissues of many Cnidarians and other sea life.

Aquarists who are dive travelers realize that our tanks are artificial replacements in many ways; one big one: How they’re illuminated. Yes; it is bright near the equator; even underwater… at “high” noon. But the intensity of light is never constant and quickly drops off with the angle of the sun to the water’s surface, the depth of water, waves and more. Suffice it to state that it is rare indeed that the corals that are wild collected or aquacultured in situ in the ocean receive the amount of light energy we provide. Newly acquired specimens/colonies need to be gradually photo-adapted to new settings, placed in shadier settings, deeper in the water, or the light attenuated, possibly shaded itself to prevent over-driving photosynthesis. Here a new Acanthastrea is set on the bottom off to the side of overhead lighting.


Sudden or extended overheating may result in bleaching; the expulsion of endosymbiotic algae. Below, a Galaxea fascicularis was overheated from a combination of low tide and sun exposure in the upper Gulf of Aqaba, Red Sea. IF the skeleton remains intact and doesn’t become overgrown with algae, there is hope that tissue growth may return to the lost coralites.


Chemical Stressors:

There are as many types of chemical stressors as there are chemicals that occur in marine environments. Too little or too much of some is real trouble. In particular the mentality of many aquarists that “cleanliness is sterility”; utilizing high tech. equipment and chemical filtrants, along with scant feeding to produce a nutrient-limited system. Know then that all photosynthetic life requires the essential elements N, P, K… Unless you’re supplying Nitrogen, Phosphate and Potassium via foods; you are starving your corals if there is no measurable amount of these in your water. Too much is of course as bad as too little; you want some percent of Nitrate, and a few hundredths of a percent of soluble Phosphate. Below is an example of a coral lost and being overgrown by algae from eutrophication (too much nutrient) in Palau Redang, Malaysia.


Biological Stressors: Abundant and diverse are life forms that can challenge LPS; most notably other Cnidarian life can pose serious risk in the way of allelopathogenic attack. Allelopathogens are chemicals released by one species that mal-affect others, not necessarily immediately next to them. Unfortunately most aquarium systems are smallish in volume and overcrowded. Should “something” trigger a toxic species (of which there are MANY) they can produce and excrete undesirable compounds into the water that impugn susceptible species in the system. This is a very common source of stress and loss in reef aquariums.

Many other ways that Cnidarians contest with each other exist. There is over-shading for instance where one species grows out blocking light and possibly current from a colony below. Here in Bonaire a sea fan (Gorgonia ventalina) blocks light and current from the stony corals around its base.


Many folks misconstrue the world’s reefs to be idyllic, peaceful places where life is somehow living in co-dominant co-existence. This is not so; reef areas are battle grounds where life competes for space, food, reproduction… Below are two Montipora spp. fighting across a demilitarized zone for turf. Stressful? You bet.


Stinging, via mesenterial filaments and more is a type of “digestive dominance” where one or both parties lose. Providing plenty of space twixt colonies is important with very stinging species like Galaxeas (family Oculinidae), Euphylliids and Caryophylliids. A good foot (30 cm.) is not too much gap to provide. Below; a scrunched down stung Catalaphyllia.

Sudden to permanent polyp withdrawal from a living skeleton is cause of dire concern. Some agent is assuredly at work here; stinging perhaps crawling or worse, sampling the living tissue as food. Be alert and observant, consider moving the impacted specimen, possibly to another system or lighted refugium.
Below, a mal-affected Goniopora and a Euphyllia with tissue-removed skeletal area.


Indications of Coral Stress:

The easiest sign to spot early on is that your corals are simply not opening when they should. Most species extend their polyps by night in the wild… for feeding on nocturnal plankton and avoiding predation by day. Many do become reverse adapted due to being fed during lights on hours in captivity. Below, a fully extended Acanthophyllia in Raja Ampat, Indonesia.

Losers in allelopathogenic battles should be removed to another system if possible as soon as practical. Supplying them with a trebled dose of iodide-ate, a slightly lowered specific gravity (a thousandth or so) and adding a simple/hexose sugar at a level teaspoon per ten gallons may enable to speed recovery. The main, display system may benefit from  massive water change as well as application of granulated activated carbon and Polyfilter or equivalent in the filter, circulation path.


Stress Avoidance:

            The best way to combat the ill-effects of stressing your corals is to avoid pushing their buttons period. Stocking with hardy LPS species is a good idea, especially for beginners; initial isolation/quarantine to assure health, proper acclimation, introduction of new specimens to your established system and careful placement to avoid upsetting potentially unfriendly competitors.

            I should make a comment concerning only adding LPS, actually any corals to a just set-up system. Don’t do this. These animals require thoroughly established circumstances. Wait a good few months into a just new aquarium to stock your corals; better to cure your live rock in place, start your fish and other hardy invertebrate stocking ahead of introducing large polyp stony corals.

Some of the easier LPS Corals to keep.



Caulastrea species; Candy Cane corals.

Usually peaceful toward other Cnidarians; undemanding in terms of water flow and moderate lighting; easily placed at all levels in the aquarium.  Here’s a small C. furcata colony in Raja Ampat, Indo.




Cynarina species; Button Corals. These uber-fleshy polyps are amongst the safest LPS to stock; getting along with most all fishes and non-fish livestock. Moderate lighting and reduced current suits Cynarina well. Here’s a C. lacrymalis in S. Sulawesi, Indo.




Favites species; Pineapple corals. Aggressive species that need to be placed apart of other corals. Appreciate moderate light intensity and medium water flow. Several color varieties and species are offered from time to time in the trade. Here’s a F. halicora in Fiji.



Lobophyllia species; another group called Brain Corals. These corals can be aggressive toward other Stinging-Celled species, so you’ll want to allow several centimeters of space around their colonies. Lobo’s get along with moderate current and a range of light intensity. There are many color varieties to choose from; these L. hemprichii in Bali, Indo.



Nemenzophyllia turbida; Fox Coral. A peaceful species that can be placed anywhere in the aquarium; even on the substrate. Does fine with moderate lighting and current. This one in N. Sulawesi, Indo.



Plerogyra species; Bubble Coral. A group of species that are aggressive with other corals; needs a good 15 cm. (six inches) of no-man’s land about it to disallow it to reach out and touch someone with its stinging mesenterial filaments. Moderate light and current will do for Plerogyras. Here’s a typical colony of P. sinuosa off of Queensland, Australia.



Trachyphyllia geoffroyi; Brain Coral (one of a few species with this common name. A compact species that may be aggressive toward other corals (needs to have several inches empty space about it); placed on the bottom is best, amongst lower current and light intensity. This specimen in an aquarium in Sacramento, CA.




Turbinaria species; Pagoda et al. corals. A peaceful genera of Dendrophyllids; best kept on the bottom in medium current and subdued lighting. This small T. peltata in an aquarium.


Do know that with proper acclimation, introduction and growing together, many would-be incompatible corals can be grown together. The practice of isolation, quarantine of new specimens, the gradual mixing of water between the systems to introduce contenders, placement to allow for growth; and the all important element of patience is rewarded by all getting along; as these two Euphyllias here in captivity.


General Treatment for Coral Stress:

            It is a matter of course that avoiding stress is better than treating for its mal-affects. This involves providing optimized, stable conditions: Proper water quality including the usual values, range for pH, alkalinity and biominerals of use; circulation, lighting regimen, nutrition…

            Immediate response to apparent stressing is identification of the stressor/s and their alleviation. Really; should the temperature be too high, turn it down; the specific gravity too low, raise it. If nothing is apparently awry, when, where in doubt, execute a water change of good percentage (25 or so); add a few times dose of iodide-ate and STAY OBSERVANT. Addition of granulated activated carbon, PolyFilter or equivalent in the water, filter flow path may be warranted.

Examples of overt stress in corals: Tissue loss; along with bleaching and not opening polyps are first observable evidence of stress. Below a Cynarina lacrymalis is showing its septal teeth as it has withdrawn and lost flesh over the calcareous skeleton. Heron Island, Australia. Compare this with a full-fleshed robust specimen in the Red Sea.



Bibliography, Further Reading:

Blue Zoo Aquatics, 2016. LPS & SPS; Less than ideal terms.


Borneman, Eric. 2002, The Coral Whisperer: Bleaching and Tissue Loss in Corals - What's the Difference?



National Ocean Service (NOAA), 2005. What is Coral Bleaching? http://oceanservice.noaa.gov/facts/coral_bleach.html

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