Stimulating Acropora Polyp Extension

Introduction

The main problem faced by approximately 50% of Acropora enthusiasts is insufficient polyp extension. In their natural environment, Acropora polyps can reach incredible sizes - up to 1 centimeter in length, especially in Australian species. In aquariums, polyps typically have a length of about 3 mm, though at night they can grow up to 1 cm, particularly at the base of the coral and on the stem. These long polyps aren't coincidental - they serve an important function.

Function of Polyps

Acropora polyps perform a predatory function. They specialize in catching small food from the water, which they then consume through tiny mouth openings. Their structure differs from large LPS corals (such as Acanthophyllia), which have one large polyp with a large mouth opening capable of capturing and consuming significant pieces of food.

In some Acroporas, the polyps resemble small umbrellas with protruding predatory filaments. They have very small, practically microscopic mouth openings. Unlike Acanthophyllia, which can evert their mouths at night and attach large food (pieces of shrimp, squid, fish) to themselves, Acroporas cannot capture and consume large food.

Montipora corals, for example, only have small umbrella-shaped polyps without predatory filaments and cannot actively hunt prey. They feed exclusively on substances dissolved in water and microscopic particles.

Feeding Characteristics of Acroporas

Contrary to popular belief, Acroporas cannot consume powdered or other dry food that we spray on them. Multiple observations show that even if food remains on the coral after turning off the current, when it's turned back on, almost all of this food is blown away by the current.

Acroporas feed on:

• Substances dissolved in water, amino acids

• Microscopic particles, phosphates

• Bacteria

The shape of SPS corals has evolved to trap microplankton and bacteria in the recesses of the colony. They have branches, edges, and depressions in the middle, which promotes swirling and retention of food.

When we add food to the aquarium, Acroporas consume not the food itself, but the products of its processing that form in the water later. Today's feeding will only be consumed by corals several hours later, when it dissolves and transitions to another form.

Nocturnal Coral Behavior

At night, Acropora polyps extend further due to the activation of their feeding. During the night on the reef, there is active movement of organisms, various substances are released, and corals try to catch more nutrients. In the hollows between coral polyps, night microplankton gets trapped as in a snare.

Observations show that although polyps can trap food particles, they don't pull them inside as LPS corals do. They likely extract some nutrients from these particles through external digestion and absorption of decomposition products. Particle trapping may be a mechanism for obtaining minimal nutrients during the breakdown of these particles.

Main Factors for Polyp Stimulation

1. Proper Nutrition

Corals feed around the clock but require certain types of nutrients. In nature, they consume food more actively at night, but in an aquarium under the right conditions, polyps can be extended constantly.

The most effective approach is using specialized products such as "Acropower," which contains special amino acids.

The advantage of such a product is that it doesn't cause outbreaks of protozoans, algae, or cyanobacteria, as it represents a more "advanced" form of nutrients that corals can directly consume.

An alternative can be dosing organic additives such as Reef-Roids, which are converted by bacteria into a nutritional form over time. However, this can lead to an excess of organics and phosphate spikes, which is undesirable and will cause coral reactions such as polyp contraction and even death.

2. Creating a Light Bacterial Bloom

Acroporas feed on bacteria, which in turn consume nitrates and phosphates from the water. Bacteria saturate with nitrates and phosphates in a ratio of approximately 1 to 0.14 units.

To stimulate bacterial growth, you can use:

• Glycerin (maximum dosage approximately 3-4 ml per 1000 liters of water)

This method allows bypassing the decomposition phase of complex food and immediately creates a nutrient medium for bacteria. The optimal bacterial bloom should create a light whitish haze in the water, visible when looking across the entire aquarium from the side. If the haze becomes obvious, this may indicate an excess of bacteria that can significantly reduce nitrate and phosphate levels. Be careful with this method as a bacterial bloom can last several days and lead to serious consequences.

3. Maintaining Optimal Water Parameters

• Phosphates: 0.07-0.10 mg/l (up to 0.20 mg/l is acceptable)

• Nitrates: 5-10 mg/l

• Bright full-spectrum lighting (not just blue) with an intensity of 350-600 PAR

It's important to maintain stable levels of phosphates and nitrates. A sharp drop in phosphates can lead to Acropora death. To maintain phosphate levels, you can use foods high in phosphorus (Nori, Spirulina, Reef-Roids) or special additives.

4. Water Temperature

Cooler water significantly stimulates polyp extension. The recommended temperature is around 23-24°C (73-75°F), maximum 25°C (77°F). Many deep-water corals (e.g., Blastomussa) tolerate temperatures above 25°C (77°F) poorly for extended periods.

At high temperatures (27-28°C/81-82°F), deep-water corals can live for 1-3 months but then begin to degrade, as they are adapted to cooler conditions at depth, where the temperature is usually 23-24°C (73-75°F).

5. Trace Elements

Three key trace elements for stimulating polyps:

Manganese

• Stimulates polyp extension

• Creates a metallic sheen on the coral body, protecting from UV radiation

• Allows corals to better tolerate intense light

• Should be maintained at medium values within the normal range

Iodine

• Necessary for many biological processes

• Affects metabolism

• Deficiency can disrupt biological cycles (e.g., shrimp molting)

• Excess can cause bleaching and polyp contraction

• Is a powerful biostimulant

Iron

• Biologically active element involved in many processes

• Affects zooxanthellae reproduction

• Overdose can cause phosphate depletion

• Excess can lead to coral darkening due to enhanced zooxanthellae reproduction

• Corals may hide polyps when iron levels are high

The "Slight Hunger" Principle

For maximum polyp extension, it's necessary to maintain a state of "slight hunger." Corals should always be slightly hungry to constantly search for food and extend polyps to catch it.

If there are too many nutrients in the water:

• Corals reduce the size of polyps (they no longer "need" to search for food)

• They stop active feeding

• Zooxanthellae continue to multiply

• The coral darkens due to excess zooxanthellae

• Coral degradation begins

Under normal conditions, corals should constantly extend polyps to obtain nutrients. If they are "overfed," the feeding tool (polyps) becomes unnecessary, and they contract them.

Impact of Lighting

Full-spectrum lighting is critically important for proper coral coloration. Using only blue light does not provide biologically complete lighting. In nature, corals are adapted to full-spectrum light.

Bright full-spectrum light promotes proper coral metabolism. Under dim light, corals become heavily "zooxanthellated" - dark with thick skin, transitioning to a more zooxanthellae-dependent feeding style.

With elevated ORP (oxidation-reduction potential), corals become brighter, and the water cleaner, which also favorably affects polyp extension.

Practical Recommendations

Coral Adaptation

Coral adaptation to new conditions usually takes about a week. During this time, the coral will extend its polyps as much as the environment allows. If a coral arrives hungry and there are many nutrients in the aquarium, it may first extend large polyps and then begin to retract them as it becomes saturated.

Dosing Additives

• Dose nutrients (Acropower or amino acids) daily in small amounts

• Avoid overfeeding to prevent an excess of nutrients

• Begin dosing Acropower only after stabilizing phosphate and nitrate levels

• Be prepared to maintain phosphate levels when using Acropower, as consumption may increase

Signs of Proper Conditions

• Polyps extended around the clock

• Corals have a "meaty" appearance - the body is slightly inflated (approximately 10% thicker than the skeleton)

• Bright coloration with depth and undertones

• Metallic sheen on the coral body

Signs of Improper Conditions

• Polyps extend only at night

• Corals have a "waxy" color without depth

• Too dark coloration without undertones

• Thin "dry" skin on the skeleton

• Complete absence of polyps (critical condition)

Conclusion

To achieve maximum Acropora polyp extension, it's necessary to create a balanced system:

• Maintain slightly hungry corals in cool water (23-24°C/73-75°F)

• Provide constant dosing of specialized foods (like Acropower) in small amounts

• Control phosphate (0.07-0.1 mg/l) and nitrate (5-10 mg/l) levels

• Maintain the necessary level of key trace elements (manganese, iodine, iron)

• Provide bright full-spectrum lighting (350-600 PAR)

• Create a light bacterial bloom using glycerin (3-4 ml per 1000 l)

If all these measures don't help, use Activated Carbon - it will remove everything unnecessary from the water, and your Acroporas will increase polyp size.

Following these recommendations will create conditions that maximize Acropora polyp extension, making corals healthier, more beautiful, and more similar to their natural counterparts.