Most corals rely on symbiotic zooxanthellae (brown algae) within their tissues to obtain nutrition through photosynthesis. However, there is a group of corals called "azooxanthellate" that lack these symbiotic algae. This group is entirely dependent on 100% planktonic feeding, and their care methods differ significantly from typical corals. This article explains the representative species of azooxanthellate corals and techniques for long-term husbandry through proper feeding.
What Are Azooxanthellate Corals?
Corals without symbiotic relationships with zooxanthellae rely entirely on capturing planktonic food from external sources for all their energy. Therefore, they cannot survive without continuous daily feeding.
Main Representative Species:
- Octopus Coral (Goniopora genus): An LPS coral with 24 tentacles
- Plate Coral (Fungia genus): A fleshy solitary polyp coral
- Menebripora: A soft coral with delicate small polyps
These corals are known in the wild to inhabit deep waters (light-limited environments) and exhibit nocturnal feeding behaviors. They have traditionally been considered difficult to keep in aquariums. However, with proper feeding strategies, long-term aquarium care is achievable.
Basic Feeding Principles
Feeding Frequency and Amount
Daily feeding is essential. Feeding only 3-4 times per week will result in malnutrition and decline.
Example feeding schedule:
- Morning (08:00): Phytoplankton + Rotifers
- Midday (15:00): Reef-Roids (dry food)
- Evening (20:00): Copepods + Phytoplankton
Three daily feedings are ideal, but at minimum, feed twice daily.
Types of Planktonic Feed and Their Uses
Phytoplankton (Plant-based):
- Species: Tetraselmis chuii, Isochrysis galbana, etc.
- Feeding amount: 5-10ml per feeding (cultured liquid)
- Benefits: Vitamin and mineral supplementation, nutrient supply
Rotifers (Wheel animals):
- Size: 100-200μm
- Nutritional value: High protein content; living food stimulates capture feeding behavior
- Culturing method: Can be self-cultured by feeding plant-based plankton to rotifers
Copepods (Copepoda):
- Size: 200-300μm
- Nutritional value: Most nutrient-rich, abundant in fatty acids
- Source: Commercially available live copepods or naturally occurring from live rock
Reef-Roids (Dry Food):
- Composition: Dried plankton powder
- Advantages: Easy to store, high practicality for daily feeding
- Usage amount: Approximately 1/4 teaspoon per feeding, mixed with a small amount of seawater to form a paste
Lighting Requirements and Rearing Environment
Since azooxanthellate corals lack zooxanthellae, lighting is not essential. Rather, they tend to prefer dimmer environments (fluorescent lighting or illumination of 4,000-6,000 lux).
Recommended Lighting Pattern:
- Lighting duration: 6-8 hours daily (low light)
- Color temperature: Approximately 5,000K (warm spectrum)
- Night: Complete darkness is acceptable
Water Quality Management Tips
Daily feeding presents the challenge of nutrient accumulation.
Nutrient Management
Azooxanthellate corals require moderate nutrient levels. Guidelines are:
- Nitrate: 20-50 ppm (higher than zooxanthellate symbiotic corals)
- Phosphate: 0.5-2.0 ppm
With daily feeding, increase weekly water change volume to 30-50%. Standard 25-30% water changes will result in nutrient accumulation and algae blooms.
Feeding and Water Flow Timing
During feeding, reduce or stop water flow so plankton contacts coral tentacles more easily. After 5-10 minutes of feeding, gradually return the water flow. With constantly strong water flow, fed plankton will be swept away before the coral can capture it.
Species-Specific Care Guidelines for Azooxanthellate Corals
Goniopora (Octopus Coral)
The most challenging LPS coral. However, with consistent daily feeding, long-term care of several years is possible.
- Target feed: Rotifers + Reef-Roids
- Water temperature: 24-26℃
- Feeding frequency: At least twice daily (minimum requirement)
- Decline indicators: Polyps do not extend, coloration fades, tentacle tips turn white
If decline is observed, increase feeding frequency to three times daily or try changing plankton species.
Fungia (Plate Coral)
A solitary polyp coral where feeding is relatively easy.
- Target feed: Reef-Roids (fine grain)
- Feeding frequency: At least once daily
- Lighting requirement: Not necessary (even in dim conditions)
- Characteristic: Retracts during the day; extends at night for feeding
Timing evening feedings is key to successful management.
Menebripora Species
A soft coral with small, delicate polyps. Relatively hardy.
- Target feed: Fine particle food (ultra-fine Reef-Roids) + Phytoplankton
- Feeding frequency: Twice daily
- Characteristic: Exhibits pulsing behavior; reasonably priced
Care difficulty is equivalent to soft corals like sea anemones.
Addressing Feeding Failures and Recognizing Decline Indicators
Recognizing Decline Patterns
Early stage: Polyps extend for shorter periods; coloration becomes lighter
Mid stage: Loss of feeding response; tentacle tips turn white
Late stage: Complete retraction; whole coral shrinks
Corrective Actions:
- Increase feeding frequency (once daily → 2-3 times daily)
- Change plankton species (rotifers → copepods, etc.)
- Isolate for intensive management (small container)
Recovery often occurs when frequent feeding of 3-4 times daily is provided in an isolation tank.
Establishing a Self-Culture System
Consistent daily feeding requires stable planktonic food supply.
Minimal Equipment:
- Rotifer culture bottle (1L)
- Phytoplankton culture bottle (500ml)
- Small aeration device
Removing a small amount of rotifers daily for feeding and adding fresh culture medium weekly creates a "semi-continuous culture" that is both sustainable and practical.
Conclusion
While azooxanthellate coral husbandry requires continuous feeding effort, it offers commensurate satisfaction and learning opportunities. Due to the high difficulty for beginners, it is recommended to attempt this as an "advanced step" after becoming proficient in typical coral care.
