The science of heterotrophic feeding in Acropora

If we think our Acropora are only light-dependent organisms, we are ignoring their true nature as elite predators.

The coral is not an isolated individual but a holobiont: a complex entity that Yuri Sorokin describes in Coral Reef Ecology as the symbiotic union of the polyp (the animal), the zooxanthellae (the algae) and the microbiome (bacteria and viruses in the mucus).

The energy cycle: why light is not enough

In clear water the zooxanthellae supply glucose and glycerol, covering the cost of respiration. However, this "sugar" contains no nitrogen and phosphorus. To grow and repair tissue, the holobiont has to switch on heterotrophy.

• Autotrophy (light): the fuel for survival.
• Heterotrophy (food): the bricks for building (proteins and DNA).

1. 1Autotrophy · light sugars from the zooxanthellae: the fuel to stay alive
2. 2Heterotrophy · food nitrogen and phosphorus: the bricks for proteins and DNA
3. 3From phosphate to food with carbon dosing (tiger, vodka) bacteria lock up PO₄; the coral captures them with its mucus. An inhibitor becomes food.

Light is the fuel, food is the bricks.

Sources: [1] [2]

Autotrophy and heterotrophy: fuel and bricks.

Feeding mechanics: how does an Acropora eat?

We need to distinguish three ways of feeding that happen at the same time.

Stinging capture (zooplankton): the polyps use their nematocysts (venomous harpoons) to paralyse prey as large as small crustaceans.

Muco-ciliary capture (bacteria and particles): this is Sorokin's discovery. The coral secretes a sticky mucus that works as a "net". Bacteria get caught in it, and microscopic hairs (cilia) push the mucus towards the polyp's mouth. The mucus captures, the polyp conveys.

Pinocytosis (direct absorption): the skin cells "drink" tiny droplets of water loaded with amino acids and dissolved nutrients. It is almost "intravenous" feeding, and it happens even with the polyps closed.

1. 1Stinging capture nematocysts paralyse prey as large as small crustaceans (zooplankton)
2. 2Mucus and cilia mucus traps bacteria and particles, cilia push it to the mouth
3. 3Pinocytosis the skin "drinks" amino acids and dissolved nutrients, even with polyps closed
4. 4Flow is life the pumps must push the food against the coral

Flow is life.

The three ways an Acropora eats.

The gladiator's feeding mash: the bio-reaction

Our preparation technique is not random, but based on biochemistry.

Soaking (4-5 hours): it starts hydrolysis. Proteins break down into free amino acids (DFAA) that the coral absorbs straight away by pinocytosis.

The bacterial graft: by adding live bacteria to the mix we turn dry food into fresh biomass. The bacteria eat the food, multiply and synthesise vitamin B12 and organic phosphorus.

The result: we pour a living "reactor" into the tank that boosts the coral's microbiome and supplies pre-digested food.

Dry food"hard" and inert particles

Soaking 4-5 hoursproteins become free amino acids (DFAA)

Bacterial graftbacteria multiply: vitamin B12 and organic phosphorus

The reactor in the tankpre-digested food and a stronger microbiome

The feeding mash brings pre-digested food into the tank.

Bacteriotrophy and the nutrient cycle

In the aquarium, when we dose carbon (the tiger or vodka protocol), we stimulate the growth of bacterioplankton.

These bacteria lock up inorganic phosphate (PO₄) from the water.

The coral captures these bacteria with its mucus.

Conclusion: we turn a pollutant that inhibits growth (phosphate) into organic food for the Acropora.

Why this changes the way we feed

Flow is life: as Hovland teaches, the pumps must push the food against the coral to break up the "boundary layer" and let the mucus intercept the particles.

Bacteria are the "primer": without the bacterial part of the feeding mash we lose the absorption efficiency described by Sorokin.

Polyp extension is a sign of active hunting but, thanks to pinocytosis, we know that our feeding mash feeds the holobiont even when the polyps look shy.

Who wrote this article

Sources

1. NOAA National Ocean Service (2026). Corals Tutorial: What is Zooxanthellae?. National Oceanic and Atmospheric Administration.
2. Houlbrèque F., Tambutté E., Allemand D., Ferrier-Pagès C. (2004). Interactions between zooplankton feeding, photosynthesis and skeletal growth in the scleractinian coral Stylophora pistillata. Journal of Experimental Biology 207(9): 1461-1469.
3. Grover R., Maguer J.-F., Allemand D., Ferrier-Pagès C. (2008). Uptake of dissolved free amino acids by the scleractinian coral Stylophora pistillata. Journal of Experimental Biology 211(6): 860-865.