Sea anemone feast

Photographed by Dr Julian Finn on a dive trip to Nelson Bay, New South Wales, this sea anemone is taking on a shrimp feast to rival that of an Aussie BBQ. 

sea anemone and shrimp
A sea anemone, Phlyctenanthus australis, chowing down on a Hinge-back Shrimp, Rhynchocinetes serratus. There's also a photobombing chiton in the background.

Little has been documented about the diets of sea anemones, particularly in Australia. These chance encounters and images help us understand these predominately sedentary animals (although, they can set a cracking pace if they so desire) and what role they play in the marine ecosystem. 

Sea anemones are opportunistic feeders that catch whatever food passes by. Prey is ensnared and then immobilised with specialised stinging cells (nematocysts) found in the tissue of sea anemones.

There are many different types of nematocysts and each has its own function; some are sticky for catching prey, some poisonous, others are used in self-defence. When feeding, the anemone extrudes its mouth and throat (actinopharynx) over the prey, sometimes completely enclosing it. The sea anemone then crushes and digests the food in the throat, which also acts as the gullet. Food waste is then ejected back out the mouth, which doubles as the anus.

Not all sea anemones are totally reliant on eating; some have a symbiosis with zooxanthellae (microscopic algae) that live in their tissues, and the sea anemone can use nutrients created by the photosynthesising algae.

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