Thursday, February 08, 2018

Worm caves and oyster grins

I bought an old abalone shell in a garage sale for a buck, 11 years ago. It sat on a shelf until I decided to use it in the aquarium as a hermit crab gym set. It has been very popular. The plumose anemone has chosen it as her permanent base, worms have built their tubes on the back, limpets sleep on the shiny floor, and the hermits still climb to the top to look at the world.

Over these ten years, much of the shell has dissolved into the water, and assorted algae have coated the rough outer side, creating interesting patterns. And colonies of tiny worms have made their homes in the pores, by now eroded into deep caves.

Outer rim of abalone shell, with algae and worms

Abalone shell, before being tanked, 2007. The outer shell is porous. The barnacle and tubeworm remains dissolved long ago.

The oyster, picked up on the beach after a storm, has been here only a few months. The shell was scrubbed white by wind and waves, but tank algae are at work here, too. And the oyster, not in the least fazed, is grinning.

Toothy grins

The oyster is a filter feeder, and pumps large volumes of water in, over the gills, where edibles are caught in mucus and moved down to the mouth.  What looks like teeth in those smiles are tiny tentacles. The gills are just behind them, sometimes visible when the oyster opens a bit wider.


  1. Does having a natural filter feeder like the oyster reduce the need for mechanical tank filtration? The mechanical filtration probably provides a necessary water disruption to facilitate the dissolved gas exchange so it can't be eliminated entirely.

  2. It may, slightly. But there is so much life in the tank, and the water doesn't get changed twice daily, as it is on the shore, so the mechanical filter is essential. It cleans out larger particles, too, that no oyster will touch. I have an air pump as well. When the temperature goes up, so that less oxygen is available, I notice that everything slows down, even with the pump and the filter going full blast.


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