Pebbles with holes made by boring sponges

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Pebble with holes in close-up: Close-up details of the holes bored by sponges in a pebble (1)

We mostly think of sponges as being soft-bodied organisms. So it may be surprising to learn that some types of sponge can bore holes in soft stones and seashells. They do this not by drilling but by secreting acids that dissolve the calcium-based substrates on which they live.

Typically a pebble or shell that has been affected by this kind of sponge infestation will have a series of regular-shaped circular holes on the surface. These holes may cover the entire surface of the object in severe infestation. Sometimes there are only a few holes when the sponge is just starting to colonise the pebble. These may appear as a single row of holes with a range of increasing size. There may be inter-connected surface lines or grooves which look like the impressions of rows of beads.

Below the surface, deeper down inside the pebble, the sponge creates a fairly hap-hazard network of spaces that resembles bubbles or an irregular sort of honeycomb. This inner damage is revealed when the outer surface of a badly sponge-infested pebble is either broken or worn away.

Cliona celata (Grant) is one of the sponges that commonly makes these holes in pebbles and shells in the UK at the present time. There is more information about sponge borings in shells in the earlier post: Sponge borings in Flat Oyster shells.

Holes in a pebble: Pebble with regular round holes made by boring sponge (2)

Pebble with holes: Sponge borings making a regular pattern of circular holes on a pebble (3)

Pebble with holes: Probable sponge borings in a pebble: outer surface of stone worn away to reveal inner honeycomb texture (4)

Pebble with holes made by sea creatures: Probable sponge borings in a pebble: outer surface of stone worn away to reveal inner honeycomb texture (5)

Macro photograph of honeycomb holes in a stone: Close-up view of bubble-like or honeycomb texture that forms inside a pebble infested with boring sponge (6)

Chalk pebble with infestation damage caused by sponge and small bristle worms (7) 

Revision of a post first published 18 December 2009


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10 Replies to “Pebbles with holes made by boring sponges”

  1. Thank you Jessica. I collected a couple of specimens from a beach in Turkey near Cinar beach Akyaka and I wondered what they were. I am now off to search for a picture of the boring sponges!


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