Mystery spawning in tidepool

I witnessed something really strange in a small tide pool among the rocky outcrops on the beach at Fall Bay in Gower. I can only imagine that it was some seashore creature spawning into the still salt water. Some pools were already totally clouded and milky with the substance. It occurred in several pools all at the same time – a sort of synchronised spawning. The odd thing was that I could not locate the organism responsible – despite probing the seaweed and under the rocks. Whatever it was, it must have been quite large because it seemed to be a continuous, steady, but pulsating stream of the fluid being ejected and a substantial quantity of the stuff. Maybe a fish, or a large sea slug, sheltering in a crevice?

I managed to capture this short video clip of the event.  I’d be very interested to hear from anyone who could explain the phenomenon.


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7 Replies to “Mystery spawning in tidepool”

  1. Not a bad idea, Ian. I’ve looked at your linked video but I am not sure that bristle worms are the answer. What I observed was a steady pulsating flow rather than a number of short spurts. Also, the activity persisted for maybe upto five minutes or more; and the width of the stream was a centimetre or so across. Some larger animal was responsible, I think.


  2. Lunar influence?

    Each of the epitoke segments is packed with eggs and sperm and features a single eyespot on its surface. The beginning of the last lunar quarter is the cue for these animals to breed and the epitokes break free from the atokes and float to the surface. The eye spots sense when the epitoke reaches the surface and the segments from millions of worms burst, releasing their eggs and sperm into the water.



  3. You are probably right about the synchronous element of the spawning activity in the different pools. The spawning took place at 1324 on 18th August this year (2011) which immediately followed the spring tides (lowest/highest tides) of that month, on a fine sunny and warm afternoon when the tide was still ebbing. The spawning and fertilisation products would have been washed out of the pools at the subsequent high tide. Still not convinced that it was bristle worms – although they were undoubtedly present in the pools but not in the densities that would be needed to produce such volumes of spawning products. Other animal organisms that were readily visible included orange sponges, calcareous encrusting algae, beadlet sea anemones, and various molluscs of which limpets and common winkles were the most abundant plus a few small fish. However, something must have been well hidden.


  4. That’s why I simply love the seashore! Hundreds of different creatures and organisms to discover, and inter-relationships to understand, in a fascinating geological setting, with a constantly changing environment…….all that colour, pattern and texture to provide artistic inspiration, and the elements for mood setting to uplift the spirit. Great!


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