After going on holiday by the sea, that question has stayed with me. I remember how as a child I already collected shells and see that other children do too. Will that supply never be exhausted or will shells be born? And how? And if so, do they still grow? And how is it determined what kind of shell such a shell will become?
Answer
You should know that the majority of the shells you find on the beach do not grow on the beach itself, but in the bottom of the sandbanks and the channels in between that are located just off our coast. Shells spend their entire lives there, produce offspring at regular intervals and eventually die after X number of years.
After a storm and onshore wind, entire dead shell banks can wash up on the beach. On the Belgian coast, many stretches of beach are artificially raised with sand from the sea. This is done to make the beaches more resistant to storms and rising sea levels. There are often a lot of shells in that sand.
These shells are then used for the summer trade in paper flowers. A while ago we devoted a full article to it in the magazine ‘De Grote Rede’: www.vliz.be/docs/groterede/GR19_PapierenBloemen.pdf.
Shells reproduce by releasing eggs and sperm into the water at a certain point in time. These fuse and the formed larva ‘hangs around’ for a while. They may be carried along with the current to other areas. After a few days or weeks (depending on the species, water temperature and other environmental factors), this larva starts to develop a tiny shell. This makes them heavier and sinks to the bottom. They will remain there for the rest of their lives.
You can read about how such a shell grows and gets its shape in a previously answered question in ‘ikhebeenvraag.be’: How is a shell formed? (see question 1165
Answered by
dr. Nancy Fockedey
Marine, estuarine and coastal sciences in the broadest sense of the word.
Wandelaarkaai 7 8400 Ostend
http://www.vliz.be
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