Waikowhai School had lots of fun sampling at their local beach. One of the groups came across these eggs on the underside of a rock. Does anybody know what they are?
Great spotting! The snails look like Oyster borer whelks, Haustrum scobina, and the dome shaped capsules are likely their egg cases. It looks like some are empty but the cream coloured ones look like they may still be full of developing whelks.
There are on average 235 embryos per capsule, however on average only 10 fully develop with the remaining embryos providing a food source for the ones that survive. About 10 weeks after the egg cases are laid, fully formed juvenile whelks crawl out.
The Marine Metre Squared website, mm2.net.nz, is a citizen-science project and is owned and managed by the NZ Marine Studies Centre, University of Otago. Content is licensed under the Creative Commons Attribution-NonCommercial–ShareAlike license, unless otherwise stated.