24 Sea urchin rendezvous

Two sea urchins meet on a rock at the bottom of the Lauvøy Fjord (Norway). Even the echinoderm that looks so well-armed is threatened by ocean acidification. Sea urchins start their lives as free-swimming pluteus larvae. At this stage, ocean acidification can hamper their development.

One reason could be that the animals regulate the pH of their stomachs in order to maintain their digestion in more acidified waters. This requires additional energy – which is then lacking for other functions such as growth. Also, forming so-called “spicules” – skeletal elements of calcium carbonate – costs more energy in more acidified conditions. This can slow down their development. And the longer sea urchins need to develop before going through a metamorphosis and settle at the seafloor, the easier they can be caught by the many predators of the open waters.

Photo: Solvin Zankl