Polar sea star

Northern sea star has an unusual way of reproducing. As winter approaches and water temperatures drop to around 2°C, individuals that have been solitary until then begin seeking contact.

During mating, the male releases his gametes (reproductive cells) onto the seafloor as a sticky film. This triggers a female to lay 1,000 to 3,000 eggs on top of it.

Fertilization happens outside the body, and what follows is striking: the female covers the eggs by curling her arms into a spiral around them. She guards them for five to seven months, without feeding during that time.

Embryos develop into larvae that live off their internal reserves and do not drift in the plankton (unlike many other Asteroidea). This direct development, under maternal protection, reduces dispersal and boosts the young’s chances of survival in cold, stable waters.