sex in the sea

Eleven-armed Sea Stars again folks. This time the report comes from Dave Bryant. A couple of years ago Dave and Paul Baumann were scuba diving at Rye Pier at night.

The water was really cloudy, not ideal for camera toting scuba divers, but Dave and Paul soon found the reason why. Eleven-armed Sea Stars Coscinasterias muricata had massed under the pier and were all spawning.

The photographs that Dave has sent to me show how the sea stars raise up on their 11 arms when they spawn. Looking at the photographs I assume that the white liquid oozing out of the first sea star is sperm and the clumpier, pink material in the second photograph to be masses of eggs.

Because fertilization would take place in the water, the sea stars need to get together in one place and release masses of eggs and sperm at the same time.

An Eleven-armed Sea Star Coscinasterias muricata releasing
sperm into the water (at Rye Pier)
(click thumbnail for full image)

A second Eleven-armed
Sea Star releasing egg
masses into the water
(click thumbnail for full image)

Seems as if Dave and Paul happened to hit the water at just the right time to witness this event. Certainly it was all over by the following night.

Like many marine invertebrates, almost all sea stars reproduce in this way. Fertilization of a sea star egg produces a sea star larva. This minute creature looks nothing like an adult sea star and is the first of a number of stages in the sea star's life. The larva drifts about and feeds as plankton until it is large enough to change into a young sea star and settle out to begin its adult life.