Spawning in the air

Spawn slick. Photo by Maikani Andres.

We raced through the Rock Islands to our study site. The tropical sun shone bright against a clear blue sky and a matching sea. The breeze in my hair felt invigorating. It was a typical day on the boat in Palau. 

"Spawn slick!" Matthew shouted from the bow. We were passing an area of schmutz on the sea surface - honestly, it looked like someone had vomited. White mucus coiled in the waves, punctuated by pink dots. Leaves and twigs were tangled in the mix. Matthew leaned far over the side for a better look, then grabbed a container to take a small sample. Sure enough, the pink dots were eggs, and the white mucus mess strongly resembled sperm. Whoever had spawned these gametes must have been a hermaphrodite, because both types of gametes were found together and covered in their typical mucus. Based on the time difference (corals spawn at night, and we found the slick in mid-afternoon) and the state of development of the embryos (not far along), Matthew guessed the spawn was from Acropora, a type of branching coral. It was a magnificent find. 

We had a brief debate about whether to collect the embryos and try to use them in an experiment, but we decided to leave them be. We weren't actually ready for coral babies yet, and besides, we didn't know what species they were. Onward we drove to collect our own corals for spawning: Porites lobata. We picked up the labeled corals we had left behind last fall and also grabbed a few new ones to round out our collection of parents. They'll live in the tanks at PICRC for a few days while we monitor them and collect their gametes.

Some mating worms near PICRC's dock.

Later that night, as we checked our corals for any sign of spawning, we noticed some reproductive activity off the dock. It wasn't corals this time, but worms! A long, yellow, segmented worm twirled in our light at the surface. The forward portion of his body was flared wide, but the back end was coiled tightly. As the worm unfurled, a milky white substance shot out of the back end of his body - it had to be sperm. The dance repeated a few times, and then we noticed a second worm emerging from the darkness. This one wasn't coiling up like the first one; rather, it swam in a more sinusoidal pattern while releasing small packets from its rear end. Those had to be eggs. A third worm eventually showed up to join the party - another male. It was utterly fascinating to watch, and I was reminded of the mating rituals of nereid worms in Woods Hole. 

Our corals haven't gone yet, but there is definitely spawning in the air in Palau! With any luck, we will get some gametes of our own soon!