"It is remarkable that we observed sexual reproduction simultaneously in two species," Sarno, a researcher at the Stazione Zoologica Anton Dohrn, told me. "One of the two species during the event attained one of the highest abundance values ever recorded for any Pseudo-nitzschia species at the sampling station over a period of more than 20 years."
The diatoms can reproduce both asexually and sexually. The 2006 event was all about the latter.
On that day, anywhere from 9 to 14 percent of the organisms were pairing up and reproducing in the Gulf of Naples near the Mediterranean Sea. Diatoms aren't exactly full of romance, which requires higher level development. The sex act is more like a chemistry happening, with the diatoms producing gametes, which are sexual reproductive cells that have a single set of unpaired chromosomes. These pair up, other sexual cells called auxospores form and the diatoms multiply.
Good news for the sexually active organisms, but bad news for us.
That's because both of the identified species produce a toxin called domoic acid.
"It is the cause for Amnesic Shellfish Poisoning syndrome in humans and for mass mortality in marine mammals and birds," Sarno explained, adding that the organisms can sometimes cause a "red tide," but that didn't happen during the event they documented.
(Image: Red tide off the coast of La Jolla, CA, August 2005; Credit: Alejandro Diaz)
She added, "It is likely that sex is not a rare event" for these species. It just happens so quickly and often near-invisibly that it's probably not noticed. Improved detection of these events might lead to better warnings for shellfish poisoning, which is known to occur seasonally.
The time of year and weather conditions must have perfect for diatom sex on that fateful day 3 years ago.