Massive simultaneous algal orgy

Sex is always a good topic although mostly people have the wrong idea. From the biological perspective sex is production of genetically diverse offspring via mating. Most organisms, which are mostly unicellular, reproduce asexually, so all their offspring are genetically identical, a clone. And this works so well and so efficiently that sex among some organisms is a rare event in nature, so when biologists witness one, they get excited, intellectually.
In this instance the organisms are two species of diatoms, unicellular algae that are phytoplankton, the grass of the oceans. Diatoms are pretty nifty because their cell wall is made of glass, in two halves that overlap each other rather like a petri dish. This poses a bit a biological problem because a cell cannot bend or stretch a glass cell wall so when the cell reaches a certain maximum size for its cell wall the cell divides, which is how it reproduces asexually. The two daughter cells each inherit one-half of their progenator's cell wall, and synthesizes a new inner half. This means one of the two can grow as large as the original cell, but the other having inherited the slightly smaller inner half, so it's maximum size is constrained and it becomes a bit smaller.
Now think forward. When each of these two cells divide, the larger of the two produces two daughter cells just like the two described. But when the other daughter cell divides the biggest one daughter can get is the slightly reduced size of the maternal cell, but the other receiving the inner half of the cell wall is smaller yet. Now let's do this thousands of times. Some diatoms will still be as big as the original cell, but lots of lineages were getting smaller and smaller. At some point the smaller cell size triggers sexual reproduction where the smaller cells divide into gametes, sex cells, which escape their glass prison, fuse with a suitable mate, forming a new cell that enlarges to an optimal maximum size for a diatom, synthesizes a new cell wall and starts the whole process all over again.
The environment plays a role in such events because you don't want to be the only organism at an orgy to release your gametes into the big broad ocean. So what happened here was some environmental event triggered sexual reproduction in two species of diatom simultaneously, and someone was there to watch (record some data).
Whew! Sort of gets you all sweaty just thinking about it.