So here we have an example problem that asks, which of the following marine biomes could experience turnover in the spring and fall? And we've got these 4 potential answer options down below. Now, of course, recall from our previous lesson videos that turnover refers to seasonal turnover, and seasonal turnover refers to the vertical mixing of waters in a lake or an ocean specifically during the spring and fall seasons. Recall that the vertical mixing of waters is driven by changes in the density of the water as the temperature of the water changes from season to season. And so, because turnover refers to the vertical mixing of waters, we're looking for a marine biome that has sufficient amounts of water for there to be vertical mixing.

Notice that answer option c says, coral reefs, but coral reefs themselves are not going to experience turnover because the coral reef is not water, the coral reef is those rigid calcium carbonate exoskeletons formed by the coral polyps. So, they don't experience turnover, we can eliminate option c. Now option d says the marine benthic zone, and that refers to the bottom of the ocean floor. It's literally just the floor, but it's not referring to the water actually, it's just the floor. Hence, the floor itself does not experience turnover, that's not going to involve vertical mixing, so we can eliminate answer option d.

Now, option b says, intertidal zone, but the intertidal zone is going to be quite shallow and not have a whole lot of water to begin with, so it's not going to have a sufficient amount of mixing, due to turnover, it's not going to experience turnover. So for that reason, we can eliminate option b, and this leaves answer option a as the only option, which is the best choice here, the pelagic zone. Recall that the pelagic zone includes both the nearshore neritic zone and the offshore oceanic zone, and so it's basically all of the water in the open ocean. And so, the open ocean, in some areas, under the right conditions, can experience some amounts of turnover. And so that's why option a is the correct answer to this example. That concludes this problem, and I'll see you all in our next video.