This would increase the food available to herbivores, allowing herbivores to increase in number.
Phytoplankton is also known as microalgae in that they are a plants that contain chlorophyll. As such they're a source of food for those animals that eat plants. With that in mind, let's look at the options and select the best answer.
The phytoplankton population would thrive, allowing herbivores to decrease in number.
* Yes, the phytoplankton would thrive. But the following statement doesn't make any sense. So this is a bad choice and wrong answer.
There would be no impact on the phytoplankton population, and no impact on the number of herbivores.
* We've been told that the phytoplankton grows quicker in cooler water. So where does the idea that cooler seasons would have no effect? That just doesn't make sense, so this is a wrong answer.
This would decrease the food available to herbivores, causing herbivores to decrease in number.
* More plants means less food? That's nonsense and therefore this is a wrong answer.
This would increase the food available to herbivores, allowing herbivores to increase in number.
* Precisely! Cooler seasons = cooler water = faster growth = more food. And more food leads to a higher population utilizing that food. So this is the correct choice.
