Just like plants on land, ocean-going plankton need light from the sun to prosper and grow. But light is absorbed by ocean water, and some colors of light are absorbed more readily than others.That's why nearly all photosynthesis in the ocean takes place in the sunlit upper layers.
What would most likely reduce the bias present in Elias' experimental design would be to not ask just the members of his high school team to be the subjects because they represent a very specific group of people. It would be much better to use a random group of people and have them do the same thing.
