How many plants live in the ocean?

We may see different plants in the ocean though there are also different types on how each class is called. Here are five types of ocean plants: phytoplankton, red algae, kelp, seagrass, and sargassum.

Do you know if algaes or planktons have the biggest number?

They are the same. Planktons include a wide variety of organisms such as algae, bacteria, protozoans, the larvae of some animals, and crustaceans.

Wow that is a lot. I am curious if those bacterias affect some plants or fishes?

Bacteria can be sucked into a plant through natural plant openings such as stomata, hydathodes or lenticels.
Bacterial colonization can be observed on fish skin and gills due to constant exposure to contaminated water or plants.