Most phytoplankton, i.e. unicellular algae, is eaten by zooplankton, i.e. mostly by small crustaceans, like copepods.

The fish that eat other animals vastly outnumber the fish that eat algae or aquatic plants.

> The fish that eat other animals vastly outnumber the fish that eat algae or aquatic plants.

This is why I said "if you count all sea creatures". The original comment said "most fish are predators because there isn't much vegetation". As you say, there is quite a lot of vegetation, and there are many more sea creatures in that category than there are predators.

So, most fish are predators, but not at all for the reason in the original comment. It remains true that population and total biomass drop off exponentially as you go up in the food chain (which is really the only point I was trying to make).

The main reason while the majority of big aquatic animals are eating other animals, while the majority of the big terrestrial animals are eating plants, is the disparity in size between big animals and most aquatic primary producers, which requires at least one intermediate layer of small animals, who gather efficiently the small algae, packaging the nutrients and energy into bigger bodies, which can be gathered efficiently by the big animals.

Cows can get big by eating grass because most of the land is covered in plants, but tuna can't get big by eating seaweed because most of the sea is abyss.