The correct option is D Phytoplanktons
The first species to invade the bare area during ecological succession is called pioneer species.
In case of succession in terrestrial ecosystems (xerarch succession), lichens are the pioneer species. They are followed by mosses, grasses, small plants like herbs, shrubs and then bigger trees.
In succession in aquatic ecosystems (hydrarch succession), phytoplankton are the pioneer species. They are followed by submerged plants, free-floating plants, amphibious plants, grasses, shrubs and herbs and finally the trees.