👉 In the context of marine biogeochemistry, a "holoplankton" refers to a group of photosynthetic organisms that are found in the deep ocean and near the bottom of the sea. These organisms are primarily composed of unicellular algae (a type of protist) and some bacteria, but they also include other types of microorganisms such as cyanobacteria and dinoflagellates. Holoplankton is a diverse group of organisms that play an important role in the