Marine microorganisms are organisms to small to be seen by the naked eye and live in the marine habitat, they make up 70% of the biomass in the sea and are responsible for almost all photosynthesis in the sea. These organisms are icredible diverse, they include: viruses, bacterie, archaea, microalgae, fungi and micro animals.
Prokaryotes are single celled organisms that lack a membrane bound organelle. These include archaea and bacteria. Archaea used to be classified as bacteria but this is no longer correct, they are now a seperate branch of life. They form shapes similar to bacteria apart from a few unique shapes, and were first found in extreme conditions and earning the name extremeophiles. However, now archaea are being found in an increasing number of environments. Archaea are not a threat to human welbeing and no archaea have been found to be pathogens (cause disease). Marine bacteria are typically a few micrometres in length and form a range of shapes. The largest known bacterium, the marine Thiomargarita namibiensis, can be visible to the naked eye and sometimes grows to 0.75mm! In 5ml of sea water on average there are 1 to 5 million bacteria.
Most marine viruses are bacteriophages and are harmless to plants and animals, phages are a type of virus that target and destroy bacteria. Thye kill around 20% of marine microorganism biomass each day and are essential for recycling nutrients. In 5ml of sea water there is on average 5 to 10 million viruses!
Eukaryotes are organisms that have membrane bound genetic code, a nucleus. These can be unicellular or they can be multicellular. Algae can be single celled or chains of cells, there are around 6 thousand different species of algae. Green algae are a large group of photosynthetic algae they contain chloplast which contains chlorophyl. Fungi are parasitic and feed on the decaying remains of algae, corals, sea grasses and wood. there are over 1500 species of fungi known. Another Eukaryotic organisms are micro-animals, these are microscopic animals thatc an even be unicellular, there are huge amounts of microscopic crustaceans and arthropods in marine environments, recently some anerobic organisms have been found, (dont use oxygen for respiration)!