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Marine microorganisms are defined by their habitat as microorganisms living in a marine environment, that is, in the saltwater of a sea or ocean or the brackish water of a coastal estuary. A microorganism (or microbe ) is any microscopic living organism or virus , which is invisibly small to the unaided human eye without magnification .
Pelagibacter ubique and its relatives may be the most abundant microorganisms in the ocean, and it has been claimed that they are possibly the most abundant bacteria in the world. They make up about 25% of all microbial plankton cells, and in the summer they may account for approximately half the cells present in temperate ocean surface water.
In the ocean, animal–microbial relationships were historically explored in single host–symbiont systems. However, new explorations into the diversity of marine microorganisms associating with diverse marine animal hosts is moving the field into studies that address interactions between the animal host and a more multi-member microbiome .
The ocean represents the largest continuous planetary ecosystem, hosting an enormous variety of organisms, which include microscopic biota such as unicellular eukaryotes (protists). Despite their small size, protists play key roles in marine biogeochemical cycles and harbour tremendous evolutionary diversity.
The world ocean covers an area of 3.618 × 10 8 km 2 with a mean depth of 3682 m, resulting in an estimated volume of 1.332 × 10 9 km 3. [17] If all of Earth's crustal surface was at the same elevation as a smooth sphere, the depth of the resulting world ocean would be about 2.7 kilometres (1.7 mi).
Access to the previously invisible world opened the eyes and the minds of the researchers of the seventeenth century. Antonie van Leeuwenhoek investigated diverse bacteria of various shapes, fungi, and protozoa, which he called animalcules, mainly from water, mud, and dental plaque samples, and discovered biofilms as a first indication of microorganisms interacting within complex communities.
Bacteria. In the microbial food web, bacteria play a crucial role in breaking down organic materials and recycling nutrients. They transform DOC into bacterial biomass so that protists and other higher trophic levels can consume it. Additionally, bacteria take part in the nitrogen and carbon cycles, among other biogeochemical cycles. [4] Algae
The pelagic food web, showing the central involvement of marine microorganisms in how the ocean imports nutrients from and then exports them back to the atmosphere and ocean floor. A marine food web is a food web of marine life. At the base of the ocean food web are single-celled algae and other plant-like organisms known as phytoplankton.