Microscopic Aquatic Life

Marine microscopic life is incredibly diverse and still poorly understood. For example, the role of viruses in marine ecosystems is a field barely explored to date and will undoubtedly unveil many secrets as this field opens.

The role of phytoplankton is far better understood due to their critical position as the most numerous primary producers on Earth. Simply put Phytoplankton serve as the base of the aquatic food web (excluding seaweeds and algae) providing an essential ecological function for all aquatic life. One of the more remarkable food chains in the ocean because of the small number of links is that of phytoplankton feeding krill which is then predated on by baleen whales.

Phytoplankton obtains energy through the process of photosynthesis and must therefore live in the well-lit surface layer of an ocean, sea, lake, or other body of water. Phytoplankton account for half of all photosynthetic activity on Earth and importantly are responsible for much of the oxygen present in the Earth’s atmosphere more than half of the total amount produced by all plant life, In a way the Amazon rain forest is less critical to us than this diverse group of aquatic photoautotrophic microorganisms. There are about 5,000 species of marine phytoplankton. But figures state phytoplankton is in decline by 1% per year probably due to a combination of global warming and acidification of our oceans.

The next level of plankton in the aquatic food web is Zooplankton many are too small to be seen individually with the naked eye. Included in zooplankton are many juvenile species of jellyfish, molluscs and even fish as well as crustaceans such as copepods and krill. Planktonic copepods (usually the dominant members of zooplankton) are important to global ecology and the carbon cycle, by feeding near the surface at night, then sinking into deeper water during the day to avoid visual predators, their moulted exoskeletons, faecal pellets and respiration at depth all bring carbon down to the deep sea. This vertical migration and therefore carbon sinking is also displayed by Krill. The surface layers of the oceans are currently believed to be the world’s largest carbon sink, absorbing about 2 billion tons of carbon a year, the equivalent to perhaps a third of human carbon emissions!

Zooplankton is a wide and abundant group of animals and are primarily transported by ambient water currents, however some have the power of locomotion and use this to avoid predators. Zooplankton feed on bacterioplankton, phytoplankton, and other zooplankton (often cannibalistically), detritus (or marine snow). Zooplankton form a vital role in the aquatic food web both as predator, scavenger, filter feeder and of course prey to many fish species, filter feeders, whales and even birds.

Disturbances of an ecosystem resulting in a decline in any of these micro organisms can have far-reaching effects. We are only beginning to understand the connectivity between ourselves and our natural environment and the vital role we must play in changing our ways, not for the environments sake but for our own survival. The way forward is simple live sustainably.