The Marine Environment

The Marine Environment

Over 70% of the world's surface is covered by ocean. The ocean is very important to all kinds of life, including humans. It provides food, oxygen, helps the climate, and is a source of money for many people. 


Marine environments are biodiverse ecosystems that are critical to all life. 


Participants will:  

  • Learn about the interactions found between organisms  
  • Discover how the removal of one or more organisms can impact the food web  


Ecosystem: A community of living things, non-living elements, and their interrelationships. 

Phytoplankton: Plant-like organisms that convert carbon dioxide and water into sugar and oxygen using sunlight energy. 

Decomposer: An organism that breaks down the remains of dead plants and animals.  

Food Chain: A way to show how energy passes from one organism to another.  

Food Web: A series of food chains that are connected to one another.  

Biodiversity: The variety of life in the world, in a particular habitat or ecosystem.  

Endangered Species: A species that is seriously at risk of extinction. 


With over 70% of the world’s surface is covered by water, the marine environment is home to some of the most biologically diverse ecosystems on the planet. As the world’s largest carbon sink, the ocean acts as a climate regulator as well as supplies us with more than half of the oxygen we breathe. Millions of people around the world depend on the ocean for food, medicine, recreation, and transportation.  

Healthy, well-balanced ecosystems are made up of many interacting food chains called food webs. In most ecosystems, organisms can obtain food and energy from more than one source, and commonly have more than one predator. Looking at a food web, we can visualize the interactions between organisms and how these connections determine the health of an ecosystem. If there is an imbalance, the food web as a whole becomes affected. Thus, every organism plays an important role in maintaining the overall health of an ecosystem.  

Dive Deeper

Marine Food Chain

Organisms at sea can range from small to largeThe vast majority of marine organisms are microscopically small and have large populationsThese microscopic organisms are the basis of sea life as they feed larger animals, and ultimately humans. The marine food chain begins with phytoplankton which are consumed by zooplankton and in turn are consumed by a larger species and ultimately an even larger predator.  

Did you know that blue whales can grow to be bigger than school buses?

The marine food chain begins with phytoplankton. Phytoplankton are very small, plant-like organisms.

Phytoplankton are eaten by zooplankton. Zooplankton are another type of plankton, but are actually animals and not plants.

Zooplankton are then eaten by larger zooplankton or small fish.

Finally, small fish are eaten by larger fish, like tuna and sharks.

The 10% Rule

In marine food chains, only 10% of the energy gained from food is used to grow in the next level. This means when a plant or animal is eaten, only 10% of the weight gain is passed on to the next level in the chain. The remaining 90% is lost in the form of heat or used for movement. This means an abundance of phytoplankton are needed at the base of the food chain for one big tuna or shark at the top.  

All food chains are connected in more complex food webs. After all, most organisms eat more than one type of food and can be eaten by more than one type of predator. The ultimate predators in marine food webs are humans.  

Open Ocean & Coastal Seas

The ocean is not a singular mass of water with the same life forms everywhere. It can be divided into deep open ocean and shallow coastal seas. Due to the physical and chemical differencesthe sea has many biodiverse ecosystems with many different species. The more biologically diverse an ecosystem, the more resilient it is – in other words, it can better respond to change. For example, when there are more organisms in a food chain or web, it will be less affected if one organism becomes threatened or endangered.  

Open Ocean

Coral Reef

Salt Marsh


Many shipping regulations are based on the fact that open oceans and coastal seas are so different and are susceptible to different threats.  

Particularly Sensitive Sea Areas (PSSA's)

PSSA's are a specific area that is protected by the International Maritime Organization (IMO). These areas have specific extra measures, like piloting or speed restrictions. By 2017, 17 PSSAs had been designated, including the Great Barrier Reef and the Florida Keys.


The sea is not only a blue highway useful for shipping activities; it plays an important role in balancing the planet and the oceans are teeming with life. As seafarer/shoreside personnel, it is important to know about the marine environment to be able to understand the impact each of us has on the environment. 

Scroll to Top