Types of Marine Organisms
Dana Desonie, Ph.D.
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Printed: February 11, 2015
AUTHOR
Dana Desonie, Ph.D.
www.ck12.org
C HAPTER
Chapter 1. Types of Marine Organisms
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Types of Marine Organisms
• Describe types of marine organisms.
How can you visit marine life?
It’s easiest to get to the relatively shallow seafloor just offshore. Experienced divers can descend to 130 feet (43 ft),
which gives them access to most marine life. Manned submersibles can descend to the bottom of the deep ocean.
Where would you like to go? A coral reef or a hydrothermal vent?
Living Things in the Ocean
Marine organisms range in size from tiny bacteria to the largest known animal, the blue whale. All are adapted for
life in salt water. Most are adapted for extreme pressures.
When you think of life in the ocean, do you think of fish? Actually, fish are not the most common life forms in the
ocean. Plankton are the most common. Plankton make up one of three major groups of marine life. The other two
groups are nekton and benthos ( Figure 1.1).
FIGURE 1.1
Living things in the oceans are placed in these three groups.
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Plankton
Plankton are living things that float in the water. Most plankton are too small to see with the unaided eye ( Figure
1.2). Plankton are unable to move on their own. Ocean motions carry them along.
There are two main types of plankton:
1. Phytoplankton are “plant-like” plankton. Since they make food by photosynthesis, they live in the photic
zone. Most are algae.
2. Zooplankton are “animal-like” plankton that include tiny animals and fish larvae. They feed on phytoplankton.
FIGURE 1.2
The phytoplankton (left) and zooplankton
(right) shown here have been magnified.
Otherwise, they would be too small for you
to see.
Nekton
Nekton are living things that swim through the water ( Figure 1.3). They may live at any depth, in the photic or
aphotic zone. Most nekton are fish, although some are mammals. Fish have fins and streamlined bodies to help them
swim. Fish also have gills to take oxygen from the water.
FIGURE 1.3
Nekton swim through ocean water.
Benthos
Benthos are living organisms on the ocean floor. Many benthic organisms attach themselves to rocks and stay in
one place. This protects them from crashing waves and other water movements. Some benthic organisms burrow
into sediments for food or protection. Benthic animals may crawl over the ocean floor. Examples of benthos include
clams and worms. Pictured below are two other examples ( Figure 1.4).
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Chapter 1. Types of Marine Organisms
FIGURE 1.4
These animals live on the ocean floor.
Some benthos live near vents on the deep ocean floor. Tubeworms are an example ( Figure 1.5). Scalding hot
water pours out of the vents. The hot water contains chemicals that some specialized bacteria can use to make food.
Tubeworms have the bacteria living inside them. The bacteria get protection and the tubeworms get some of the
food.
FIGURE 1.5
Tubeworms live near hot water vents on the deep ocean floor.
Summary
• Plankton are tiny organisms that are swept along on currents. Phytoplankton are tiny plant-like organisms.
Zooplankton are tiny animals.
• Nekton are organisms that go through the water under their own power. Fish and marine mammals are nekton.
• Benthos bury in the sediment, attach to rocks, or crawl over the seafloor.
Explore More
Use the resource below to answer the questions that follow.
• Marine Animal Census at http://video.nationalgeographic.com/video/news/animals-news/coml-complete-ce
nsus-vin/
1. When did the census begin? How many years did it run?
2. How many expeditions occurred during this census? How many total days were spent at sea?
3. What was the purpose of this census?
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4.
5.
6.
7.
What did the researchers find off of Australia?
What did they discover about the tuna off of Northern Europe?
What did this census create?
Why is it important to have data like this?
Review
1. Compare and contrast phytoplankton and zooplankton.
2. How are nekton adapted to life in the sea?
3. How are benthos adapted to life in the sea?
References
1. Zappy’s. Plankton, nekton, and benthos are the three groups of living things in the oceans . CC BY-NC 3.0
2. Phytoplankton: Courtesy of Dr. Yaqin "Judy" Li, NMFS/NOAA; Zooplankton: Courtesy of Matt Wilson/Jay
Clark, NOAA NMFS AFSC. Pictures of phytoplankton and zooplankton . Public Domain
3. Flickr:Mr. T in DC. Nekton, like a fish, swim through ocean water . CC BY 2.0
4. Left: Flickr:tpholland; Right: Ratha Grimes (Flickr:papertygre). Picture of an anemone and sea cucumber,
which live on the ocean floor . CC BY 2.0
5. Courtesy of C. Van Dover and the National Oceanic and Atmospheric Administration. Picture of tubeworms
living near hot water vents . Public Domain
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