CHAPTER 15.2The Diversity of Ocean Life

There is a wide variety of organisms in the ocean. There are over 250,000 species.

Most marine organisms live in water that the sunlight reaches.

CLASSIFICATION OF MARINE ORGANISMS

Marine organisms are classified based on where they live and how they move.

The groups are either plankton (floaters) or nekton (swimmers). All other organisms are benthos (bottom dwellers).

PLANKTON

This group includes that drift in ocean currents like algae, animals, and bacteria.

Algae that perform photosynthesis are called phytoplankton.

Animal plankton are called zooplankton – most of these are larval stages of animals.

NEKTON

This group include all animals capable of moving independently of ocean currents but swimming or other means of moving.

These are mostly adult fish and squid, marine mammals, and marine reptiles.

There are a few animals that move from ocean to rivers.

BENTHOS

This is a group of organisms that live on the bottom of the ocean. Most benthos organisms live in shallow areas.

MARINE LIFE ZONES

How marine organisms are distributed is based on chemistry, physics, and geology of the ocean.

3 factors divide the ocean: the availability of sunlight, the distance from shore, and the water depth.

AVAILABILITY OF SUNLIGHT

The photic zone is the upper part of the ocean where sunlight hits. How clear seawater is, is affected by the amount of plankton, suspended sediment, and decaying organic particles in the water.

Also the amount of sunlight will change with atmospheric conditions, time of day, season of the year, and latitude.

The euphotic zone is the part of the photic zone closest to thee surface where photosynthesis can take place.

In open ocean this can reach 100 M down, near shore it does not reach as far.

There is still life that occurs below the photic zone.

The aphotic zone is where there is no sunlight.

DISTANCE FROM SHORE

The intertidal zone is where the land and ocean meet. This area will be alternately covered with water and not covered due to changes in the tide.

This is a difficult place for life because there are crashing waves, period of drying out, and rapid temperature, salinity, and oxygen concentration changes.

From the low tide line is the neritic zone. This cover the continental shelf. Usually sunlight can reach this area to the ocean floor.

This area usually has many organisms that live here. There are many nutrients in this area.

The oceanic zone is the open ocean. This area usually has lower nutrient concentrations.

WATER DEPTH

The pelagic zone is open ocean. Animals swim or float in this area. The photic part of this zone is home to phytoplankton, zooplankton, and nekton like tuna, sea turtles, and dolphins.

The aphotic part has giant squid and other animals that are adapted to living in deep ocean.

The benthic zone is the ocean floor. This area includes animals like kelp, sponges, crabs, sea anemones, sea stars, and marine worms.

The abyssal zone includes the deep-ocean floor, like abyssal plains. This area has extremely high water pressure, low temperatures, no sunlight, and little life.

Food in this area usually comes from the surface. They fall down to the bottom.

HYDROTHERMAL VENTS

This are along the oceanic ridge. This area has super heated water with many minerals.

There are organisms that live here and no where else in the world.