Offshore Systems

Topic: Offshore Systems

In this learn assignment you will:

• Examine the three main categories of offshore ecosystems:
• Life near the surface (epipelagic systems)
• Life in the twilight zone (mesopelagic systems)
• Life in the deep sea (abyssopelagic, hadalpelagic, and benthic systems)

Associated Course Competencies

CC11. Provide examples and characteristics of diverse and unique ecosystems from the surface through the water column and down to, and below, the seafloor. (IV) CC12. Explain how zonation patterns are caused by environmental features and influence marine organisms’ distribution and diversity. (IV)

Image Details: You've seen this image before. The open ocean environment is any part of the ocean that isn't near land. Its different ecosystems are characterized by depth.

Defining the Zones - Review

Before begining this lecture please review the Geography of Marine Biology lecture (embedded below, you can enlarge using the ... at the bottom), focusing on open ocean zones.

Epipelagic Zone

"The Surface Layer"

• Meaning: "Above Ocean"
• Depth: Surface to 200 meters
• Temperature: Variable. Like terrestrial ecosystems, surface temperature is determined by season and latitude. You can see how surface temperature changes in the NOAA image above, which shows a six year period.
• Defining Characteristics:
• Defined by how far sunlight is able to penetrate water.
• Oxygen enters the water and is circulated by wind.
• Photosynthesis can occur.
• The biomass in this zone can be consumed by zones beneath it either through predators vertically moving through the zones or through dead organism "falls".

Epipelagic Zone Examples

Mesopelagic Zone

The Twilight Zone

• Meaning: "Middle Ocean"
• Depth: 200 to 1000 meters
• Temperature: Rapidly declines. This zone contains the thermocline, which is a region where water temperature rapidly decrease.
• Defining Characteristics:
• The exact depth and strength of the thermocline varies seasonally due to the difference of starting temperature.
• Very, very little light reaches the depths. It isn't strong enough for photosynthesis to occur.
• Bioluminescence occurs in some organisms.
• Organisms frequently have larger eyes that face upwards to aid in hunting organisms that will be silhouetted from the dim light above.

Image Details: The thermocline is the range of depth where temperature is rapidly decreasing. Notice how as depth increases (y axis) the temperature (shown on x axis, red line is the data) decreases.

Mesopelagic Zone Examples

Bathypelagic, Abyssopelagic, and Hadalpelagic Zones

The Deep Sea or the Midnight Zone

• Meaning: "Deep Ocean", "Bottomless Ocean", and "Hades' Ocean" (Yep, as in the greek god. It goes so deep it's essentially called the underworld.)
• Depth: 1000-4000m | 4000 to 6000m | 6000m+
• Temperature: About 4C, just above freezing.
• Defining Characteristics:
• Despite being called the "bottomless ocean" the abyssal zone has about 3/4 of the marine floor.
• Defined by darkness and extreme pressure.
• In the Bathypelagic zone pressure is around 5800 pounds per square inch (sea level is 14.7 pounds per square in) making it almost 400 times the pressure we exist in on land.
• The deepest part of the hadalpelagic zone is 8 tons per square inch (over 1000 times what we live in)
• Organisms survive pressure with dense anatomy structures or gelatenous bodies that use the surounding water as their support (like with jelly fish).

Deep Sea Example

Wrap-Up Activity

• You will need to submit the following:
• Two takeaways from the learn slides
• One takeaway from each video (6 in total). You must label your takeaway with the video name for credit.