ME Open Ocean Lesson
Welcome to the Ocean - Open 24/7!
We're setting sail on a vast journey across the open ocean, an immense realm that covers more than 70% of our planet’s surface. Unlike the familiar coastal areas or the mysterious ocean depths, the open ocean, or pelagic realm, is a world of its own, stretching from the sunlit surface waters to the dark, unseen depths.
This lesson will focus on the shallower open ocean, while the next lesson will focus on the deep ocean.
The open ocean is divided into distinct zones, each with its unique inhabitants and environmental conditions.
Review each zone's location and learn more about the abiotic and biotic factors (these again) at play in that zone.
Bathed in sunlight, this zone goes down to about 200 meters. It’s bustling with life, from microscopic algae to large marine mammals like whales and dolphins. These surface waters are vital for photosynthesis, contributing significantly to oxygen production.
The sunlit upper layer of the open ocean, the epipelagic zone, is teeming with life thanks to its abundance of sunlight. Here, photosynthesis is possible, making this zone the primary area for phytoplankton growth, which forms the base of the marine food web.
The abiotic factors like light intensity, temperature, and salinity vary but generally support a wide range of biotic elements, including algae, plankton, larger fish like tunas and sharks, and marine mammals such as dolphins and whales. The interactions between these organisms and their environment create a dynamic ecosystem, with nutrient cycling and energy flow driving life throughout the entire ocean.
Extending to around 1000 meters, where sunlight fades, this zone is home to fascinating creatures like bristlemouth fishes. Many of its inhabitants undertake nightly migrations to the epipelagic zone to feed under the cover of darkness.
As we descend to the mesopelagic zone, extending down to about 1000 meters, sunlight diminishes and the environment changes dramatically. Abiotic factors here include minimal light, cooler temperatures, and increasing water pressure.
Despite the limited light, the biotic factors are fascinating. This zone hosts a variety of fish, jellyfish, and squid, many of which exhibit bioluminescence. The most striking biotic phenomenon is the nightly vertical migration, where numerous species ascend to the epipelagic zone under the cover of darkness to feed, and descend at dawn to escape predators. The mesopelagic zone acts as a critical link between the upper and deeper parts of the ocean, transferring nutrients and energy.
We explored two different zones of the open ocean. The epipelagic zone is a vibrant, sunlit upper layer of the open ocean, supporting a diverse array of life, including algae, plankton, and large marine animals, thanks to abundant sunlight and suitable conditions for photosynthesis. The mesopelagic zone, characterized by diminished sunlight, cooler temperatures, and greater water pressure, is home to a range of species exhibiting fascinating adaptations like bioluminescence and nightly vertical migrations for feeding.
UP NEXT: The Deep Ocean
[CC BY-NC-SA 4.0 Links to an external site.] UNLESS OTHERWISE NOTED | IMAGES: LICENSED AND USED ACCORDING TO TERMS OF SUBSCRIPTION - INTENDED ONLY FOR USE WITHIN THE LESSON. NOAA video used with permission from site.