open+ocean

toc The Open Ocean by Austin and Morgan

= An Introduction to the Open Ocean = Oceans, which are very large bodies of water that dominate the Earth's surface, hold the Earth's largest biomes, covering approximately 70% of the planet's surface. The Earth's five oceans include the Arctic Ocean, Atlantic Ocean, Indian Ocean, Pacific Ocean, and Southern Ocean. The largest of these oceans is the Pacific, encompassing approximately 169.2 million square kilometers. Life is extremely diverse in the ocean. Some animals may be as large as 30 meters, while others may be so small that they require a microscope to be seen. Some travel all around the ocean, while others live in the same place on the ocean floor for their entire lives.

There are many different ecosystems within the open ocean. The major biomes of the ocean include the interdal zone, the coastal zone, coral reefs, the pelagic zone, and the benthic zone. The pelagic zone, also known as the open ocean, begins at the edge of the continental shelf and extends outward. It is the largest marine zone, with a surface area covering over 90% of the world's oceans. The open ocean ranges from 500 meters deep along continental slopes to more than 11,000 meters. Typical characteristics of the pelagic zone include high pressure, frigid temperatures, and continuing darkness as depth increases. Life in the open ocean is not evenly spread because it is regulated by the path of currents and varying levels of sunlight. The productivity of the open ocean biome is generally low due to its vast surface are and lack of nutrients.

= The Pelagic Zone = The pelagic zone occupies nearly 1,370 million cubic kilometers and a depth of 11 kilometers. The pelagic zone can be divided into five vertical layers of the ocean depending on how deep the body of water is. These layers include the epipelagic, mesoplegaic, bathypelagic, abyssopelagic, and hadopelagic zones.

1. Epipelagic
The term epipelagic refers to sunlight. It is often called the surface zone. This layer covers depths from the surface down to 200 meters. As the first and shallowest level of the pelagic zone, there is enough light present for photosynthesis. The ability to photosynthesize causes the plants and animals in this layer to be largely concentrated. About all of the ocean's primary production happens in this level. Many fish, such as tuna, sharks, dolphin fish, and jelly fish call this layer home.

2. Mesopelagic
The term mesopelagic refers to twilight and stems from the Greek word for 'middle.' This layer covers depths form 200 meters down to 1,000 meters. This level may receive some light penetration, but it is not sufficient for the conduction of photosynthesis. As the mesopelagic zone goes down further and further, water undergoes oxygen depletion. Life in this level have efficient gills or minimal movement. Swordfish, squids, wolffish, and cuttlefish and severl bioluminescent organisms all reside within this zone. Some creatures in the mesopelagic zone may rise to the above epiplegaic zone at night for feeding due to the mesopelagic's lack of pvital nutrients.

3. Bathypelagic
The term bathypelagic refers to midnight and stems from the Greek word for 'deep.' This layer covers depths from 1,000 meters down to 4,000 meters. The bathypelagic layer is completely black. The only possible forms of light are those from bioluminescent organisms, such as lanternfish. At this level, there are no living plants. Most organisms survive by feeding from off of detritus snow falling from above zones or by preying upon others. Giant squid, smaller squids, and Dumbo octopodes live in this level, and are prey for sperm whales.

4. Abyssopelagic
The term abyssopelagic refers to lower and midnight and stems from the Greek word 'bottomless.' This layer covers depths from 4,000 meters down to the ocean floor. At these depths, extremely cold temperatures and immense pressures prevent very many species from being sufficiently adapted for survival. Several species of squid, echinoderms, the basket star, the swimming cucumber, the sea pig, marine arthropods, and the sea spider. As a result of the complete lack of light found in the abyssopelagic zone, many species have evolved to transparency.

5. Hadopelagic
The term hadopelagic stems from the Greek word 'Hades.' This layer covers the deep water in ocean trenches. This layer of the pelagic zone is mostly unknown and very few species are known to live here. It is known, however, that many organisms live in hydrothermal vents.

= Marine Life and Adaptations = The upper level of the open ocean is pentrated by sunlight and is often referred to as the euphotic zone. Due to sunlight being a resource, photosynthesis is able to occur and plants can grow. Some of these plants include phytoplankton and algae. Plankton is a mixture of plant and animal life in the open ocean away from the shore. Plankton provides the main food source for plenty of animals and is the beginning of the food chain. Phytoplankton is the plant portion of this mixture. Zooplankton, animals that drift in the ocean water, are the main predators of phytoplankton. The Blue Whale, the largest animal in the world that reaches a length of almost 30 meters, is another predator of phytoplankton. Algae describes plants that grow under the water. Another name that commonly refers to algae is seaweed. Animal life in this sunlit region of the open ocean encompasses a wide variety of species and vitality. Dolphins travel in herds of hundreds and even thousdands near the surface of the open ocean. Sharks, tuna, jellyfish, seals, sea lions, stingrays, and mackerel can also be found within the euphotic zone. There are not very many places to hide in such a lighted region; thus, many species in the euphotic zone have undergone the adaptation of countershading. Countershading allows for animals to be darker on top of their bodies and lighter on their undersides, allowing them to blend into the water to hide from predators. media type="youtube" key="UXl8F-eIoiM" height="204" width="339" align="left" In the deeper regions of the pelagic zone, light cannot penetrate through the water and photosynthesis is unable to occur. Thus, there are no plants within the mesopelagic zone. Animals that live in this region must be able to sustain cold temperatures, dark waters, and high pressures. Typical creatures that can be found here include the hatchet fish, octopus, and squid. There are numerous adapations that animals have obtained within this zone of the open ocean. For example, numerous animals have thin-shaped bodies to help them to hide from their predators. Others are red or black so that they may blend in with the dark waters. Fish, such as the hatchet fish and viper fish, have large mouths with sharp fangs to help them catch their prey. Due to the dark waters, other fish have very large eyes to help them see in the water. A lot of creatures within the mesopelagic zone wait for their food to come, as opposed to chasing it. To help them find such food, quite a few animals have adapted to making their own light through bioluminescence. The photophores in their bodies are the special organs that allow them to produce greenish light.

At the deepest level of the open ocean, known as the midnight level, the water is very cold and pressure is enormous. Some water pressures can reach up to two tons per square inch. The few organisms that live here have very tough lives. Some do not even have eyes. There is absolutely no plant life within the deepest and darkest depths of the sea. Due to the lack of plant life, there is no start of a food chain. Many animals in the deep ocean substitute this lack of a food chain by feeding on dead carcases fallen from above.

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