Ocean Zones

The ocean is divided into various "zones" to help us better understand what is happening. Some of these zones help us to understand the environment in that location, others help us understand which creatures live in which parts of the ocean. Some zones are established to help us better predict conditions within them.



Our sun is the major source of energy for our ocean. It is not, we have discovered, the ONLY source of energy, but it is certainly a "biggie". Three temperature zones in our ocean have been identified. Each zone has a different set of conditions within it and is populated by creatures who have different needs.

THE SURFACE ZONE--- This zone can be found from the ocean's surface down to a depth of about 400 meters. All of the water in this zone is going to be fairly well mixed by such factors as currents, winds and waves. It is interesting to note that under ideal conditions, a beam of sunlight reaches only barely to the bottom of the surface zone. Under less than ideal conditions, only the top 100 meters, or less, of the surface zone receives much, if any, light from the sun. Temperatures in this zone vary of course, by climate and season, but the worldwide average temperature of the surface zone is 22 degrees Celsius.(Certainly the coastal waters of Maine fall well below this temperature for most, if not all, of the year)


THE THERMOCLINE---The thermocline is a transition zone, or zone of change. We see the thermocline as an area where the water temperatures drop rapidly from the warm surface conditions to the frigid deep water conditions. The thermocline is found between the depths of 400 and 800 meters below the ocean's surface.


THE DEEP ZONE---The deep zone is try the most typical place in our oceans, though it is a place that few creatures, especially humans, ever see or experience. It can be found starting at depths of about 800 meters below the surface. This zone extends all the way down to the ocean floor, which in most cases is at least a couple of miles deep! Clearly, more of our ocean is a part of the deep zone than any other. Yet conditions within this zone are strange and very harsh. The most obvious characteristic is the total lack of sunlight. This is a zone of eternal darkness. Temperatures hover just above the freezing point of water (between 0 and 4 degrees Celsius on average). Additionally, water pressure in the deep zone is enormous! Inhabitants (and there aren't that many of them) of the deep zone operate under a different et of rules than do most creatures. They are some of the most unique, strangest and well-adapted creatures in the world.


It is mildly interesting to note that the Arctic and Antarctic oceans have no temperature zones. The water there is uniformly cold with only slight variations in temperature with increasing depth.


Remember that temperature has an effect on the gas-holding ability of water. The cooler the water, the more gas that water will be able to hold. The cold Arctic and Antarctic water is very rich in gases like oxygen and carbon dioxide. This explains why the polar oceans are so filled with diverse sea life. Despite the bitterly cold temperatures, the oxygen charged water manages to attract a wide variety of ocean organisms.


The Shore Zone

The shore zone is the area of the ocean that lies between the high tide and low tide lines. Life is particularly difficult here for an ocean creature because it isn't always covered by water all of the time. That might not sound like such a bad thing, but an ocean creature is adapted to living underwater. It filters oxygen out of the water in pretty much the same way that we filter oxygen out of the air. For a sea creature to live in the shore zone, it must be able to spend at least part of its day exposed to the atmosphere. This means that it must either be able to function in the air as well as in water or remain dormant, in hiding, conserving its resources, until the coming high tide brings the water back. This is much more difficult a trick than it sounds. Imagine having to live for four or five hours, totally underwater each day. Now imagine doing it without a scuba tank! Okay, now imagine doing it without a snorkel! Get the picture?


In New England, there are three clear regions within the shore zone. Each differs mainly in the amount of time that it must endure exposure to the atmosphere.


The Littorina Zone: This zone is truly the boundary between the land and the sea. It is a zone of transition from a terrestrial environment to an aquatic environment. Only the most durable and well-adapted life forms can survive here. The Littorina zone is only covered with water during the highest part of the high tide. It is exposed to the atmosphere for perhaps 75% of each day. This zone is the furthest from the open ocean and is generally only kept moist by breaking waves and ocean spray. It is brownish-black in color and is populated by a small, tough, tightly clinging seaweed. the Littorina zone gets its name from another typical inhabitant of the area. Littorina Littorea is the scientific name for the COMMON PERIWINKLE. A periwinkle is a small snail about the size of your thumbnail. The periwinkle is able to withstand the dry times each day by sealing itself up in its shell where it is able to conserve both oxygen and moisture. Some of you adventurous souls from the Lincolnville Field Trip also know that periwinkles are, in a word, delicious!


The Balanoid Zone: The Balanoid zone is also known as the surf zone. This is the area being pounded constantly by crashing waves and surf. The major challenges to life here are both the nearly even split between a terrestrial and aquatic environment, and the constantly crashing waves which can hit with over 6,000 pounds of force! This zone is underwater only about 50% of each day. Inhabitants of this zone must have tough bodies and be strongly attached to the bottom to prevent being washed away, or up on shore, by the waves. The Balanoid zone gets its name from a typical inhabitant: Balanus Balanoides, the acorn barnacle. Other commonly observed inhabitants in this yellowish-brown colored zone are the Mussel, Clam, Sea Urchin, Sea Star (starfish), and several varieties of tough, stout sea weeds.


The Laminaria Zone: The Laminaria zone is the closest of the shore zones to the open ocean and is actually covered by water for most of the day (about 75% of the time). It is a reddish-brown colored zone and is the most heavily populated of all the shore zones. It has a more typical ocean-like environment. Its name is derived from a kelp-like seaweed abundantly found there, Laminaria. During the times of the day when this zone is covered by water, the tall fronds of kelp gently wave in the currents. Ocean inhabitants live in this forest of kelp. During low tide, the kelp droops over, forming a protective moisture barrier, under which many organisms pass the time until the tide returns. A few minutes devoted to exploring what lies beneath the kelp during low tide will yield surprisingly good results. You will find a variety of interesting creatures to examine.


The Ocean's Life Zones

This category could perhaps best be called "Categories" of life in the ocean...because that's what we're talking about here. Various factors affect the types of life that we will find in the oceans of the world. Perhaps the most influential factor is the presence of sunlight (or the lack of it). Other factors are: temperature, salinity, food availability, currents and water pressure. Organisms in the ocean are classified into three groups, or "zones", according to where they live and their habits and characteristics. It seems to me that these organisms are all grouped according to their swimming ability. Ocean creatures fall into the same categories that kids do at a summer camp; non-swimmers, "beginners" (meaning, sort of weak swimmers), and swimmers (those that are able to swim easily).



Plankton are a group of organisms which could be described as "non-swimmers". Plankton as a group really can't swim all that well, which can be a real disadvantage to a creature that lives in the ocean. I describe the plankton group as "floaters" because that really describes what they're able to do. Because of their poor swimming ability plankton tend to stay at or near the ocean's surface. They move by drifting with the currents and tides. They may rely on the wind and waves to move them around. Plankton may be very small, even microscopic in size. However, plankton are vitally important organisms. They play a crucial role in ocean food chains and oxygen production. Plankton are the primary food source for many larger organisms as well, such as baleen whales. We literally could not survive very long were all the plankton no longer present in our oceans. If the plankton were to disappear tomorrow, we would soon see a dreadful shortage of food in the world, as well as an ever-decreasing supply of oxygen in our atmosphere. Even though you and I are highly evolved, specialized and successful land creatures, our lives would be cut very short if something ever happened to the plankton in our oceans.

Plankton come in two varieties, depending on how they get their food.


ZOOPLANTON: These are the animal-like plankton. Zooplankton are animal-like because they must find their food, just as all animals must.


PHYTOPLANKTON: These are the plant-like plankton. Phytoplankton are called plant-like because they are able to make their own food through the process of photosynthesis, just as terrestrial plants do. Through the process of photosynthesis, plants convert Carbon Dioxide into food for themselves. A byproduct of this reaction is that plants produce the gas Oxygen into the atmosphere as a waste product. Approximately 50% of the oxygen in our atmosphere was created by the Phytoplankton in the oceans of the Earth. We hear a lot these days about saving the rain forests, which is certainly a great idea, but rain forests produce only about 20% of the world's oxygen supply! Perhaps one day soon, we'll see a SAVE THE PHYTOPLANKTON poster! Or maybe a PLANKTON-AID concert on TV! A walk-a-thon for plankton?


THE NEKTON GROUP: Members of this group could be called "swimmers". Each member is able to swim freely through the ocean. They are able to swim around and actively search for prey, and just as actively escape from predators by swimming away. This ability has given the Nekton group of creatures tremendous advantages in the area of being able to survive in the ocean environment and they have filled every available niche in the oceans of the world. Members of the Nekton group form our most prized food items, play a crucial role in the ocean's food webs, and are some of this planet's most interesting,beautiful and wonderful creatures.


THE BENTHOS GROUP: Members of this group are "non-simmers" and could be described as "crawlers and stick-in-the-muds"! Members of this group actually live on the ocean floor and do not swim at all. Some members of the Benthos group live in the deepest parts of the oceans. Members of this group include such diverse organisms as lobsters, clams, marine worms, even seaweed which is rooted to the ocean floor. Some members of the Benthos group have never seen the light of day!



Yes! For those of you still seeking to know even MORE about zones in the ocean, we come to our final set of ocean zones. Recall that the area between the high and low tide lines is called the SHORE ZONE. Next come a fairly shallow water area, located above the continental shelf. This is the NERETIC ZONE. This zone is particularly important because it contains the richest fishing grounds in the world! The neretic zone is a terrific place to fish mostly because of the fact that the water in this zone isn't all that deep. Sunlight is usually able to penetrate clear to the bottom of the neretic zone. This means that plants are able to use that sunlight to carry out photosynthesis. If their are plants present in this zone, that means that there's going to be lots of food for fish to eat, and oxygen for them to breathe. If there are lots of fish present, it makes sense that this zone would make a great and productive place to fish. After the Neretic Zone, comes the OPEN-OCEAN ZONES. The open-ocean zone is broken into two parts, an upper part called the Bathyal Zone, found between the ocean's surface and depths of about 2000 meters, and a lower part, called the Abyssal Zone, found between the depths of about 2000 meters and the ocean floor! Some of the strangest creatures you'd ever want to meet live in the Abyssal Zone.