There are numerous marine mammal habitats in the ocean—from coral reefs to estuaries to deep-sea hydrothermal vents.
The seas, which account for 70 percent of the surface of the Earth, can be as shallow as a few millimeters or as deep as 11.5 kilometers (7.2 miles) below sea level.
There are about 2000 different species of unicellular forms, plants, and animals that may be found in the water, the majority of which can be found on the seabed. Only 2 percent of the population lives on the open ocean.
Zones for Marine Mammal Habitats in the Ocean
Ocean life is divided into zones with specific species living within each zone:
- Photic zone: The photic zone is where photosynthetic activity occurs. These are the most productive zones. The photic zones cover the first few hundred meters below the surface, where sunlight bathes the water during the day. The photic zone is home to plant life and zooplankton.
- Intertidal (littoral) zone: The intertidal zone is where the sea and the sand meet. The intertidal zone is a very harsh environment but one with great diversity. Marine life living here is subject to extreme temperature changes, pounding surf, sunlight, wind, rain and erosion. There is a large supply of nutrients, however, for the creatures that live in this zone, which include limpets, snails, and barnacles.
- Subtidal (sublittoral) zone: The subtidal zone is below the intertidal zone, which is always submerged.
- Estuary: Estuaries are where fresh water flows into the sea.
- Neritic zone: The neritic zone is the shallow water zone that surrounds the continents and extends to the continental shelf.
- Pelagic zone: The pelagic zone is the open ocean. Within the pelagic zone are layers known as epipelagic (below the surface), and mesopelagic (receives dim light), and three layers of the deep ocean, bathypelagic, abyssopelagic, and hadopelagic.
Marine Mammals in the Ocean
It is known that there are numerous marine mammals in the ocean—from coastal mammals to those living in deeper waters.
- Cetaceans (dolphins, whales, and porpoises)
- Pinnipeds (seals and walruses)
- Sirenians (dugongs and manatees)
- Otters (sea otters and marine otters)
Some marine mammals, like polar bears and seals, divide their time between land and sea, while others; such as whales, spend their entire lives in the ocean.
Marine mammals in the oceans have developed mechanisms for coping with salt water. Because seawater has more substances dissolved in it than body fluids, water tends to leave the body when immersed in seawater by osmosis. Sea mammals have thick skin to keep moisture in and a slimy surface to increase waterproof capabilities.
What are Marine Mammals?
Marine mammals are warm-blooded vertebrates (animals with a backbone) that bear live young and feed them milk, just like terrestrial mammals, but spend most or all of their lives in the ocean.
They are divided into three categories that share comparable adaptations to aquatic life but have completely diverse origins and life habits.
Sirenians, manatees, and dugongs are sluggish plant eaters found in warm, shallow coastal settings.
Pinnipeds, which include seals, sea lions, and walruses, bear young on land but spend most of their time in the water.
Cetaceans, or dolphins, porpoises, and whales that spend their whole lives in the water, include both toothed species that are predatory predators and filter-feeding baleen whales that absorb massive amounts of microscopic plankton.
Marine mammals in the ocean range in size from little seals and porpoises to the blue whale, the biggest animal that has ever existed. Many cetaceans and pinnipeds dive to incredible depths to feed, which was only recently found using digital tags that record the animals’ movements, direction, and depth over time.
Marine mammals have vital ecological functions as both predators (many hunt for fish) and prey (for sharks and other, larger marine mammals). Humans have traditionally exploited marine mammals for food and fur. Although hunting pressures have decreased, marine mammals continue to suffer from low populations and unintentional human activities such as particular fishing practices, boating and shipping traffic, and increased ocean noise.
WHOI scientists have been doing research on marine mammals in the ocean for decades, beginning with the earliest underwater recordings of marine mammal noises in the 1940s and progressing through the invention of digital tracking tags and CT scanning procedures.
The WHOI Marine Mammal Center fosters study on whales, dolphins, and seals, such as their behavior, health, anatomy, and perception; strategies for releasing entangled whales and the reasons of strandings; and the link of marine mammal populations to ocean conditions and plankton abundance.
Read more: Marine Mammals in th Ocean