Ocean is the largest biomass on Earth. Each biome in the ocean is supported by a unique biodiversity, climate, geology, and oceanography. Plants and animals adapt to specific habitat conditions which are crucial for their survival success. These conditions include Water movement, Nutrient availability, Water pressure, Amount of Light, Salinity, and Temperature. Some animals are adapted to live in a shallow, warm habitat whereas, others like deep, dark, and cold ocean worlds.
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Types of Marine Habitats
Ocean habitats can be divided into two categories based on distance to the shoreline:
- Open Ocean habitat
- Coastal Ocean habitat
Alternatively, Ocean habitats can also be divided into the following categories based on depts:
- Pelagic habitats
- Demersal habitat
A. Open Ocean habitat
The open ocean is the region of the vast ocean found beyond the continental shelf. It is located far away from the coast and is characterized by its depth, expanse, and lack of direct influence from land.
Open Ocean lacks nutrients; however, rich in the primary production of Oxygen than any other marine habitat. It hosts 10% of marine species including the fastest and largest animals that live in the ocean.
Different zones within the Open Ocean:
The open ocean is divided into several distinct zones based on depth, light availability, and environment. These zones are
1. Epipelagic Zone
- This is the sunlit zone located 0-200 meters below the surface, and a region where most marine life is found.
- It supports photosynthesis by phytoplankton and is warmer depending on latitude and season
- Epipelagic zone also supports a wide variety of Zooplanktons like protists, fish, copepods, cnidarians, fish, marine mammals, sharks, and seabirds. Organisms here perform diel vertical migration meaning that they move to surfaces during night for feeling.
- This is known as the twilight zone located 200-1,000 meters below the surface as the light penetration is limited.
- The oxygen level in this zone is lower as the depth increases. However, marine life is well supported in this region.
- The animals here have a strange appearance adapted to the environment with the ability to produce light on their own through photophores (bioluminescence) for navigating in the darkness. They also, possess big sharp teeth with large mouths to catch prey and can camouflage to transparent, black, red, or silver.
- Organisms such as lanternfish, deep-sea squid, bristlemouths, and certain jellyfish may reside.
- The Bathypelagic Zone is a completely dark zone with no penetration of sunlight to this layer. It is located 1,000-4,000 m below the surface.
- This region and all zones below it experience the only source of light biologically from the phenomenon of bioluminescence.
- The temperature in this zone is constant at a chilling 39℉ (4℃)
- Organisms inhabiting this zone possess red, black, or transparent coloration. Furthermore, soft skin, small eyes, tiny pectoral fins, large mouths, and slimy bodies are a few adaptation traits in the organisms here. It includes deep-sea lanternfish, dragonfish, gulper eel, vampire squid, sleeper shark, dumbo octopus, etc.
- Many organisms here, rely on “marine snow” for food which means the organic debris falls from the zone above it.
- The Abyssopelagic Zone is a perpetually dark zone located 4,000 to 6,000 m below the surface with a pitch-black bottom hence, named abyssal translating to “bottomless”
- The zone covers 83% of the total ocean’s area, often with soft sediments, hydrothermal vents, and temperatures reaching near freezing point 3℃.
- The region also experiences high pressure up to 200 atm to 400 atmospheric pressure. Hence, the organisms living in this region are well-adapted to withstand high pressure too, such as sea cucumber, basket star, cusk-eel, and microorganisms relying on chemosynthesis through hydrothermal vents.
- The Hadalpelagic Zone is the deepest in the ocean and lies 6,000 to very deep 10,994 m below the surface. It is estimated that this zone experiences 8 tons per sq. inch as the whole oceanic layer lies above it.
- The zone has a constant temperature above the freezing point and a pressure of 600 to 1,100 atmospheric pressure.
- Life is known to exist here in the form of single-celled organisms, a Xenophyophore discovered in the Challenger deep trench. Other organisms discovered in the zone include the Polychaete worm, a type of cusk-eel called Abyssobrotula galatheae known to be the deepest living fish at 8,372 meters below the surface (Puerto Rico Trench).
- Estuaries
- Mangrove forests
- Salt marshes
- Coral reef
- Seagrass meadow
- Rocky shore
- Sandy shore
- Estuaries are partially enclosed water bodies that are formed either by flooding of river valleys due to rising sea levels or by tectonic movement of Earth’s crust.
- Fjords are a type of estuaries with a narrow inlet for the sea with cliffs enclosing it created by a glacier.
- Estuarine environments have a varying salinity as freshwater here is mixed with seawater. Therefore, animals here adapt by the process of osmoregulation and are euryhaline.
- Estuaries are often called “nurseries of the sea” because many animals come here to nest or breed. These animals include fish and shellfish (salmons, herring, oysters) which are commercially a source of food for humans. Furthermore, estuaries also serve as a feeding ground for migratory birds (Canada goose, Sandpipers, Great blue heron)
- Phytoplanktons, Barnacles, Mollusks, Sponges, Isopods, etc are invertebrates inhabiting Estuarine environments
- Mangrove forests are a unique environment of Estuaries in the tropical and subtropical regions. These trees possess specialized roots with pneumatophores which are well adapted to live in mangrove swamps i.e., water-logged soil with excess salt.
- Furthermore, a wide variety of animals can be found in mangrove forests like Jacks, Sheepshead, Lungfish, Mudskippers, Gray snappers, Gobies, and Small goliath grouper which are various fishes. Whale sharks migrating to Donsol Bay in the Philippines also include in the Mangrove community. Turtles, Snakes, Crocodile, Alligator, Toad, Treefrog, Egret, and Spoonbill are some vertebrates that inhabit mangrove forests.
- Salt marshes are water-logged environments flooded by salt water brought upon by tidal forces. Depending on the tidal forces, the marsh can be either flooded or not. Flooded conditions have a much more diverse vegetation.
- The soil in this environment lacks oxygen, and is composed of high salt levels.
- These marine habitats are found commonly in temperate regions characterized by plants adapted to live in high-salt environments.
- Similar to Estuaries, many fish species come to salt marshes as a nursery. Invertebrates like Fiddler crab, hermit crab, stone crab, bivalves, clams, and whelk are found in this environment. Furthermore, birds inhabiting salt marshes abundantly include egrets, herons, and shorebirds. Chemoautotrophic bacteria such as ammonia-oxidizing microorganisms, Nitrosococcus, Nitrosomonas, Nitrospira, etc are critical members of Salt marsh in maintaining the carbon: nitrogen ratio.
- Coral reef is the most diverse marine habitat among all and is located mainly in the tropical and subtropical regions. It is a biological structure built out of calcium carbonate and secreted by polyps. It can be referred to as the “rainforests of the sea” cause of its biodiversity.
- Coral reefs support a huge communities of living organisms especially, algae, and zooxanthellae with which they undergo symbiotic relationships. This symbiosis protects algae from corals; in return, algae live inside the coral’s body and produces energy through photosynthesis.
- Coral reefs can take various forms due to the distance to the shoreline.
- It serves as a breeding ground for fish, crustaceans, mollusks, and sponges.
- Iconic species of coral reefs include clownfish, reef sharks, manta rays, sea turtles, sea anemones, giant clams, parrotfish, stonefish, lionfish, nudibranchs, butterflyfish, and Moorish idols.
- Seagrass meadows are a marine habitat characterized by seagrasses on its layer which is a flowering plant. This habitat is found in the pelagic zone of all continental shelves except in Antarctica. Seagrass is salt-tolerant. They possess long and narrow leaves that appear green. These grasses are found in abundance in the form of meadows (grassland) hence, seagrass meadows.
- Seagrass meadow supports a rich biodiversity of marine life as a nursery for many juvenile fish. They play a crucial role in the biogeochemical cycle, and filtering water pollutants to improve water clarity.
- As an important habitat within the marine environment, Seagrass meadows a home to several species of fish, turtles, sharks, marine mammals (dugongs and manatees), mollusks (octopus, squid, cuttlefish, snails, bivalves), crustaceans (shrimp, crabs, copepods, isopods and amphipods) polychaete worms, sea urchins and sea anemones and so on.
- Hydrothermal vents are an extreme marine habitat located below the ocean floor, and appear as hot springs on the oceanfloor. They are cracks and fissures formes as a result of tectonic plates of oceanic crust moving apart and breaking.
- The vents release super-heated, mineral-rich chemicals to the ocean making the environment adaptable for thermophilic and chemosynthetic organisms. Animals such as red-tipped tube worms, ghostly fish, strange shrimp with eyes on their backs, scaly foot gastropods and yeti crabs have been known to thrive in these extreme deep-sea hydrothermal vents.
- Unlike other ecosystems that rely on sunlight for source of energy. Microorganisms here use chemicals such as Hydrogen sulfide as a primary source of energy like Thiobacillus and Beggiatoa. Other groups of microbes found here include hyperthermophiles and methanogens.
- Sandy shores and rocky shores are those marine habitat highly influences by tidal forces, and vulnerable to human-driven changes. Sandy shore is a broader term where, sand is the dominating substrate. It extends from the intertidal zone to the upper shoreline.
- In the Rocky shore, these substrates are highly consolidates and stable to its postition where, rocks are the dominating substrate.
- Beach is a region where, the shore is beneficial for human recreation purpose. It was previously a region for small boats to be landed to.
- Organisms harboring in the sandy shores include bivalves, seastars, crabs, polychaete worms, birds (sandpiper and gulls). Furthermore, organisms harboring the rocky shores are mostly sessile or have an adaptation to withstand consolidated substrate below it. These include Barnacles, mussels, sea anemones, algae, snails, all of these animals have a different strategy to avoid predation.
- Kelp forest is a highly productive marine habitat dominated by Kelp, which is an underwater group of brown algae extending to upto several meters. A species of Kelp, Macrocystic pyrifera can extend upto 60 meters of length. These kelps are attached to a substrate called holdfasts. It can grow in cool and relatively shallow water. Kelps are dependent to essential nutrients drifted by the waves.
- Kelp forests provide shelter for many organisms including fish, marine mammals like sea lion, whales, sea otters and invertebrates that include bristle worms, prawn, snails, and brittle stars. Furthermore, it acts as a nursing ground for several juvenile species.
- Some iconic species of kelp forests include kelp bass, rockfish, garibaldi, sea otter, sea urchin, purple sea star.
- U.S. National Park Service, Open Ocean – Oceans, Coasts & Seashores, Retrieved from https://www.nps.gov/subjects/oceans/open-ocean.htm
- National Oceanic and Atmospheric Administration, Layers of the ocean, Retrieved from https://www.noaa.gov/jetstream/ocean/layers-of-ocean
- National Oceanic and Atmospheric Administration, Life in an estuary, Retrieved from https://www.noaa.gov/education/resource-collections/marine-life/life-in-estuary#:~:text=Importance%20of%20estuaries,estuaries%20for%20nesting%20and%20breeding.
- U.S. National Park Service, Estuaries – Oceans, Coasts & Seashores, https://www.nps.gov/subjects/oceans/estuaries.htm
- U.S. National Park Service, Coral Reefs – Oceans, Coasts & Seashores, Retrieved from https://www.nps.gov/subjects/oceans/coral-reefs.htm
- Reddy S.(2019)Four types of coastal habitats and why they matter. The Pew Charitable Trusts Retrieved from https://www.pewtrusts.org/en/research-and-analysis/articles/2019/05/31/four-types-of-coastal-habitats-and-why-they-matter
- Marine Biodiversity Portal of Bangladesh (2024) Marinebiobd. Sandy Shore Retrieved from https://marinebiodiversity.org.bd/sandy-shore/
- National Oceanic and Atmospheric Administration, What is a kelp forest? https://oceanservice.noaa.gov/facts/kelp.html
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2. Mesopelagic Zone (Twilight Zone)
3. Bathypelagic Zone (Midnight Zone)
4. Abyssopelagic Zone (Abyssal Zone)
5. Hadalpelagic Zone
B. Coastal Ocean habitat
Coastal ocean habitats are diverse environments where the ocean comes in contact with the land or other words, the tide meets the shoreline. Even though the coast hosts a small portion of ocean habitat, it is diverse in marine life. The coastal habitat is influenced by both marine and terrestrial processes, making it rich in biodiversity.
Coastal ocean habitats include the following
1. Estuaries
2. Salt marshes
3. Coral reef
4. Seagrass meadows
5. Deep-sea hydrothermal vents
6. Sandy or Rocky Shores
7. Kelp forest
References