Types of Habitats

Types of Habitats in Biology

First, let's take a look at the definition of a habitat.

Habitats must meet all the requirements for an organism to survive, such as having enough resources to sustain populations of organisms that can mate and reproduce.

Traditionally, when we think of habitats, we think of a place we inhabit or live in. And while this is true, habitats often include many types of organisms that can survive in the same area because of their adaptations.

We need to consider abiotic and biotic factors when we talk about habitats. Abiotic factors are non-living things such as water, the sky, and other physical surroundings of the environment. In contrast, biotic factors are composed of living things, such as the different organisms in the habitat.

We also must consider that almost any space on earth can be a habitat as illustrated in Figure 1. Habitats can range from microscopic, such as intestinal flora and fauna, to biomes, such as land or terrestrial.

Microhabitats are tiny areas that differ from the surrounding environments. A microhabitat's distinctive features allow it to house unique habitats. An example of a microhabitat could be an overturned log, an organism's gut, etc.

Generally, we think of terrestrial, land, and water or aquatic habitats when referring to habitats. The following sections will review some of the different terrestrial and marine habitats.

Figure 1: Almost any space on earth can be a habitat. Daniela Lin, Study Smarter Originals.

Marine Habitat

Marine habitats are areas located in the sea or ocean. The generally agreed upon marine habitats are split into the open ocean and the coastal regions. A coastal zone is a region between land and water. Even though these zones only occupy around 7% of the earth's oceans, they are essential because most of the world lives in these zones. The open sea, or the pelagic zone, is the deeper area outside the coastal zone.

The open ocean comprises around 99% of the earth's inhabitable spaces. Scientists usually divide the open sea into:

• Epipelagic zone: This part is the upper part of the ocean, and enough sunlight characterizes it for photosynthesis. It's around 2-3% of the open sea; beyond this level, it's too dark for photosynthesis. Generally, this zone begins at the ocean's surface till around 600 ft or 200 meters. Algae in the epipelagic area are responsible for about 50% of the oxygen in the earth's atmosphere and create most of the original nutrients for other organisms.

• Mesopelagic zone: This zone is also called the middle part of the ocean or the twilight zone. It begins from the end of the epipelagic area to around 3000 ft or 1000 m deep. Most vertebrate fishes live here and migrate up to the epipelagic zone at night in search of food.

• Bathypelagic zone: This zone can also be referred to as the lower open ocean. This zone begins at the bottom of the mesopelagic area till 13,000 ft or 4000 meters. It's the largest ecosystem on our planet, and there's no sunlight. Some species here have lost the ability to see and use bioluminescence to attract prey. Animals that commonly live here are anglerfishes and bristlemouths.

• Abyssal zone: This zone has almost no life and stretches from the bathypelagic area to the bottom of the ocean floor.

Ocean habitats generally include intertidal, mangroves, mudflats, estuaries, kelp forests, seagrass meadows, coral and oyster reefs, the open ocean, tidewater glaciers, and salt marshes.

• Intertidal environments occur where the shore or land meets the water or usually where coastal zones occur.

• Mangroves are trees and shrubs that grow near coastal areas; they serve as nursing grounds for marine life.

• Mudflats are muddy parts of water created by silt and mud brought in by the seas and oceans.

• Estuaries are areas with mixtures of fresh and salt water. We will go over this habitat in the next section.

• Kelp forests are forests of brown algae; it's home to many species due to the canopy it creates.

• Seagrass meadows consist of underwater plants and serve as an essential food source and habitat for many species.

• Coral reefs contain the most biodiversity out of any aquatic habitat. They support around 25% of all marine life, protect our coastal communities from storms, etc.

• Oyster reefs consist of many oysters. They provide habitats for many organisms, protect coastal areas from erosion, and filter particles in water, improving water quality.

• The open ocean consists of any part of the ocean away from the coast. There are different zones, as mentioned above.

• Tidewater glaciers usually serve as seals' habitats, and many are endangered due to climate change.

• Salt marshes are coastal grasslands that are flooded by water. They provide resources and shelter for around 75% of shrimp, crab, etc.

Estuarine Habitat

Lots of coastal habitats can be found where there are estuaries. Estuarine habitats are partly enclosed bodies of water where freshwater from rivers and streams mix with salt water from the ocean, resulting in brackish waters.

Brackish waters have higher salinity levels than freshwater but not as high as ocean water.

Estuaries attract many migratory organisms, such as birds, and serve as nursery areas for many different organisms. Water quality in estuaries has been affected by runoff contaminated by urban and agricultural development. Structures such as dams that control drainage, electricity, etc., have also affected freshwater flow.

Water continually cycles through estuaries as tides create the most significant flows of saltwater while the mouth of rivers creates freshwater flows. Within estuaries, salinity levels rise and fall with tides. When it's rainy, estuaries flood with fresh water, and in drier seasons, they have higher amounts of saltwater. Salinity levels are significant as they affect the organisms in this habitat. This means that many living things that inhabit estuarine habitats must get used to varying salinity levels. Organisms that can do this include halophytes or plants that can tolerate salty conditions, animals such as clams that are filter feeders, etc.

There are usually four kinds of estuaries:

• Tectonic estuaries are formed by tectonic or volcanic activity. When plates shift about, they create tectonic estuaries. An example of a tectonic estuary is San Francisco Bay. The San Francisco Bay lies between the Hayward and San Andreas fault lines which interact to cause the downward movement of land or down warping.

• Fjord estuaries occur when glaciers make steep valleys and water fills the area. An example of a fjord estuary is Glacier bay in Alaska. Fjord estuaries are usually cold and narrow; water flows seasonally from rivers and streams.

• Coastal plain estuaries are made when water levels rise and fill river valleys and glacier troughs. The Chesapeake bay was formed when massive glaciers retreated at the end of the last ice age. Afterward, the Atlantic Ocean filled the space with water and created a coastal plain estuary.

• Bar-built estuaries occur when barrier islands or sandbars protect them from the ocean. Barrier islands are long islands parallel to an island's mainland and usually protect it from storms and erosion. Bar-build estuaries are common along the coast of Texas and Florida, such as the Matagorda bay in Texas.

Freshwater Habitat

Freshwater habitats are places with low or less than 1% salinity content. Plants and animals here are adapted to low salt content and would not be able to survive in areas with high salinity, such as oceans.

The different freshwater areas are ponds, lakes, rivers, and wetlands.

Ponds and lakes can differ in size from a few meters to kilometers. Ponds are usually seasonally lasting a few months, while lakes usually last much longer. Both often have limited species diversity because they are not close to rivers and oceans. They are divided into three zones: littoral, limnetic, and profundal.

• The littoral zone is the shallow surface of a lake or pond, making it the warmest part due to the sun's rays. Organisms here include algae, crustaceans, fishes, and other aquatic plants. Turtles, ducks, etc., consume the animals and plants here.

• The limnetic zone is the open and well-lit area of a lake or pond with mostly plankton and freshwater fish. Plankton is an essential base of the food chain that allows many organisms to exist.

• The profundal zone is colder and denser than the limnetic and littoral zone. The organisms here are heterotrophs who consume other organisms, such as dead plankton, to survive.

• Temperatures in ponds and lakes can differ seasonally. The surface is always warmer than the bottom; during the spring and fall, the top and bottom layers usually mix, circulating oxygen around.

Rivers and streams are water that flows in one direction. The water is cooler in temperature and fresher at the source than at the mouth. Freshwater fish are usually found at the source. Towards the middle, rivers and streams widen, leading to more species being here, such as algae and other aquatic plants. Near the mouth, the water becomes less clear, resulting in less sunlight and less flora and fauna. Organisms near the mouth, such as carp and catfish, require less oxygen.

Wetlands are areas made up of marshes, swamps, and bogs. Hydrophytes, or aquatic plants that have adapted to low oxygen levels, dominate here. Hydrophytes include pond lilies, cattails, etc. They have the highest levels of species diversity compared to other ecosystems and are not connected to the oceans, unlike estuaries.

Terrestrial Habitat

Terrestrial habitats are habitats found on land as opposed to water. They include deserts, forests, grasslands, and mountains.

Deserts are areas that receive less than 50 cm/year of rainfall. Most deserts occur at low latitudes, but colder deserts can occur in Nevada, Utah, and parts of western Asia. Deserts have specialized vegetation, such as shrubs and cacti. Most animals are reptiles, as the desert doesn't provide sufficient covering or water for other organisms to survive. The four major types of deserts are hot and dry, semiarid, coastal, and cold.

Forests are regions dominated by trees; they contain 70% of the carbon in living organisms. The anthropogenic impact caused by deforestation and pollution affects the living organisms here. The three major types of forests are classified based on latitude: tropical, temperate, and taiga forests. Tropical forests have the greatest diversity of species and are primarily rainy and dry. The temperate forest has all seasons compared to tropical forests and around 200 days of the growing season. Taiga or boreal forests are the largest terrestrial biomes, characterized by low temperatures, snow, and plants that consist of cold-tolerant conifers.

Grasslands are areas dominated by grasses and shrubs instead of tall trees like forests. The two main types of grasslands are the savanna and temperate grasslands. Savannas have scattered trees, while temperate grasslands have mostly grasses with more varied temperatures.

The mountains are windy and cold. Examples include the Alps and the Rocky mountains. It's hard for any vegetation or animals to live here. The ones have adaptations such as layers of insulating fat and fur.