What is the Marine Biome?

Stefanie Spikell

The marine biome is basically the environment of the world’s oceans, and is a way of categorizing and understanding the life and general characteristics of undersea habitats. Biomes as a whole are ecological zones or regions that scientists use to classify plants, animals, and mineral nutrients. The marine biome is usually understood to cover oceanic life. Most of the time freshwater is its own category, and sometimes coral reefs are too, even though these occur in the ocean. There are usually five main zones in the biome, namely intertidal, pelagic, benthic, and abyssal, each with its own dominant plant and animal species. The diversity of life across these zones is usually quite abundant, and many researchers believe that the marine habitat is one of the richest in the world when it comes to the number of different life forms that coexist. Perhaps as a consequence, the biome is also particularly sensitive to pollution and human degradation. Problems related to temperature shifts and toxicity aren’t always immediately felt or noticed, but a growing number of scientists have been speculating that the oceans play a larger role in the stability of climates and environments on land than may have previously been believed. As such, protecting the ocean space and the life within it has become a priority for many people, industries, and governments.

Oil spills are a threat to the marine biome.
Oil spills are a threat to the marine biome.

Biome Basics

In its simplest sense, a biome is any specific habitat where the animals and plants share a common environment. There are a couple of different ways of categorizing these spaces; the simplest system names only land-based and water-based systems, but the categorization can also be much more granular. Aquatic biomes are usually divided into marine, freshwater, and estuary, which is sort of a combination of the two — often where a river meets the sea, or where the ocean feeds into other predominantly freshwater systems. On land, common divisions include temperate forest, rainforest, savannah, grassland, desert, tundra, and alpine.

The marine biome covers three quarters of the Earth.
The marine biome covers three quarters of the Earth.

Marine Zones

Researchers often break the marine biome into five distinct zones, primarily corresponding to ocean depth. The boundaries are often somewhat fluid and are usually more estimations than fixed points, and there is some crossover when it comes to the life, climate, and habitat of each, particularly around the edges. The animals and plants that live in different parts and particularly different depths of the ocean can be pretty varied, though, which does make zoning distinctions useful in certain contexts.

The first zone when coming from the shore is usually the intertidal zone, which is where the ocean meets the land; these waters are the shallowest and usually also the warmest, and are where most coral reefs are found. Many of these regions are profoundly impacted by the pull of the tides, and smaller creatures are often shifted from place to place very regularly. Next is the pelagic zone, which is often also known simply as the “open ocean.” This is deeper water where bigger fish and sea mammals like whales and dolphins live. Ocean currents bring a mix of colder and warmer waters, which helps sustain these and other creatures.

Things are darker and colder in the benthic zone, which is deeper ocean that doesn’t get much sunlight. Small shellfish, worms, sea stars, and various algae grow near the sea floor in this region, and some fish also make their home here. The darkest and deepest part of the biome is the abyssal zone, which is on or near the core tectonic plates of the earth; the water here is usually very cold and completely cut off from light. Fungi, spores, and bacteria are usually the most plentiful life forms.

Circulation Patterns and Movement

The circulation patterns in the open ocean move in a horizontal manner and affect the upper surface waters. There is also vertical circulation and this has more of an influence on marine life. In the upwelling type of vertical circulation of ocean water, deep ocean water filled with dissolved nutrients travels into coastal surface waters and encourages plankton growth. Plankton, in turn, is the basis of the entire food chain throughout the oceans. In thermohaline circulation, the nutrient-rich waters rise and mix, but only in the polar regions where differences in the temperature, density, and salinity of the ocean water are distinct.

Relationship to Land Climate

Marine currents affect all the coastal areas and the winds usually match the water temperature. Since water does not heat up or cool down very quickly, there are only small changes in the biome but, over time, these can and often do lead to big shifts when it comes to the sustainability of certain species or groups of plants and animals. Everything in the ocean is usually connected, be it through a food chain or some symbiotic relationships. Changes in one place are often felt in many others. The changes may be small at first, but often build cumulatively over months and years.

Pollution and Other Dangers

The introduction of foreign materials to the ocean can and does impact the dynamics of the biome, often very negatively. The coast of Alaska, the Persian Gulf, and the Gulf of Mexico are some of the worst places for oil spills, for instance, which have caused major destruction of marine wildlife and plants. Dumping of trash and toxic wastes in the ocean by companies is another major issue affecting the world's water sources. Even the laziness of everyday citizens who dump their trash waterways or shipping companies who are irresponsible with waste removal are affecting life in the ocean and, through it, the overall health and life of the planet as a whole.

The circulation patterns in the open ocean move in a horizontal manner and affect the upper surface waters.
The circulation patterns in the open ocean move in a horizontal manner and affect the upper surface waters.

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