The ocean environment is varied and vast, and also greatly influences life on land. From     driving climate and working as a carbon sink, to providing coastal communities with a means of employment, there is an interconnectedness between aquatic and terrestrial environments. 

The ocean supports a huge diversity of life. Water is 300 times more dense than air, meaning animals have evolved and adapted to living in water. The blue whale, the largest animal that has ever lived on the planet, is able to grow to its enormous size living in water as its weight is supported by the density of its environment. This would be impossible on land. 

Oceanic Zones

The ocean is a 3-dimensional environment, allowing life to evolve and adapt in different ways. The ocean is separated into different zones, with pressure and light being two of the main drivers of life. 

Despite not having the amount of pressure as deeper oceans, the ocean surface and intertidal zone are also incredibly harsh environments. Temperature can vary drastically in shallower ocean zones, including both the ocean surface and the intertidal zone. Tides can expose intertidal animals to the air, while the heat of the sun can create a huge variation in temperatures making life in these regions difficult. The mechanical action of waves and wind can also influence life in this ocean zone.

The epipelagic zone (0m – 200m) is easily penetrated by light, with pressure at the surface remaining relatively low. This zone is characterised by the presence of enough light for photosynthesis, and as a result, the epipelagic zone has the highest density of life in the ocean, as micro and macro algae support a number of different ecosystems. All marine mammal species are found within the epipelagic, as they are required to breathe air at the surface. 

In the mesopelagic zone (200m – 1000m), there is an increase in the amount of pressure with depth, along with a decrease in the availability of light, so photosynthesis cannot occur. There is also a large variation in temperature, known as a thermocline, as temperature decreases in depth from the ocean surface limiting the distribution and movement of some species. Animals which are found in the mesopelagic include sharks, hatchetfish, lanternfish, swordfish, ctenophores and the firefly squid, to name a few.  

The bathypelagic zone (1000m – 4000m) is devoid of light, and the pressure of water is immense. The temperature in the bathypelagic zone is a constant temperature of approximately 4 degrees Celsius. As a result of these challenging conditions, animals in this zone display many diverse and unique adaptations. Many animals in the bathypelagic are red or black in colour to avoid detection, while others display bioluminescence to attract prey. Animals such as the vampire squid, giant isopod, dumbo octopus, Greenland sharks and the giant octopus are all found in the bathypelagic zone. Even some marine mammals including the sperm whale, several species of beaked whale, and elephant seals can all dive to the depths of the bathypelagic.

 

The abyssopelagic zone (>4000m) and the hadopelagic zone (deep ocean trenches) also have no available light along with incredible amounts of pressure. However, conditions in these zones are relatively stable, with a constant temperature of approximately 2 degrees Celsius. Animals such as the tripod fish, hagfish, and grenadiers can be found in these zones, along with many benthic animals. 

Oceanic Currents 

Oceanic currents are the forces driving the continuous movement of ocean water around the globe. Oceanic currents are driven by wind, temperature, salinity and the contours of shorelines. As water is transported via currents, water of different temperatures and salinity mix. Many animals are reliant on currents for dispersal and transportation, along with the nutrients and oxygen circulating currents provide. 

Surface currents are currents within the top 500m of the ocean surface, and are predominantly driven by wind. Marine biota is dependent on these currents, as they transport nutrients and disperse animals and plants.

Deep ocean currents are driven by temperature and salinity, and are known as the thermohaline circulation. As water is transported away from the equator to the poles, it cools and sinks. In addition, dense, saline water also sinks into ocean basins. As this cold, saline water sinks, it transports water from the deep ocean back to the surface, warming as it rises. In this way, the thermohaline circulation transports water around the worlds oceans.