There are probably many answers, here are a couple that I am familiar with to get started.
Cold currents are generally from deep water that has sunk at the poles and travelled deep below the surface. When this cold, nutrient rich water surfaces at an upwelling the nutrients become available to phytoplankton that photosynthesise them powered by the sun. This explosion of growth fuels the food chain and is associated with some of the major fisheries in the World; eg the Peruvian Sardine fishery, which support local populations.
During periods of El Nino the trade winds in the Pacific lessen interfering with the driving of warm surface waters West and eliminating the upwelling cool currents resulting in reduced fisheries productivity.
El Nino years are also associated with warmer surface waters which cause coral reef bleaching. When the sea surface temperature exceeds a threshold temperature for the coral over a period of time the organism becomes stressed and releases the zooxanthellae essential for photosynthesis within the coral tissue. In time the coral will die and be replaced by more vigorously pioneering algal species that prevent the recolonisation of the reef by coral polyps. Once this happens the fish leave and it is difficult for the reef to recover. This is one of the greatest challenges being faced by countries that rely on reefs for food and tourism.
no
water
The currents that keep coastal regions cooler than inland climates year-round are called maritime currents. These currents bring cool oceanic air to coastal areas, moderating temperatures and creating milder climates compared to the more extreme temperatures found inland.
They create currents and micro climates for different sea life.
Currents in the coastal water masses
The type of current that creates warmer climates along a coastal area is a warm ocean current. Warm ocean currents bring warm water from the tropics to higher latitudes, resulting in milder temperatures along the coast.
Warm Ocean currents warms the air above it and some move from the tropic towards both poles ---------------------------------------------------------AND----------------------------------------------------------------------------- Cold Ocean currents also affect weather patterns by bringing cold water from polar to the equator
Currents in the coastal water masses
Ocean currents that originate from high latitudes and flow towards the equator create cooler climates in coastal areas. These currents bring cold water from polar regions, which in turn cools the surrounding air and moderates temperatures along the coast. An example of this is the California Current along the west coast of the United States.
Areas with hotter water tend to have drier climates because the warm water increases evaporation rates, leading to more moisture in the air. Higher salinity in coastal waters can actually lead to less evaporation and contribute to higher humidity in cooler, more humid areas. Additionally, the direction of prevailing winds can also affect the distribution of moisture from the coastal waters.
Vertical movement of water surface refers to the changes in elevation of the water level at a particular location, usually caused by factors such as tides, waves, or water currents. This movement can affect the depth of water in a given area and can impact navigation, coastal erosion, and other coastal processes.
"Currents affect fish by bringing in rubbish, dirty water, and other stuff"