Necessary Climate
Coral reefs are made up of very delicate organisms and therefore are very sensitive to climate, resulting in many limiting factors for this biome. They predominantly exist in only the tropics zone where the temperature is most suited for the survival of their organisms. There are two types of coral reefs; deep and shallow water reefs. Very little is known about deep water coral reefs except that they can survive further north of the tropics zone under more frigid temperatures and at greater depths. Shallow water coral reefs mostly exist between 30ºN-30ºS latitude in the tropics where there is a preferable average annual water temperature of about 21ºC or 69.8ºC (close to the ideal 26-27ºC or 79-81ºF temperature). In addition, shallow water reefs can rarely be found at lower than 50 meters (or 160 feet) below sea level due to a lack of necessary sunlight (for photosynthesis) and cooler temperatures. Another climate restraint for most coral reefs is that they can seldom exist in water with temperatures below 18ºC or 64ºF (though there are a few reefs near the Persian Gulf that have adapted to live at extreme temperatures).
The average salinity of the water is about 34 or 35 parts per thousand (ppt) or 34/1000 and 35/1000. The salinity of the ocean is important for coral reefs because they can rarely survive when the salinity levels are too low (below 28 ppt) where the water is fresher, or too high (above 38 ppt) where the water is significantly saltier. As you can see below, the average salinity levels since 1920 have gone up and down, rising to a peak and then falling rather consistently. However, you can observe that over the years, the rising and falling of the ocean salinity has significantly been reduced and the salinity levels have been slowly going down. You can predict from this concerning trend that in the coming years, the salinity levels will continue to fall slowly and prevent coral reefs from surviving with the decreasing salinity levels or force them to adapt.
The average salinity of the water is about 34 or 35 parts per thousand (ppt) or 34/1000 and 35/1000. The salinity of the ocean is important for coral reefs because they can rarely survive when the salinity levels are too low (below 28 ppt) where the water is fresher, or too high (above 38 ppt) where the water is significantly saltier. As you can see below, the average salinity levels since 1920 have gone up and down, rising to a peak and then falling rather consistently. However, you can observe that over the years, the rising and falling of the ocean salinity has significantly been reduced and the salinity levels have been slowly going down. You can predict from this concerning trend that in the coming years, the salinity levels will continue to fall slowly and prevent coral reefs from surviving with the decreasing salinity levels or force them to adapt.