External factors are factors that affect the growth of seaweed from outside the body. At planting seaweed external factors affecting the growth is from the ecological or live media seaweed. Water temperature is one factor that is very important in the study of physics symptoms seawater and waters which could affect animal and plant life in these waters. Water temperature affects the rate of photosynthesis. The optimal water temperature values for the rate of photosynthesis is different for each type.
In principle, higher temperatures can menyababkan proteins undergo denaturation, and can damage cell membranes and enzymes that are unstable to high temperatures. According to Mubarak and Wahyuni (1981) temperature is a secondary factor for the life of seaweed and high fluctuation will be able to avoid the presence of water mixing. Crebs (1972) in Apriyana (2006), states that the seaweed will be able to thrive in areas corresponding to the temperature at sea.
Each species of seaweed require different temperatures for growth. Therefore, there is little difference in the type of seaweed that grows in the tropics, the subtropics and in cold regions. Climate change is real to inhibit the growth of seaweed can either morphological and physiological changes can even turn it off. The water temperature is affected by solar radiation, air temperature, weather and location.
Solar radiation is the main factor affecting the rise and fall of the water temperature. Water has a great capacity to store heat so that the temperature is relatively constant compared to the air temperature. The air temperature has exceeded the limit of the range that can be lethal, so the kelp on the rocky coast can die, either from the cold or heat. Temperature has a direct influence, where seaweed can die due to run out of water, running out of water can be accelerated by increasing temperature.
Seaweed has a specific temperature range because the enzyme content of the seaweed. Sea grass will thrive in areas corresponding to the growth temperature. Dawes et al., (1974), stating that isoforme Eucheuma, Eucheuma sp, respectively Gelidium achieve optimum value at a temperature of 21C, 24C and 21-27 ° C which is the same light intensity conditions. Furthermore it is said on the condition of different light intensities, the rate of photosynthesis is also influenced by water temperature.
According Sulistijo and Atmadja (1996) good water temperature range for the seaweed Eucheuma sp is 27-30C, while according Zatnika (1987) in supit (1989) amounted 24-30C. Bird and McLanchian (1986) in supit (1989), Soegiarto (1984) in Eidman (1991) says that a good temperature range for growth Kappaphycus cattonii is 24-31C.