Complex sentence: In contrast, the natural marine ecosystems, a major supplier of food to human societies, are less vulnerable to sudden temperature fall, but are highly sensitive to reduced incident sunlight and increased level of UV-B radiation.
Split into simpler sentences: In contrast, the natural marine ecosystems, a major supplier of food to human societies, are less vulnerable to sudden temperature fall. However, they are highly sensitive to reduced incident sunlight and increased level of UV-B radiation.