Reduced water availability during the dry season could stress crops, while warmer temperatures could also reduce yields of certain crops. Studies in other tropical countries indicate that climate change may reduce plantain, banana, and coffee yields". "Hot days can be unhealthy—even dangerous. Certain people are especially vulnerable, including children, the elderly, the sick, and the poor. Rising temperatures will increase the frequency of hot days and warm nights. High air temperatures can cause heat stroke and dehydration and affect people’s cardiovascular and nervous systems. Warm nights are especially dangerous because they prevent the human body from cooling off after a hot day. Since 1950, the frequency of warm nights in Puerto Rico has increased by about 50 percent. Currently in San Juan, the overnight low is above 77 degrees about 10 percent of the time. Puerto Rico’s climate is suitable for mosquito species that carry diseases such as malaria, yellow fever, and dengue fever. While the transmission of disease depends on a variety of conditions, higher air temperatures will likely accelerate the mosquito life cycle and the rate at which viruses replicate in mosquitoes". "Certain types of water-related illnesses already occur in Puerto Rico, supported by its warm marine environment. These include vibriosis, a bacterial infection that can come from direct contact with water or eating infected shellfish, and ciguatera poisoning, which comes from eating fish that contain a toxic substance produced by a type of algae. Higher ocean temperatures can increase the growth of these bacteria and algae, which may increase the risk of these associated illnesses.