(Reuters) - Nearly 3 billion people, or two-fifths of the world's population, were at risk of contracting malaria in 2009 and closer study of the mosquito's life cycle is needed to combat the disease, researchers said in two reports.

In the first study, scientists mapped out the geographical spread of the Plasmodium vivax -- the most common parasite that causes malaria -- using reported cases of malaria and details on temperature and aridity.

OSLO, July 21 (Reuters) - Small fish play a big role in the oceans and catches should be cut sharply to safeguard marine food chains from plankton to blue whales, an international team of experts said on Thursday.

Rising human exploitation of little fish -- including anchovy, sardine, herring, mackerel and capelin -- had had far less attention in marine research compared to big commercial species such as cod, tuna, swordfish or salmon, they said.

Climate change could result in "sudden and abrupt" shocks to countries around the world and have "far-reaching implications for global stability and security," a senior United Nations' official has warned.

Achim Steiner, executive director of the U.N. Environment Program, told the U.N. Security Council Wednesday that natural resources would be "at increasing risk from climate change and its impacts."