This movement will also cause northern boreal forests to invade tundra ecosystems in the long-term future. Whilst heat-stress is not expected to become a large issue on land, particularly in Northern Norway, warmer conditions will support the spread of disease-bearing insects (especially those limited by the cold temperatures) and invasive species into Norway, thus increasing the vulnerability of native species, livestock and the human population alike. Rising temperatures have affected local Norwegian ecosystems in many ways. Sea ice is diminishing, threatening ice-dependent species quicker than first imagined. The absence of sea ice leads to more rapid warming, due to the feedback mechanisms associated with the absorbance of sunlight. It also leads to a reduction in biodiversity, as several species are dependent on sea ice. For example, ice algae that grow in and under the ice, seals that need sea ice to give birth to their young, polar bears that prey on seals and several species of bird too. The rising temperatures are having direct impacts on freshwater and wetlands biodiversity. Atlantic salmon is a keystone species in rivers along the coast of Norway. Salmon have an upper temperature limit in the twenties so future warming may make it increasingly difficult to maintain current population levels. Higher initial temperatures could lead to increased growth and production in the short-term but ultimately there could be a massive collapse if warming trends continue. This has been made evident by the recent decline in mean individual mass and annual mean length of the fish. It is suggested that the size change of Atlantic salmon is made by the collapse and rebuilding of the pelagic fish abundance in the North Atlantic Ocean, a gradual decrease in zooplankton abundance and climate change. It could also promote genetic abnormalities and the spread of disease such as Pancreas Disease (PD) and Infectious Salmon Anemia Virus (ISA). Furthermore, lake and river surface water temperatures are projected to increase further, resulting in a longer summer stratification period and more cyanobacterial blooms. Furthermore, both the Atlantic salmon and the Arctic charr have experienced changes in abundance. Whilst both species coexist it has been the Arctic charr who seems to be more vulnerable to environmental changes, hence leading to its overall decline in numbers. A rise in sea temperatures will also affect marine, estuarine and intertidal ecosystems. Warmer seawater can lead to more phytoplankton and zooplankton but it is not known if other species can utilise this increase in food stocks. This change also favours species that prefer warmer waters and they will start to out-compete local species.