For example, coral reefs—home to some 25% of marine species—have been declining rapidly since 1950 due to rising waters temperatures caused by global warming; other pollutants like sewage runoff threaten coral reef health even further by introducing toxins which can disrupt coral ecosystems or make them inhospitable for certain organisms such as algae or plankton on which many animals depend upon for food sources or sheltering grounds during times when they are most vulnerable (i.e., spawning).