When multiple threats interact—some local (such as removing mangroves) with global ones (such as climate change)—the impacts can be disastrous. For example, “dead zones” (areas of very low oxygen content), are worsening because of steadily warming temperatures, acidification and pollution among others.
The ocean - warmer and more acid
The average sea surface temperature has increased over the past 50 years, as a result of human activities such as the burning of fossil fuels and deforestation. The warming of the ocean is felt through changes in weather patterns, and the frequency of extreme events, as well as sea level rise. More intense storm systems are increasing the energy of waves and winds in some regions, and consequently the stress on coastal ecosystems.
According to the scientific consensus of the Intergovernmental Panel on Climate Change
(IPCC), the speed at which these changes are occurring has no parallel in at least the last 65 million years. Changes have been observed in almost every part of the ocean, with marine wildlife relocating to higher latitudes, consistent with warming trends.
Changes in ocean temperature are also altering the timing of key life history events such as plankton blooms, and the spawning and migratory behaviour of turtles
, fish and invertebrates.
The domino effect of climate change
These changes are already affecting human systems and industries. Shelled molluscs (like clams and oysters), for example, are being harmed by an increase in water acidity. The oyster industry in the Pacific Northwest of the United States has already lost nearly US$110 million in revenue and some 3,200 jobs due to ocean acidification.