Scientific Background
The ocean supplies us with food, oxygen, and life-sustaining medicines. However, many stressors are currently placed on the ocean and its ecosystems are pressured, threatening the very life-giving services it provides for everyone world-wide. Many widely-known dangers currently damage the Pacific. For example, over-fishing, rising sea-levels, plastic debris, and fossil fuel contamination are each well-publicised hazards. As a result, we want to highlight emerging, and equally disturbing threats, such as dead zones, ocean acidification, and noise pollution. Whilst not always visible, these growing dangers affect our oceans, escalating the effects of other threats. We have set our oceans on a perilous path of eventual permanent damage. Addressing each of these issues now, we’ll be able to nurse our oceans back to health and save ourselves along with it.
Ocean “Dead Zones”
Hypoxic or low oxygen zones in the ocean, also known as “dead zones,” threaten fisheries and food resources, change the migrations of marine animals, and compromise their habitat, growth, and reproduction. Hypoxia occurs when fertilizer-rich river water (mainly from agricultural run off) flows into the ocean, causing algae to grow and then die, zooplankton (tiny aquatic animals) to feed on the algae, and the rotting matter (dead algae and waste products from the zooplankton) to sink. Finally, bacteria feed on the decaying matter and use up the oxygen in the water, which marine animals need to breathe and live. The fresh water from rivers stays on top, preventing oxygen from the air to get to deeper depths in the ocean. Marine life either flees or dies (at very low oxygen levels). In the Gulf of Mexico, dead zones have reached 22,000 sq. km in area. Dead zones are growing in size and have become a global epidemic, with over 400 areas identified worldwide. Fertilizers from corn and soybean crops, pasture and range, and other crops are the main sources of the agricultural runoff. Many fertilizers are from crops grown for biofuels. Government subsidies to corn and soybeans contribute to the problem. Fertilizer run-off combines with climate change in the oceans to worsen the dead zone situation.
Ocean Acidification
Increasing CO2 in our atmosphere has meant that the oceans have become more acidic and will continue to do so. Ocean acidity has increased substantially--30%-- since the Industrial Revolution 250 years ago. Ocean acidification is a very straightforward, predictable, certain chemical reaction between seawater and CO2, resulting in carbonic acid. Surface waters near and around the poles will become corrosive to shells and skeletons made up of calcium carbonate (similar to lime) within decades (2030-2050), with large disruptions predicted to the marine food web. Some carbonate-containing organisms (including crabs, lobsters, mussels, oysters, corals, and sea urchins) may be able to adapt, but we cannot say yet how fast that adaptation will be. A huge problem is the rate of change: by 2050, ocean acidity is predicted to increase by 150%. Marine life has not experienced this fast rate of change in acidity for 65 million years. Extensive extinctions are likely. Already responses such as reductions in growth rate, size, and body weight, delayed reproduction, reduced hatching success, reduction in calcification rates, increased mortality, and shell dissolution have been observed in calcifying organisms under present conditions. Ocean acidification is irreversible over periods of thousands of years.
Ocean Noise Pollution
Most marine animals depend on sound to survive. Noise from human activities such as shipping, seismic exploration for oil and gas, and naval sonar degrade their acoustic habitat. Such losses in acoustic habitat represent a cost to the individuals, marine populations, and ocean ecosystems. Noise can shrink an animal’s range of communication from hundreds of kilometers down to just a few kilometres. Highly endangered North Atlantic right whales, for instance, lose more than 70% of their opportunities to communicate when drowned out by shipping noise. This likely reduces their feeding efficiency and could interfere with mating, resulting in lower survival and population numbers. Naval sonars have been shown to cause the death of whales in some cases. Other impacts from noise include hearing loss, reduced fisheries’ catch rates, and stress.
Impacts of Many Stressors at Once
Ocean acidification, rise in ocean temperature, and sea level rise all occur globally, though their severity can vary from place to place. Local stressors that occur around the world include low oxygen, pollution, and harvesting. Ocean temperature, low oxygen, and acidification can interact in ways that even further reduce the health of marine organisms (e.g. ocean warming increases the effect of acidification and low oxygen, and low oxygen worsens ocean acidification). Sea urchins, for instance, develop more abnormally under a combination of high temperature and more acidic conditions. In conclusion, all areas of the ocean will be impacted by many man-made stressors at once, which can interact in complex, often unpredictable ways to produce a magnified response.
