Threat 4: Pollution

Overview

The oceans are enormous but they are not infinite. In the past the oceans were treated as a giant disposal area for all types of refuse (including radio-active waste as recently as 1982) with the belief that the enormous size of the oceans would be enough to dilute and render harmless any materials we put into them.¹

Today, we are starting to realise that the ocean ecosystem as a whole is under tremendous stress from a variety of sources of pollution. By putting too much pollution into the oceans, humans are threatening to permanently alter the oceans and all life within them in ways we are only beginning to understand.

Plastic

One of the most common pollutants in our oceans is plastic. Plastic as we know it, really only came into mass production after the first world war and in the relatively short amount of time that it’s been in use, it has already spread to every corner of the globe. Estimates show that marine litter is now 60–80% plastic, reaching 90–95% in some areas.⁶

It’s not known exactly how long it takes plastic to biodegrade. Estimates for plastic shopping bags range from 500 years to a 1,000 years or even longer.⁵ What we do know is that plastic is accumulating in vast quantities in our oceans. Since the 1950s, one billion tons of plastic have been discarded and may persist for hundreds or even thousands of years.⁶

Ocean currents collect the plastic into concentrated areas known as gyres resulting in vast areas of ocean being completely saturated with plastic.⁸ Given that a little more than half of all thermoplastics will sink in seawater² while what we see at the surface is scary, it’s only a part of the story.

Plastic is often mistaken for food by marine animals such as turtles (plastic bags look a lot like jellyfish), sea birds and even the oceans smallest feeders can be misled by tiny plastic fragments which are indistinguishable from plankton. An estimated 86% of turtle species, 43% of seabird species, and 44% of marine mammals have plastics in their gut.⁴ Plastic can fill the digestive system of these animals causing them to starve. Scientists are also finding that plastic often acts as a carrier for other pollutants (such as persistent organic pollutants or POPs) making it even more harmful as it becomes extremely toxic to marine life.⁷

Noise

Marine pollution is not always visible. Many animals rely heavily on the use of sound for navigation, feeding, and communication as water is a very good medium for sound to travel far distances. However, with the increased use of the sea by man we are changing the underwater sound environment dramatically. One study notes that in the preindustrial ocean the mating calls of baleen whales could have been heard about 280 km away, but the low-frequency propulsion noise of modern commercial ships has so elevated ambient noise in the sea that the detection range for whale calls could be as low as 90 km.^3b

In at least three well-documented cases there is a relationship in time and space between the use of mid-frequency sonar (usually in military exercises) and the stranding of cetaceans, mostly beaked whales. We also now know of one or two dozen atypical mass strandings of beaked whales that have occurred in the presence of naval ships that might have been using sonar.^3a The results are still inconclusive but there seems to be a mounting case for limiting the use of sonar during times of the year when cetaceans are likely to be present in particular areas.

Other sources of pollution

Climate change is another major cause of marine pollution. As a result of the increased levels of C02 in the atmosphere our oceans are becoming more acidic. The ocean’s naturally absorb a certain amount of C02 but are now absorbing more as the levels present in the atmosphere increase. This is resulting in a more acidic ocean which has the potential to alter marine ecosystems completely – read more in our climate change section.

Eutrophication is the process of chemical nutrients being absorbed into the oceans – usually from runoff and rivers washing excess fertilizers and farm waste from land. This causes disruptions as algal blooms occur which rob areas of the ocean of oxygen and can result in great swathes of ocean becoming dead zones. Read more about this issue in our habitat loss section. A related issue is that of sedimentation as development (particularly in coastal areas) results in larger amounts of silt and sand being deposited into the oceans with drastic consequences for coastal ecosystems.

Industrial pollution leaks toxins and heavy metals into the marine environment often from factories and mining activities. These toxins are concentrated as one moves higher up the food chain. Mahmood Shivji from the Save Our Seas Shark Center in Fort Lauderdale, USA has shown that 1 in 4 shark fins have dangerously high levels of heavy metals including mercury and arsenic posing a grave danger to humans who consume shark meat in dishes such as shark fin soup.

Pharmaceutical pollution is another issue we are only beginning to understand. Drugs enter the oceans after being disposed of in domestic sewage systems. As these pollutants filter into marine food webs they can cause a range of problems in marine animals including infertility and increased mortality rates.

Remedies

• Do your bit to minimise your impact on ocean pollution. Recycle, reuse and reduce. Avoid plastic wherever possible. Don’t use cosmetics that contain plastic micro-beads (particularly facewash containing polyethylene). Take part in beach cleanups. Reduce you carbon footprint.
• Put pressure on governments and regulatory bodies to tighten regulations on industrial, agricultural and domestic pollution.
• Be a wise consumer. Support companies that are environmentally conscious. Buy organic foods as these the minimise agricultural impacts from chemical fertilizers and pesticides.
• Support research projects aimed at understanding pollution better and finding ways to reduce the amount of pollution in our oceans.

Continue to Habitat destruction →