Ocean environments in danger

-Debapriya Mukherjee
Contd from previous issue
The world has been a witness to one of the biggest threats to our oceans on account of  man-made pollution despite knowing the fact that  ocean is the heart of the planet covering  more than two-thirds of the Earth’s surface. Coral forests, mountains, volcanoes, minerals, microbes, algae, complex plants, mammals, fish, reptiles, birds, crustaceans, mollusks and a very long list of life forms including unknown forms are present in the oceans covering 370 million square km containing 1.4 billion cubic km of water. These ocean environments  support a remarkable biodiversity maintaining a large number of different species ranging from microbes to marine mammals and form a wide variety of ecosystems from coastal areas to abysses more than 11,000 m deep. Contrary to popular belief, sea plants produce 70% of the oxygen (phytoplankton  and marine plants exchange some 200,000 million tons of CO2/O2) whereas rainforests produce 28% oxygen. Phytoplankton- the tiny little organism,  which spends its life being carried by oceanic currents, act in the same way as tree leaves do on land. Everyone loves the ocean and enjoys by watching  the waves come in and out but does not realize the function of this tiny organisms  as the Earth’s lungs and role to  create  the ozone layer that protect us from harmful ultraviolet-B rays. Furthermore, evaporated seawater forms clouds  which empty their contents over the earth to create rivers, lakes and other ecosystems as well as provide the levels of moisture necessary to sustain life.
The deep waters are home to wildlife and some of the biggest creatures on earth that provides us with food, jobs, life, entertainment, and sailing and  key services like climate regulation, through the energy budget, carbon cycle and nutrient cycle. For decades, the oceans have served as a crucial buffer against global warming, soaking up roughly a quarter of the carbon dioxide  emitting  from anthropogenic activities and absorbing more than 90 percent of the excess heat trapped on Earth by carbon dioxide and other greenhouse gases.
Without that protection, the land would be heating much more rapidly and holding 97% of the water of our planet, almost all rain that drops on land comes from the sea.
Despite its significant importance to humanity, the governments in many countries simply violate the norms of probity and overlook the acts of unethical practices of discharging untreated waste , over-fishing and over-hunting, mining, the destruction of the oceans’ richest areas, the massive occupation of the coasts and the alteration of their chemical composition and temperature. Almost 80% of the pollutants dumped into the sea come from inland operations , either through rivers, direct dumping and coastal drainage (44%), or transported through the atmosphere (33%). The remaining 20% come from accidental or deliberate spills from vessels and marine facilities. From coral bleaching to sea level rise, entire marine ecosystems are rapidly changing. 
Though natural formation of dead zone that is  low oxygen (hypoxic) areas to small extent, can not be ruled out but excessive nutrients from sewage outfalls and agricultural runoff containing residual fertilizer have triggered  the number of  dead zones, where most marine life cannot survive, resulting in the collapse of some ecosystems. There are now close to 500 dead zones covering more than 245,000 km² globally. 
One such zone is present off the west coast of India, in the Arabian Sea.  The bright green color of the water in winter is the clear evident of  the excessive delivery of nutrients from agriculture and urban centers that stimulates algal productivity, and the subsequent microbial degradation of this organic matter reduces oxygen levels, contributing towards hypoxia. In reality, low oxygen waters are also related to the acidified waters. So Hypoxia and acidification are increasingly co-occurring in the ocean and  have additive and synergistic negative effects on the growth, survival, and metamorphosis of early life stage bivalves. Rising levels of atmospheric CO2 due to the burning of fossil fuels are exacerbating the ocean acidification.  Since the industrial revolution, the average pH of the ocean has been found to have fallen from 8.2 to 8.1, which may seem small but corresponds to an increase in acidity of about 26%. Many marine creatures have shells and skeletons of calcium carbonate (basically chalk), which can erode as pH falls. Ocean acidification prompts some plankton species to grow faster, while slowing growth for several others, disrupting the natural linkages and competition between species and putting entire ocean ecosystems at risk. As acidification worsens and the sea surface warms, the ocean becomes less effective in absorbing CO2.
The fate and behaviour of contaminants in the environment, particularly their persistence, their ability to be taken up by organisms and how they behave once absorbed, is strongly driven by environmental factors such as salinity, pH and temperature – and these are all subject to change under climate change scenarios. This means, organisms may be more or less susceptible to pollutants; the degree of change will depend on the specific pollutants and the organism species involved.
The above observations have clearly established  severe consequences for both humanity and nature.  Now there is the urgency of timely, ambitious, coordinated and enduring action. Now implementing effective waste reduction initiatives, recycling and effective waste and sewage management as well as sharp reduction of green house gas emission are the keys to improving the healthy longevity of our oceans. As Fish populations are already declining in many regions as warming waters throw marine ecosystems into disarray,  fishery managers will need to crack down on unsustainable fishing practices to prevent seafood stocks from collapsing otherwise we face a food crisis. Nations could also expand protected areas of the ocean to help marine ecosystems stay resilient against shifting conditions. The crisis in our fisheries and in our oceans and climate are not mutually exclusive problems to be addressed separately – it is imperative that we move forward with comprehensive solutions to address them.
The writer is Former Senior Scientist, Central Pollution Control Board based in Kolkata and can be reached at 919432370163 & 916290099509 or [email protected]