Oxygen-deprived zones in oceans across the world have emerged as a huge threat to marine ecosystems
Iwithout oxygen.That is MAGINESURVIVING what aquatic creatures in huge dead areas in oceans are going through the world over. Currently, there are more than 400 dead zones, or areas with extremely low levels of oxygen, appearing at least once a year (see ‘Suffocated spots’). They harm fisheries, destroy biodiversity of the regions they occur in and can damage major ecosystems of the world.
Such abnormal depletion in dissolved oxygen levels has intensified exponentially over the past 40 years. One such zone is present off the west coast of India,in the Arabian Sea. Here, the colour of the water becomes bright green every winter. The colour is so intense that it can be seen from space. The cause is a microscopic plankton, Noctiluca scintillan, that “blooms”and spreads over the sea surface.
Recent studies have shown how marine communities are affected by depleting oxygen levels.A study published in in April 2015, showed that a dip in oxygen levels drastically changed the structure of the community of seafloor organisms, replacing the original biodiversity with fewer,hardier species.These changes occurred over a relatively short period (about 150 years), but the recovery from this collapse took more than 1,000 years.
Industrial scale use of fertilisers is one of the main reasons behind the formation
Excessive sewage from Mumbai and Karachi has created huge oxygen-depleted zones in the Arabian Sea