High-tech geoengineering might one day just be able to return atmospheric carbon dioxide to below 350 parts per million, at which level coral reefs can persist. But long before then the multiplying effects of changing climate and human pressure will have crippled marine ecosystems. For the ocean to survive, we need to throw it five lifelines by doing the following:
1: Establishing marine reserves
Less than 0.01 per cent of the ocean lies within reserves, but reserves do work: they boost biomass and biodiversity and allow ecosystems to grow resilient. Around the British-controlled Chagos Islands in the Indian Ocean, for example, the seas are not part of a formal reserve but have effectively been protected since 1965 by the presence of the US base at Diego Garcia; reefs here have been able to recover quickly from bleaching events.
2: Ending the freedom of the seas
Only by zoning and controlling access to the ocean can it be rescued. The present situation has led to a depletion of the ocean’s biomass, something which is as important as biodiversity for the resilience of ecosystems. For instance, 95 per cent of filter-feeders have been removed from the ocean. The North Sea and our estuaries once had clear waters full of oyster beds; restoring even a fraction of these will lead to cleaner water and an increase in sunlight for seabed organisms.
3: Controlling fishing fleets
The fishing industry is destroying essential biodiversity and biomass because of huge subsidies and overcapacity. Ending both will mean more fish in the sea as well as on the plate, while cutting the amount of fuel used to catch them.
4: Banning bottom trawling
A widespread ban would allow seabed habitats to recover. The hidden complexity of seabed life is a key component of the ocean’s ability to recycle nutrients.
5: Controlling pollution
Agricultural fertilisers being washed into rivers are a major cause of the growth in deoxygenated dead zones in coastal waters worldwide, and plastics are pulling poisons into food webs.
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