Coral bleaching due to global warming.
Coral bleaching due to global warming. Photo Credit - Rainer von Brandis -

Today’s Oceans—Are They Too Damaged to Fix?

Our oceans have been transformed by human activities and the mindset that they are “too vast to spoil”. Below are a few facts that help illustrate the current state of our oceans. See Resources for references to the literature cited below.


  • 33 per cent of marine fish stocks are now overfished and in decline or facing collapse; this is up from 10 per cent in 1974. (FAO, 2018).
  • 60 per cent of all marine fish stocks are fully exploited, which means that catches are at a maximum sustainable level and there is no scope for further expansion. (FAO, 2018).
  • The number of marine fishing vessels globally doubled between 1950 and 2015—from 1.7 to 3.7 million. Over the same period there was a huge reduction in catch per unit effort, which is now only about a fifth of what it was in the 1950s; this means fishers now have to fish five times harder to catch an equivalent amount of fish as in the 1950s. (Rousseau et al., 2019).
  • One in four of the 1,041 species of sharks and rays are threatened with extinction, mainly because of overfishing. (Dulvy et al., 2014).
    Fishing boats, Diu, India
    Fishing boats, Diu, India (Photo credit: Nirmal Rajendharkumar,


  • The number of coastal dead zones (areas with very low oxygen concentrations) has roughly doubled every decade since the 1960s; there are now more than 500 dead zones in coastal waters, up from less than 50 in 1950; dead zones are biological deserts created by nutrient pollution from agriculture and sewage discharges. (Breitburg et al., 2018; Mladenov, 2020).
  • Plastic waste has been accumulating in the oceans for more than half a century; currently about 10 million tonnes of new plastic waste enters the oceans each year; in Indonesia, there is an average of more than 29,000 pieces of plastic along a kilometre of shoreline; more than 5 trillion pieces of plastic are floating on the surface of the oceans. (Eriksen et al., 2014; Mladenov, 2020).
    Marine debris litters a beach on Laysan Island in the Hawaiian Islands National Wildlife Refuge
    Marine debris litters a beach on Laysan Island in the Hawaiian Islands National Wildlife Refuge, where it washed ashore. (Photo credit: Susan White/USFWS)

Invasive species

  • Historically, sub-regions of the world’s oceans were populated by distinct communities of marine life separated by natural barriers such as land masses, current systems, differences in temperature, and sheer distance. But humans have breached these barriers (e.g., construction of canals that link sub-regions; transportation of foreign species in ship ballast water and attached to the hulls of ships; intentional or accidental release of exotic species) and many species have moved well beyond their natural ranges. In many cases these invasive species have a huge impact on their new environment including loss of biodiversity, introduction of novel parasites, alteration of habitat, disruption of natural food webs, collapse of fisheries, and the creation of toxic phytoplankton blooms that kill local marine life and sometimes humans. (DePoorter et al., 2009; FAO, 2019; Mladenov, 2020).
    Invasive lionfish in Caribbean
    Invasive lionfish in Caribbean (Photo credit: LASZLO ILYES)


  • There have been at least 20 global marine species extinctions since the 18th century due to overexploitation, habitat loss and invasive species: 4 species of mammals, 8 species of seabirds, 3 species of molluscs and 1 species of algae. In addition, numerous ecological extinctions have occurred on regional and local scales. A further major wave of extinction of ocean species may now be unfolding (Dulvy et al., 2009).
    Reconstruction of Steller measuring a Steller's sea cow (now extinct) on Bering Island
    Reconstruction of Steller measuring a Steller’s sea cow (now extinct) on Bering Island, July 12, 1742
    Source: Steller’s Journal of the Sea Voyage from Kamchatka to America, p. 228

Ocean warming and marine heatwaves

  • The oceans are now on average close to 1°C warmer than 140 years ago and more than 3°C warmer in some regions. This is causing oceanic ‘heatwaves’ to regularly sweep through the oceans. A series of heat waves during 2015-17 resulted in coral bleaching on a global scale. Its effects on the Great Barrier Reef were catastrophic—49 per cent of all corals on a 1600 kilometre stretch of the reef died. (Mladenov, 2020).
  • The Arctic Ocean will become nearly or completely ice free for several months a year before 2040, which will have profound effects on Arctic Ocean ecosystems. (Screen and Deser, 2019; Mladenov, 2020).
    A still image of the Arctic sea ice on September 12th, 2013 when the sea ice reached the annual minimum extent of 5.22 million square km
    A still image of the Arctic sea ice on September 12th, 2013 when the sea ice reached the annual minimum extent of 5.22 million square km –

Ocean acidification

  • The surface waters of the oceans are now 30 per cent more acidic than in 1870; by 2100 they will be 170 per cent more acidic. This rate of change is about ten times faster than anything that has occurred over the last 65 million years. This is affecting the biology of many kinds of marine organisms, particularly those with skeletons or shells containing calcium carbonate, and will cause substantial changes to ocean ecosystems over the next 50 years. (Wittmann and Pörtner, 2013; Mladenov, 2020).
    Unhealthy pteropod showing effects of ocean acidification,
    Unhealthy pteropod showing effects of ocean acidification, including ragged, dissolving shell ridges on upper surface, a cloudy shell in lower right quadrant, and severe abrasions and weak spots at 6:30 position on lower whorl of shell
    Source: fis01026

Ocean industrialization

  • The oceans have become the new economic frontier as land-based resources become depleted. Many competing interests are making claims on the oceans for food production, minerals, reclamation projects, offshore structures, waste disposal, fibre optic cables, military installations, climate geoengineering projects, etc. This is intensifying pressure on the oceans and raising into question whether the ‘blue economy’ can exist alongside sustainable use of the oceans. (Jouffray et al., 2020).
    Schematic of deep ocean mining operation for polymetallic nodules
    Schematic of deep ocean mining operation for polymetallic nodules
    Source: IUCN Issues Brief: Deep-sea Mining (

A new mindset – Conditional Optimism

Clearly, our oceans are now in a critical state of health—overexploited, over-developed, polluted, their life forms artificially dispersed, and their waters subject to unnatural warming and acidification. This has destroyed their natural beauty, depleted their bioabundance and biodiversity, eroded their capacity to support intact marine ecosystems, and harmed their ability to provide the ecosystem services that sustain human well-being and prosperity. Unfortunately, these stressors on the oceans are intensifying as the population increases from 7.7 billion to close to 10 billion over the next 30 years. This poses an increasingly serious, potentially existential, threat to human society.

Many people today are thus depressed and despairing about the current state of our oceans and have fallen into the belief that the problems are simply too big to fix. Such pessimism, although understandable, is a self-fulfilling prophesy associated with disengagement and inaction. What we really need is a new mindset based on conditional optimism. If we think boldly, identify solutions, and take effective action then it is entirely possible to shape a better, more sustainable, future for our oceans.

References for Today’s Oceans

Link to Yesterday’s Oceans pageLink to Tomorrow’s Oceans page