Marine Fisheries

  • Global fish production peaked in 2016
  • Aquaculture represents 47% of the total
  • Average annual global fish food consumption outpaced population growth between 1961 and 2016
  • Average annual consumption of global fish food exceeded that of meat from all terrestrial animals during the same period
  • Food fish consumption has grown at about 1.5%/year since 1961
  • Fish accounted for about 17% of animal protein for the global population (2015)
  • Fish provides about 3.2 billion people with almost 20% of average per capita intake of animal protein
  • The state of marine resource fisheries has continued to decline (See 14-20 below)
  • Illegal, Unreported and Unregulated fishing (IUU) pose a significant problem to sustainable fisheries (See below)

1.  Seafood is the world’s most traded food commodity, with global exports worth more than US$148 billion in 2014 (Boerder et al., Global hot spots of transshipment of fish catch at sea, Sci. Adv. 2018; 4 : eaat7159 25 July 2018)

2.  Total marine wild fish catch (reported and unreported) estimated to be 110 million metric tons, with a value of US$171 billion (McCauley, et al., Wealthy countries dominate industrial fishing, Sci. Adv. 2018; 4 : eaau2161 1 August 2018)

3.  Industrial fishing is dominated globally by wealthy nations. Vessels flagged to higher-income nations, for example, are responsible for 97% of the trackable industrial fishing on the high seas and 78% of such effort within the national waters of lower-income countries. (McCauley, et al)

4.  The United States and Japan have been essentially tied in recent years as the largest single country import markets for seafood, both importing between 13% and 14% of the global total. The EU is the largest overall market, importing about 27% of the total. Together these three markets account for about 55% of global seafood imports. (Pramod, et al., Estimates of illegal and unreported fish in seafood imports to the USA, Marine Policy 48 (2014) 102–113 http://dx.doi.org/10.1016/j.marpol.2014.03.019)

5.  Seafood consumption in the USA totaled about 2.1 million tonnes, second only to China representing 6.8 kg per capita in 2011. (This includes domestic production that is consumed inside the USA.) American consumers spent an estimated $85.9 billion on fish products in 2011, with about $57.7 billion spent at foodservice establishments, $27.6 billion at retail, and $625 million on industrial fish products. Tuna, crab, pollock and cod are the most consumed wild-caught seafood products. (Pramod, et al.)

6.  In 2011 roughly 90% of seafood consumed in the United States was imported, and about half of this was wild-caught. (Pramod, et al.)

Trends in total catch and area fished by global fisheries, 1950-2014. (A) global industrial fisheries catch (8), (B) percentage of ice-free ocean area exploited, and (C) industrial catch per unit ocean area. Dashed line indicates year of peak global catch in 1996, with percentage growth/decline since 1996 labeled on each time series.
(Source:  Tickler, et al., Far from home:  Distance patterns of global fishing fleets, Sci. Adv. 2018;4:eaar3279 1 August 2018 )

Capture Production by Country:


Source:  FAO. 2018. The State of World Fisheries and Aquaculture 2018 – Meeting the sustainable development goals. Rome. Licence: CC BY-NC-SA 3.0 IGO.
Fisheries production has been trending upwards in the tropics, but decreasing elsewhere

Source:  FAO. 2018. The State of World Fisheries and Aquaculture 2018 – Meeting the sustainable development goals. Rome. Licence: CC BY-NC-SA 3.0 IGO.
Global fish production peaked in 2016, with capture fishery production relatively static since the late 1980’s.
Source:  FAO. 2018. The State of World Fisheries and Aquaculture 2018 – Meeting the sustainable development goals. Rome. Licence: CC BY-NC-SA 3.0 IGO.

Challenge to Sustainable Fisheries: Transshipment of Catch at Sea; recent findings from Boerder, et al.

A major challenge in global fisheries is posed by transshipment of catch at sea from fishing vessels to refrigerated cargo vessels, which can obscure the origin of the catch and mask illicit practices. Transshipment remains poorly quantified at a global scale, as much of it is thought to occur outside of national waters. We used Automatic Identification System (AIS) vessel tracking data to quantify spatial patterns of transshipment for major fisheries and gear types. From 2012 to 2017, we observed 10,510 likely transshipment events, with trawlers (53%) and longliners (21%) involved in a majority of cases. Trawlers tended to transship in national waters, whereas longliners did so predominantly on the high seas. Spatial hot spots were seen off the coasts of Russia and West Africa, in the South Indian Ocean, and in the equatorial Pacific Ocean. Our study highlights novel ways to trace seafood supply chains and identifies priority areas for improved trade regulation and fisheries management at the global scale. (Boerder et al., Global hot spots of transshipment of fish catch at sea, Sci. Adv. 2018; 4 : eaat7159 25 July 2018 )

A Tale of Tuna:  An albacore’s journey to the supermarket

1.  Fishing vessel fishes for 2-3 weeks

2.  Vessel meet a “reefer” (refrigerated cargo ship) on the high seas to off-load

3.  Reefer returns to port (about once a month) to land the transshipped tuna

4.  Whole fish is processed into “loins”(a cut, normally of uniform thickness, with no taper and no bones*)    and shipped in sealed containers to canning facilities in the United States, which takes 4-8 weeks

5.  Reprocessing and canning occur over another 4 weeks

6.  Distribution to retail within 2-12 weeks

  • Total time from sea to shelf:  18-35 weeks
  • Travel distance from sea to shelf:  average 17,000 km (13,000-20,000km, excluding traveling on the fishing boat and transport to final retail

         * http://www.jjmcdonnell.com/product-information/loin-prime-cut

9.  57% of managed tuna stocks are considered to be at a healthy level of abundance, 13% are overfished, and even those that are not overfished show slight declines in biomass over time

10.  Oceanic sharks, of which 44% are threatened, spend a great deal of time in the high seas, where shark fishing is largely unregulated and unmonitored

11.  Only six countries (China, Taiwan, Japan, Indonesia, Spain, and South Korea) accounted for 77% of the global high-seas fishing fleet and 80% of all AIS/VMS-inferred fishing effort

12. Of these six countries, five (excluding Indonesia) account for nearly two-thirds (US$4.9 billion) of the global high-seas fishing revenue (US$7.6 billion)

13.  Without government subsidies, high-seas fishing at the global scale would be unlikely (Source 9-13:  Sala, et al., The economics of fishing the high seas, Sala et al., Sci. Adv. 2018;4:eaat2504 6 June 2018)

14.  The fraction of fish stocks that are within biologically sustainable levels has exhibited a decreasing trend from 90.0% in 1974 to 66.9% in 2015 (FAO)

15. In 2015, nearly 60% of marine stocks were maximally sustainably fished

In 2015, maximally sustainably fished stocks accounted for 59.9 percent and underfished stocks for 7.0 percent of the total assessed stocks (separated by the white line in the figure). The underfished stocks decreased continuously from 1974 to 2015, whereas the maximally sustainably fished stocks decreased from 1974 to 1989, and then increased to 59.9 percent in 2015. Source:  FAO. 2018. The State of World Fisheries and Aquaculture 2018 – Meeting the sustainable development goals. Rome. Licence: CC BY-NC-SA 3.0 IGO.
16. The percentage of stocks fished unsustainably varies considerably globally

The percentage of stocks fished unsustainably varies considerably globally Source:  FAO. 2018. The State of World Fisheries and Aquaculture 2018 – Meeting the sustainable development goals. Rome. Licence: CC BY-NC-SA 3.0 IGO.
17. Productivity and stock status vary greatly among species. Of the ten species with the largest landings between 1950 and 2015, 77.4% were fished within sustainable levels in 2015–better than average for all stocks
18. In 2015, 43% of principal tuna species were fished unsustainably
18. The world’s marine fisheries had 33.1% of stocks classified as overfished in 2015
19. Progress towards global sustainability is uneven; overcapacity and stock status has worsened in developing countries, while management and stock status in developing nations has improved
#14-19 Source:  FAO. 2018. The State of World Fisheries and Aquaculture 2018 – Meeting the sustainable development goals. Rome. Licence: CC BY-NC-SA 3.0 IGO.

Illegal, Unreported and Unregulated Fishing

Illegal, unreported and unregulated (IUU) fishing is a significant global problem jeopardizing ecosystems, food security, and livelihoods around the world.

(Pramod, et al., Estimates of illegal and unreported fish in seafood imports to the USA, Marine Policy 48 (2014) 102–113

http://dx.doi.org/10.1016/j.marpol.2014.03.019)

1.    Estimates of IUU extent by country and region have revealed substantial IUU world wide between 13% and 31% of reported catches, and over 50% in some regions. This illegal catch is valued at between $10 and $23.5 billion per year.  IUU fishing distorts competition, harms honest fishermen, weakens coastal communities, promotes tax evasion, and is frequently associated with transnational crime such as narcotraffic and slavery at sea.

2.  The highly internationalized seafood supply chain feeding imports into the United States and other major markets is one of the most complex and opaque of all natural commodities. It involves many actors between the fisherman and the consumer, including brokers, traders, wholesalers and other middlemen, often distant from the consumer markets they supply.

3.  IUU in the USA

20–32% by weight of wild-caught seafood imported by the United States in 2011, with a value between $1.3 billion and $2.1 billion (or 15–26% of total value of wild-caught seafood), were from illegal and unreported (IU) catches. This trade represents between 4% and 16% of the value of the global illegal fish catch and reveals the unintentional role of the USA, one of the largest seafood markets in the world, in funding the profits of illegal fishing.

Source: Pramod, et al (above)

Mangroves

Mangrove Deforestation between 2000 and 2012 Source: Section 3.2.3.1; http:// https://www.ipbes.net/assessment-reports/asia-pacific


USGS ecologists produced this map of mangrove deforestation in Burma’s (Myanmar’s) Irrawaddy Delta using an older version of the Global Land Survey dataset. Recent improvements are allowing them to map mangrove deforestation worldwide. (Map adapted by Robert Simmon from Giri et al., 2008.)  NASA Earth Observatory  
Legend

Significance:  Mangroves represent a unique ecosystem in coastal area supporting a rich biodiversity and providing a range of nature’s contribution to people including provisioning, regulating and supporting, crucial for the sustenance of local communities.  There ecosystem service benefits have been valued at an average of 4200 US$/hectare/year.*  They provide coastal protection against storms and flooding, are critical nursery habitats for fish, birds and marine mammals, act as effective nutrient filters.* South-East Asian mangroves are among the most species diverse in the world, having 268 plant species including 52 taxa growing exclusively in mangrove habitat. Mangrove forests and forests soils can also store significant amounts of organic carbon.*

Status:  Recent changes in land use primarily for aquaculture has led to transformation of mangroves (up to 75 per cent in the last 3 decades.  Mangroves exist in coastal areas where development demand is high and are being highly threatened by land-use change (see 4.1.2; 4.4.1). An estimated 1,140 km2 of mangroves have been lost between 2000 and 2012 in South-East Asia, with an average rate of 0.7-3.0 per cent per year.

Source: http:// https://www.ipbes.net/assessment-reports

Threats include rapid urbanization (Philippines, Thailand, Vietnam), aquaculture (e.g., shrimp farming), paddy farming (Myanmar), expansion of oil palm (Malaysia and Indonesia, including new development in Papua) (See Figure above and chart below) In Asia, more than 50 per cent of mangroves have been lost to support aquaculture, with 40 per cent of mangroves in the Philippines lost to agriculture.

Indirect anthropogenic changes include those related to climate change—drought (e.g., Gulf of Carpentaria, Australia Nov-Dec 2016); rising sea levels pose a threat to mangroves in Bangladesh, New Zealand, Vietnam and China. Loss of mangrove forests and soils also removes carbon storage; Indonesia, Malaysia and Myanmar contributed 77% of global mangrove organic carbon storage loss between 2000-2015.*

*Source:  Jonathan Sanderman et al 2018 A Global map of mangrove forest soil carbon at 30m resolution. Environ. Res. Lett. 13 055002

http:// https://www.ipbes.net/assessment-reports
Top 20 nation rankings for (a) total mangrove area lost between the years 2000 and 2012, (b0 area loss as a percent of year 2000 mangrove area, (c) total soil organic carbon stocks, (d) carbon loss as a percent loss of year 2000 soil carbon stock. Range in values for (c) and (d) come from 25%-100% loss of carbon in upper meter in pixels identified as being deforested between the years 2000 and 2015.

Coral Reefs

Source: Section 3.2.3.5; Karki, et al., http:// https://www.ipbes.net/assessment-reports/asia-pacific

  • Coral reefs are the most diverse coastal ecosystems on earth and of disproportionate ecological, economic and food security importance to the Asia-Pacific region which has an inordinate proportion of the world’s healthy coral reefs.  Coral diversity is highest in the Asia-Pacific region.
  • The death of reef-forming corals undermines resilience of coastal communities, and can lead to the collapse of important coastal ecosystems.
  • One third of reef- building corals in the region are threatened.
  • Loss of habitat quality, heavy damage to entire reefs are major threats in the region. In the case of El Niño event in 1998, 16 per cent of the world’s coral reefs and 50 per cent of those in the Indian Ocean were destroyed
  • Increase in sea temperature and ocean acidification have been projected as major drivers of change along coastal environments which may lead to decline in coral reefs.
  • Increasing outbreaks of crown of thorns starfish, a native predator that has boom bust cycles linked to environmental pollution from farm lined estuaries affected The Great Barrier Reef.
  • Coral bleaching events are also increasingly devastating to the northern two thirds of the reef over the last few years where coral-algae associations are disrupted by high sea temperature.  Habitats and communities in the Great Barrier Reef ranged from poor to worsening at the end of 2015, although some species like green turtle populations improved.
  • Among the most serious emerging threats to coral reefs are coral diseases, which have devastated coral populations throughout the Caribbean since the 1980s and accompanied the mass coral bleaching there in 2005 and 2006. Over 90 per cent of the main reef forming corals in the Caribbean have now died due to coral disease with the severity of disease outbreaks commonly correlated with corals stressed by bleaching.  Coral diseases are also being observed more frequently on Indo-Pacific reefs in heretofore unrecorded places such the Great Barrier Reef, areas of Marovo Lagoon in the Solomon Islands and the Northwestern Hawaiian Islands. The outbreaks seem to be related to bacterial infections and other introduced disease organisms, increasing pollution, human disturbance and increasing sea temperature, all of which have put reef-forming corals at serious risk.

Marine Ecosystems

Marine ecosystems, from coastal to deep sea, now show the influence of human actions, with coastal marine ecosystems showing both large historical losses of extent and condition as well as rapid ongoing declines (established but incomplete) {2.2.5.2.1, 2.2.7.15}

  • Direct exploitation of fish and seafood has the largest relative impact in the oceans (well established) {2.2.6.2}.
  • The direct driver with the second highest impact on the oceans is the many changes in the uses of the sea and coast land (well established) {2.2.6.2} (See Summary of Observed Changes)

Distribution Of Changes In The Global Ocean

Source:  Halpern  (B. S., Walbridge, S., Selkoe, K. A., Kappel, C. V., Micheli, F., D’Agrosa, C., … Watson, R. (2008). A Global Map of Human Impact on Marine Ecosystems. Science, 319(5865), 948–952.doi:10.1126/science.1149345 

1.  Every square kilometer of the ocean is affected by some anthropogenic driver of ecological change

2.  Over 41% of the world’s oceans have medium to very high cumulative impacts:

  • North and Norwegian seas, South and East China seas, Eastern Caribbean, North American eastern seaboard, Mediterranean, Persian Gulf, Bering Sea, and the waters around Sri Lanka.

3.  Lowest impact areas include high-latitude Arctic and Antarctic poles, but this may change due to future polar ice loss

4.  Ecosystems with highest impacts include hard and soft continental shelves and rocky reefs, and coral reefs.

Summary of Observed Changes

Temperature Changes

  •  Rising sea surface temperatures; reduction in oxygen content; stratification; coral bleaching
  • Heat content increasing deeper into the ocean
  • Global ocean animal biomass consistently declines with climate change, and that these impacts are amplified at higher trophic levels (Source: Lotze, et al., Global ensemble projections reveal trophic amplification of ocean biomass declines with climate change. http://www.pnas.org/cgi/doi/10.1073/pnas.1900194116) Ocean biomass declines with climate change
Source: Ocean biomass declines with climate change

Rising Sea Levels (“Looking past the horizon of 2100” Nature Climate Change)

  • Thermal expansion (warmer water expands)
  • Increased runoff from land-based ice sheets
    • Greenland
    • Antarctica
    • Mountain Glaciers

Changes in the Salinity of Seawater

  • Changes to the thermohaline circulation
  • Increased likelihood of seawater stratification

Threats to Coastal Populations and Infrastructure

  • Salt-water intrusion
  • Drowning forests
  • Inland migration of wetlands

Arctic Sea Ice is Shrinking

  • Warming air temperatures increase rate of melting
  • Positive feedback albedo loop

Increasing Ocean Acidity

  • Absorption of CO2 from atmosphere
  • Impacts to shell-forming species, including coralsAbsorption of CO2 from atmosphere

Land-Based Impacts

1.  Inorganic and organic pollutants

2.  Nutrient runoff (point and non-point) and associated hypoxia

Gulf of Mexico Dead Zone

3.  Aquaculture

4.  Invasive species

5.  Habitat destruction and alteration; e.g., coastal engineering; tourist development;  salt marshes, mangroves, seagrass beds, coral reefs

6.  Input and transfer of waterborne pathogens (runoff, aquaculture)

7.  Air pollution

a.  Toxic chemicals; e.g., POP’s over the Arctic zone by airborne volatilization;

b.    Mercury                          

Source:  Lavoie, R.A., Bouffard, A., Maranger, R., Amyot, M., 2018. Mercury transport and human exposure from global marine fisheries. Sci. Rep. 8, 6705.

Significance:  Human activities have increased the global circulation of mercury, a potent neurotoxin. Mercury can be converted into methylmercury, which biomagnifies along aquatic food chains and leads to high exposure in fish-eating populations.

Trends:  Mercury export from the ocean increased over time as a function of fishing pressure, especially on upper-trophic-level organisms. In 2014, over 13 metric tonnes of mercury were exported from the ocean. Asian countries were important contributors of mercury export in the last decades and the western Pacific Ocean was identified as the main source.

Estimates of per capita mercury exposure through fish consumption showed that populations in 38% of the 175 countries assessed, mainly insular and developing nations, were exposed to doses of methylmercury above governmental thresholds.

Given the high mercury intake through seafood consumption observed in several understudied yet vulnerable coastal communities, we recommend a comprehensive assessment of the health exposure risk of those populations.


Temporal trends (1950‒2014) of marine fisheries catches (dashed lines) and mercury exported (full lines). (a) Entire ocean (blue) and coastal (red) and high seas (orange) with breakpoint (circle) ± standard error (horizontal line). (b) Entire ocean (blue) and trophic levels (TL) rounded to the nearest integer: 4 (red), 3 (orange), and 2 (green).

Nutrients (N,P): Eutrophication, Dead Zones

Plastics (shipping, fishing, land-based sources)

  • Microplastics (nanoparticles; food chain)
  • Macroplastics (ingestion, entanglement, habitat loss (shorelines))
    • Great Pacific Garbage Patch

Source:   Lebreton, L, Slat, B, Ferrari, F, Sainte-Rose, B, Aitken, J, Marthouse, R, Hajbane, S, Cunsolo, S, Schwarz, A, Levivier, A, Noble, K, Debeljak, P, Maral, H, Schoeneich-Argent, R, Brambini, R & Reisser, J 2018, ‘Evidence that the Great Pacific Garbage Patch is rapidly accumulating plastic‘, Scientific Reports, vol. 8, no. 4666. https://doi.org/10.1038/s41598-018-22939-w

  • Ocean plastic can persist in sea surface waters, eventually accumulating in remote areas of the world’s oceans.
  • Our model, calibrated with data from multi-vessel and aircraft surveys, predicted at least 79 (45–129) thousand tonnes of ocean plastic are floating inside an area of 1.6 million km2; a figure four to sixteen times higher than previously reported.
  • Over three-quarters of the GPGP mass was carried by debris larger than 5 cm and at least 46% was comprised of fishing nets. Microplastics accounted for 8% of the total mass but 94% of the estimated 1.8 (1.1–3.6) trillion pieces floating in the area.
  • Plastic collected during our study has specific characteristics such as small surface-to-volume ratio, indicating that only certain types of debris have the capacity to persist and accumulate at the surface of the GPGP.

Finally, our results suggest that ocean plastic pollution within the GPGP is increasing exponentially and at a faster rate  than the surrounding waters.


Decadal evolution of microplastic concentration in the GPGP. Mean (circles) and standard error (whiskers) of microplastic mass concentrations measured by surface net tows conducted in different decades, within (light blue) and around (dark grey) the GPGP. Dashed lines are exponential fits to the averages expressed in g km−2: f(x) = exp(a*x) + b, with x expressed in number of years after 1900, a = 0.06121, b = 151.3, R2 = 0.92 for within GPGP and a = 0.04903, b = −7.138, R2 = 0.78 for around the GPGP.

Land Loss in Coastal Areas

Source:  Mentaschi, et al., Global long-term observations of coastal erosion and accretion, Scientific Reports volume 8, Article number: 12876 (2018) https://www.nature.com/articles/s41598-018-30904-w

On a global scale, between 1984 and 2015, the loss of permanent land in coastal areas amounts to almost 28,000 km2, roughly equivalent to the surface area of Haiti (Fig. a). This is almost twice as large as the surface of gained land (about 14,000 km2) over the same period. On the other hand, the overall surface of gained active zone (about 25,000 km2) is more than two times larger than the surface of lost active zone (about 11,500 km2). Overall, the gain of active zone roughly balances the loss of land, and the gain of land balances the loss of active zone. This translates into a net loss of approximately 14,000 km2 of surface for human settlements and terrestrial ecosystems (Fig. b).


Source:  Mentaschi, et al., Global long-term observations of coastal erosion and accretion, Scientific Reports volume 8, Article number: 12876 (2018)
 
On a global scale, between 1984 and 2015, the loss of permanent land in coastal areas amounts to almost 28,000 km2, roughly equivalent to the surface area of Haiti (Fig. a). This is almost twice as large as the surface of gained land (about 14,000 km2) over the same period. On the other hand, the overall surface of gained active zone (about 25,000 km2) is more than two times larger than the surface of lost active zone (about 11,500 km2). Overall, the gain of active zone roughly balances the loss of land, and the gain of land balances the loss of active zone. This translates into a net loss of approximately 14,000 km2 of surface for human settlements and terrestrial ecosystems (Fig. b).

Size distribution of cross-shore transition length above 50 m, for erosion and accretion of land (a) and active zone (b). Lost (c) and gained (d) land around the world; lost (f) and gained (g) active zone; balance gained – lost land (e) and active zone (h). Maps show the length of cross-shore erosion and accretion aggregated on coastal segments of 100 km. In all the maps the 4 spots with the highest local transition along a 250 m transect are indicated.
 

Drivers of shoreline change around the world

List of local cases of erosion/accretion discussed in Mentaschi, et al https://www.nature.com/articles/s41598-018-30904-w The legend provides for each spot a brief summary of the drivers of shoreline change
Land Loss in Coastal Areas: Shoreline modification “masks” true rates of shoreline change along the Atlantic Seaboard

Source:  Armstrong, S. B., &  Lazarus, E. D. 2019).  Masked shoreline erosion at large spatial scales as a collective effect of beach nourishmentEarth’s Future,  7,  74– 84https://doi.org/10.1029/2018EF001070

 (R)ecent rates of shoreline change along the U.S. Atlantic Coast are, on average, less erosional than historical rates. This shift has occurred despite evidence of intensified environmental forcing, including acceleration in rates of relative sea‐level rise and increased significant wave height in offshore wave climates. We suggest that the use, since the 1960s, of beach nourishment as the predominant form of mitigation against chronic coastal erosion in the United States…could explain the unexpected reversal in shoreline‐change trends.

Using U.S. Geological Survey shoreline records from 1830–2007 spanning more than 2,500 km of the U.S. Atlantic Coast, we calculate a mean rate of shoreline change, prior to 1960, of −55 cm/year (a negative rate denotes erosion). After 1960, the mean rate reverses to approximately +5 cm/year, indicating widespread apparent accretion despite steady (and, in some places, accelerated) sea‐level rise over the same period.

Cumulative sediment input from decades of beach‐nourishment projects may have sufficiently altered shoreline position to mask “true” rates of shoreline change. Our analysis suggests that long‐term rates of shoreline change typically used to assess coastal hazard may be systematically underestimated. We also suggest that the overall effect of beach nourishment along of the U.S. Atlantic Coast is extensive enough to constitute a quantitative signature of coastal geoengineering and may serve as a bellwether for nourishment‐dominated shorelines elsewhere in the world.

Oxygen Minimum Zones

Declining Oxygen in the World’s Ocean and Coastal Waters

Source for the following material unless otherwise noted:   Breitburg, D., Grégoire, M. and Isensee, K. (eds.). Global Ocean Oxygen Network 2018. The ocean is losing its breath: Declining oxygen in the world’s ocean and coastal waters. IOC-UNESCO, IOC Technical Series, No. 137 40pp.  The Ocean is Losing its Breath

Significance:

  1. Insufficient oxygen reduces growth, increases disease, alters behaviour and increases mortality of marine animals, including finfish and shellfish. The quality and quantity of habitat for economically and ecologically important species is reduced as oxygen declines.
  2. Finfish and crustacean aquaculture can be particularly susceptible to deoxygenation because animals are constrained in nets or other structures and cannot escape to highly-oxygenated water masses.
  3. Deoxygenation affects marine biogeochemical cycles; phosphorus availability, hydrogen sulphide production and micronutrients are affected.
  4. Deoxygenation may also contribute to climate change through its effects on the nitrogen cycle. When oxygen is insufficient for aerobic respiration, microbes conduct denitrification to obtain energy. This produces N2O – a powerful greenhouse gas – as well as N, which is inert and makes up most of the earth’s atmosphere.

Impacts of Excess Nutrients (eutrophication) on ocean oxygen

Nutrients – primarily nitrogen and phosphorus – from human waste, agriculture and industry, fertilize coastal waters. In a process called eutrophication, these nutrients stimulate photosynthesis, which increases the growth of algae and other organisms (See figure below). This results in more organic material sinking into deep water and to the sediment. Increased respiration by animals and many microbes eating or decomposing this organic material uses oxygen. The consequence can be oxygen concentrations that are far lower than those that would occur without human influence, and in some cases a complete lack of oxygen in bottom waters. Strong density differences between surface and bottom waters (referred to as ‘stratification’), due to temperature and salinity, can isolate bottom waters from the atmosphere and reduce or prevent re- oxygenation through ventilation. Semi-enclosed seas (e.g. the Black and Baltic Sea) can be sensitive to eutrophication and related deoxygenation because of their characteristic limited water exchange with the open ocean, and low ventilation rates.

Eutrophication:  nutrient flux of nitrogen and phosphorus from human waste, agriculture and industry, fertilize coastal waters


Impacts of excess nutrients (eutrophication) on ocean oxygen. (Figure modified from https://upload.wikimedia.org/ wikipedia/commons/d/dd/Scheme_eutrophication-en.svg)

Deoxygenation Facts

Oxygen Minimum Zones (OMZs)

OMZs are places in the world ocean where oxygen saturation in the water column is at its lowest, are shown in blue.  Areas with coastal hypoxia are shown in red.   Hypoxic conditions are often defined as 2 mg/L O2.

The number of water bodies in which hypoxia associated with eutrophication has been reported has increased exponentially since the 1960s; hundreds of systems worldwide have been reported with oxygen concentrations <2 mg L-1, lasting from hours to years. The increasing severity and prevalence of this problem reflects the invention and increasing use of synthetic fertilizers and the growing human population. Global fertilizer use shown includes data of fertilizers with nitrogen, phosphate and potash.

World’s two largest dead zones

Source:  European Environment Agency Ocean Oxygen Content Indicator Assessment 


Distribution of oxygen-depleted ‘dead zones’ in European seas

Oxygen-depleted zones in the Baltic Sea have increased more than 10-fold, from 5 000 to 60 000 km2, since 1900, with most of the increase happening after 1950. The Baltic Sea now has the largest dead zone in the world. Oxygen depletion has also been observed in other European seas in recent decades.

The Gulf of  Mexico dead zone is the world’s second largest in the world

Source:  EPA Gulf of Mexico Dead Zone


(The Mississippi River/Gulf of Mexico Watershed Nutrient Task Force, a group working to reduce the Gulf dead zone through nutrient reductions within the Mississippi River watershed, has set a 5-year average measured size target of 1,900 square miles.)

2019 Forecast: Summer Hypoxic Zone Size, Northern Gulf of Mexico

NOAA and the United States Geological Survey (USGS) released their 2019 forecast for the summer hypoxic zone size in the Northern Gulf of Mexico on June 10, 2019. Scientists are expecting the 2019 area of low oxygen, commonly known as the ‘Dead Zone,’ to be approximately 7,829 square miles, or about the size of Massachusetts. This prediction is large primarily because of high spring rainfall and river discharge into Gulf.

Biogeochemical Flows: Nitrogen

Planetary Boundary

  • Global boundary: 62 Tg N/year
  • Source: *Steffen, W., K. Richardson, J. Rockström, S.E. Cornell, et.al. 2015. Planetary boundaries: Guiding human development on a changing planet. Science 347: 736, 1259855
  • Overall, the fixation of nitrogen through Haber–Bosch (120 Tg N yr−1) in 2010 was double the natural terrestrial sources of Nr (63 Tg N yr−1).
  • The overall magnitude of anthropogenic relative to natural sources of fixed nitrogen (210 Tg N yr−1 anthropogenic and 203 Tg N yr−1natural) is so large it has doubled the global cycling of nitrogen over the last century. 
  • The overall magnitude of anthropogenic relative to natural sources of fixed nitrogen (210 Tg N yr−1 anthropogenic and 203 Tg N yr−1 natural) is so large it has doubled the global cycling of nitrogen over the last century.
  • Source: Fowler, et al., The global nitrogen cycle in the twenty-first century, Philos Trans R Soc Lond B Biol Sci. 2013 Jul 5; 368(1621): 20130164.

Significance

The supply of Nr–reactive nitrogen (NH3, NH4, NO, NO2, HNO3, N20, HONO, PAN and other organic N compounds) is essential for all life forms, and increases in nitrogen supply have been exploited in agriculture to increase the yield of crops and provide food for the growing global human population. It has been estimated that almost half of the human population at the beginning of the twenty-first century depends on fertilizer N for their food. (Source: Fowler, et al.)

As nitrogen is a major nutrient, changes in its supply influence the productivity of ecosystems and change the competition between species and biological diversity. Nitrogen compounds as precursors of tropospheric ozone and atmospheric particulate material also degrade air quality. Their effects include increases in human mortality, effects on terrestrial ecosystems and contribute to the radiative forcing of global and regional climate. (Source: Lee, et al., see figure below)


Global N budget. Numbers represent global land N storage in TgN or annual N exchange fluxes in TgN yr−1 for contemporary (1991–2005 average) and preindustrial (1831–1860 average in parenthesis) times. See notes for this figure and the table below in:  Lee, et al., Prominence of the tropics in the recent rise of global nitrogen pollution.  Nature Communications (2019)10:1437 https://doi.org/10.1038/s41467-019-09468-4  and Supplementary Table 1 (modified below) and Supplementary Note 1 (https://doi.org/10.1038/s41467- 019-09468-4.)
Nitrogen Stores & Fluxes Published Estimates 1990’s Published Estimates 2000’s
Biological N Fixation 112; 139  
Agricultural 32 50-70
Preindustrial 58; 195  
Non-agricultural NA  
Natural 107; 128  
     
Atmospheric Deposition 59  
     
Haber-Bosch (Synthetic fetilizers) 100 120
     
Fluxes to the ocean 48 45
     
Fluxes to the atmosphere 189  
Denitrification N2 115 96
Other emissions 74 70
     
Fluxes to the land storage 60 27
     
Soils/litter storage 95,000  
     
Fluxes:  TgN/year    
Storage:  TgN    
Source: https://sedac.ciesin.columbia.edu/data/set/ferman-v1-nitrogen-fertilizer-application/maps

Biogeochemical Flows: Phosphorus

Planetary Boundary

  • Global P Boundary: 11 Tg P/year*
  • Regional (watershed) P Boundary: 6.2 Tg P/year*
  • Current global rate of P fertilizer to croplands* (primary source of P to regional watersheds): 14.2 Tg P/year*
    • Total P flow through international agricultural trade increased from 0.4Tg to 3.0 Tg between 1961-2011**
    • The fraction of P taken up by crops that is subsequently exported increased from 9% to 20% between 1961 and 2011**
    • Global P flows through international trade of agricultural products have become an important feature of the global P cycle, accounting for 20% of the P in global crop production, 17% of the P globally used as mineral fertilizer, and 27% of the P that was traded as mineral fertilizers in 2011.**
  • (Sources: *Steffen, W., K. Richardson, J. Rockström, S.E. Cornell, et.al. 2015. Planetary boundaries: Guiding human development on a changing planet. Science 347: 736, 1259855, **Nesme, T.,  G.S. Metson, and E.M. Bennett. 2018. Global phosphorus flows through agricultural trade. Global Environ. 50:133–141.Change 50:133–141. doi:10.1016/j.gloenvcha.2018.04.004 https://www.sciencedirect.com/science/article/pii/S0959378017310026

*Phosphorus and Agricultural Trade

Source: https://sedac.ciesin.columbia.edu/data/set/ferman-v1-phosphorus-fertilizer-application
Global phosphorus fertilizer application to cropland

Highlights

  • Critical element for all living organisms
  • Availability drives the productivity of many aquatic and terrestrial ecosystems worldwide
  • In agricultural systems, additional P can be supplied to soils as mineral fertilizer or manure to support crop growth and sustain high yields
  • Mineral P fertilizer production is dependent on the physical and economic availability of mined rock phosphate resources (non-renewable, diminishing, geopolitically concentrated)
    • The P cycle has been greatly transformed since the pre-Industrial era through increased agricultural mineral P fertilizer use
  • P losses to water bodies through runoff and erosion from fertilized agricultural soils and from the inadequate management of animal manure or human excreta has led to aquatic eutrophication
  • International trade of agricultural products (food, feed, fiber and fuel) are a key component of the global phosphorus cycle; agricultural flows of P are driven by trade of cereals, soybeans, and feed cakes
  • 28% of global P traded in human food, 44% in animal feed and 28% in crops for other uses in 2011