Local threats

(i) Overfishing and destructive fishing practices

One of the most explicit forms of human pressure on reefs are fisheries, which provide employment, income, and food. When well-managed, fisheries can act as a sustainable resource, yet current estimates show that 55 percent of the world’s reefs are endangered by overfishing and/or destructive fishing.⁵⁰ Overfishing occurs when the capture of fish is done with a sufficiently high intensity to deplete the breeding stock levels to such an extent that the fish cannot sustain their population.⁵¹ The reasons for overfishing are multifold: population growth; a response to the increased demand for fish and seafood products; the continual improvement of fishing methods to make them more efficient;

poor management and/or insufficient enforcement practices; a lack of alternative employment opportunities; as well as simply an immediate monetary incentive that is based on the perceived high value of certain target species, such as sharks and lobsters.

The main issue with overfishing is the ecosystem-wide consequences engendered by reducing just one group of fish from the reef food web. As the previous sections illustrated, the reefs depend on mutualistic relationships that keep the stability of the ecosystem in check. The overfishing of one species will have cascading effects

49 Burke 2011:2.

50 Reef Resilience, 2016, ‘Overfishing and Destructive Fishing Threats.’ Accessed 16 March 2017.

http://www.reefresilience.org/coral-reefs/stressors/local-stressors/overfishing-and-destructive-fishing-threats/

51 Pepijn Koster, ‘Overfishing – a global disaster,’ Overfishing.org. Accessed 16 March 2017.

http://overfishing.org/pages/what_is_overfishing.php

across the entire coral reef system. Moreover, while “large predators are often the preferred target species, as their numbers decline, fishers move to smaller, often herbivorous fish” in a process called ‘fishing down the food chain’.⁵² Consequently, areas of reef that experience heavy fishing may be prone to algal overgrowth, which in turn may lead to an increase of unwanted pathogens, aquatic hypoxia (oxygen deficiency),⁵³ and zooxanthellae expulsion, making the reefs more vulnerable to disease, preventing nutrient absorption, and delaying growth and recovery.

Furthermore, some fishing techniques in themselves are detrimental to the reefs.

Destructive fishing practices include:

 Bottom trawling – dragging a large fishing net called a ‘trawl’ along the sea floor, indiscriminately gathering everything in its path. The main consequences of bottom trawling are, firstly, its bycatch (collateral damage), which can amount to 90 percent of its total catch and may include engendered fish, juvenile species, vulnerable deep-sea corals, and other organisms that were not targeted for capture; and secondly, as the net is equipped with heavy weights to submerge it to the seafloor, its weight and width can destroy large coral reef areas, destroying the marine ecosystem.⁵⁴

 Cyanide/poison fishing – using cyanide to stun and capture fish live. This is mainly done for the live reef food fish market or as aquarium stock. Again, two main issues arise here: firstly, attempts to collect the fish often result in the damaging of corals, and secondly, poison causes coral bleaching and the annihilation of polyps.⁵⁵

 Dynamite fishing – using dynamites or other explosives to kill fish, completely destroying the underwater environment in the process. Despite it being illegal in many countries, dynamite fishing nevertheless remains a popular fishing

52 Burke 2011:26.

53 Rebecca Vega-Thurber et al., 2012, ‘Macroalgae Decrease Growth and Alter Microbial Community Structure of the Reef-Building Coral, Porites astreoides,’ PLoS ONE 7(9): e44246.

doi:10.1371/journal.pone.0044246. Accessed 23 March 2017.

54 Marine Conservation Institute, ‘Destructive Fishing.’ Accessed 16 March 2017. https://marine-conservation.org/what-we-do/program-areas/how-we-fish/destructive-fishing/

55 Burke 2011:26.

method in Southeast Asia, contributing to the massive destruction of coral reefs in the past two decades.⁵⁶

 Ghost fishing – this occurs when discarded or lost nets/traps continue to ensnare prey for months/years after their original use. These nets may also become snagged on the seabed, smothering corals and causing damage to the seafloor.⁵⁷ (ii) Land-based pollution and coastal development

Human activities both far inland and in the coastal zone are adding increased pressure to nearshore ecosystems. As Figure 2 illustrates, approximately 850 million people live within 100 km of a reef.⁵⁸ Development is altering the landscape, increasing terrestrial runoff of sediment, pollution, and nutrients into adjacent waters, thus lowering coastal water quality and marine ecosystem health.

Sedimentation, both in low and high amounts, can weaken the health and resilience of coral reefs and other organisms. The contribution of sediment to watersheds stems from anthropogenic activities such as deforestation, road construction, storm water runoff, and chemical spills. Notably, high fertilizer and pesticide usages accompany the intensifying demand for agricultural products. Estimates conducted by the Food and Agriculture Organization of the United Nations state that the global fertilizer consumption will grow 1.8 percent annually, with the highest rates in South Asia and Africa.⁵⁹ Problems with agricultural runoffs are compounded with factory farming, livestock waste, and erosion of natural vegetation by invasive species.

Furthermore, the destruction of native plants for coastal development or fish farming purposes facilitates sediment runoff to the coast. Mangrove forests are a prime example of natural buffers that help shelter coastal coral reefs by trapping sediments, dissolving nutrients from the water, and removing a fraction of the riverine inflow of mud.⁶⁰ Overall, such anthropogenic activities create a more competitive environment for the reefs, making them more vulnerable to disease outbreaks or climate impacts.

56 WWF, ‘Fishing problems: Destructive fishing practices.’ Accessed 16 March 2017.

http://wwf.panda.org/about_our_earth/blue_planet/problems/problems_fishing/destructive_fishing/

57 Ibid.

58 World Resources Institute, ‘Number of People Living Near Coral Reefs in 2007,’ February 2011.

Accessed 15 March 2017.

59 Food and Agriculture Organization of the United Nations, ‘World Fertilizer trends and outlook to 2018,’ Rome 2015, p. ix. Accessed 3 March 2017. http://www.fao.org

60 Teina Rongo et al., 2007, ‘Watersheds and Coral Reefs: Conservation Science, Policy, and Implementation,’ BioScience, Vol. 57, No. 7, July 2007, p. 600.

Sedimentation has two major dimensions: physical and chemical. In large quantities, the physical accumulation of sediments can smother, weaken, and kill corals and other benthic organisms.⁶¹ High turbidity levels affect the transparency of water and limit the penetration of sunlight, which can inhibit the ability of aquatic plants and algae to photosynthesize. Sedimentation, even in low levels, may thus slow down or fully disrupt the process of photosynthesis by zooxanthellae, which in turn would impact coral growth.⁶² Chemical pollution refers to contaminants such as nitrogen and phosphorus that are transported by sediment into the aquatic system.⁶³ Eutrophication, that is to say, excessive levels of nutrients in bodies of water, encourages the growth of phytoplankton and algae, which in turn reduces the clarity of coastal waters and impacts the fragile environment that the zooxanthellae and corals depend on. Additionally, this chemical invasion may strengthen one group of organisms over another, destabilizing the ecosystem as a whole. Indeed, a burst of certain algae or seaweeds on the seafloor may outcompete corals for resources, leading to reef degradation.⁶⁴ Finally, a significant threat of nutrient enrichment is hypoxia – the depletion of oxygen levels which creates ‘dead zones’ in biotic environments, leading to their collapse.⁶⁵

Direct development on the reef in the form of dredging or land filling is also detrimental to coral reef health.⁶⁶ Unsustainable coastal development and reclamation activities generally cause irreversible and widespread damage to the biodiversity and ecological balance of coral reefs, as epitomized by People’s Republic of China building of artificial islands in the South China Sea.⁶⁷ China’s direct physical damage to thousands of acres of reef has been labeled as the quickest permanent loss of coral reefs in human history.⁶⁸ Reefs are extremely susceptible to a number of factors, and the

61 Burke 2011:23.

62 Ibid.

63 Natural Recourses Management and Environment Department, ‘Chapter 2: Pollution by sediments’, Food and Cultural Organization of the United Nations. Accessed 17 March 2017.

http://www.fao.org/docrep/W2598E/w2598e05.htm

64 Alex Ritchie, ‘The Effects of Three Species of Macroalgae on Acropora Aspera Physiology,’ The Stanford Undergraduate Research Journal, p.39.

65 Camilo Mora, 2015, Ecology of Fishes on Coral Reefs, UK: Cambridge University Press, p. 149.

66 Burke 2011:21.

67 Floyd Whaley, 2015, ‘China’s Island-Building Is Ruining Coral Reefs, Philippines Says,’ The New York Times. Accessed 17 March 2017. https://www.nytimes.com/2015/04/14/world/asia/chinas-island-building-is-ruining-coral-reefs-philippines-says.html?_r=0

68 Oliver Holmes, 2015, ‘South China Sea Images Reveal Impact on Coral of Beijing’s Military Bases.’

The Guardian. Accessed 17 March 2017.

https://www.theguardian.com/world/ng-interactive/2015/sep/17/south-china-sea-images-reveal-impact-on-coral-of-beijings-military-bases

cumulative impact of land-based pollution and perpetual coastal development may soon result in a colossal and rapid destruction of the entire ecosystem.

(iii) Marine-based pollution and damage

Threats to coral reefs from marine-based sources occur on multiple fronts. The movement of commercial, recreational, and passenger vessels takes place on a quotidian basis and in vast numbers all around the world [Figure 5]. Firstly, vessel spillages and waste, such as contaminated bilge water, oil spills and fuel leakages, as well as raw sewage and solid waste discharge directly undermine the health of coral reefs. For brevity purposes, the example of oil spillages will be expanded upon below.

Figure 5: The data points show the movements of the world's commercial shipping fleet on 17 May 2012. The red dots represent huge tankers, the blue dots show dry bulk ships that move cargo like ores, and the yellow dots show ships that carry manufactured products. Green shows gas bulk and purple shows ships carrying vehicles.⁶⁹

The impact of oil spills on corals varies in severity depending on oil toxicity, coral species, time and length of exposure, et cetera. The toxicity of oil is similarly difficult to determine, as “each spill presents a unique set of physical, chemical, and biological conditions.”⁷⁰ Nevertheless, literature shows that oil swiftly and readily bioaccumulates in coral tissues, reduces coral fertility, and damages two fundamental bioenergetic components for the entire ecosystem, namely the “primary production by

69 Ellie Zolfagharifard, 2016, ‘Watch cargo ships sale Earth’s oceans: Hypnotic interactive map follows the route of giant vessels over a year.’ The Daily Mail. Accessed 23 March 2017.

http://www.dailymail.co.uk/sciencetech/article-3562440/Watch-cargo-ships-sail-Earth-s-oceans-Hypnotic-interactive-map-follows-route-giant-vessels-year.html

70 Ruth A. Yender et al., 2010, ‘Oil Spills in Coral Reefs: Planning and Response Considerations,’

National Oceanic and Atmospheric Administration, July 2010, p. 25.

the zooxanthellae symbionts in coral, and energy transfer via coral mucus.”⁷¹ Oil also has an adverse effect on species of fish, invertebrates, plants, as well as turtles, marine mammals, and other seasonal reef-dwellers that are to a varying degree sensitive to direct oil exposure. Despite technical advancements and other efforts to avoid oil spillages, global demand for oil is on the rise and will continue to do so for the foreseeable future.

Secondly, direct contact with ships/vessels may lead to extreme damage or permanent killing of coral reefs. This physical destruction occurs as a result of perching or grounding of ships on coral reefs, contact with ship hulls, anchors, propellers, as well as damage caused by fallen debris.⁷² The grounding and anchoring of cruise ships in particular has aggravated the marine habitat, as most cruise ships have the capability to enter shallow, sensitive areas. By doing so, their anchors and anchor chains inflict severe destruction on coral reefs and the seabed. Figure 6 succinctly depicts marine-based pollution of ships as a result of oil spills, ballast water discharge, and direct damage to the reefs.

Figure 6: Vessels are a major source of marine-based pollution and damage. Inadequate waste management at port and marinas, uncontrolled ballast discharge, and a lack of strictly managed safe shipping lanes and boating areas are just a few of the causes behind this.⁷³

Lastly, it is crucial to acknowledge invasive species as a marine-originated threat to coral reefs. A 1999 report estimated that vessels may carry in their ballast water anywhere between 3,000 and 10,000 species of marine organisms globally in any given 24-hour period.⁷⁴ This ‘modern invasion’ is also a result of aquarium releases,

71 Ibid, pp. 30-31.

72 Burke 2011:25.

73 Yender 2010:38.

74 James T. Carlton, 1999. ‘The Scale and Ecological Consequences of Biological Invasions in the World’s Oceans,’ Invasive Species and Biodiversity Management. Dordrecht: Kluwer Academic Publishers, p.195.

and the effects are detrimental to both coral reefs and native species. The lionfish (Pterois volitans, Pterois miles) is a well-documented example of an invasive species whose population has swelled most likely as a result of aquarium releases, then has become established to varying degrees across the entire Caribbean region via larval dispersal in ocean currents.⁷⁵ Originally native to the Indo-Pacific, lionfish have driven the Atlantic coral reef fish into decline and have caused a major disruption of the ecosystem. Overall, the invasion of marine predators has detrimental impacts on natural communities and is a serious threat to the well-being of coral reefs and the native species that rely on them.

In summary, the major local threats discussed include overfishing and destructive fishing practices, land-based pollution and coastal development, as well as marine-based pollution and damage.