Coral reefs - Human impacts
Coral Bleaching
Vulnerability and resilience of ecosystems is determined by factors such as location, extent, linkages and diversity. Climate change and associated ocean acidification and increased ocean temperatures are resulting in widespread coral mortalities, The ability of corals to return to close to their natural state is determined by how resilient the reefs remain. A resilient reef will either be able to resist a bleaching event (i.e. not bleach to any great extent) or recover from it.
The changes in temperature and associated bleaching are resulting in a different mix of species on the reef. This will impact reefs in the long term.
Loss of species
Fish, whales, dolphins, sharks, rays and the many other organisms found in reefs rely on the complexity of the ecosystem for survival. Some fish rely on the colour of the corals for camoflauge and the structure of the coral for hiding. Many organisms are unable to carry out normal functions and processes as a result of the increased ocean acidification associated with climate change. Shellfish are less able to create their shells due to increased pH. Slow growing corals will take 100-200 years to recover, meaning that the reef will not exist in the form that we have known it in the past.
Dispersal of spawn
Ocean warming impacts on the dispersal or coral spawn (eggs). Increased ocean temperatures result in a decline in the dispersal distance of coral spawn from the origin (parent coral) to the destination site. This change in dispersal patterns can impact on species' distribution, abundance or corals in particular areas and genetic diversity across reefs. Changes to dispersal patterns can also impact on the connectivity (interconnections) between different areas of the reef by limiting the areas of reef that particular coral species are located.
Poleward shift of species
Ocean warming can also result in a poleward shift of species from tropical zones to more temperate zones. Warmer waters are found further from the tropics and species are able to take advantage by increasing their range.
In Western Australia, a species of wrasse - cheorodon rebuscens has started to shift its range with displacement of recruits south of its usual habitat. There is evidence of high recruitment at the temperate edge and no recruitment at the tropical edge. The range shift provides limited expansion opportunities, reducing resilience of the species.
Irukandji are migrating further south on the Great Barrier Reef as a result of warmer waters and are also having longer seasons in other areas. There have been anecdotal reports of increases in reports of stinging and hospitalisations on islands within the Great Barrier Reef (e.g Fitzroy Island) and snorkellers are being strongly advised to wear stinger suits outside of usual peak Irukandji seasons. Irukandji and associated stingings have also been reported on western side of the southern tip of Frazer Island where they haven't previously been found.
Symbiotic relationships
Following bleaching events or even natural disasters, corals can become overgrown with algae, making it difficult for coral recruits to settle and grow. The mix species on a reef can impact on how resilient that particular reefs is. For example in Moorea in French Polynesia experienced high coral mortality in the 1980s. Recovery of the reef was enabled in part as a result of grazing fish such as parrot fish removing some of the algae in the process of eating corals. In this way the biodiversity of the reef contributed to high levels of resilience on the reef in comparison to some other reefs globally. The scale of the bleaching on GBR make it unlikely that these types of natural processes will have much of an impact on recovery.
The changes in temperature and associated bleaching are resulting in a different mix of species on the reef. This will impact reefs in the long term.
Loss of species
Fish, whales, dolphins, sharks, rays and the many other organisms found in reefs rely on the complexity of the ecosystem for survival. Some fish rely on the colour of the corals for camoflauge and the structure of the coral for hiding. Many organisms are unable to carry out normal functions and processes as a result of the increased ocean acidification associated with climate change. Shellfish are less able to create their shells due to increased pH. Slow growing corals will take 100-200 years to recover, meaning that the reef will not exist in the form that we have known it in the past.
Dispersal of spawn
Ocean warming impacts on the dispersal or coral spawn (eggs). Increased ocean temperatures result in a decline in the dispersal distance of coral spawn from the origin (parent coral) to the destination site. This change in dispersal patterns can impact on species' distribution, abundance or corals in particular areas and genetic diversity across reefs. Changes to dispersal patterns can also impact on the connectivity (interconnections) between different areas of the reef by limiting the areas of reef that particular coral species are located.
Poleward shift of species
Ocean warming can also result in a poleward shift of species from tropical zones to more temperate zones. Warmer waters are found further from the tropics and species are able to take advantage by increasing their range.
In Western Australia, a species of wrasse - cheorodon rebuscens has started to shift its range with displacement of recruits south of its usual habitat. There is evidence of high recruitment at the temperate edge and no recruitment at the tropical edge. The range shift provides limited expansion opportunities, reducing resilience of the species.
Irukandji are migrating further south on the Great Barrier Reef as a result of warmer waters and are also having longer seasons in other areas. There have been anecdotal reports of increases in reports of stinging and hospitalisations on islands within the Great Barrier Reef (e.g Fitzroy Island) and snorkellers are being strongly advised to wear stinger suits outside of usual peak Irukandji seasons. Irukandji and associated stingings have also been reported on western side of the southern tip of Frazer Island where they haven't previously been found.
Symbiotic relationships
Following bleaching events or even natural disasters, corals can become overgrown with algae, making it difficult for coral recruits to settle and grow. The mix species on a reef can impact on how resilient that particular reefs is. For example in Moorea in French Polynesia experienced high coral mortality in the 1980s. Recovery of the reef was enabled in part as a result of grazing fish such as parrot fish removing some of the algae in the process of eating corals. In this way the biodiversity of the reef contributed to high levels of resilience on the reef in comparison to some other reefs globally. The scale of the bleaching on GBR make it unlikely that these types of natural processes will have much of an impact on recovery.
Other human impacts
Turbidity
Turbidity and salinity restrain coral growth. Muddy waters along coast lines at the point of river mouths dampen coral reef growth in 2 ways: sediment particles interfere with the ability of zooxanthellae to photosynthesise by decreasing the amount of light in the water. Secondly, sediment may be deposited on top of the coral itself burying them, or preventing them from feeding.
Sewage
Sewage outflows can impact negatively on reefs by introducing high levels of phosphorous and encouraging algal growth. Eutrophication can result in extensive algal blooms and reduced levels of invertebrates. Rates of coral morbidity are increased due to smothering. It can also result in a shift from an area with hard coral species to softer corals and fleshy algaes. The severity of the impact of sewage can be determined by ocean currents, tides and flushing rates.
Fishing
Sea floor trawling ruins marine habitats, destructive trawling practices.
Overfishing
Modern fishing equipment increases the number of fish caught.
Fishing nets become "dolphin and turtle graveyards", because animals become trapped in the nets and die. This has implications for the whole ecosystem.
Any physical contact with anchors, feet, fishing nets or diving gear can result in sections of coral being broken and destroyed.
When predator becomes prey
Sea cucumbers may be key to reef health
Sea turtles caught up in ghostnets’ random harvest
Pollution
Marine debris (human generated litter) in our marine environment is one of the major pollutants of oceans. Plastics such as shopping bags, containers, bottle, discarded nets etc result in the death of many animals.
Chemical runoff.
Oil spills
Dumping
Discharge from different buildings and industries.
Agriculture
Cattle grazing, urban development and land clearing - increased erosion and sediments in the water block out sunlight for coral and fish.
Feed and faeces from tuns pens can cause marine pollution as well as extensive damage to the sea floor.
Agricultural runoff main threat to Reef water quality
Turbidity and salinity restrain coral growth. Muddy waters along coast lines at the point of river mouths dampen coral reef growth in 2 ways: sediment particles interfere with the ability of zooxanthellae to photosynthesise by decreasing the amount of light in the water. Secondly, sediment may be deposited on top of the coral itself burying them, or preventing them from feeding.
Sewage
Sewage outflows can impact negatively on reefs by introducing high levels of phosphorous and encouraging algal growth. Eutrophication can result in extensive algal blooms and reduced levels of invertebrates. Rates of coral morbidity are increased due to smothering. It can also result in a shift from an area with hard coral species to softer corals and fleshy algaes. The severity of the impact of sewage can be determined by ocean currents, tides and flushing rates.
Fishing
Sea floor trawling ruins marine habitats, destructive trawling practices.
Overfishing
Modern fishing equipment increases the number of fish caught.
Fishing nets become "dolphin and turtle graveyards", because animals become trapped in the nets and die. This has implications for the whole ecosystem.
Any physical contact with anchors, feet, fishing nets or diving gear can result in sections of coral being broken and destroyed.
When predator becomes prey
Sea cucumbers may be key to reef health
Sea turtles caught up in ghostnets’ random harvest
Pollution
Marine debris (human generated litter) in our marine environment is one of the major pollutants of oceans. Plastics such as shopping bags, containers, bottle, discarded nets etc result in the death of many animals.
Chemical runoff.
Oil spills
Dumping
Discharge from different buildings and industries.
Agriculture
Cattle grazing, urban development and land clearing - increased erosion and sediments in the water block out sunlight for coral and fish.
Feed and faeces from tuns pens can cause marine pollution as well as extensive damage to the sea floor.
Agricultural runoff main threat to Reef water quality
Seaweed quality could affect marine grazers
Shocking state of seas threatens mass extinctions, warn experts.
Health of oceans declining fast.
Earth's oceans on course for mass extinction.
Viral disease may contribute to coral reef die-offs.
Coral reefs are being decimated, all for a few gaudy trinkets.
Rising ocean acid levels are 'the biggest threat to coral reefs'.
Shocking state of seas threatens mass extinctions, warn experts.
Health of oceans declining fast.
Earth's oceans on course for mass extinction.
Viral disease may contribute to coral reef die-offs.
Coral reefs are being decimated, all for a few gaudy trinkets.
Rising ocean acid levels are 'the biggest threat to coral reefs'.
