There is a huge amount of information available about coral reef health and in particular the mass coral bleaching events that have occurred over the past two years. Two of my previous posts are linked below, but if you scroll to the bottom of the page there are a range of other articles, reports and websites regarding coral bleaching that you might find useful.
Mass coral bleaching events
Coral bleaching - reef resilience
Students should define the following key terms:
- natural selection
Answer the questions below. Conduct internet research to find articles and reports which support your answers.
Coral bleaching - GBRMPA
Coral bleaching and the Great Barrier Reef - ARC CoE
Coral bleaching: Extreme heat pushes parts of the Great Barrier Reef beyond recovery - ABC
Coral bleaching events - AIMS
Great Barrier Reef: a "hopping hotspot" - Australian Geographic
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.
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.
Below: A parrot fish on the outer reef, 2015.
I had the pleasure of hearing Professor Terry Hughes present as part of the Sydney Ideas talks being run by the University of Sydney. Professor Hughes is Centre Director at the ARC Centre for Excellence for Coral Reef Studies at James Cook University. I use the term "pleasure" because I am a big fan of his work, and think that some of the visual representations that he has created have been incredibly powerful in explaining coral bleaching to students, but actually the information presented was really quite depressing.
Image left: Photograph of bleached corals at Fitzroy Island April 2017.
Hughes described some of the main drivers of degradation of coral reefs: pollution, overfishing and climate change. He explained how overfishing had resulted in the reduction of stock sizes for different species in the past century, how pollution from inland activities resulted in coral mortalities and encroachment of different ecosystems like mudflats in areas previously thriving with corals. He went on to say that the scale and extent of these changes were being dwarfed by the immediate and irreparable changes being wrought by back to back bleaching events.
Below right: Bleached coral on Fitzroy Island April 2017.
Mass bleaching events have occurred in both 2016 and 2017 as a result of increased ocean temperatures. The bleaching is as a result of corals expelling their symbiotic algae. Coral bleaching tends to occur after the summer temperature maximum, and relates to where the hottest water is. In 2016 coral bleaching severely bleached the northern third of the Great Barrier Reef, the middle section was bleached to a lesser extent, but still quite severely, while the bottom third of the reef largely escaped bleaching in 2016. This was established by the surveying of 1160 reefs through 9000km of aerial surveys, and 75 hours of flying. The 2017 bleaching event impacted the central section of the GBR, while the bottom third is again largely unbleached. Cycle Debbie, a chance weather event, lowered temperatures in the southern part of the reef, which contributed to reducing bleaching in this section. The combination of both the 2016 and 2017 bleaching events has been extremely damaging.
There have been reports that the recent cyclone that affected Queensland, Cyclone Debbie may play a role in reducing the impact of coral bleaching. It was reported in the Cairns Post that the cyclone would reduce ocean temperatures, bring cooler waters to the surface and increase cloud cover, thus reducing bleaching, providing stressed corals with an opportunity to recover. The Cairns Post reported that temperatures off Lizard Island had dropped by three degrees and that this would reduce the severity of bleaching. It also provided quotes from a free diver describing the amazing colours and marine life of the outer reef. In reality, as already stated Lizard Island and the top third of the Great Barrier Reef were already severely affected by bleaching in 2016 (well before Cyclone Debbie) and were again affected in 2017. In any case, the path of the cyclone was too far south to have any real impact on areas severely affected by bleaching.
Will the Great Barrier Reef recover?
There is a narrow opportunity for limited recovery, but the Great Barrier Reef as we know it (complexity, extent, etc) is already dead in many areas. It will continue to exist but with reduced biodiversity.
Any real opportunities to protect the reef as it remains is reliant on halting temperature increases and stabilising the climate through reducing reliance on fossil fuels. With negotiations underway between the Australian Government and Adani for for the creation of the Marmichael mines this seems highly unlikely.
For more detail on coral bleaching see my article in this term's GTA NSW HSC edition of the Bulletin.
Symbiosis is a long term relationship between two organisms. There are three types of symbiotic relationship: mutualism (where both organisms benefit), commensalism (where one species benefits, but there is no benefit or harm to the other species), and parasitism (where one organism benefits tot he detriment of the other). There are many examples of symbiosis on coral reefs.
Corals and zoozanthallae
The relationship between the corals and the zoozanthallae is beneficial to both. Corals provide the zoozanthallae with an environment suitable for survival. It is moist and the coral's waste gives energy to the zoozanthallae. Through the process of photosynthesis the zoozanthallae produce compounds that the coral use for food.
Clownfish and Sea Anemones
The Sea Anemones have tentacles with stinging cells. These stinging cells kill many organisms and it is in this way the anemones get their food. Clownfish hide in amongst the tentacles of the Sea Anemone, but are not harmed by them. In this way the clownfish are protected from other predators. Occasionally the Clownfish will catch food for the Sea Anemone.
Sharks and Remoras
Sharks sometimes get parasites which live on the external surface of the shark. Remoras are cleaner fish, and they attach themselves to the shark and kill the parasites. When the shark feeds the Remora are able to eat the scraps from the feed.
Watch the videos below, and take notes about the following symbiotic relationships:
- Christmas tree worms and porites corals
- Coral shrimps and corals
- Goby shrimp and Hawaiian Shrimp Goby
- Cleaner Wrasse and cleaning stations
•Coral Reefs support a large number of plants and animals.
•Coral Reefs are built by millions of tiny animals called polyps.
•Some coral polyp species receive more than 60% of their food from algae.
•Each coral colony begins life as a single polyp, which then reproduces itself as a single polyp, which then reproduces itself by budding or by dividing.
Types of coral reefs
There are eight main categories of corals: branching, corals with meandering ridges and valleys, massive or thick colonies, thin plates and crusts, solitary/isolated/free-living corals, coral with large, daytime expanded polyps, column corals and blue/fir/organ pipe/lace corals. Some examples of coral are found below:
Where are coral reefs found?
Special conditions are needed for reef-building corals. Coral reefs will only grow in waters warmer than 18oC, and no deeper than 50metres. Therefore coral reefs are limited to clear, shallow tropical seas found either side of the equator. Corals may not develop properly in waters that receive freshwater runoff or sediments from rivers.
This is part of a unit of work for Changing Places - Australia's Urban Future.
Lesson 1: Australia's Projected Population Growth
Lesson 2: Implications for Future Growth and Sustainability
Lesson 3: Sydenham to Bankstown Urban Renewal Precinct
Lesson 4: WestConnex - Sydney, Sustainability and Transport
Lesson 4: Sydney Sustainability and Transport (Teacher's Notes)
Lesson 5: The GreenWay
Lesson 5: Deindustrialisation
Lesson 6: Create an infographic
Lesson 7: Contributing to a Sustainable Urban Future
Lesson 7: WestConnex - Protest Movements and Impacts
Lesson 7: Conflict Over Dulwich Hill
OR See the complete unit on the Changing Places website.
Stage 1 of the WestConnex project involves the widening of the M4, a connection between Parramatta Road and the City West Link and new connections at Concord Road. A tunnel will run from the end of the current M4 to the City West Link,
M4 East concept design
WestConnex Stage 1
WestConnex interactive map
A section of Ashfield along Parramatta Road was acquired and demolished for WestConnex. The exit to the M4 tunnel will be opposite Bunnings Warehouse near the crossroads of Frederick St/ City West Link and Parramatta Road.
WestConnex plan jeered by Ashfield residents
Save Ashfield Park Rally
Some of the issues raised in relation to WestConnex in Haberfield include home acquisitions, destruction of heritage architecture, noise and vibrations for homes adjacent to construction sites, changes to traffic flows and the impact of all of these factors on the nature of the suburb.
Haberfield homes acquired for building of WestConnex
Three month closure of Ramsay Street Haberfield
Talking WestConnex and Mike Baird ignoring compulsory aquisition reforms
WestConnex private contractors sell items from heritage homes ahead of demolition
WestConnex unused land should be handed back say inner west residents.
Residents in Haberfield and Beverley Hills claim WestConnex work is cracking walls of houses near motorway construction sites.
What we are facing is the destruction of Haberfield
Deputy Principal at a Sydney high school. Coordinating author of the new Geoactive book series.