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Manage the land to protect the reefs

The world’s coral reefs are both beautiful and rich in biodiversity, supporting a number of marine species. However the negative effects of climate change and human activity have begun to take their toll…

Better land management and reforestation will protect the coral reefs of Madagascar from the damage caused by sedimentation. Flickr/Frontierofficial

The world’s coral reefs are both beautiful and rich in biodiversity, supporting a number of marine species. However the negative effects of climate change and human activity have begun to take their toll on these delicate ecosystems, with coral bleaching, damaged structures and the loss of species already occurring.

Though there are many issues threatening the health of coral reefs, for those that have grown near the shore, sedimentation is a major problem.

Deforestation can cause high amounts of soil erosion. With rainfall the loose soil finds its way into coastal waters through waterways. The muddy freshwater smothers the coral, blocking light and damaging coral tissue, which can lead to bleaching and deterioration of the reef and its ecosystem.

Our recently published study found that a hotter and drier climate will limit the flow of sediment into coastal waters, however these climate change-driven declines are outweighed by the impact of deforestation.

When it comes to dealing with this risk in the future, the best policies will be those that focus on the land, promoting better management and increased forest cover.

To Madagascar

Madagascar is a well-known biodiversity hotspot with its different regions representing a wide range of tropical climates. However the human population has struggled with preserving the island’s environmental integrity. Around 90% of the original forest cover has been lost in the 2000 years since human contact.

This has placed pressure on the conservation of the coral reefs that exist off the shores of Madagascar as they are damaged by the freshwater and sediment that flow from the river systems.

By modelling four river systems adjacent to Madagascar’s major coral reef systems we aimed to find an understanding of how best to protect these reefs.

The modelling involved computer simulations of sediment released near coral reef areas for the present day and 2090. These were carried out for different scenarios of projected temperature and rainfall, while also modelling the impact of reduced or increased forest cover.

On average, temperature is expected to increase while rainfall is expected to decline by 2090, with a tendency for wet season to become wetter and dry season to become dryer. These changes will lead to a decline in the flow of sediment into coastal coral reefs. Therefore, climate change alone will not accelerate reef sedimentation, as was previously thought.

Land use however, and in particular changes in forest cover, have significant impact on the amount of sediment discharged to coral reefs. Already sediment has increased five-fold since human settlement in Madagascar. This surge will continue if forests keep being cleared. Increasing forest cover in Madagascar through reforestation will reduce the amount of soil washing into coastal waters and further protect the reefs from the adverse effects of sedimentation.

Widespread deforestation in Madagascar has threatened the island’s coral reef system. Flickr/Effervescing Elephant

The predicted drier climate may also have wider implications for the biodiversity of Madagascar beyond the protection of coral reefs. Future hydrological changes may have severe consequences for certain fauna and flora. This is especially so in the south west of the island where our simulations show the largest decrease in rainfall.

These changes may also set off a chain of socio-ecological problems. Many traditional pastoralists in the southwest have already swapped farming for fishing. This may lead to potential problems in managing marine resources, as their practises will differ from those of traditional fishers. As the climate becomes drier and less suitable to farming, these marine stocks will become increasingly important as food for the local population.

Beyond Madagascar

Most coral reef research in Australia has concentrated on the Great Barrier Reef (GBR), where many coastal reefs are affected by sediment flowing from rivers draining the Queensland hinterland. Land clearing for farming and agriculture has transformed the hinterland since Europeans first set foot in Australia. As a result river sediment discharge has increased at least 5 to 10-fold since the mid-1850s.

More recent surveys since the mid-1980s have revealed that coral growth and calcification (the amount of coral skeleton formed yearly) in inshore reefs along the vast Great Barrier Reef have suffered from the adverse impacts of sediment and nutrients from river runoff.

Projections for future Queensland rainfall are highly uncertain. More research is needed to get a better handle on future trends in rainfall and river runoff. Certainly modelling similar to what was used in Madagascar may be able to capture the most likely future climate of the GBR hinterland catchments and could be of great benefit for GBR management.

In the meantime, a likely effective management action is to further reduce pesticide and nutrient runoff from the hinterland to improve water quality in the GBR. This means, that it becomes increasingly important to engage with all stakeholders to develop targeted solutions to preserve our valuable coral reefs and buy time for coral reef ecosystems to cope with warming oceans, the most severe immediate threat from climate change.

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29 Comments sorted by

  1. Jon Brodie

    Research scientist

    Good article but it's important to get the GBR story correct. The coral reefs analysed by De'ath et al 2012 and showing severe coral cover decline (at least the ones in the central and southern GBR) are mid and outer shelf reefs and basically not affected by sedimentation or increased turbidity. The causes of the decline for these reefs are crown of thorns starfish outbreaks (linked to nutrients from agriculture), cyclones, coral bleaching and coral diseases. Inner shelf reefs in the central and…

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    1. Dianna Arthur
      Dianna Arthur is a Friend of The Conversation.

      Environmentalist

      In reply to Jon Brodie

      Agree with your points that more needs to be publicised regarding the influence of land practices in the hinterland having a direct impact on coast, reefs and on to oceans.

      Would prefer to see more articles looking at changes to local ecosystems over past 100 years. People have began to tune out the words "climate change", more home studies need to be brought to public awareness. Changes are occurring right in our back yards and too many remain ignorant of these facts.

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    2. Mike Jubow

      forestry nurseryman

      In reply to Jon Brodie

      Jon, from my perspective, the runoff problems seem to be the only ones where there is any attempt to do something about it. In Qld, there are many Landcare and farmer groups who, through the Reef Rescue program, are doing positive work in identifying the source of detrimental runoff and taking steps to actually limit them. I have cane farms all around my property and the farmers I know are committed to reducing or limiting runoff through developing new techniques of applying fertilizer and chemicals…

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    3. Rotha Jago

      concerned citizen

      In reply to Mike Jubow

      Do those careful farmers spray their drains?keeping them bare of vegetation?

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    4. Mike Jubow

      forestry nurseryman

      In reply to Rotha Jago

      Due to the fact that our wet season rain is very heavy, sprayed out drains would wash out leaving huge gullies. In almost all cases, they are slashed so that there is still groundcover to stop erosion. Also, if they have gone to the expense of building silt traps, they would be overwhelmed if they sprayed out drains. Where ever possible, drains are constructed wide and shallow and are placed where ever possible with the shallowest of gradient to keep water velocities low.

      This is all part of…

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    5. Rotha Jago

      concerned citizen

      In reply to Mike Jubow

      That all sounds good. A pity that while farmers are making all these efforts Local Councils are spraying creek banks and roadsides.
      In spite of high rainfall, eroded creeks were an oddity 10 years ago.
      Now they are the rule.

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    6. Mike Jubow

      forestry nurseryman

      In reply to Rotha Jago

      Not only that Rotha, councils do not make anything more than a token attempt to control noxious weeds when they are spraying the roadsides. At the same time, these weeds are escaping into farmers properties where it is an ongoing and costly battle battle for the farmer to control. Yet, if the farmer makes an attempt to control the weeds outside his boundary on the road reserve he is prosecuted. Now please tell me how you make sense of that?

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    7. Rotha Jago

      concerned citizen

      In reply to Mike Jubow

      I am not sure what you are referring to.
      In my experience weeds grow as a consequence of spraying weed killers. It sounds strange but the more our local council sprays, the more weeds grow. We have instances of roadside mixed vegetation being sprayed usually with Glyphosate, and when vegetation eventually grows back it is all weeds.

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    8. Mike Jubow

      forestry nurseryman

      In reply to Rotha Jago

      Rotha, If you killed weeds or, for that matter, any vegetation with a steam spray, you would still have weeds and other species emerge on the same patch of ground. This is due to the simple fact that virtually any patch of ground has a load of dormant seeds. The moment that there is no competition and the soil born seeds are exposed to sunlight and moisture, they germinate. It has nothing to do with glyphosate or weed killers, nature will fill any empty space.

      A classic illustration of this is…

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    9. David Arthur

      resistance gnome

      In reply to Mike Jubow

      Mike, you mention that: "... the coal mining industry will continue to keep putting silt and mineral nutrients in our rivers, the coal export ports will continue dredging ..."

      Perhaps there is Good News in increasing recognition in China that coal use is cactusing up their environment, and that they'll be acting to decrease coal use sooner rather than later?

      While this is not Good News to the present generation of Australian politicians and their corporate backers, there may be hope of some recovery in the future, when the Boom is over.

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    10. Mike Jubow

      forestry nurseryman

      In reply to David Arthur

      Yes David, I agree with you. Things are going to get worse before any positive action happens in Oz. I firmly believe that under Abbotts leadership, we will have a government cosied up in bed with the miners and to hell with the environment. And this statement is from a conservative voter of some 40 years standing. We are in a great position, if we vote in a LIB/NAT government, nothing will change and if we vote in a LAB govt, they are too incompetent to make anything happen. Lovely. The only chance we have is if Turnbull rolls Abbott for the leadership. Then our environment has a standing chance of some rectification work being done.

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    11. David Arthur

      resistance gnome

      In reply to Mike Jubow

      Meanwhile, perhaps we could all take to preferencing the LibLab Party last - each of us can chose as to which wing (Lib or Lab) is last, and which is second last.

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  2. Geoffrey Harold Sherrington

    Boss

    We can expect many diverse theories to be presented at proven mechanisms when it comes to the poster child of the Great Barrier Reef.
    It is beautiful to observe, no doubt about that. A wonder of nature.
    But, to be scientifically hard, we know very little about what the Hand of Man does to the Reef, if anything.
    Global Warming used to be blamed, but as we have had none for 16 years, it must make research harder.
    Sure, fertilizers do need to be watched, but we lack a cradle to grave understanding…

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    1. Rotha Jago

      concerned citizen

      In reply to Geoffrey Harold Sherrington

      Corals are what makes the reef "Great" but if we look at waters closer to the mainland shore, the state of sea grass beds and their occupants gives an indication of ecosystem health which emerges much faster. More research of, and discussion about seagrass health would be welcome.

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    2. Wade Macdonald

      Technician

      In reply to Rotha Jago

      Where have you been Rotha Jago?

      https://theconversation.com/search?q=seagrass

      The only problem is that real regeneration of seagrasses isn't the main agenda. The main agenda is pretending to care so multinational corporates can make money from this important resource through carbon sequestion based trading offsets to their pollution.

      I wonder if this will sea large areas of this resource privatised just like the Amazon and other forests at the access expense of local communities?

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    3. Wade Macdonald

      Technician

      In reply to Rotha Jago

      Do you know about the 'carbond wax' that was only ever really brought in to start an emissions trading scheme so the multinationals could offset their pollution costs through trading credits???

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    4. Wade Macdonald

      Technician

      In reply to Geoffrey Harold Sherrington

      Geoffrey,

      It appears the coral is more resilient than ever according to AIMS...

      http://www.bairdmaritime.com/index.php?option=com_content&view=article&id=14065:western-australias-scott-reef-recovers-from-mass-bleaching&catid=76:marine-environment&Itemid=212

      Who would of thought that in this age of unprecedented extinction rates and carbon induced climate change that corals could recover from an 80% loss in 12 short years?

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    5. Rotha Jago

      concerned citizen

      In reply to Wade Macdonald

      I'm sorry you have completely lost me. I am not trying to wind you up. Just no idea what you are referring to.

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    6. Wade Macdonald

      Technician

      In reply to Rotha Jago

      Are you an Australian resident who watches the news? If so you would know about the carbon tax and resultant emmissions trading scheme.

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    7. Rotha Jago

      concerned citizen

      In reply to Wade Macdonald

      Yes. I have often wondered why everyone talks about too much CO2 and not decreasing Oxygen which seems a bigger problem to me. I feel that the 'Carbon Market' is just another market, an opportunity for banks to make money. All those conferences around the world about carbon markets were sponsored by banks.

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    8. David Arthur

      resistance gnome

      In reply to Geoffrey Harold Sherrington

      While corals may eventually recover from the damage inflicted in the course of the looting inflicted by the present generation of corporate "leaders", it won't be until long after that generation are in their grave, and their grandchildren are cursing the memory of their forebears for their moronic vandalism.

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    9. David Arthur

      resistance gnome

      In reply to Wade Macdonald

      Wade, of course a reef can and will recover from a coral bleaching episode if in the case of that reef it is a one-off event and it is not near major coastal dredging or drainage from a disturbed river basin.

      Scott Reef is in the Timor Sea, well away from such disturbances as Qld coal operations; as far as human disturbance is concerned it ranks as one of the more remote reefs in the world; it may even still be around for Mr Sherrington's grandchildren to visit.

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    10. Wade Macdonald

      Technician

      In reply to David Arthur

      How David? Carbon ppm atmospheric levels are too high causing mass extinction remember?

      This global killer is not confined to coastal mainlands.

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    11. Rotha Jago

      concerned citizen

      In reply to Geoffrey Harold Sherrington

      Science is really limited where the GBR is concerned. Insisting on collecting data to support one hypothesis, which may take years is really painful for a non scientist to watch.
      The Great Barrier Reef Marine Park Authority, for reasons of it's own believes that only nutrients like phosphorus and nitrogen are worth worrying about. Why? One of their scientists wrote that Roundup or Glyphosate could not be a problem because so much research has been done on it already. ???? Monsanto's studies document…

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    12. David Arthur

      resistance gnome

      In reply to Wade Macdonald

      Thanks Wade.

      It may be a difficult concept to grasp, but in certain cases there may be more than one (for example, three) processes that are threatening a given entity.

      Where the "given entity" is Scott Reef, then it may be threatened by just one factor, namely bleaching events.

      In another case, the "given entity" might be the Barrier Reef offshore from the Capricorn Coast (Gladstone to Bundaberg), in which case threats include (and may not be limited to)
      1) bleaching events,
      2) sediment from port dredging operations and
      3) sediment and nutrients from contaminants in water discharging from Calliope and Fitzroy Rivers.

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    13. Wade Macdonald

      Technician

      In reply to David Arthur

      I agree but the carbon ppm destroys all coral regeneration according to many on here. How could this happen if they are right about carbon ppm and coral impacts?

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    14. David Arthur

      resistance gnome

      In reply to Wade Macdonald

      Thanks again Wade, I completely failed to grasp that you are already familiar with multiple causes for a given effect.

      Noting that corals have been around for hundreds of millions of years, through periods of much higher atmospheric CO2 than present, and also much lower atmospheric CO2 than present. I'm therefore a little less concerned about the survival of corals per se than these "many" you mention; present corals of the Great Barrier Reef cannot be more than 10-15 millenia old, since sea levels were ~100-200 metres lower than at present through the millenia prior to that.

      What I am concerned is the survival of individual reefs for the duration of my lifetime and of my heirs and successors. It is the rapidity of anthropogenic climate change that is therefore of concern, just as anthropogenic changes to runoff water quality is also a cause for major concern.

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