Saturday 7 May 2011
Monday 2 May 2011
THANK YOU.
One final and very quick post to thank my followers of the last 10 weeks. Once again I apologize for the sometime sporadic blogging!! Pre planning is clearly not my strong point. I still haven't discovered how to upload my poster so if anyone would like a copy please feel free to email me and I'll send you one.
Thanks and kind regards,
Emma
SO ARE CORALS FACING A CRISIS?
Simply put YES.
But is there hope? I think so.
· Modern day corals have faced three main extinction highs, each associated with large scale environmental perturbations but they have always survived. In the past, global coral biodiversity has survived climate change by changing its geographic distribution, however abrupt change have caused considerable reductions in diversity e.g. The Permian Mass Extinction.
· Corals unique and complex physiology (water no deeper then 30meters and warmer than 22 ˚ C) instantly sets them at a disadvantage. However it is not only sea level which influences reef formation the community structure is also influenced by wave energy and depth alongside species diversity.
· Modern corals are facing a challenging future with rising temperatures and carbon dioxide levels that both pose major threats through coral bleaching and ocean acidification. Corals have however overcome these issues in the past, what makes this time different is the massive anthropogenic pressure on coral reefs. The greatest challenge currently facing corals is that of human exploitation and interference (e.g. over fishing, destructive fishing practices, pollution, tourism).
· However in my mind there is still hope for the survival of coral reefs:
- Over the last decade, some adaptations to climate change have been seen and species are becoming more resilient.
- This, in addition to widely dispersing larvae and large population sizes of important reef builders, may provide some protection against extinction.
- I don’t believe coral reefs will become extinct they will simply alter and evolve in response to a changing climate. Coral reefs might become increasingly patchy with a lower topographic relief as pioneer corals (quick growing, short lived and thus better adapted to abrupt climate change) tend to be free living solitary corals.
- The development of cryopreservation of corals means endangered species can be preserved and later released in a suitable environment.
· Ultimately the survival of coral reefs will greatly depend on what is done now to protect and conserve them. With an international and local commitment to conservation I think reefs can be saved and we can help ensure a rich diversity of corals for future generations.
CONSERVATION CONCLUSION
The greatest challenge of reef conservation is one that no international regime on its own can fully address, given that so many of these threats are local in nature and thus require local solutions and enforcement. However on the other hand, an international solution to coral reef conservation is absolutely vital, given that two of the biggest threats facing reefs—climate change and ocean acidification—are global in nature and cannot be “fixed” by any one nation alone.
Reef protection needs to be treated on a larger scale as part of who ecosystem or area rather than protecting individual threatened species. Having researched and analysed the possible solutions I believe No Take Areas (NTAs) are the best solution for coral conservation. NTAs, when properly supported and policed, are effective in preserving fish stocks because they change human behaviour. Any conservation project must not solely address the biodiversity aspect they must to accommodate people livelihoods and economic value of the ecosystem. BUT NTA’s do not prevent or hold back warm water, or stop bleaching.
NTAs do not provide a refuge from bleaching, but they can help protect coral reefs from climate change. Overfishing, particularly of herbivorous parrotfish and surgeonfish, affects more than just the size of harvestable stocks it alters the entire dynamics of a reef. Reduced herbivory from overfishing, increased levels of disease, and excess nutrients can impair the resilience of corals and prevent their recovery following acute disturbance events like cyclones or bleaching, leading instead to a phase shift to algal dominated reefs. Resilience is also eroded by chronic human impacts that cause persistently elevated rates of mortality and reduced recruitment of larvae. Although climate change is by definition a global issue, local conservation efforts can greatly help in maintaining and enhancing resilience and in limiting the longer term damage from bleaching and related human impacts. Managing coral reef resilience through a network of NTAs, integrated with management of surrounding areas, is clearly essential to any workable solution. This requires a strong focus on reducing pollution, protecting food webs, and managing key functional groups as insurance for sustainability. NTAs also act to spread risk, whereby areas that escape damage can act as sources of larvae to aid recovery of nearby affected areas. This highly desirable property of NTAs raises the issue of how close they need to be to promote connectivity the migration of larvae and/or adults between them. Critically, coral reef organisms, including different species of corals, vary greatly in their larval biology and potential for dispersal. The clear implication is that NTAs must be substantially more numerous and closer together than they are currently to protect species with limited dispersal capabilities.
CONSERVATION: NON INTERNATIONAL APPROACHES.
So far we have looked at the international approaches but there are two other non international approaches for coral reef conservation and protection which warrant discussion:
- Efforts to address land-based marine pollution affecting coral reefs.
- Efforts to educate the public about threats to coral reefs and how our choices as consumer can impact the survival of reefs.
As part of the international year of the coral reef (1997) the NOAA publish 25 things you can do to save coral reefs. They range from ..
Number 10: Don’t pollute. Never put garbage or human waste in the water. Don’t leave trash on the beach.
.. to...
Number 20: If you dive, don’t touch! Take only pictures and leave only bubbles! Keep your fins’ gear, and hands away from the coral, as this contact can hurt you and will damage the delicate coral animals. Stay off the bottom because stirred-up sediment can settle on coral and smother it.
For the complete list please visit this link
NO TAKE ZONES.
NO take zones take the marine protected area one step further. They are areas e.g. New Zealand’s marine reserves, where all forms of exploitation are prohibited and severely limit human activates. Generally a No Take Zone can cover the whole MPA or specific vulnerable portions that enjoy elevated protection.
The Great Barrier Reef.
One well known reef, the Great Barrier Reef became a no take zone as part of a controversial decision in 2004. However despite initial hesitation the decision to halt commercial and recreational fishing across vast areas of the reef has proven remarkably effective for reviving coral trout numbers.
Fishing was totally banned across a third of the park, more than 100,000km2 including parts of 70 biologically distinct bioregions.
Within 18 months of the fishing ban, coral trout stocks had increased by 60% in two areas (Palm Island and the Whitsundays) within the no take zone. In contrast coral trout numbers in nearby fished areas did not change at all. In the long term it is hoped that the number build up in the protected areas and over spill and spawning means number will thus increase in unprotected areas too.
This recovery was further supported by a second team of scientists led by Hugh Sweatman of the Australian Institute of Marine Science in Townsville. They found coral trout number had increased significantly in no take zones around reefs from 32 to 200 kilometres off shore. In four of these offshore regions, numbers of coral trout were between 31 and 64% higher compared to unprotected regions nearby, just two years after the zoning took place. It is a very positive result but the full recovery of coral trout will take 10-15years to access.
The no take reserve has also seen other benefits; protecting corals reefs from the predatory starfish, Acanthaster planci is one of them. The crown-of-thorns starfish, Acanthaster planci, is a predator of corals that is a major management issue on coral reefs (Sweatman 2008). It occurs throughout the Indo–Pacific and shows boom–bust population dynamics with low background densities and intermittent outbreaks. Three waves of population outbreaks have affected Australia's Great Barrier Reef since the 1960s. The waves of outbreaks cause major losses of living coral on many reefs across a large area and dwarfing losses from other disturbances such as storms or coral bleaching over the same period. Humans can potentially influence starfish population dynamics by exploiting predators. Extensive surveys in the Great Barrier Reef Marine Park show that protection from fishing affects the frequency of outbreaks: the relative frequency of outbreaks on reefs that were open to fishing was 3.75 times higher than that on no-take reefs in the mid-shelf region of the GBR, where most outbreaks occur, and seven times greater on open reefs if all reefs were included. Although exploited fishes are unlikely to prey on starfish directly, trophic cascades could favour invertebrates that prey on juvenile starfish.
NO take zones clearly have their benefits for coral reefs but to make a significant difference more needs to be done.
A newspaper article by Eccleston (2008) states “current conservation zones ‘no take zones’ are too small, vulnerable to climate change and are in the wrong place to prevent reefs collapsing”. This statement was based upon joint research by Newcastle University and the Wildlife Conservation Society, New York. This team concluded that existing conservation zones should not be removed but new zones are urgently needed to protect coral reef and to aid their recovery from mass die offs caused by rising temperatures.
References.
Sweatman 2008: doi:10.1016/j.cub.2008.05.033
Russ et al. 2008: doi:10.1016/j.cub.2008.04.016
Sunday 1 May 2011
VIDEO BLOG: MARINE PROTECTED AREAS.
The first few minute briefly review what a coral reef is, the threats faced by them and looks at their importance as a biodiversity hotspot, as protection to islands and as a food source for subsidence farmers.
Approximately half way through (at 11.30mins) they start to discuss some of the local effects and their management methods: the very effective conservation method of over spill from Marine Protected Areas. They specifically look at Tanzania and Madagascar to describe this management tool.
Marine protected areas help by reducing stress such as destructive fishing practices and over fishing. This makes these ecosystems more resilient and so less vulnerable to other threats like global warming, pollution and sediment run off from the land.
One key point made by this video is that conservation and protection isn’t simply about helping the corals biodiversity it also works to maintain livelihoods and ensure economic success.
NOTE: Like everything technical I cannot get the video to upload!!! So I attach the link from which the video can be down load. It is a natural history question time video. ENJOY.
CORAL REEF CONSERVATION AND PROTECTION: INTERNATIONAL INTERVENTION.
It is now generally acknowledged that coral reefs are among the most threatened global ecosystems and among the most vital (West & Salm, 2003). Reefs are of critical importance to human survival ( especially in developing countries) because they provide subsistence food for a substantial portion of the population, serve as the principle coastal protection structures for most tropical islands, and contribute major income and foreign exchange earnings from tourism. The impressive worldwide economic value alongside untold medical benefits inherent worth of the worlds coral reefs create strong arguments for conserving these threatened living structures.
Historically management practices have focused on the coral reef as a single unit and not considered associated communities, such as seagrasses, mangroves, mudflats or defined watersheds (which transport complex mixtures in their waters). This method managed the reef in isolation, like an island.
However recently there have been increasing efforts to establish better management and conservation measure to protect the diversity of these biologically rich areas. Current management efforts recognise the importance of including reefs as part of a larger system. Where integrated coastal zone management tools and watershed concepts can be used in the development of comprehensive management and conservation plans.
There are three existing and emerging approaches to international reef conservation, all use a basic method of marine protected areas but vary in the area in which they cover, worldwide, regional and individual.
- Special protection status for coral reefs e.g. Convention on Biological Diversity.
- Regional reef protection agreements and regional coordination e.g. Coral Triangle Regional Agreement.
- Protection of individual reef species.
Conservation: Convention On Biological Diversity.
Approximately 6% of the worlds land is in parks but at sea less than one half of a one percent is in any kind of protected area. The convention on biological diversity (CBD) has worked to implement Marine Protected Areas (MPA’s) as a means by which to protect coral reefs. MAP’s are broadly split into three distinct groups. Areas managed for sustainable use, which may allow extractive uses, areas where extractive uses are excluded and other significant human pressures are minimised (known as no-take zones) and finally sustainable management over the wider marine and coastal environment.
The CBD Parties acknowledge that individual MPAs are not enough to adequately protect biodiversity within those MPAs, and this is why they see an MPA network approach as “essential.” The CBD Parties have also taken up the issue of how coral bleaching relates to the establishment of MPAs, creating a “Work Plan on Coral Bleaching” that includes some “high priority actions.” These actions include identifying “coral reef areas that exhibit resistance and/or resilience to raised sea temperatures” and “integrating bleaching resilience principles into MPA network design” and “reducing other localized stresses (water quality, overfishing, etc.).”
Conservation: Coral Triangle Regional Agreement.
The “Coral Triangle” is a 2.3 million square mile area in the Indo-Pacific Ocean that boasts the highest biodiversity of any reef system on the planet. Between 500 to 600 reef-building coral species live here, compared to 350 such species in Australia’s Great Barrier Reef, and just 70 such species in Belize’s Barrier Reef. Unfortunately, the reefs of the Coral Triangle face all the threats discussedin previous blogs, including coral bleachings that hit these reefs hard, particularly in 1997 and 1998. Also, destructive fishing practices, such as the use of dynamite, are “quite prevalent” in the area, damaging corals all the more. And perhaps worst of all for the area’s reefs is the concentrated human population—approximately 150 million people live in the Triangle area, producing large amounts of pollution that further limit the ability of corals to persist.
Yet it is not all bad news for the reefs of the Coral Triangle. In December 2007, top officials from the six Coral Triangle nations (Indonesia, Malaysia, Papua New Guinea, the Philippines, the Solomon Islands, and Timor-Leste) agreed to create an action plan to manage the Triangle sustainably. These countries finalized this plan in October 2008, and formally adopted it in May 2009, at the World Ocean Conference in Indonesia. Numerous entities, including the World Bank and the Asian Development Bank, have offered to help these six nations pay for their planning efforts. The United States also pledged nearly $40 million to the project.
Conservation: Protection of Individual Reef Species.
Unlike the previous two approaches to coral reef protection this third and final approach focuses on individual species within coral reef ecosystems. Essentially this approach uses the convention on international trade of endangered species to prevent the trade of wild and endangered coral species. However it is difficult to firstly get corals listed on the CITES appendices and once it is it is difficult to enforce with counterfeit documentations .
Join me over the next twenty for hours where I'll discuss the non international approaches for coral conservation, examples of marine protected areas, no take zones and draw my final conclusion on whether coral reefs really are suffering a crisis.
THE BLOG I FORGOT: NATURE OR NURTURE, THE CONCLUSION.
Prior to starting this blog I had made a plan of where I wanted to go with it, with ideas for each blog. Despite this remarkable organisation on my part it would appear I have forgotten to draw my own conclusions for the series of blogs titled CURRENT DAY THREATS TO CORAL REEFS: NATURE OR NUTURE? So, as the saying goes, better late than never!!!
This series looked at the threats faced by coral reefs and broadly split them into two categories nature (natural environmental change) and anthropogenic inputs (nurture).
Climate change is a very natural process that has occurred throughout the earth’s history. Both extremes (warm and cold) have been experience; they have been both abrupt and long lived in terms of formation and duration. However despite this corals have survived previous episodes of climate change.
In my opinion the risk of extinction and threat to modern day corals is not a result of natural climate change. Yes, climate change plays a role but it is the added anthropogenic factor which is ultimately the biggest threat to corals. In previous warm periods Corals and their mutualistic zooxanthellae have acclimatised, however research suggests that at the present rate of climate change they are not acclimatising quick enough. So what is different this time round ......
.....the anthropogenic factors. Industrialisation and subsequent population growth have exacerbated the natural climate change with an increase in carbon dioxide and thus sea surface temperatures and increasing ocean acidification and bleaching events. Coral are also threatened directly by human activities e.g. over fishing, destructive fishing practices, tourism and introduction of invasive species.
Thursday 28 April 2011
CORAL REEFS IN THE NEW: ANCIENT CORALS PROVIDE INSIGHT ON THE FUTURE OF CARIBBEAN REEFS.
Climate change is widely recognised to be a major threat of current day coral reefs. In a paper published last week in the Journal of Geology, University of Miami (UM) scientists use the geologic record from nine Caribbean sites to understand how reef ecosystems might respond to climate change expected for this century. The Pilocene epoch (some 2.5 million years ago) provide some insight into what coral reefs may look like in the future. Estimates of carbon dioxide and global mean temperatures of this period are similar to environmental conditions expected in the next 100 years.
This science daily article provides a brief over view of the a paper and its finds .........
Or if you prefer here is the link to the paper.......
P.S. don't forget to join me over the weekend to discover what we can do to help save the coral reefs for future generations.
Wednesday 27 April 2011
WHY ARE CORAL REEFS IMPORTANT?
All of these human induced threats serve to alter sediment levels (thus light), salinity and nutrients and such threatening the survival of coral reefs.
Hidden beneath the oceans’ water, coral reefs teem with life. Fish, corals, lobsters, clams, seahorses, sponges, sharks and sea turtles are only a few of the hundreds of thousands of creatures that rely on reefs for their survival. Reefs are home to an amazing variety of plants and animals from microscopic bacteria and protists to invertebrates and 1000’s of species if fish. With 58% of the worlds coral reefs potentially threatened by anthropological and environmental threats (see WWF link before) we look at why they are important before we access how best to protect them.
Intrinsic value.
Coral reefs are also living museums and reflect thousands of years of history. Coral reefs are an integral part of many cultures and our natural heritage. In fact, coral reefs are some of the oldest and most diverse ecosystems on the planet.
Economic Value.
Beyond their intrinsic value and their role as a breeding ground for many of the oceans fish and other species, coral reefs provide human societies with resources and services worth billions of dollars each year. Millions of people and thousand of communities all over the world depend on coral reefs for food, protection and jobs. These numbers are especially staggering considering that coral reefs cover less than one percent of the earth’s surface.
Healthy coral reefs support commercial and subsistence fisheries, as well as jobs and businesses that support tourism and recreation. Coral reefs are vital to the world’s fishers. They form the nurseries for about a quarter of the oceans’ fish and thus provide revenue for local communities as well as national and international fishing fleets. An estimated one billion people have some dependence on coral reefs for food and income from fishing. In the United States, coral reef ecosystems support hundreds of commercial and recreational fisheries worth millions of dollars to state and local economies. One estimate suggests the commercial value of U.S. fisheries from coral reefs is over $100 million (NOAA). In the U.S. territory American Samoa, coral reefs play an important cultural role and supply over 50 percent of the fish caught locally for food. Fish caught on reefs are a vital source of protein. Nearly ten percent of all fish consumed worldwide is caught on reefs, with one square kilometre of healthy reef providing enough fish to feed three hundred people (Mulhall 2007).
Local economies also receive billions of dollars from visitors to reefs through diving tours, recreational fishing trips, and other businesses based near reef ecosystems. Every year, scuba divers, snorkelers, and fishermen visit coral reefs to enjoy their abundant sea life. Reefs provide millions of tourist related jobs in more than 100 countries. In the 1990s, over four million tourists visited the Florida Keys each year, contributing $1.2 billion annually to tourism-related services (NOAA). In fact, the Florida Keys are the prime dive destination in the world. In Hawaii, a state with many coral reefs, one popular reef alone is visited by over three million tourists each year. In the U.S. territories of Guam and the Northern Mariana Islands, over 90 percent of new economic development is dependent on coastal tourism, including reef tourism (NOAA).
Protective Barrier.
The coral reef structure also buffers shorelines against waves, storms, hurricanes and floods, helping to protect loss of life, property damage and erosion. More than 450 million people live within 60 kilometres of coral reeds, the well-being of their communities and economies is directly dependent on the health of nearby coral reefs (Mulhall 2007). Healthy reefs absorb as much as 90% of the impact of wind generated waves and thus help to prevent coa stal erosion, flooding and loss of property on the shores (Mulhall 2007). These reefs save billions of dollars each year in terms of reduced insurance and reconstruction costs and reduced need to build costly coastal defences – not to mention the reduced human cost of destruction and displacement.
Medical Benefits.
Finally, coral reefs are sometimes called the “medicine cabinets” of the 21st century (NOAA). Coral reef plants and animals are important sources of new medicines being developed to treat cancer, arthritis, human bacterial infections, heart disease, viruses, and other diseases. Thus far researchers have identified dozens of antimicrobial, anti-inflammatory, and other medical properties in reef species. For example, chemicals from a Caribbean reef sponge are used to produce AZT, a treatment for the human immunodeficiency virus (HIV) (Mulhall 2007). Some coral reef organisms produce powerful chemicals to fend off attackers, and scientists continue to research the medicinal potential of these substances. In the future, coral reef ecosystems could represent an increasingly important source of medical treatments, nutritional supplements, pesticides, cosmetics, and other commercial products.
Conclusion.
Despite their great economic and recreational value, a range of human activities now threatens these important habitats (previous blogs). Many of the world’s reefs have already been destroyed or severely damaged by water pollution, overfishing and destructive fishing practices, disease, global climate change, and ship groundings. Once coral reefs are damaged, they are less able to support the many creatures that inhabit them. When a coral reef supports fewer fish, plants, and animals, it also loses value as a tourist destination. Further, the absence of reefs acting as natural barriers can increase the damage to coastal communities from normal wave action and violent storms. Therefore, the health of coral reefs depends on sustainable human uses that promote economic development while protecting sensitive coral ecosystems and the creatures that reside there.
References.
Mulhall, M. 2007. Saving the rainforest of the sea: an analysis of international efforts to conserve coral reefs. Duke environmental law and policy forum. 19: 321- 351.
Wednesday 13 April 2011
CURRENT DAY THREATS TO CORAL REEFS: NATURE OR NURTURE? (PART 4)
Part 3 looks at the existing and emerging threats to corals reefs as a result of non-climatic anthropogenic factors. Here I review Mulhall (2007) SAVING THE RAINFORESTS OF THE SEA: AN ANALYSIS OF INTERNATIONAL EFFORTs TO CONSERVE CORAL REEFS (PART III A).
The world’s coral reefs are on a downward trajectory. A study in 2004 estimated that since the 1950’s twenty percent of all reefs worldwide had been destroyed, with no chance of recovery, and an additional twenty-four percent of reefs were under imminent threat of collapse. These worldwide declines are a result of numerous causes; they can be global threats (part 1 & 2) whilst others are localised to specific countries and regions (like those discussed below).
Overfishing: Overfishing is a worldwide problem, having wiped out a third of the world’ s fish stocks. Fishermen are catching smaller fish species which are lower down the food chain, not only to make a living but for a rich source of protein and to ensure they and their families survive. Coral reefs are known for the biodiversity and abundant fish numbers, however over fishing here has many problems. It not only causes harm to the humans who depend on them for food but also harms the coral reefs where these fish once lived. Coral reefs have a complex relationship with the fish that live within them. Reefs provide security and habitat for many species of fish and in return herbivorous fish control the abundant algae found in reef environments. Without adequate number of plant-eating fish a reef can become overwhelmed by algae.
Destructive Fishing: there are two types of fishing practices which not only deplete fish stocks but also damage the reefs themselves:
Blast fishing- involves the use of dynamite to stun and kill the fish which then float to the surface. This method almost certainly guarantees the fisherman a large catch BUT the dynamite kills all marine life in the area including sensitive corals and leaves nothing to replenish fish stocks with.
The use of cyanide : cyanide is poured into the water around the reefs, stunning tropical fish and allowing for their capture, albeit for the ornamental aquarium fish market or for food. Despite being outlawed in many countries, one million kilograms of cyanide has been illegally used for fishing in the Philippines since the early 1960s. As with blast fishing, cyanide has a devastating impact on surrounding corals and other marine life.
Pollution: because coral reefs only live in warm environments with abundant sunlight, they are found in shallow waters along the coastline. Unfortunately for coral reefs 40% of the world population also live along these coast lines. Approximately 80% of all marine pollution now comes from land-based activities, including agricultural, municipal and industrial runoff, agricultural wastes, and atmospheric deposition. Coral reefs’ close proximity to land renders them especially vulnerable to this land based pollution. Agricultural and industrial runoff carries herbicides and other chemicals that harm corals, in addition to excess nutrients that create algae and phytoplankton blooms that suffocate corals. Other types of land-based pollution, such as sewage, wreak havoc on coral reefs as well. In Indonesia, a country located at the centre of the greatest known land and marine biodiversity on the planet, massive migration of the population from rural areas to coastal cities is taking its toll on the country’s reefs. Of all the pollution washing off the land and into the reef systems, untreated sewage is likely the worst. In Jakarta, the capital city, enough untreated sewage is released directly into the bay “to fill seventy-five Olympic-sized swimming pools, each day.” By 1993, one biologist had noted that all the coral reefs in Jakarta Bay were “functionally dead”.
Tourism: When done in the wrong way, tourism associated with coral reefs threatens the very reefs on which the industry depends. The global economics of reef based tourism are huge, (just under 10 billion dollars a year); Australia’s Great Barrier Reef supports a $4.2 billion tourism industries alone, with nearly two million tourists each year.
Irresponsible tourism threatens reefs in a variety of ways: from careless swimmers and divers, to improperly placed boat anchors, to discharges of sewage and other water waste from hotel and resorts. The cruise ship industry is of particular concern for reefs, given the sheer magnitude of the business. Cruise ships regularly “disgorge” throngs of passengers onto coastal reef areas, with around two thousand cruise ship passengers diving in Cozumel, Mexico’s reefs, in any given day.
Mining: in East Africa Southeast Asia and the Pacific Ocean coral reefs are mined for their large quantities of limestone (calcium carbonate). This limestone can be mixed with sand and water to create cement and be used in the building industry. Alternatively it is used in the pharmaceutical industry to make pills and more recently researchers have mined corals for bone graft clinical trials. Often the corals are mined simply for piece of dead and living coral which can be used in home as decorations and in jewellery worldwide.
Invasive Species that are discharged into reef areas from the ballast of ships also pose a threat, especially when no predators or parasites for these introduced species exist in the host reef environment. One of the most noticeably damaging invasive species is the crown-of-thorns starfish of the Great Barrier Reef. This is a voracious coral polyp eater and is increasingly damaging reefs. Declines in predators of this spiny toxic starfish, due to over fishing and pollution have led to population explosions which is currently destroying huge areas of the coral reef.
Other Threats: In addition to those described above coral reefs are threatened by an array of challenges. These include SEDIMENTATION associated with coastal development and deforestation, DREDGING of reefs to create deep water channels and marinas and coral DISEASE. The occurrence of coral disease has increased dramatically in the past ten years, a likely combination of the threats discussed above and in parts 1&2.
CURRENT DAY THREATS TO CORAL REEFS: NATURE OR NURTURE? (PART 3).
Rising Sea Level.
Along with sea temperature increase, ocean acidification corals are also under threat from the rising sea levels associated with climate change. With a predicted sea level rise (of 6cm/ decade) the potential exists for reefs to ‘drown’ (i.e. be covered with such a depth of water that they are below the photic zone or otherwise connect calcify sufficiently to catch up with sea level), but this requires a protracted imbalance between reef accretion rates and sea level rise (Smith & Buddemeier 1992).
Depending on water clarity and other environmental conditions, the depth range of maximum reef calcification may extend from several metre s to more than 20 metres. This depth range represents a safety factor; transient sea level rise may inundate oceanic reefs to a depth of metre s or even tens of metre s without terminating reef growth if sea levels rise subsequently returns to a rate less than reef vertical accretion rates. A reef accretion rate of 10 mm/yr is commonly taken as the consensus value for maximum sustained reef vertical accretion rates (Smith & Buddemeier 1992). The predicted for sea level rise over the next century is on average 6 mm/yr (Smith & Buddemeier 1992); this is well within the range of reef accretion rates, and even with no net accretion sea level rise would submerge reefs by less than a metre by the year 2100.
On the shorter time scale of years to decades, sea level is a changing environmental variable that may interact with other changes and be reflected in organism and community response. Because sea level has been within 1-2 m of its present elevation for several thousand years, many present-day reefs have grown to an elevation where further upward growth is constrained by sea level. Sea level rise can be expected to remove this constraint and result in increases in successful recruitment and coral longevity on intertidal and shallow subtidal reef flats, with a consequent increase in reef flat calcification (Smith & Buddemeier 1992). If rising sea level creates more benign conditions on shallow reefs, diversity and community structure may change as species other than the extremely hardy are able to survive. Increases in coral community diversity and productivity can also be expected in enclosed lagoons where salinity extremes, nutrient depletion, or other aspects of restricted circulation have restricted reef development (Smith & Buddemeier 1992), since the probable effect of rising sea level on circulation will be to maintain reef/lagoon water composition closer to that of the local oceanic water. On the other hand, if deepening water subjects currently sheltered communities to more physical (wave) stress, calcification and sediment accumulation may not increase.
Sea level rise is also strong associated with coral bleaching (Part 1) and associated mortality may selectively remove faster growing taxa, resulting in less rapid CaCO3 accretion and more rapid net removal of framework material by bioerosion.
References
Smith, S.V. & Buddemeier, R.W. 1992. global change and coral reef ecosystems. Annual review of ecological systems. 23: 89-118.
Saturday 9 April 2011
CURRENT DAY THREATS TO CORAL REEFS: NATURE OR NURTURE? (PART 2)
A Review of Hoegh-Guldberg et al. (2007) CORAL REEFS UNDER RAPID CLIMATE CHANGE AND OCEAN ACIDIFICATION.
Introduction: Atmospheric carbon dioxide concentration is expected to exceed 500 parts per million and global temperatures to rise by 2 degrees between 2050 and 2100. This significantly exceed conditions of the last 420,000 years during which most extant marine organisms evolved. Under expected conditions for the 21st century, global warming and ocean acidification will compromise carbonate accretion, with corals becoming increasingly rare on reef systems.
What is ocean acidification? During the 20th century, increasing atmospheric CO2 concentrations has driven an increase in the global oceans’ average temperature by 0.74°C, sea level by 17 cm, and has depleted seawater carbonate concentrations and increased acidity by 0.1 pH units. Approximately 25% of the CO2 emitted from all anthropogenic sources currently enters the ocean where it reacts with water to produce carbonic acid. Carbonic acid dissociates to form bicarbonate ions and protons, which in turn react with carbonate ions to produce more bicarbonate ions, reducing the availability of carbonate to biological systems (Fig. 1A). Decreasing carbonate ion concentrations reduce the rate of calcification of marine organisms such as reef-building corals, ultimately favouring erosion.
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| Figure 1: Links between the buildup of atmospheric CO2 and the slowing of coral calcification due to ocean acidification. |
Modeled scenarios: Hoegh-Guldberg et al. (2007) projected three scenarios for coral reefs over the coming decays and centuries.
1) 375ppc and 1˚C increase (stabilising at the present atmospheric CO2 concentration) coral reefs will continue to change but will remain coral dominated and carbonate accreting in most areas of their current distribution (Fig 2A).
2) However if we move towards higher CO2 concentrations (450-500ppm and 2˚ increase) coral community compositions will change with some areas becoming dominated by more thermal tolerant corals and others potentially dominated by thermally sensitive but rapidly colonising genera. The density and diversity of corals on reefs are likely to decline leading to vastly reduced complexity and loss of biodiversity including losses of coral associated fish and invertebrates (Fig 2B).
3) As atmospheric carbon dioxide levels of more than 500ppm are approached levels of carbonate ion concentrations fall well below today’s value and we exhibit an increase of more than 3˚ in sea surface temperature. These changes will reduce coral reef ecosystems to a crumbling frame work with few calcareous corals. Continuously changing climate (which might not stabilise for hundreds of years) is likely to impede migration of corals. Reefs will be rapidly eroded and ultimately become drowned reefs (corals and reef growth fail to keep up with rising sea levels). Under this climate scenario coral reefs become non-functioning (Fig 2C).
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| Figure 2: Extant reefs from the Great Barrier Reef that are used as analogs for the ecological structures under scenarious 1-3. A). reef slope communities at Heron island. B). mixed algal and coral community & C). Inshore reef slope. |
Impacts: These three scenarios are likely to have serious consequences not only on the corals reefs diversity and density but through wider regional economies e.g. coastal protection, fisheries, and tourism. These consequences become progressively worse as we move through the three potential scenarios.
Conclusion: It is worrying to think that when using the lowest rage of IPCC scenarios there is still devastating effects for coral reefs. At carbon dioxide atmospheric concentration of more than 500 ppm the consequences for coral reefs are extremely risky for both corals and those that depend on them. Climate change also exacerbates local stresses from declining water quality and overexploitation of key species, driving reef increasingly toward the tipping point for functional collapse.
*ppm – parts per million.
Thursday 24 March 2011
CURRENT DAY THREATS TO CORAL REEFS: NATURE OR NURTURE?
A Review Of Hoegh-Guldberg (1999) ‘CLIMATE CHANGE, CORAL BLEACHING AND THE FUTURE OF THE WORLD’S CORAL REEFS’.
Like all good scientists first they give you the back ground information and only at the very last minute do they draw their conclusions and give you their interesting finds, facts and theories. So to follow suit here is the background;
Despite corals importance (see future blogs) and their persistence over geological time (previous blogs) corals appear to be one of the most vulnerable marine ecosystems of modem day. Dramatic reversals in their diversity and health have been reported worldwide. It is estimated that between 50%-70% of all coral reefs are under direct threat from humans (through fishing, deforestation, nutrient enrichment, burning of fossil fuels, and use of toxic chemicals), whilst 100% of coral reefs are exposed indirectly through modifications of interactions with their competitors, predators, pathogens and mutualists. Mass coral ‘bleaching’ is also a major contributing factor to a decline in coral reefs. Since 1979, six major episodes of coral bleaching have occurred (Fig 1), each with associated reef mortality affecting reefs in every part of the world.
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| Fig.1. Number of reef provinces bleching since 1979 (from Hoegh-Guldberg 1999) |
Whilst reef mortality had started to receive some attention at top levels of world governments there are still many unanswered questions. Houegh-Guldberg (1999) looks at the scientific evidence that suggests coral bleaching is a sign of climate change and builds a case for the prediction that thermally triggered coral bleaching events will increase in frequency and severity in the next few decades. He sets out to answer the following;
1) Is coral bleaching a natural signal that has been misinterpreted as a sign of climate change.
2) Has the incidence of coral bleaching increased since 1979? Or has it simply been over looked prior to 1979?
3) Are bleaching events likely to increase or decrease in intensity in the next 100 years?
Symbiosis in coral reefs: zooxanthellae are intracellular organisms that live within the membrane bound values in the cells of the coral. Studies by Trench and Rowen have revealed that zooxanthellae are a highly diverse group of organism which include 100s of taxa with two or three species per host. Corals benefit from this mutualism by receiving photosynthetic sugars and amino acids, whist in return provide the zooxanthellae are provide with crucial plant nutrients e.g. ammonia and phosphate from their waste material, with this island of productivity amid this arid desert.
The role of temperature: reefs dominate tropical environments between 30 degrees North and 30 degrees South these roughly coincide of water temperature between 18 degrees and 30 degrees C. Tropical latitudes further suit corals because seasonal and diurnal fluctuations in tropical sea temperatures are generally very small. However, Thunnell et al. (1994) suggest sea surface temperatures of the tropical oceans have increased by 2 degrees in that last 18,000 years. There is a strong correlation between warmer than normal conditions (at least 1 degree higher than a summer maximum) and the incidence of mass coral bleaching. Increasing water temperature evident rapidly cases zooxanthellae to leave the tissue of reef building corals resulting in a reduced number. Heat stress does not only cause a reduced population density of zooxanthellae but it also acts to reduces their photosynthetic rate. Basically, light that is essential for high productivity of coral reefs under normal conditions becomes a liability under higher than normal temperatures.
NOTE: A rise in water temperature is not the sole cause of colour loss and reduced salinity, altered light intensity and exposure to chemicals can all cause corals to become pale, although the physiological response and mechanism by which they do is not the same as true ‘bleaching’.
So why has the incidence of bleaching increased? Some commentators have suggested that it is simply a reflection of the number of observers and the ease with which reports can be made and brought to public attention e.g. by internet.
However, palaeo-sediments have shown that tropical seas have under gone a warming in the past 100 years. In many tropical seas, rates of change are now greater than 2 degrees per century. By comparing simulated sea temperatures to the thermal thresholds of corals estimates of frequency with which sea surface temperatures will exceed the thermal maximum of corals and their zooxanthellae (Fig 2.).
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| Fig. 2.Weekly sea surface temperature data for Tahiti, arrows indicate bleaching events in the literature. |
Hoegh-Guldberg (1999) ran fours analysis from three climate change models, which thus stimulate changes in sea temperature. In all four runs he found (Fig 3);
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| Fig. 3. Number of times per decade that predicted temperarures exceed coral threshold levels (bleaching events). |
- The frequency of bleaching is set to rise rapidly, with the rate being highest in the Caribbean and slowest in the Central Pacific.
- Secondly, the intensity of bleaching will increase at a rate proportional to the probability that the thermal maxima of the corals will be exceeded by future Sea Surface Temperatures.
- Thirdly, most regions will be experiencing bleaching conditions every year within 30-50 years.
- Lastly, the reason for the relatively low frequency of bleaching events before 1979 becomes clear; tropical sea temperatures have been rising over the past 100 years (Bijlsma et al. 1995) and have brought corals ever closer to their upper thermal limit. The ability for an El Niño event to trigger bleaching was only reached in most oceans in the period from 1970 to 1980. This explains why mass bleaching events are not seen to any great extent before 1979.
It is thought Reef building corals and their zooxanthellae are unable to adapt (genetically) fast enough or acclimatise (phenotypically) to thermal stress. If corals are incapable of changing their physiological response to cope with this stress, bleaching will increase with frequency and intensity with serious consequences.
The acclimatisation of corals and their zooxanthellae refers to the modifications of cellular metabolism which might make them more tolerant to higher temperatures. Whilst adaptation refers to the selection of individual corals within a population that are better able to cope with the new high temperatures and thus survive. Individuals which have a poor affinity to high temperatures either do not survive or do not breed. Acclimatisation can occur over a few hours or days whilst adaptation may require hundreds or thousands of years.
Adaptation: corals and zooxanthellae have variety of thermal optima and maxima across various species. Corals have adapted to local temperatures, this is not surprising since it is universal to all living organisms e.g. the Masi who are adapted to high temperatures and Eskimos adapted to low. The variation of thermal tolerance suggest that there are genotypes within current coral populations that may be selected for under regimes of increasing temperature. However, this change towards a population dominated by high temperature tolerant genotypes is a slow process and may depend on the stabilization of sea temperatures.
However, the multiple recurrence of bleaching at the same sites over the past 20 years (some coral reefs have bleached during every major bleaching episode) strongly suggests that populations are not rapidly changing their genetic structure to one dominated by more heat-tolerant individuals. A second way that corals might increase their survival is to change their zooxanthellae for more heat-tolerant varieties (Adaptive bleaching hypothesis). Although this idea has attracted much discussion, it is not well supported by evidence. The observation that corals may have a variety of different types of zooxanthellae in the one colony and experience the selective loss of one type during temperature stress (Rowan et al. 1997) does not necessarily demonstrate that bleaching is adaptive.
Acclimation: Corals and zooxanthellae are able to acclimatise to changes in their environment on a daily or weekly bases e.g. zooxanthellae acclimatize to higher light intensity during the day by modify the concentrations of photoreceptors and associated chemicals. Despite their ability to acclimatize to changing environmental conditions, reef building corals do not appear to have acclimatized to the rapid increases in sea temperature over the past 20 years. There is no broad pattern suggesting that corals are better at coping when their maximal temperatures are exceeded. Corals seem to be just as close to their thermal limits as they were at the beginning of the 1980s, suggesting that acclimatisation (as well as adaptation) does not seem to have occurred to any great extent. If corals were acclimating (or adapting), then we should see a reduced number of corals affected by bleaching.
Conclusion: Even under moderate greenhouse scenarios (a doubling of current greenhouse gas concentrations by 2100), present and future increases in sea temperature are likely to have severe effects on the worlds coral reefs within 20-30 years. Most coral reef systems are predicted to experiencing near-annual bleaching events that will exceed the extent of the 1998 bleaching event by the year 2040. Some coral reefs (e.g. Caribbean, South-east Asian) will reach this point by 2020. Cooling by anthropogenic aerosols will have little effect on the time that the endpoint is likely to be reached. A better understanding of the capacity for corals and zooxanthellae to adapt to these rapid and on-going changes is required. Present evidence, however, suggests that corals and their zooxanthellae are unable to acclimate or adapt fast enough to keep pace with the present rapid rate of warming of tropical oceans. If the mortality of reef-building corals continues to increase, changes in the distribution of corals will almost certainly occur. Given the central role of corals and zooxanthellae in the structure and function of coral reefs, these changes are likely to have severe and negative effects on the health of coral reefs world-wide by the middle to end of next century. The ecological and economic effects of these changes have not been properly assessed and should be a priority of future research. If, however, the scenario presented in this paper continues to be supported, then a rapid reduction of greenhouse gas emissions over the next decade must be put into effect immediately.
Join me over the weekend for the second instalment of CURRENT DAY THREATS TO CORAL REEFS: NATURE OR NUTURE? Where I will review the atmospheric carbon dioxide.
Reference
Bijlsma, L. Ehler, C. N. Klein, R. J. T. Kulshrestha, S. M. McLean, R. F. Mimura, N., Nicholls, R. J. Nurse, L. A. Perez Nieto, H. Stakhiv, E. Z. Turner, R. K. & Warrick, R. A. 1995. Coastal zones and small islands. In .Climate Change 1995.Impacts, adaptations and mitigations of climate change: scientific-technical analyses: the second assessment report of the Inter-Governmental Panel on Climate Change. (Eds R. T. Watson, M. C. Zinyowera and R. H. Moss.) pp. 6-12. (Cambridge University Press: New York.)
Rowan, R. Knowlton, N. Baker, A. & Jara, J. 1997. Landscape ecology of algal symbionts creates variation in episodes of bleaching. Nature. 388: 265-9.
Thunnell, R. Anderson, D. Gellar, D. & Miao, Q. 1994. Sea-surface temperature estimates for the tropical western Pacific during the last glaciation and their implications for the Pacific warm pool. Quaternery Research. 41: 255-64.
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