Fish living near the equator will not thrive in the warmer oceans of the future

According to an international team of researchers, the rapid pace of climate change is threatening the future presence of fish near the equator.”Our studies found that one species of fish could not even survive in water just three degrees Celsius warmer than what it lives in now,” says the lead author of the study, Dr Jodie Rummer from the ARC Centre of Excellence for Coral Reef Studies (Coral CoE) at James Cook University.Dr Rummer and her colleagues studied six common species of fish living on coral reefs near the equator. She says many species in this region only experience a very narrow range of temperatures over their entire lives, and so are likely adapted to perform best at those temperatures.This means climate change places equatorial marine species most at risk, as oceans are projected to warm by two to three degrees Celsius by the end of this century.”Such an increase in warming leads to a loss of performance,” Dr Rummer explains. “Already, we found four species of fish are living at or above the temperatures at which they function best.”The team measured the rates at which fish use oxygen, the fuel for metabolism, across different temperatures — at rest and during maximal performance. According to the results, at warmer temperatures fish lose scope for performance. In the wild, this would limit activities crucial to survival, such as evading predators, finding food, and generating sufficient energy to breed.Because many of Earth’s equatorial populations are now living close to their thermal limits, there are dire consequences ahead if these fish cannot adapt to the pace at which oceans are warming.Dr Rummer suggests there will be declines in fish populations as species may move away from the equator to find refuge in areas with more forgiving temperatures.”This will have a substantial impact on the human societies that depend on these fish,” she says.A concentration of developing countries lies in the equatorial zone, where fish are crucial to the livelihoods and survival of millions of people, including those in Papua New Guinea and Indonesia.In an era of rapid climate change, understanding the link between an organism and its environment is crucial to developing management strategies for the conservation of marine biodiversity and the sustainable use of marine fisheries.”This is particularly urgent when considering food security for human communities.”Story Source:The above story is based on materials provided by ARC Centre of Excellence in Coral Reef Studies. Note: Materials may be edited for content and length.

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Clues in coral bleaching mystery

Sep. 5, 2013 — Coral reefs are tremendously important for ocean biodiversity, as well as for the economic and aesthetic value they provide to their surrounding communities. Unfortunately they have been in great decline in recent years, much of it due to the effects of global climate change. One such effect, called bleaching, occurs when the symbiotic algae that are essential for providing nutrients to the coral either lose their identifying photosynthetic pigmentation and their ability to perform photosynthesis or disappear entirely from the coral’s tissue. Without a healthy population of these algae, the coral cannot survive.There has been much attention given to the environmental conditions that trigger a reef’s demise due to bleaching, but little is certain about the precise cellular and molecular mechanisms of the bleaching process. New research from Carnegie’s Arthur Grossman brings into question the prevailing theory for how bleaching occurs on a molecular level. It is published in Current Biology.Photosynthesis, the process by which plants, algae, and select bacteria convert the sun’s light energy into chemical energy, takes place in a cellular organelle called the chloroplast. It has been theorized that the major cause of bleaching is the result of chloroplast damage due to heat stress, which results in the production of toxic, highly reactive oxygen molecules during photosynthesis.Grossman and his team — led by Carnegie’s Dimitri Tolleter and in collaboration with John Pringle and Steve Palumbi of Stanford University — demonstrated that bleaching still occurs if the algae are heat stressed in the dark, when the photosynthetic machinery is shut off. This is surprising since it means that toxic oxygen molecules formed in heat-damaged chloroplasts during photosynthetic reactions during the light are likely not the major culprits that cause bleaching.Therefore other, as yet unexplored, mechanisms for bleaching must exist. This work suggests the existence of potentially novel mechanisms associated with coral bleaching. …

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Bringing coral reefs back from the brink

Sep. 3, 2013 — Shocks caused by climate and seasonal change could be used to aid recovery of some of the world’s badly-degraded coral reefs, an international team of scientists has proposed.A new report by Australian and Swedish marine scientists in the journal Frontiers in Ecology and the Environment suggests that it may be possible to restore living coral cover to a badly-degraded reef system — though not easy.With 70 per cent or more of the world’s coral reefs now assessed as degraded, adopting a business-as-usual approach to how we use and manage reefs is no longer an option, says lead author of the report Nick Graham.”We are unlikely to be able to keep many of the world’s reefs in a pristine state, but with good management we may be able to maintain them in a coral-dominated condition and in some cases we may be able to bring back reefs from a degraded state,” he explains.The researchers have taken heart from examples on land in desertified landscapes; exceptional falls of rain, in combination with controls on grazing pressure, can result in widespread regrowth of natural vegetation.They argue that coral reef managers may be able to take advantage of shocks like tropical storms, periods of cloudy weather or even strong seasonal effects on abundance to restore coral cover on degraded reefs.”Normally we think of these shocks as damaging to coral reefs — but research suggests they are just as damaging to the organisms that can replace coral. In other words, they may act as a circuit-breaker that allows corals to regain control of a reef.”The key to the new thinking is resilience: healthy corals reefs are naturally resilient to shocks — but damaged ones may become overgrown with sea weeds, and the corals vanish.”Weed-dominated systems are pretty resilient too and, once established, it is very hard to restore the corals,” Dr Graham explains.”However a weed-dominated reef can be damaged by big storms too. Cloudy weather and seasonal changes in water temperature can also cause the weeds to die back.”This dieback of weeds opens a window through which corals can re-establish.”The key to bringing back corals is exactly the same as preventing coral cover being lost in the first place, Dr Graham says — reducing human impacts through regulation of fisheries and water quality. If reefs are prepared in this way, they may bounce back when a window for recovery opens.Prof David Bellwood emphasized that “When it comes to saving our coral reefs, prevention is always better than cure and early action is important to slow or reverse degradation.”The researchers emphasize that both protection and recovery of the world’s coral reefs call for a fundamental change in how people interact with and use reef ecosystems.”Until now, the focus has mainly been on conserving small parts of a reef in marine protected areas,” said Prof Bellwood, “- we’re talking about broader approaches to change the relationship between humans and coral reefs to reduce human impacts across the whole ecosystem.”The paper concludes, “Although the composition of coral reefs will likely continue to vary over time, it may be possible to maintain coral-dominated reefs and their associated ecosystem goods and services… Scientists and managers could take advantage of opportunities for change by harnessing shocks and natural variability as potential stimuli for beneficial shifts in ecosystem states.”

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Epic ocean voyages of coral larvae revealed

Aug. 20, 2013 — A new computer simulation conducted at the University of Bristol (UB) and University of Miami (UM) Rosenstiel School of Marine & Atmospheric Science has revealed the epic, ocean-spanning journeys travelled by millimetre-sized coral larvae through the world’s seas.The study, published in Global Ecology and Biogeography, is the first to recreate the oceanic paths along which corals disperse globally, and will eventually aid predictions of how coral reef distributions may shift with climate change.Coral reefs are under increasing threat from the combined pressures of human activity, natural disturbances and climate change. It has been suggested that coral may respond to these changing conditions by shifting to more favourable refuges, but their ability to do this will depend on the ocean currents.Sally Wood, a Ph.D. candidate at UB, explains: “Dispersal is an extremely important process for corals. As they are attached to the seafloor as adults, the only way they can escape harmful conditions or replenish damaged reefs is by releasing their young to the mercy of the ocean currents.”Where these intrepid explorers end up is therefore an important question for coral reef conservation. However, tracking the movement of such tiny larvae in the vast oceans is an impossible task. “This is where computer simulation comes in,” adds Wood.Collaborating across the pond, Wood used the Connectivity Modeling System (CMS) developed by Dr. Claire Paris, associate professor of Applied Marine Physics at UM to identify the billions of paths taken. This larval migration model had been tested in a previous study against the reef-building coral Montastraea annularis in the Caribbean, where consensus between modeled estimates of genetic structure were found.”Simulating an unprecedented number of mass spawning events from all known shallow reefs in the global ocean proved essential to identifying critical long dispersal distance events that promote the establishment of new coral colonies. What we found using the CMS are rare long distance dispersers that are thought to contribute to species persistence in isolated coral reefs, and to geographic range shifts during environmental changes,” said Paris.Some of the results yielded by the team were surprising. …

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A new coral reef species from the Gambier Islands, French Polynesia

July 26, 2013 — The new speciesEchinophyllia taraeis described from the remote and poorly studied Gambier Islands, French Polynesia. Although the new species is common in the lagoon of Gambier Islands, its occurrence elsewhere is unknown.Echinophyllia taraelives in protected reef habitats and was observed between 5 and 20 m depth. It is a zooxanthellate species which commonly grows on dead coral fragments, which are also covered by crustose coralline algae and fleshy macroalgae.Share This:This species can grow on well illuminated surfaces but also encrusts shaded underhangs and contributes to the formation of coral reefs in the Gambier. It is characterized by large polyps and bright often mottled colourations and it is very plastic in morphology like most hard corals. Patterns of partial death and recovery of the species were often observed and could be due to competition with other benthic invertebrates like the soft-bodied corallimorpharians or zoanthids which can co-occur with this species.Stony corals are currently under threat by the effects of global warming, ocean acidification and anthropogenic changes of reef structures. Although corals represent a relatively well studied group of charismatic marine invertebrates, much has still to be understood of their biology, evolution, diversity, and biogeography. The discovery of this new species in French Polynesia confirms that our knowledge of hard coral diversity is still incomplete and that the exploration efforts of recent scientific expeditions like Tara Oceans can lead to new insights in a remote and previously poorly studied locations.This species is named after the Tara vessel which allowed the exploration of coral reefs in Gambier. Moreover, the name “tara” in the Polynesian language may refer to a spiny, pointed object, which applies well to the new species typically featuring pointed skeletal structures. In the same language, Tara is also the name of a sea goddess.Share this story on Facebook, Twitter, and Google:Other social bookmarking and sharing tools:|Story Source: The above story is based on materials provided by Pensoft Publishers. The original story is licensed under a Creative Commons License. …

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New approach to measuring coral growth offers valuable tool for reef managers; Surprising growth patterns in the Florida Keys

July 12, 2013 — A new more sensitive weight-based approach for monitoring coral growth in the wild has been developed by U.S. Geological Survey researchers leading to more definitive answers about the status of coral reefs.Corals and other marine organisms build their skeletons and shells through calcification, the biological process of secreting calcium carbonate obtained from ocean water. This new approach to measuring corals can provide finer-scale resolution than traditional linear measurements of coral growth.”A coral may grow two millimeters in height on the left side of the colony and five millimeters on the right, so linear measurements are inherently variable and require sampling hundreds of corals to detect changes in growth over time… our method requires only 10 corals per site,” said Ilsa Kuffner, USGS scientist and lead author of the study, published in the journal Coral Reefs.Using the weight-based approach, Kuffner’s team discovered that colonies of the Massive Starlet coral calcified about 50 percent faster in the remote Dry Tortugas National Park compared to three sites along the rest of the island chain from Miami to Marathon, Fla. The reasons behind this surprising pattern are not clear, leaving a mystery sure to pique the interest of many reef managers.The new approach could be highly useful to managers because it can detect small changes over space and time due to its high level of precision. Also, the method uses inexpensive and easy-to-find materials, and no corals are harmed in the process.”This tool provides the kind of scientific information needed to manage coral reefs at the ecosystem scale by looking at the relationships between coral health, climate change, and water-quality. It provides partners and reef managers with better, more sensitive metrics to assess coral growth, identify the most important variables, and prioritize strategies to protect and preserve these valuable ecosystems,” said Acting USGS Director, Suzette Kimball. “It is also one of the ways USGS science is advancing the National Ocean Policy by supporting a number of on-the-ground priority actions.”A next step in understanding declines in coral growth is discerning the different components of water-quality that are driving calcification rates, and this can only be achieved through the cooperation of reef managers and scientists around the world. The real power in the new approach will be realized if it is applied across many reefs that naturally have different temperature regimes, water quality, and pH conditions.”The study results suggest that we should pay more attention to different aspects of water-quality if we hope to understand and predict what will happen to coral reefs as oceans continue to change,” said Kuffner.According to Kuffner, managers already know coral reefs are in decline, but they want to know why. They need a linkage between cause and effect that explains why reefs are not growing like they used to or are not recovering from disease or die-off events. Correlating finely measured coral growth rates with water quality and other environmental information is an important step to making these linkages so they can inform management decisions.Coral reefs are in decline globally with the National Oceanic and Atmospheric Administration currently proposing to list 66 reef-building coral species under the Endangered Species Act. …

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Cloud brightening to cool seas can protect coral reefs: Targeted cooling could offer a 50-year ‘breathing space’ for coral protection

July 10, 2013 — The seeding of marine clouds to cool sea surface temperatures could protect threatened coral reefs from being bleached by warming oceans. Research, published in Atmospheric Science Letters, proposes that a targeted version of the geo-engineering technique could give coral a fifty year ‘breathing space’ to recover from acidification and warming.”Coral bleaching over the last few decades has been caused by rising sea temperatures and ocean acidification,” said Dr Alan Gadian, from Leeds University. “Our research focuses on how Marine Cloud Brightening (MCB) could quickly lower sea temperatures in targeted areas.”There is a strong association between warmer-than-normal sea conditions and cases of coral bleaching. Bleaching is most likely to occur when a 1˚C temperature rise over a prolonged period, typically a 12-week period.To brighten clouds unmanned vehicles are used to spray tiny seawater droplets, which rise into the cloud, thereby increasing their reflectivity and duration. In this way, more sunlight is bounced back into space, resulting in a cooling sea surface temperature.While MCB was originally envisaged to be a global counter measure against warming, in principle the technique could be more targeted. In 2012 Dr. Gadian wrote how the use of MCB in the Atlantic could tame hurricanes.The new modeling study focuses the impact of seeding marine stratocumulus clouds over the Caribbean, French Polynesia, and the Great Barrier Reef. The study shows how the projected increases in coral bleaching, caused by rising CO2 levels, were eliminated while sea surface temperature cooled to pre-warming levels.Mild and severe coral bleaching events were projected over a 20-year period for the three target regions. Without MCB the amount of coral bleaching was seen to be severe; however, simultaneous deployment of MCB eliminated the risk of extra bleaching.”We estimate that MCB would have an annual cost of $400 million, however political, social and ethical costs make a true figure difficult to estimate, said Gadian. “Whatever the final figure, it will be less expensive than the damage the destruction of coral would wreck on neighboring countries, the local food chain and global biodiversity.”Public and political skepticism of geo-engineering projects remains a hurdle to their development; however, as the least disruptive form of Solar Radiation Management, the authors believe small-scale use of MCB for conservation would be unlikely to generate public opposition.The authors propose field-testing of MCB on a scale of 100 square metres, which could demonstrate its use, without producing significant climate effects. …

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Boat noise stops fish finding home

June 28, 2013 — Boat noise disrupts orientation behaviour in larval coral reef fish, according to new research from the Universities of Bristol, Exeter and Liège. Reef fish are normally attracted by reef sound but the study, conducted in French Polynesia, found that fish are more likely to swim away from recordings of reefs when boat noise is added.Sophie Holles, a PhD researcher at the University of Bristol and one of the study’s authors, said: “Natural underwater sound is used by many animals to find suitable habitat, and traffic noise is one of the most widespread pollutants. If settlement is disrupted by boat traffic, the resilience of habitats like reefs could be affected.”Sound travels better underwater than in air and reefs are naturally noisy places: fish and invertebrates produce feeding and territorial sounds while wind, waves and currents create other background noise. Boats can be found around all coastal environments where people live and the noise they make spreads far and wide.Co-author, Dr Steve Simpson, a marine biologist at the University of Exeter, said: “Boat noise may scare fish, affecting their ecology. Since one in five people in the world rely on fish as their major source of protein, regulating traffic noise in important fisheries areas could help marine communities and the people that depend on them.”The study used controlled field experiments with settlement stage coral reef fish larvae. Larvae in a long plastic tube could decide to swim towards or away from a speaker playing back different sounds. In ambient noise equal numbers of fish were found in each section of the tube and in reef noise most fish swam towards the sound. But when boat noise was played along with reef noise more fish swam away from the sound than in reef noise alone.Co-author, Dr Andy Radford from the University of Bristol, said: “This is the first indication that noise pollution can affect orientation behaviour during the critical settlement stage. Growing evidence for the impact of noise on fish suggests that consideration should be given to the regulation of human activities in protected areas.”The research is published in Marine Ecology Progress Series.

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Major changes needed for coral reef survival

June 28, 2013 — To prevent coral reefs around the world from dying off, deep cuts in carbon dioxide emissions are required, says a new study from Carnegie’s Katharine Ricke and Ken Caldeira. They find that all existing coral reefs will be engulfed in inhospitable ocean chemistry conditions by the end of the century if civilization continues along its current emissions trajectory.Their work will be published July 3 by Environmental Research Letters.Coral reefs are havens for marine biodiversity and underpin the economies of many coastal communities. But they are very sensitive to changes in ocean chemistry resulting from greenhouse gas emissions, as well as to coastal pollution, warming waters, overdevelopment, and overfishing.Ricke and Caldeira, along with colleagues from Institut Pierre Simon Laplace and Stanford University, focused on the acidification of open ocean water surrounding coral reefs and how it affects a reef’s ability to survive.Coral reefs use a mineral called aragonite to make their skeletons. It is a naturally occurring form of calcium carbonate, CaCO3. When carbon dioxide, CO2, from the atmosphere is absorbed by the ocean, it forms carbonic acid (the same thing that makes soda fizz), making the ocean more acidic and decreasing the ocean’s pH. This increase in acidity makes it more difficult for many marine organisms to grow their shells and skeletons, and threatens coral reefs the world over.Using results from simulations conducted using an ensemble of sophisticated models, Ricke, Caldeira, and their co-authors calculated ocean chemical conditions that would occur under different future scenarios and determined whether these chemical conditions could sustain coral reef growth.Ricke said: “Our results show that if we continue on our current emissions path, by the end of the century there will be no water left in the ocean with the chemical properties that have supported coral reef growth in the past. We can’t say with 100% certainty that all shallow-water coral reefs will die, but it is a pretty good bet.”Deep cuts in emissions are necessary in order to save even a fraction of existing reefs, according to the team’s results. Chemical conditions that can support coral reef growth can be sustained only with very aggressive cuts in carbon dioxide emissions.”To save coral reefs, we need to transform our energy system into one that does not use the atmosphere and oceans as waste dumps for carbon dioxide pollution. The decisions we make in the next years and decades are likely to determine whether or not coral reefs survive the rest of this century,” Caldeira said.

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Human deforestation outweighs climate change for coral reefs

June 5, 2013 — Better land use is the key to preventing further damage to the world’s coral reefs, according to a study published this week in the online science journal Nature Communications.The study, by an international team including a researcher from The University of Western Australia’s Oceans Institute, has important implications for Australia’s Great Barrier Reef.The study authors write that preventing soil erosion and sediment pollution arising from human activities such as deforestation are crucial to reef survival.The study — ‘Human deforestation outweighs future climate change impacts of sedimentation on coral reefs’ — looked at the effects of future climate change on the hydroclimate of Madagascar’s reefs and different deforestation scenarios.”The findings are very relevant for Australia since intense land use and past deforestation have transformed the river catchments tremendously and are seen as a major threat to coral reefs in the Great Barrier Reef and elsewhere,” said Dr Jens Zinke, of UWA’s Oceans Institute.”Managing hinterland land use is the major action needed to buy time for corals growing near rivers.”Dr Zinke said the study looked at four watersheds near coral reef ecosystems in Madagascar, which has different climate zones that mimic most of the world’s coral reef climate and a range of different land uses.”With Madagascar, we wanted to understand how soil erosion and sediment discharges into coral reefs adjacent to river catchments are going to change with these two factors,” he said.”Curbing sediment pollution to coral reefs is one of the major recommendations to buy time for corals to survive ocean warming and bleaching events in the future.”Our results clearly show that land use management is the most important policy action needed to prevent further damage and preserve the reef ecosystem.”The major question is: how do we manage the sedimentation through reforestation efforts and proper coastal management?”Our study clearly shows that we need to have specific reforestation goals/targets for specific regions and make sure that the amount of land allocated for reforestation is enough to reduce sediments significantly.”Until we precisely understand these relationships, reforestation as a tool for coral reef conservation might not meet its objective of sediment and pollution reduction.”The study was the result of a collaboration between the UWA Oceans Institute, the Australian Institute of Marine Science, Macquarie University, the Institute for Environmental Studies at the VU University Amsterdam (Netherlands) and the Wildlife Conservation Society in the US.The lead author is Joseph Maina from Macquarie University.The study was funded through the Marine Science for Management program of the Western Indian Ocean Marine Science Association.

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Coral reefs suffering, but collapse not inevitable

May 9, 2013 — Coral reefs are in decline, but their collapse can still be avoided with local and global action. That’s according to findings reported in the Cell Press journal Current Biology on May 9 based on an analysis that combines the latest science on reef dynamics with the latest climate models.

“People benefit by reefs’ having a complex structure — a little like a Manhattan skyline, but underwater,” said Peter Mumby of The University of Queensland and University of Exeter. “Structurally complex reefs provide nooks and crannies for thousands of species and provide the habitat needed to sustain productive reef fisheries. They’re also great fun to visit as a snorkeler or diver. If we carry on the way we have been, the ability of reefs to provide benefits to people will seriously decline.”

To predict the reefs’ future, the researchers spent two years constructing a computer model of how reefs work, building on hundreds of studies conducted over the last 40 years. They then combined their reef model with climate models to make predictions about the balance between forces that will allow reefs to continue growing their complex calcium carbonate structures and those such as hurricanes and erosion that will shrink them.

Ideally, Mumby said, the goal is a carbonate budget that remains in the black for the next century at least. Such a future is possible, the researchers’ model shows, but only with effective local protection and assertive action on greenhouse gases.

“Business as usual isn’t going to cut it,” he said. “The good news is that it does seem possible to maintain reefs — we just have to be serious about doing something. It also means that local reef management — efforts to curb pollution and overfishing — are absolutely justified. Some have claimed that the climate change problem is so great that local management is futile. We show that this viewpoint is wrongheaded.”

Mumby and his colleagues also stress the importance of reef function in addition to reef diversity. Those functions of reefs include the provision of habitat for fish, the provision of a natural breakwater to reduce the size of waves reaching the shore, and so on. In very practical terms, hundreds of millions of people depend directly on reefs for their food, livelihoods, and even building materials.

“If it becomes increasingly difficult for people in the tropics to make their living on coral reefs, then this may well increase poverty,” said the study’s first author, Emma Kennedy. It’s in everyone’s best interest to keep that from happening.

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Coral reef fishes prove invaluable in the study of evolutionary ecology

May 16, 2013 — After reviewing recent research based on the study of habitat-specialist coral reef fishes, Boston University post-doctoral researcher Marian Y. L. Wong and Peter M. Buston, assistant professor of biology, have found that these species have proven invaluable for experimental testing of key concepts in social evolution, noting that studies of these fishes already have yielded insights about the ultimate reasons for female reproductive suppression, group living, and bidirectional sex change. Based on this impressive track record, the researchers maintain that these fishes should be the focus of future tests of key concepts in evolutionary ecology.

A major focus in evolutionary ecology lies in explaining the evolution and maintenance of social systems. Although most theoretical formulations of social system evolution were initially inspired by studies of birds, mammals, and insects, incorporating a wider taxonomic perspective is important for testing deeply entrenched theory. In their new study, the researchers suggest that habitat-specialist coral reef fishes provide that wider perspective.

“While such coral reef fishes are ecologically similar, they display remarkable variation in mating systems, social organization, and sex allocation strategies,” says Wong. “Our review of recent research clearly shows the amenability of these fishes for experimental testing of key concepts in social evolution.”

The new study highlights recent contributions made by one specific group of coral reef fishes — habitat-specialist reef fishes — to testing the robustness of mating system, cooperative breeding, and sex allocation theories. Habitat-specialist reef fishes are small bodied and well adapted to living within discrete patches of coral, anemones, and sponges. They include such species as the Pomacentridae (damselfish), Gobiidae (goby), Caracanthidae (coral croucher), and Cirrhitidae (hawkfish) families.

Being habitat specialists, these fishes are highly site attached and have limited mobility. They rely on their particular habitat for food, shelter, and breeding sites, and they experience high risks of mortality from predation if they venture outside their immediate habitat. Mating systems are highly variable both among and within these species, including monogamy (one male mates with one female), harem polygyny (one male mates with several females), and polygynandry (multiple males and females mate with each other). These fishes also exhibit great variability in social organization, including pair and group formation, with group members’ being reproductive or non-reproductive depending on the mating system. “This behavioral variability, despite the relative ecological similarity of these species, presents a unique opportunity to test the various hypotheses for the evolution of different social systems,” says Buston.

According to the authors, habitat-specialist reef fishes are a tried and tested group of model organisms for advancing the understanding of the evolution and ecology of social systems in animals; the study of these species already has revealed many things about the evolutionary ecology of mating, social, and sexual systems. Despite their ecological quirkiness, they have been instrumental for testing the generality and robustness of key concepts that are widely applicable to other taxonomic groups. In fact, in some cases, they have been the only species in which experimental tests of key hypotheses have been performed, largely because of the ease with which their habitat and social organization can be manipulated in the lab and in the field. For these reasons, the authors argue that these species should be the focus of future tests of key concepts in evolutionary ecology.

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Rare species perform unique roles, even in diverse ecosystems

May 28, 2013 — A new study, published 28 May in the open access journal PLOS Biology, has revealed the potential importance of rare species in the functioning of highly diverse ecosystems. Using data from three very different ecosystems — coral reefs, tropical forests and alpine meadows — a team of researchers led by David Mouillot at the University of Montpellier 2, France, has shown that it is primarily the rare species, rather than the more common ones, that have distinct traits involved in unique ecological functions. As biodiversity declines, these unique features are therefore particularly vulnerable to extinction because rare species are likely to disappear first.

“These unique features are irreplaceable, as they could be important for the functioning of ecosystems if there is major environmental change,” explained Dr Mouillot.

Biodiverse environments are characterized by a large number of rare species. These rare species contribute to the taxonomic richness of the area, but their functional importance in ecosystems is largely unknown. Represented by few individuals or distributed over narrow geographic areas, rare species are generally considered to have little influence on the functioning of an ecosystem compared with more common species. Indeed, it is often assumed that they fulfill the same ecological roles as those of common species but have less impact because of their low abundance; a phenomenon known as ‘functional redundancy’. This redundancy suggests that rare species merely serve as an “insurance” policy for the ecosystem, in the event of an ecological loss.

To test this, the team of researchers analyzed the extent to which rarer species in the three different ecosystems performed the same ecological functions as the most common ones. They examined biological and biogeographical information from 846 reef fish, 2979 alpine plants and 662 tropical trees and found that most of the unique and vulnerable functions, carried out via a combination of traits, were associated with rare species.

Examples of such species supporting vulnerable functions include the giant moray (Gymnothorax javanicus), a predatory fish that hunts at night in the labyrinths of coral reefs; the pyramidal saxifrage (Saxifraga cotyledon), an alpine plant that is an important resource for pollinators; and Pouteria maxima, a huge tree in the rainforest of Guyana, which is particularly resilient to fire and drought. Not only are they rare but they have few functional equivalents among the more common species in their respective ecosystems.

“Our results suggest that the loss of these species could heavily impact upon the functioning of their ecosystems,” said Dr Mouillot. “This calls into question many current conservation strategies.”

The work emphasizes the importance of the conservation of rare species, even in diverse ecosystems. Rare species are more vulnerable and serve irreplaceable functions, explained Dr Mouillot: the preservation of biodiversity as a whole — not just the most common species, but all those who perform vulnerable functions — appears to be crucial for the resilience of ecosystems.

“Rare species are not just an ecological insurance,” he said. “They perform additional ecological functions that could be important during rapid transitions experienced by ecosystems. The vulnerability of these functions, in particular biodiversity loss caused by climate change, highlights the underestimated role of rare species in the functioning and resilience of ecosystems. Our results call for new experiments to explicitly test the influence of species rarity and the uniqueness of combinations of traits on ecological processes.” This line of research will also inform the lively debate about the relationship between biodiversity and ecosystem functioning.

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