Petites maisons colorées sur un bout de terre entourée de mer

L'Île-aux-Marins in the archipelago of Saint-Pierre-et-Miquelon


Islands and island environments faced with global changes

Updated 07.06.2022

Openness to the outside world, incorporation within the global economy but also the growth in natural risks and rising sea levels.... With their unique characteristics, often under threat, island environments and communities are today faced with unprecedented destabilising factors.

ilot Kumawa

Island environments such as this small island in the Kumawa area in West Papua (Indonesia) possess a number of distinctive characteristics.

© Jean-Marc Porte, Lengguru 2014

Unique and fragile living environments

Island biotopes are not simply miniature continents. They possess numerous distinctive characteristics related to their distance from the continental land masses, the difficulties encountered by animal and plant species when it comes to colonising them, the ecological constraints affecting those that have done so and the high degree of endemism characterising them. “All of these particularities, which make them so incredibly rich and diverse, also constitute vulnerabilities the moment human activities begin to interfere with these natural mechanisms characterised by their extremely slow pace of change”, explains Éric Vidal, conservation biologist at the ENTROPIE JRU.

A long biogeographical history 

Argyroxiphium sandwicense, endemic to Hawaii, grows at an altitude of between 2,100 and 3,000 metres. Due to the distance, a new plant species only takes hold on this archipelago every 30,000 years.

© IRD - Jean-Michel Boré

Bloc de texte

Whether marine or terrestrial, macro- or microscopic, animal, plant or fungi, the organisms living in island environments are all descended from ancestors originating from the continents or their coasts. That said, it’s easy to understand why they have not all fared the same when some have simply experienced geological separation between their habitat and the continental land mass such as Madagascar for example, while others have had to colonise ocean islands often situated several thousand miles from any coastline, such as Hawaii. Conquering these latter environments, which emerged directly in the middle of the ocean thanks to volcanic activity, is a real challenge for any forms of life. For land-based species, which can be kept out by just a strip of sea several kilometres wide, it’s even a miracle: “So when we consider the emergence of the native fauna and flora of the Hawaiian archipelago, we should bear in mind that a plant species only arrives every 30,000 years, a gastropod species every 200,000 years and a bird species every 350,000 years!”, adds Éric Vidal. Although seeds and spores can be carried by the wind, the few mammals and reptiles to reach the island by natural means have floated and drifted here on uprooted trees which fell in the sea along the continental coast. 

Huge areas of ocean to be covered

For marine organisms, things are not necessarily much easier: “Although the ocean is a continuous liquid mass, it’s certainly not an easy continuum to cross”, explains Claude Payri, Marine biologist in Nouméa, also with the ENTROPIE JRU. “The currents and the existence of ocean trenches create heterogeneity in the environment and have consequences concerning the diversity, abundance and distribution of the different species”. As most of the marine speciesWith the exception of migratory and planktonic species and large marine mammals1 are dispersed by the ocean currents at the larval stage, those whose life cycle is short at this stage do not have enough time to cross the huge expanses of liquid and to reach the ocean islands to establish themselves thereOther variables, such as body size, behaviour in shoals and nocturnal activities for fish, or, for some forms of algae, the possibility to float on “rafts” formed from other algae separated from their substrate also have an influence on colonisation capacity1. Despite this, the existence of island strings and seamounts can enable some of them to colonise distant island environments in successive stages, drawing nearer and nearer. 

The conquest of oceanic islands sometimes thousands of kilometres from the continent, such as Nuku Hiva (one of the Marquesas Islands), is a real challenge for land-based organisms.

© IRD - Jacques Iltis

Bloc de texte

In the Indo-Pacific area as a whole, the colonisation of islands by marine species is partially dependent on their position in relation to the Coral TriangleThe epicentre of marine biodiversity located between the Philippines, Malaysia and Indonesia, explains the specialist. The greater the distance separating an island from this region, the lower its marine diversity”. This distinctive insular biogeography even has its own theory, put forward in the1950s by the mathematician and ecologist Robert Helmer Mac Arthur and the biologist Edward Osborne Wilson, after whom it is named. It establishes a relationship between the diversity of an island’s species, its size and its distance from the continent.

Spectacular richness in terms of species

The distance and natural confinement of island environments, especially the far-flung oceanic islands, make them ideal locations for geographical speciation, i.e. the creation of new species due to isolation from the continental source populations and from those of other islands. It gives these environments an outstanding richness in terms of species and unrivalled ecological value: “Though accounting for just 5% of the land mass, the main 200,000 islands in the world are home to 20% of known bird species and 17% of flowering plants”, explains Éric Vidal. These endemic speciesthose found nowhere else in the world therefore represent a high proportion of life on the islands: three quarters of New Caledonia’s flora is endemic, with this percentage rising to 80% in New Zealand and 89% in Hawaii.

A young giant grouper, with a shoal of snappers in the background and a shoal of surgeon fish in the foreground: island ecosystems are home to an unrivalled richness in terms of species.

© IRD - Serge Andrefouet

Bloc de texte

Naturally, the level of endemism is lower in the continental islands (situated near a continent from which they were separated in the recent or distant past), particularly for marine organisms. However, they can become the ultimate host environment for those terrestrial species most under threat on the neighbouring continent due to human-induced activities. With this in mind, scientists from the IMBE MRU are studying the ecosystems of small Mediterranean islands. They have discovered organisms which are today absent from the continental regions but also from islands more affected by human activity. They provide an opportunity to observe the persistence and adaptation processes, to understand how animals and plants can resist environmental change.

Vulnerability hotspots 

But this richness and uniqueness of species comes at a price: “Island ecosystems and species are naturally fragile”, explains Éric Vidal. “They’ve lived in isolation for a long time, with reduced or atypical environmental pressures, and are highly exposed when other species arrive from the outside”. Consequently, in addition to the slow natural dispersion and colonisation process, human activity has now become an added factor. 

Invasive species, such as the fire ant in New Caledonia, pose a threat to endemic island species.

© IRD - Hervé Jourdan

Bloc de texte

According to the location, humans arrived at different times in the recent or more distant past, with their arrival dating back tens of thousands of years for Australia and less than a thousand years for Polynesia. From the outset, this has been accompanied by the extinction of endemic species, swept aside by the voluntary or unintentional introduction of more effective competitors such as small livestock or rodents. However, these irregular events were joined from the 16th century onwards by the advent of a trade-based economy reliant on seafaring, creating genuine artificial migratory corridors for species. Island environments account for two thirds of the extinctions witnessed over the last thousand years and are home to more than half of the species today considered as endangered. The phenomenon of the introduction of invasive species has skyrocketed with today’s globalised trading environment. Animals, plants and microorganisms are deliberately introduced into an environment to be grown or reared there or involuntarily enter the water through the ballast water of ships or imported plant products. In this way, hundreds of insect pests and disease vectors have already arrived in New Caledonia for example. 

Diagnosis, conservation and rehabilitation

These biological invasions and their environmental and economic impacts pose a real challenge for scientists. Firstly, they must diagnose the phenomenon and identify the impacts suffered by the species and ecosystems on the islands. With this in mind, the teams from the IRD are exploring the role played by the newly-introduced wildlife in the dispersion process of native plant species in New Caledonia, the predation performed by rats on bird eggs and endemic reptiles, in addition to the possibility of eradicating invasive mammals to save endangered island vertebrates…The specialists are also seeking to propose biosecurityBy controlling, limiting or even banning imports likely to carry invasive species.1 solutions to the authorities in order to limit the introduction of allochthonous speciesof foreign origin, not native to the ecosystem in question thereby preserving the native environments and species. Finally, the research will also be focusing on the rehabilitation of the environments being invaded to help them recover their initial state. “The maintenance of island ecosystems, whose uniqueness is just as precious locally as it is globally, depends on the conservation and restoration of their endemic biodiversity. The specialists and authorities are aware of these challenges and are keen to tackle them”, concludes Éric Vidal.  


    © IRD - CNRS / Thibaut Vergoz

    The feral cat, a domestic cat which has returned to its wild state, can inflict considerable losses on island biodiversity.

    Biodiversity: the cat’s out of the bag  

    The worst enemy to island biodiversity is one of man’s oldest friends! The cat, which has accompanied humans wherever they travel since time immemorial because they appreciate its company and its effectiveness at killing rodents (themselves involuntarily introduced) is responsible for a substantial percentage of the extinctions of land-dwelling vertebrates on the world’s islands over the last 500 years. Indeed, despite 9,000 years of domestication, it has not lost its old habits. It has retained both its hunting instinct and a capacity to rapidly revert to its wild state, to form what are referred to as populations of “feral cats” living in the natural environment. Once free of its master, its ability to thrive is impressive: five cats were introduced into the Kerguelens Islands in the southern Indian Ocean in 1950. They today number several thousand!  
    This feralisationthe phenomenon of domestic animals returning to their wild state among cats is all the more destructive on islands, where the endemic species have often never known any predator before the arrival of the cats”, explains conservation biologist Éric Vidal. “They have therefore lost all of the self-preservation mechanisms which typically characterise prey species, including vigilance, a propensity to flee or camouflage, displayed by their ancient continental ancestors. It’s by no means rare to see birds and reptiles on the islands allowing themselves to be captured and eaten without even reacting…”. As an example, cat predation risks bringing about the extinction of the iguana in the Lesser Antilles, of Barau’s petrel on Réunion Island, of Polynesia’s Luzon bleeding-hearts or New Caledonia’s reptiles. As most of the endangered species are endemic, their disappearance from the islands will result in their permanent extinction.
    The impact of feral cats on island biodiversity has become a matter of concern for the authorities in certain countries. The importation of domestic cats is controlled on certain islands (it may even shortly be banned in the south of New Zealand) and Australia has set about eradicating them by the million in some regions and particularly the islands bordering the continent.
    At the IMBE and ENTROPIE JRUs, we are studying the ecology, distribution and impact on local fauna of these invasive predators in the French islands of the Pacific and particularly French Polynesia”, explains the specialist. This information will make it possible to draw up coherent strategies for the preservation of Polynesia’s land-based biodiversity”.  

    Petite île entourée d'une mer turquoise

    © Martakz - Pixabay

    Islands such as St-John in the Florida Keys are perfect for the small-scale observation of processes of natural or human-induced origin.

    Valuable ecological laboratories 

    The island ecosystems are of great interest when researching evolution, ecology and conservation. These are systems which function in a simpler manner, with fewer species present, in addition to different and more limited biotic interactions, all in a reduced geographical area. As a result, the islands are perfect for the small-scale observation of natural or human-induced processes which are difficult to clearly define on the continental landmasses due to the increased interactions there. And some island chains which have dozens of similar islands, such as the Florida Keys, offer experimental conditions which cannot be found elsewhere, with comparable natural conditions and enclosed environments. 
    Island environments also make it possible to study and understand the biodiversity crisis currently underway, as the species there are particularly fragile and sensitive to all forms of environmental pressure.

    Ben H. Warren et al., Islands as model systems in ecology and evolution: prospects fifty years after MacArthur-Wilson, Ecology Letters ; 2015 ; doi: 10.1111/ele.12398

    Characters sitting on a pontoon from behind

    Island communities often share similar natural constraints and have developed similar strategies to deal with them.

    © IRD -Catherine Sabinot

    Communities subject to environmental constraints

    If there is one concept which is discussed and even decried by specialists in human sciences, it is that of insularity. For decades, scientists have been debating the existence or absence of characteristics specific to island communities. The fact nevertheless remains that they share comparable natural constraints and that they have developed similar strategies to deal with them. But this traditional social engineering, which has enabled them to survive for thousands of years in an environment marked by sparse resources and constant risks, is reaching its limits. “Openness to the world, increased trade and participation in the globalisation process are all factors shifting the balance”, explains Gilbert David, a geographer specialising in island environments at the ESPACE-DEV MRU. “The research seeks to identify the aspects of these communities to support their sustainable development in a changing environment”. The Pacific islands offer a particularly valuable environment for observation in this field.

    Extending the available space to overcome confinement

    With isolation, reduced and fragmented space, limited resources and permanent natural threats, the inhabitants of the 200,000 islands worldwide experience living conditions very different to people living on the continents. According to the scientists, this particular environment and its constraints have given rise to four essential characteristics found in many island societies: their relationship to space, their attachment to the land, the multiple social roles of each stakeholder and the integrated management of natural risks.


    For the inland inhabitants, a strategy to “extend” the limited island environment involves not coming to the coast and exchanging fish for agricultural products with the fishermen, as is the case in the Belep archipelago.

    © IRD-Catherine Sabinot

    Bloc de texte

    When you live in a restricted area like an island, it’s important to extend your space”, adds the researcher. “And this involves a number of social strategies”. Accordingly, in the islands in the upper part of Oceania, people are frequently encountered living inland just a few kilometres from the sea as the crow flies, who have never actually seen the coast. And when they want to eat fish, they ask the coastal dwellers to exchange this for products from inland on the island. Another identified strategy involves a village growing only the products best suited to the agronomic characteristics of the soil such as taro, to organise trade with other communities growing other crop species… Similarly, villages are often separated by a no man’s land of several hundred metres populated by spirits rather a simple borderline. This strategy makes it possible to both artificially extend the territory but also to significantly reduce conflicts, which is particularly important due to the limited space in which the island communities live.


    Attachment to the land

    As there is so little space available, a constraint which must be worked around, the island’s inhabitants are all more attached to their land. “In as far as possible they stay where they are, but if they have to migrate because natural resources or sources of income are insufficient locally, they retain a strong emotional link with their land of origin”, explains the geographer.

    Strongly attached to their island of origin, those members of the island community forming the island’s diaspora regularly come back on their holidays and often choose to live there when they retire.

    © IRD-Jean-Christophe Gay

    Bloc de texte

    This often takes the form of a constant dream of returning but also of ongoing interactions with their society of origin, including periodic returns for holidays or a permanent return at the end of their active life, in addition to substantial economic support from the migrants to relatives remaining on the island. This valuable financial contribution can account for a decisive part of some islands’ resources which, due to a lack of products which can be marketed internationally, have developed an economic specialisation based on migration, financial contributions from the diaspora and a bloated civil service. This phenomenon is referred to by specialists as MIRAB (MIgrant/Remittances and Aid/Bureaucracy). There are plenty of examples of this attachment to the land of origin: People from Corsica, Fiji or the Antilles rarely renounce their island roots, or Marseille’s Comorians, who once a year become known as the “Je viens”, a term referring to the migrants who come back to the island chain each summer to enjoy island life.

    A multiplication of social roles and natural risks

    Lacking sufficient numbers, island communities also tend to meet the needs of this restricted environment by increasing the number of interactions between their members: “Just like the island ecosystems, in which organisms occupy ecological niches far outstripping their counterparts on the continent due to a lack of competitors, the social systems are characterised by a ratio between the number of species-related elements / relations between species-related elements” explains the geographer. “As result, each stakeholder on the island performs more social roles than those on the continent”. Consequently, for someone coming from outside the island communities, it is difficult to know exactly what role the person plays when you first meet them.

    With careful regional planning and using traditional agricultural methods, such as here in Vanuatu, the island community are better able to deal with unexpected circumstances than they would if producing cash crops using modern techniques.

    © IRD-Catherine Sabinot

    Bloc de texte

    Finally, due to the omnipresence of natural and human-induced hazards which affect the islands and their inhabitants, risk management is a fundamental cultural factor shared by many island communities. “Volcanic eruptions, seismic activity, tsunamis, cyclones and droughts often pose more of a threat in these areas, which are small in size and offer very few fall-back options”, adds the researcher. “And the communities have successfully adapted to these omnipresent constraints: our work has shown that staple crops, managed traditionally, are significantly less affected and more quickly re-established after a major event such as a cyclone than cash crops derived from modern agricultural techniques”. Based on simple architectural techniques making it possible to rebuild shelters quickly after they have been destroyed, or horticultural techniques and cultural practices which maintain production, these strategies minimise the negative effects of unexpected hazards and favour the survival of individuals and the reproduction of the community. Naturally, all of these cultural aspects are less in evidence at a time when island communities are opening up to the rest of the world, but they nevertheless constitute a component which must be taken into account, particularly when introducing policies to adapt to climate change in the villages.

    Distinctive economies

    Thanks to these strong cultural foundations, island communities appear more resistant than continental communities”, explains Gilbert David. “When they have not been destroyed by major changes such as slavery or contact with the rest of the worldIn the past, contact with Westerners often resulted in the devastation of island populations due to the inability of their immune systems to resist viruses and bacteria brought in by the seafarers.1, they integrate such changes and deviate them from their initial purpose, shaping them in the "island mould"The emergence of money as a source of social promotion for example is not always accepted by island inhabitants, many of whom are still highly rural. The most classic form of resistance involves introducing wealth redistribution mechanisms, particularly via religion. Consequently, the construction of churches, mosques or other community centres enables the better-off island inhabitants to give something back to the whole community and it can become a prestigious source of competition with neighbouring communities to have the best place of worship.2”.

    Obtaining a tuna fishing fleet to supply international markets such as in the Seychelles can represent an investment which exceeds the available local resources.

    © IRD-Thibaut Vergoz

    Bloc de texte

    But at an economic level, this isn’t enough to make a difference. Other than a few exceptions such as Singapore, which has enjoyed indisputable economic development, most island communities are listed among the developing nations or regions. For some economists, these inherent difficulties in emerging are chiefly due to their size and their low demographic weight. Very few of them have a population of one million inhabitants, a threshold considered as minimal by specialists to envisage an economic policy based on import substitutionEmergence of local products to replace the often costly importation of goods and foodstuffs from abroad. As their domestic market is too limited, in most cases they must obtain supplies from the outside world and find the resources needed to do so.


    Tourism, fish and migration

    To achieve this, tourism is often an obligatory choice for island economies. It offers the advantage of providing work in a highly unfavourable job market. However, competition between the different destinations is intense and profits often go to investors from outside the island community. “The greatest challenge to be faced concerns tourism’s capacity to boost local development”, adds the researcher. “When 100 euros are spent by a tourist on an island, at least 80 leave the island to purchase the food, drinks and services provided to him. Viewed from this angle, international tourism is significantly less effective than family B&Bs, which obtain their supplies from local farmers and fishermen”.
    The blue economy, which refers to the exploitation of marine resources present in the exclusive economic zoneA maritime area extending 360 km from the coast in which the coastal state has sovereignty for the exploitation of the resources, can be a substantial boon for isolated islands with a huge liquid territory at their disposal. “But here too, obtaining a tuna fishing fleet to supply international markets can represent an investment which exceeds the available local resources”, relates the geographer.



    Due to a lack of local employment, the future for many islanders lies in economic expatriation.

    © Catherine Sabinot

    Bloc de texte

    Finally, for many island inhabitants, ultimate salvation lies in exile. Workers from the islands are departing in large numbers to work in more prosperous regions, in Australia, New Zealand or the west coast of the United States for those from Oceania, in Europe or Asia for the inhabitants of the Indian Ocean, and in Europe, Canada or the east coast of United States for those of the Atlantic islands.…

    Distant markets

    In the view of analysts, the particularity of island economies lies in their far-flung nature. “The islands’ distance from the main consumption and decision-making centres in the global system is a variable which poses a handicap at least as significant as their reduced size”, adds the scientist. Thus, as with their biodiversity, the particularity of the islands’ economies lies in their isolation. Based on this analysis, the specialists from the Espace Dev MRU, studying the conditions for sustainable development in the islands of Oceania feel that only certain island economies can genuinely succeed where outward expansion is concerned. This is the case with those which are sufficiently close geographically to the world’s markets or which are highly connected through abundant and competitively priced links. For others, the challenge is instead to succeed with integrated development nationally and regionally. They need to overcome the geographical fragmentation which exists on the islands and among themselves and to focus on security of supply for food and energy. The production of such resources (food and energy) are the only two sectors for which an import substitution policy can be introduced for the island and the archipelago.
    As we can see, insularity is a complex and essentially contradictory factor”, acknowledges Gilbert David. “It is illusory to seek to establish an “island law” applicable to people, as wherever we look we find only variety and diversity. For this reason, research is needed in order to establish and develop models suited to the requirements of each island community, to environmental changes and to globalisation”.


      Asian tourists on a beach wearing umbrellas

      © IRD -Jean-Christophe Gay

      Island environments are at the forefront of a leisure and tourism revolution, with tourism being responsible for the surge in middle-class Chinese looking for change of scenery, as seen on Hainan island.

      The epicentre of tourism development

      Tropical island environments are directly associated with the dawn of the tourism and leisure era, but also a number of technical, historical and geopolitical revolutions accompanying its breathtaking expansion. “It all began on islands growing cash crops in the emerging modern economy,” explains Jean-Christophe Gay, a geographer specialising in tourism. "To improve their profits, companies built hotels near the plantations and used the incoming and outgoing vessels (which visited the islands to collect agricultural produce) to also transport the first tourists”. This was the case with Jamaica or Cuba in the late 19th century. Hawaii became a much sought-after destination, celebrated by a number of influential writers including Mark Twain and Jack London. And once there, the visitors keenly discovered the leisurely relationship to the ocean enjoyed by the locals. The beach scene, swimwear, tanning and surfing all emerged as a result. Specialists have highlighted the attractions sought by the visitors. An island is considered all the more attractive when it epitomises isolation. If it has a high peak allowing for a 360° view of the ocean it’s a must !
      A technological revolution with the appearance of jet aircraft in the late 1950s led to an explosion in demand. The islands were now just a few hours’ flight from Western cities. Island tourism became increasingly available to everyone, sometimes taking on a virtually industrial dimension. Previously unknown destinations took advantage of the opportunity to develop a huge range of tourist attractions and facilities: The Caribbean, Mauritius, Guam, Fiji, etc., and always well ahead of the pack... Hawaii. In the early 2000s for example, 16 Boeing 747s from Japan landed each morning in Honolulu. According to specialists, the supply side of tourism is dependent on an equation incorporating the distance and level of services offered: the more distant an island is from its commercial target, the more it must propose top of the range services for tourists as is the case with the Maldives, the Seychelles or French Polynesia.    
      Island tourism is today continuing to grow at a sustained pace and is experiencing a revolution linked to globalisation: the arrival en masse in the market of middle-class Chinese. As result, Hainan, a tropical island at China’s far southern end, recently beat Hawaii in terms of visitor numbers. It currently welcomes more than 35 million tourists annually, almost 4 times more than America’s 50th state…

      Gay J.-Ch. et Mondou V., 2017, Tourisme et transport : deux siècles d’interactions, Bréal, 256 p.

      • Gilbert David / UMR ESPACE-DEV

        Jean-Christophe Gay /UMR ESPACE-DEV

      • Gilbert David, La gestion des risques comme base de la viabilité des sociétés de l'Océanie insulaire. In David, G. (eds.). Espaces tropicaux et risques, du local au global. Orléans,  Presses univ. Orléans / IRD, coll. CEDETE, 2004, pp. 353-364.

        Gilbert David, Dumas P.S., Laurent Durieux, Catherine Sabinot, Le développement durable à la dérive du monde, enjeux et défis de l'Océanie, dans Le développement durable en Océanie : vers une éthique nouvelle ?; Presses universitaires de Provence, 2015.

        Gilbert David, Dominique Guillaud, P. Pillon (eds.). La Nouvelle-Calédonie à la croisée des chemins. Paris, Société des Océanistes / IRD, 1999, 324 p.

        Gilbert David. Mondialisation et recompositions territoriales et identitaires en Océanie insulaire, dans Les îles rêvées. Paris, Presses Univ. de la Sorbonne, 2003, pp. 140-170

        Gilbert David. Le Pacifique sud et ses ZEE, des ressources à la géopolitique du thon. dans Dehoorne, O. et Saffache, P (dir.), Mondes insulaires tropicaux : Géopolitique, économie et développement durable. Paris, Ellipses, 2008, dossier n°2, pp.33-59.


      • Olivier Blot

      Due to the geographical conditions, the concentration of the populations and the specific development of vectors and diseases such as A. albopictus, the islands’ inhabitants are subject to particular health threats.

      © IRD - Michel Dukhan

      An explosive health situation in an enclosed environment

      Including dengue, chikungunya and diabetes, the island environments are the scene of spectacular epidemics of infectious and chronic diseases. These afflictions reach a scale unequalled anywhere else, affecting a major percentage of the population and often driven by dynamics the like of which are not seen elsewhere. They represent a major public-health problem. “The geographical isolation, the population density in a limited area, the sudden move from a frugal lifestyle to the abundant consumption of products derived from the agri-food industry and the significant impact of climate change on the islands are all factors involved, which are likely to combine with one another in this unusual health-related situation”, explains Patrick Mavingui, biologist on Reunion island at the PIMIT MRU. Scientists are exploring these themes and their possible interactions.  

      Isolation and pathogenic speciation

      The infectious diseases encountered on the islands can be a little different from those found on the continents… “It has been established that the geographical isolation of the island environment is behind the speciation of macroorganismsAnimal and plant species on the islands evolve independently from their original populations, which remained on the continents.1, explains the specialist. Everything leads us to believe that the same applies with microorganisms, including those they host, mutualistically, which have a reciprocally beneficial interaction with their host] commensually which have an interaction benefiting themselves but whose impact is neutral vis-à-vis the hostor pathogenically. The research conducted within the PIMIT MRU has shown that one of the bacteria responsible for leptospirosis a serious infectious diseasein the Indian Ocean belongs to a particular species which is different from that than on the continent. Similarly, the animal reservoirs for this bacterium are part of the endemic fauna, bats and rodents, found only on islands in the region. This suggests co-adaptation between the insular pathogen and its reservoirs. “Although these endemic infectious agents appear to have a lower pathological impact than microorganisms from the rest of the world, our knowledge of their evolution, their ecology and their interaction with human health is still insufficient”, warns Patrick Mavingui. “These subjects are among the scientific priorities with a view to modelling and anticipating future health threats”.


      A reduced geographical area and epidemiological dynamics

      Apart from the diversity of the diseases specific to the islands, the islands’ geography also plays its part in the epidemiological dynamics of infectious diseases: “The concentration of populations in a reduced space with a great deal of contact and movement among people can significantly influence the transmission scale of vector-borne diseases”, explains the scientist.


      The reduced area, the population density and the high degree of human circulation as seen in Mayotte can significantly influence the transmission of vector-borne diseases.

      © IRD-François Taglioni

      Bloc de texte

      In this enclosed environment between mosquitoes and humans, the introduction of a diseaseA visit by an infected traveller bitten by a mosquito on the island can be all it takes to start an epidemic.1, can trigger epidemics of exceptional intensity. The chikungunya virus transmitted by the Aedes albopictus mosquito caused an unprecedented epidemic on the island of Reunion in 2005-2006, affecting almost 30% of the population. Such an impact has only been seen in island environments. “Paradoxically, this impressive intensity contributed to the end of the endemic at least as much as the vector-control measures”, explains Patrick Mavingui. “Because the people previously infected (and therefore now immune) eventually came to account for a sufficiently large percentage of the population to interrupt contagion”. However, this mechanism cannot function for dengue epidemics, which have been recurrent in many island regions for several years now, as four types of the virus exist, with no cross-protection.

      Out-of-control diabetes

      The islands’ communities are experiencing a genuine epidemic of chronic diseases the likes of which has not been seen elsewhere. Until very recently, the islands’ populations lived in a self-sufficient economy with a frugal diet based on subsistence farming, food produced by the families themselves and fishing.

      The sudden transition from frugal local diets to the profusion of rich food derived from the agri-food industry, accessible in all island grocery stores such as here in Vanuatu, has brought about a real epidemic in early metabolic diseases.

      © IRD - Sophie Thiron

      Bloc de texte

      But very suddenly, over the space of barely two generations, they have had access to the abundant consumption of rich and unbalanced processed products. This sudden nutritional transition among a population whose frugality had genetically modelled a spartan metabolic profile, came as a bombshell. The explosion in obesity and chronic illnesses - type 2 diabetes and its related complications - is a major health problem. This is the leading chronic illness on the island of Reunion for example, with the rate being twice as high as in mainland France and the populations of several island chains in the Pacific have been affected by spectacularly early forms, from adolescence onwards, which until now had never been seen.

      Interactions between metabolisms and diseases

      In addition to the health policies so vital to limiting the incidence of chronic diseases, the existence of interactions with the infectious island environment must be considered. “We recently began examining the possible link between metabolic ailments and infections”, explains the virologist Philippe Desprès. “Is diabetes a factor favouring infections or making them more severe? Or conversely, do these infections increase the propensity to or the severity of diabetes?” The question arises for example concerning the chronicity of chikungunya: are the risk factors in islands struggling with a wave of diabetes the same as those in other parts of the world? Similarly, what is the situation concerning the Zika virus known for its ability to survive for a long time in the kidney cells of diabetics, who are often affected by renal complications?


      Climatic pressures

      The islands also face another kind of threat: with the increasing risks related to the atmosphere and the ocean surrounding them, island environments find themselves on the front line faced with the impact of climate change. And this naturally has an effect on the health situation: “The temperature plays a powerful role, for example in the life cycle of the dengue virus, which replicates more quickly in the vector mosquito, and in the mosquito’s metabolism, which digests more quickly, can reproduce earlier and complete its larval, pupal and adult (gonotrophic) cycle more quickly when the temperature increases”, explains climatologist Christophe Menkes. “Consequently, up to a certain extent, the warmer it is, the faster the disease will be transmitted”. And the colder seasons of the year, which interrupt the vectors’ activity and therefore the circulation of the diseases, now tend to be less intense, thereby removing these periods of respite.



      Global warming is significantly affecting the life cycle of the dengue virus and its vector Aedes aegypti.

      © IRD-Nil Rahola

      Bloc de texte

      The researchers at the ENTROPIE unit have established a clear link between climate change and the frequency of dengue epidemics in New Caledonia. They can predict the likelihood of such episodes a month in advance with 70-80% reliability based only on the variables of temperature and humidity. “If the climate warms by 3°C by 2100, the climatic risk of having dengue epidemics - which come around roughly every five years in New Caledonia at the moment - will become an annual one (i.e. an endemic situation in which the virus has firmly taken root)If the rise in temperature is limited to 1.5°C, which is the objective of the Paris agreements, the climatic risk of epidemics is halved to a frequency of once every two years. 1”, he believes.
      The researchers, who are also exploring the effects of the climate on other transmissible diseases found in island environments such as leptospirosis, are involved in an ambitious biological control project in New Caledonia. This project seeks to eradicate dengue, chikungunya and Zika from the island by infecting mosquitoes with Wolbachia. The presence of this bacterium in the vector insect prevents the arbovirus from multiplying. Additionally, the infected mosquitoes pass on the bacteria to their offspring, thereby creating generations of vector insects unable to transmit these viral diseases. The dispersion of Aedes aegypti infected with Wolbachia has already begun in New Caledonia’s capital and the scientists are monitoring the spread of the bacteria through mosquito populations.


        Plage érodée par les flots avec cocotiers tombés à la mer

        The lowest-lying islands are threatened with submersion in the short term.

        © IRD-Bruno Marty

        Preparing for the forecast submersion

        Sometimes barely rising above the waves and with limited possibilities to withdraw inland, island environments are some of the geographical areas most vulnerable to rising sea levels and the related loss of land. Climate change is seen as the culprit. But there is more to it than that! “Not all of them are exposed in the same way and for the same reasons, but some are already finding themselves in the front line”, explains Rafael Almar, oceanographer at the LEGOS MRU. The specialists from the IRD and their partners are on a war footing to try and understand the physical mechanisms at play, to study the resulting changes and to support island communities as they adapt to this sudden change.  

        Subsidence and relative sea level

        The risk of islands becoming submerged is not only due to rising sea levels. It’s certainly true that with global warming, the melting of the ice and the expansion of the oceans, the sea levels are rising overall at a rate of 3 mm per annum. On a very low coast barely rising above sea level, such as those often found on the Pacific islands, this can quickly cause problems. However, other processes also contribute to causing flooding or even substantial losses of land. “More than rising sea levels, it’s land subsidence – on the islands in this case – which is currently causing the most trouble”, explains the researcher. This phenomenon results from ground sinkage, bringing about a relative increase in sea level. Resulting from human-induced local activities, it is linked to pressure on an island’s water table. The sustained draw-off of water removes volume from the ground, which can collapse by a few millimetres a year.

        Reefs under pressure

        In Polynesia, as elsewhere, the sinkage of the islands, the rising sea levels and the vulnerability of the protective coral reefs are contributing to coastal erosion and flooding in the islands.

        © IRD-Bruno Marty

        Bloc de texte

        Additionally, the deterioration of the barrier reefs surrounding many tropical islands leaves them more exposed to the ocean swell and its effects. The coral, which comprise natural barriers between the lagoon and the high sea, are undergoing deterioration related to both the warming and acidification of the oceans but also mechanical destruction caused by cyclones whose intensity is increasing significantly due to climate change. Subsidence, the weakening of the reefs but also the exploitation of sand resources and the destruction of the mangrove forestsA specific coastal tropical forest growing in intertidal zones are encouraging coastal erosion: the coastline sometimes retreats several metres a year, eaten away by the mechanical action of the ocean swell and the removal of construction materials In just a few decades, traditional buildings made from plant-based materials have been replaced by solidly built structures in almost all island environments.1. Finally, more occasionally, the tidal waves accompanying cyclones can cause destructive flooding, as was the case with the recent arrival of Dorian in late 2019 in the Bahamas, or even make the land unfit for farming or contaminate the island’s water table with salt.  
        The local human impact is the key factor in coastline changes and erosion-submersion phenomena, more than the effects of climate change”, states Rafael Almar. “Local planning and the overexploitation of limited resources related to the adoption of a globalised lifestyle are not always compatible with the long-term future of fragile island environments”. The current work conducted by specialists from the LEGOS MRU into the frequency of extreme meteorological events, into the dynamics involved in the dissipation of wave power by the reefs and into the circulation of water in the lagoon is intended to identify changes in the phenomena according to the overall relative rise in sea levels.

        Atolls and high ground

        Not all island environments are in the same situation: the lowest and the smallest are those most threatened. The volcanic islands are sinking and eroding inexorably at a rate of one centimetre a year. After tens of millions of years, the oldest of these now stand just a few metres above the waves, with just a ring of coral to demarcate their lagoon and a few small islands which have developed on the coral deposits. These atolls, like the Maldives, Kiribati, Tuvalu or the islands of Fiji are extremely exposed to the risk of submersion.

        Les inondations venues de l’océan peuvent détruire les cultures - comme cette cocoteraie à Vanuatu -, submerger les villages ou saler les nappes phréatiques.

        © IRD -Valérie Ballu

        Bloc de texte

        In practice, the advancing sea results in a loss of coastal land, sometimes farmland, the destruction of infrastructure and the decline or disappearance of freshwater resources, all disastrous consequences which make life difficult for the inhabitants or even force them to leave. Several villages have already had to be moved in Fiji. Sometimes complete submersion simply occurs: five of the Solomon Islands, an archipelago in Oceania, have already disappeared between 1947 and 2014. For the highest islands in altitude terms, the sharply emerging continental islands or the youngest volcanic islands which still have enough high land on the side of their volcano, the problem is far less urgent.

        Face à l’urgence de la situation pour certains habitants des îles, comme ceux du village de Lataw sur les îles Torrès au Vanuatu - premiers réfugiés climatiques de l’histoire déplacés en 2004 -, les autorités insulaires s’organisent.

        © IRD -Valérie Ballu

        Bloc de texte

        Emergence of a united political front

        To tackle the situation, the authorities concerned have taken their destiny in hand: the island states have taken centre stage on the international scene during climate negotiations: the Alliance of Small Island States (AOSIS) has been campaigning hard on this issue since the 1990s. After the failure of COP 15 in Copenhagen in 2009, the focus has switched to more regional initiatives (the Pacific Islands Forum) and even sub-regional ones (the Polynesian Leaders Group for example) when it comes to defending the interests of small island states and territories in the Pacific. More recently, Fiji directed the work of COP 23 in 2017 in Bonn (Germany). Since 2018, these states have also banded together to form a forum of Archipelagic and Island States at Indonesia’s initiative. “The challenges are both diplomatic - attempting to have agreements adopted and respected which seek to restrict greenhouse gas emissions and global warming -, economic - obtaining aid from the industrial nations - and legal”, explains Victor David, a legal expert for GRED MRU. The maintenance of sovereignty over exclusive economic zonesA maritime zone extending 360 km from the coast in which the coastal state has sovereignty for resource exploitation after the submersion of an island, or the possibility to obtain land on other less exposed islands to settle climate refugees there are both key concerns.   
        At a national level, the governments of island states have adopted plans for adaptation to the environmental changes threatening or already affecting their territories. Others have built dikes to attempt to slow down coastal erosion while others have relocated communities whose living space was under threat to higher ground. Still others have acquired land on high altitude islands possessing a reserve of available land.

        À Kiribati, le projet FRAGILE vise à impliquer les communautés insulaires exposées aux changements environnementaux, pour élaborer des réponses adaptées à leurs attentes

        © IRD-Victor David

        Bloc de texte

        Mobilisation by the community

        However, the island environments are extremely fragmented and rising awareness by the authorities will not be enough to mobilise the populations concerned. “In many cases these are poor regions which are badly interconnected and information doesn’t get through”, explains Victor David. “Many of their inhabitants still live traditional lifestyles and are unaware of all the action plans put together in the capital cities, which in any case are often not implemented due to a lack of resources”. In view of this, with the support of the Pacific Fund, between 2016 and 2018 the scientists from the GRED MRU based in New Caledonia developed a participatory research programme named FRAGILESFonder la Résilience et l’Adaptation aux changements Globaux dans les ÎLES du Pacifique, which seeks to involve island communities. Launched in Ouvéa, in New Caledonia’s Loyalty Islands Province, then adopted in other atolls under threat in the South Pacific (including North Tarawa, in the Republic of Kiribati), this work has enabled inhabitants to appreciate the reality and pace of the environmental changes underway. With the aim of boosting capacity, it has also made it possible to involve them in the search for solutions best meeting their needs. 


          • Rafael Almar / UMR LEGOS

            Victor David / UMR GRED

          • Contribution des vagues générées par le vent aux changements du niveau de la mer à la côte
            Guillaume Dodet, Angélique Melet, Fabrice Ardhuin, Xavier Bertin, Déborah Idier & Rafael Almar. The Contribution of Wind-Generated Waves to Coastal Sea-Level Changes, Surveys in Geophysic, novembre 2019.

            Contribution sous-estimée des vagues à l'élévation du niveau de la mer à la côte
            Angélique Melet, Benoit Meyssignac, Rafael Almar & Gonéri Le Cozannet, Under-estimated wave contribution to coastal sea-level rise ; Nature climate change, 26 février 2018.

            L’historique du niveau de la mer dans le Pacifique Sud, à partir des archives, des mesures géodésiques et de l'altimétrie satellitaire
            Jerôme Aucan, M. A. Merrifield , N. Pouvreau. Historical sea level in the South Pacific from rescued archives, geodetic measurements, and satellite altimetry, Pure and Applied Geophysics, 2017.

            Les régions côtières et insulaires, des zones sous pression anthropique
            Gilbert David, Jerôme Aucan, Daniel Guiral , Serge Andréfouët,  Marie-Christine Cormier Salem. (2015). Coastal and island zones : areas under anthropic pressure. In : M. Reinert , Serge Janicot (ed.), Catherine Aubertin (ed.), Bernoux Martial (ed.), Edmond Dounias (ed.), JeanFrançois Guégan (ed.), Thierry Lebel (ed.), Hubert Mazurek (ed.), Benjamin Sultan (ed.), Y. Sokona  (pref.), Jean-Paul Moatti  (pref.). Climate change : what challenges for the South ?. Marseille : IRD, 101-113. ISBN 978-2-7099-2172-5

            Victor David, Marc Despinoy & Scarlett Mitran. Rapport final du Projet FRAGÎLES, IRD Nouméa, août 2018.


          • Olivier Blot