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Les espèces envahissantes dans l’archipel néo-calédonien

 | 
Marie-Laure Beauvais
, 
Alain Coléno
, 
Hervé Jourdan

Part one. Synthesis and recommendations

Invasive species in New Caledonia

Texto completo

1The first international programme on invasive species was started in 1982. Entitled Ecology of biological invasion, it was launched on the initiative of the Scientific Committee on Problems of the Environment (SCOPE), a body established by the International Council for Science (ICSU). One of the first publications issued by the programme, in 1986, concerned Australia, where the number of species introduced and naturalised in at least four States has increased in linear fashion since the arrival of the Europeans in 1788. There followed several publications on other parts of the world: North America and Hawaii, South Africa, Europe and the Mediterranean Basin, the Tropics. A synthesis of the entire programme was published in 1989 under the title Biological invasion, a global perspective (J.A. Drake et al., John Wiley & Sons Ltd.).

2As regards New Caledonia, it may be assumed that species introductions have been occurring for about 4000 years. In fact humans reached the islands fairly late; one of the oldest archaeological remains discovered so far, on Île des Pins, dates from 2000 BC. Since then, humans seem to have been permanently present on the islands. James Cook discovered Grande-Terre in 1774 AD.

3The eventful geological history of the hundred-odd islands that make up the territory of New Caledonia, their geographical isolation dating back to very early times, and their topographical, hydrological and climatic particularities, all suggest? as has been extensively confirmed? that they vary widely in the richness and composition of their indigenous flora and fauna. This chapter presents an initial assessment of the number and type of invasive plant and animal species present.

DEFINITIONS

4In this document we define invasive species as "any alien, non-native or imported species intentionally or accidentally introduced and whose proliferation in natural or semi-natural environments causes or is likely to cause damage."

  • 1 For greater precision in these definitions, see the papers by M. Pascal et al. and J-Y Meyer etal. (...)

5We define alien species as a species living in a biogeographical area outside its natural range, in contrast to an indigenous species. The definitions of alien and indigenous refer to the concept of a species’ natural range, which bears no relation to the geographical boundaries between countries, let alone lesser administrative regions. Given the large number of islands that make up New Caledonia, a given species may very well be indigenous (and in many cases endemic) in one island or even part of an island, and alien in others. Of course, not all alien species are invasive1.

A PARTICULARLY VULNERABLE GROUP OF ISLANDS

6New Caledonia has a somewhat temperate tropical climate, with two main seasons: a hot season from mid-November to mid-April and a cool season from mid-May to mid-September. Between them come a short dry season from mid-April to mid-May and the main dry season from mid-September to mid-November. Mean annual temperatures vary between 21.9°C and 24.1°C, with a maximum in January and February. This relatively clement climate provides favourable conditions for very many potentially invasive species to establish themselves. However, there are significant differences between the different parts of the archipelago, owing to its geographical configuration (see Map 1): the West and North coasts are much drier than the East and South coasts. The differences in rainfall from one area to another limit the spread of invasive species to all parts of the territory, because each species has its particular moisture requirements.

Map 1. New Caledonia
New Caledonia spreads out between 18° and 23° S and between 164° and 167° E. It consists of a main island, Grande-Terre, and - numerous outliers, a total of 18,585km2 of land. Stretching beyond Grande-Terre (16,890km2) are small, isolated islands such as Île des Pins to the south and the Belep islands in the lagoon north of Grande-Terre. Further north are the coral atolls of Huon and Surprise (Entrecasteaux reefs). The Loyalty Islands, northeast of Grande-Terre, have three main islands, Ouvéa, Lifou and Maré. West of Grande-Terre lies the Chesterfield plateau with the Chesterfield and Bellona atolls.

7A major source of New Caledonia’s vulnerability is trade (see paper by M. Delos et al. particularly). New Caledonia trades with almost 150 countries, from Western, Central and Eastern Europe to the United States, Asia, Africa and the Near East. Half its trading partners are temperate industrialised countries (in 2003, 46% of imports, in value terms, came from France), the other half from tropical countries (35%) and island countries with climates similar to its own (15%). Among the good imported (see Table 1) are foodstuffs (+ 24% in 1994 values between 1999 and 2003), machinery (+ 85%), equipment and transport (+ 238%) and wood (stable).

8Owing to New Caledonia’s economic development, agriculture now accounts for only 1.9% of GDP, a similar percentage to mainland France and other French overseas territories.

Table 1 - Imports into New Caledonia between 2001 and 2003, in F.CFP million (FCFP 1000 = €8.38)

Table 1 - Imports into New Caledonia between 2001 and 2003, in F.CFP million (FCFP 1000 = €8.38)

Source: Direction régionale des douanes

9While the food sector still depends massively on imports of products that for technical or economic reasons cannot be produced locally (about 70,000 tonnes of fresh animal and vegetable produce per year of temperate-climate produce and frozen foods), the farm situation has changed considerably in the past 15 years. Over that period, the rate of coverage from local output has increased by 41% to 53% owing to a steady increase in farm output, which has increased in value from €34.5m in 1991 to €88.8m in 2004.

10New product chains have emerged during this period, particular exports of squash to Japan (3,029 tonnes in 2002) and other exports of fruit and vegetables which have grown remarkably fast, with a production value increasing from €8.4m to €24.3m.

11However, local produce and particularly fruit and vegetables are periodically affected by tropical cyclones (Rewa in 1994, Beti in 1996, Frank in 1999, Erica in 2003) which increase demand for imports. Fruit and vegetables are the main vectors for Tephritidae (fruit flies); the introduction of new species of fruit fly to New Caledonia is not desirable. As regards cereals, output has increased 18-fold in 10 years (6,095 tonnes of maize and 19 tonnes of wheat in 2003). And the quarantine lists (which are not yet exhaustive) include numerous pests of maize.

Table 2 - Origin of ornamental horticulture material (cut flowers and ornamental plants)

Table 2 - Origin of ornamental horticulture material (cut flowers and ornamental plants)

12Ornamental horticulture is a fast-growing sector in New Caledonia. The number of ornamental horticulture holdings increased from 37 in 1989 to 168 by 2003 and is still increasing. Seventy per cent of these holdings are in Southern Province, where demand is strongest. This region concentrates 95% of the 100 ha growing ornamentals commercially in New Caledonia. Three quarters of their basic plant material is imported and represents a significant risk factor (see Table 2).

13The species most commonly marketed as cut flowers are roses (over a million stems), anthurium (several hundred thousand stems), sunflower, strelizia (several tens of thousands), gerbera and orchids, most of these latter two being directly imported. All these species, as cut flowers or pot plants, are potential carriers of major plant pests on the quarantine lists, be they insects [Aleurodes (Bemisia sp.), leaf miners (Lyriomyza sp.), fruitworms (Helicoverpa sp.)] or bacteria (Xanthomonas). For example Xanthomonas campestris pv dieffenbachiae has become established in many tropical countries where anthurium can be grown. Some of these organisms feed on a range of different species, which makes them as much of a danger to wild plants as to the cultivated plants on which they arrived.

14Tourists too may introduce alien plant or animal species. The risk seems relatively slight today, in view of the low level of tourism in New Caledonia? about 100,000 tourists a year, a figure that has remained stable for ten years. However, the number of tourists did double between 1986 and 2003, so vigilance is called for, especially as some points of entry by cruise passengers may not be under sufficient surveillance.

15The influx of people working in the nickel mining sector is a major hazard, however. New Caledonia, which holds about 20% of the world’s nickel reserves, is to date the third largest producer. Output is still increasing and is largely based on foreign labour.

16New points of entry to the territory have been established in connection with the mining industry, others will be in the near future: Koumac (northern Grande-Terre), Goro (southern Grande-Terre), Koné (western Grande-Terre). Traditionally, the main points of entry to be monitored have been the port of Nouméa, which handles 99% of goods traffic, and the international airport at Tontouta, through which 200,000 travellers pass each year, half of them tourists and half residents. Returning residents are more likely than tourists to bring in exotic species. Postal traffic is another way for alien species to arrive. This risk is increasing rapidly with the success of online shopping, the goods being delivered by post. Seeds, bulbs and rhizomes for private gardens and horticulture all arrive by post.

17Controlling international entry points is of course one of the key points in any system of biosecurity and prevention against invasive species. But domestic traffic, island-to-island traffic especially, is also an important factor for contamination.

INVASIVE VERTEBRATES

18To be accurate, the question of biological invasions must be considered over the long term. Too many studies have been limited to the recent past, and assume, wrongly, that human societies have only recently had an impact on their environment. This leads to biased interpretation: situations that have resulted from many centuries of Neolithic human activity are assumed to be natural. In this study, we will cover the period from 2000 BC to 2005 AD, 2000 BC being the date of the earliest archaeological evidence of human presence in New Caledonia. We will also refer to the date of introduction of a species, where known, rather than estimating when it became established in the wild.

19Not all the indigenous and non-native species considered to be a part of New Caledonia’s fauna actually breed there; some only spending time there at other stages of their life cycle. This applies to many bird species, but also some fish and mammals (such as cetaceans, which breed at sea). In this document, therefore, we consider indigenous species and established aliens to include only those that reproduce in New Caledonia and constitute one or more permanent populations. Otherwise we would have to list all the non-native species that have been present in New Caledonia for short periods, which cannot be done in the present state of knowledge. Nor would it be useful for the purposes of this study to try to do so.

20That said, the New Caledonia archipelago counts 295 terrestrial, freshwater and brackish water vertebrate species. Of these 295 species, nine belonging to the order Anguilliformes and seven belonging to the Mugiliformes are reputed to breed only at sea, taking the number considered for this study down to 279. Over the past 4000 years (Melanesian period to 1774, historical period thereafter) 18 species disappeared from the territory; 15 of them, endemic to New Caledonia, became extinct (8% of the territory’s endemic and indigenous vertebrates). Of these disappearances, 14 (76%) occurred during the Melanesian period: four species of reptile, ten of birds. The other four (24%), all birds, occurred during the historical period. Which means that 0.4 species disappeared per century during the Melanesian period, compared to 1.6 per century in the modern period? four times as many.

2115% of all recorded vertebrate species in New Caledonia are aliens. Subtracting those species that have already died out, alien species account for 16% of currently existing species in New Caledonia: 17% of fish, 100% of amphibians (only one species), 4% of reptiles, 17% of birds and 57% of mammals. Of the 42 alien vertebrates currently recorded, 4 have invaded the territory recently and apparently spontaneously. These four are all birds: the dusky moorhen (Gallinula tenebrosa), masked lapwing plover (Vanellus miles), little bittern (Ixobrychus minutus) and greater cormorant (Phalacrocorax carbo). Of the other 38, 37 have been introduced, intentionally or inadvertently, since the historical period began, and only one, the Pacific rat (Rattus exulans), was certainly introduced during the Melanesian period.

22Some other species are thought to have arrived spontaneously from elsewhere or been introduced by humans. They are the Pacific or Solomon Islands tree boa (Candoia bibroni), five geckos (Gehyra vorax, Hemidactylus garnotii, Hemiphyllodactylus typus, Lepidodactylus lugubris, Nactus pelagi-cus) and a skink (Emoia cyanura). If this hypothesis is confirmed, it would bring the number of alien species in New Caledonia to 49? 80% of existing species. If they prove to have arrived during the Melanesian period, 8 invasions would have occurred during that time compared to 41 during the historical period? 16% and 84% of total invasions respectively.

23Naturally enough, it is the inhabited islands that have the highest percentage of alien species (see Table 3 and the detailed inventory in the paper by M. Pascal et al.). Grande-Terre, where all New Caledonia’s alien species can be found, has nearly twice the proportion of alien species as the various Loyalty Islands (the very low number recorded on Île des Pins seems to be an underestimate). Very isolated islands that have never been inhabited have the lowest rates (Entrecasteaux 2 group, Walpole, Hunter). Grande-Terre is thus a major potential source for the introduction of such species to the other islands, given their geographical proximity and close trading ties. (NB: Belep, Beautemps-Beaupré and some satellite islands of the larger islands are not included in this study owing to lack of data). In the light of the available information, the Chesterfield Plateau islands are treated as a single group and the Entrecasteaux Reef islands as two groups.

Table 3 - Number of indigenous, endemic, alien and lost vertebrates of each island unit considered in the study

Table 3 - Number of indigenous, endemic, alien and lost vertebrates of each island unit considered in the study
  • * In brackets: number of species potentially present and whose absence is not specified in the liter (...)
  • Percentage of alien species present compared to endemic + indigenous species.

Note **
Note **

  • For further information see paper by M. Pascal et al.

Table 4 - Impact of non-native vertebrates in New Caledonia

Table 4 - Impact of non-native vertebrates in New Caledonia‡

24The impact of many alien species of vertebrates is unknown, as no studies have been done. Table 4 shows the species whose impact is documented for New Caledonia and those whose impact in other regions is known (see detailed data in paper by M. Pascal et al.). Some of these are on the IUCN list of the world’s 100 most damaging alien species in terms of host ecosystem disruption.

25Apart from the causes of contamination between Grande-Terre and other islands already mentioned (geographical proximity, trade and movements of people), a third cause is the deliberate transfer of alien species. This includes pets, aquarium fish, domestic pigeons, species introduced for hunting or fishing, etc. While some of these introductions may seem legitimate at first sight, none are without consequences, and they should be prohibited unless and until serious ecological studies have been performed to assess the relative risks and benefits. Measures taken to limit the introduction of alien species from outside the territory should also be applied within the territory.

26Current knowledge of the biology, ecology and local impact of the 20 species in Table 4 is not sufficient to establish a reliable ranking order according to their relative risk for New Caledonian ecosystems or human and animal health. However, since twelve of them are on the IUCN list, close attention should be paid to these twelve, and quickly. Others, like the rusa deer, require pragmatic solutions (see paper by J-Cl. Lefeuvre). The rusa deer is considered both a domestic animal and a game animal. Production of deer meat increased seven-fold between 1991 and 2002. There would be fierce opposition from the population to any attempt to eradicate the deer. The problem will need to be managed at the local level, e.g. by creating protected areas, introducing properly planned cull hunting, etc.

INVASIVE PLANTS

27This section discusses currently invasive plants and potentially invasive plants. The latter category includes plants that are already present in New Caledonia but have not yet become invasive, and others not yet present but known to cause major damage in tropical and subtropical islands of the Pacific and Indian Oceans. The goal is not to provide descriptive data sheets on these plants (these can be found in the bibliography or on relevant websites? see paper by J-Y. Meyer et al.) but to try to rank them according to their ecological and socio-economic impacts.

28The most recent inventory of introduced and cultivated plants in New Caledonia (Catalogue des plantes introduites et cultivées en Nouvelle-Calédonie, H.S. MacKee, Museum national d’histoire naturelle, 1994) lists 1,412 taxons (species, subspecies, varieties and cultivars). These include 708 cultivated taxons, 170 cultivated or spontaneous and 87 spontaneous. It would appear that 360 of these taxons have become naturalised, including 64 (4% of the introduced flora and 18% of the naturalised flora) that can be considered invasive (see list of plants considered invasive in New Caledonia in the paper by J-Y. Meyer et al.). To these 64 should be added the weeds Caribbean pine (Pinus caribaea), Imperatra cylindrica and Heteropogon contortus, bringing to 67 the number of invasive plants in New Caledonia.

Table 5 - Number and distribution of introduced plant species (invasive, naturalised, sub-spontaneous and cultivated) in the New Caledonia archipelago (adapted from MacKee, 1994)

Table 5 - Number and distribution of introduced plant species (invasive, naturalised, sub-spontaneous and cultivated) in the New Caledonia archipelago (adapted from MacKee, 1994)

29Introduced plants are to be found on all the main islands: Grande-Terre, the Loyalty Islands, Île des Pins, Îles Belep and Île Walpole. Grande-Terre has the highest percentage, with 1,294 species out of 1,412 (see Table 5). All the main islands suffer invasive plants, Grande-Terre in the lead with 64 species out of 74, followed by Île des Pins and Loyalty Islands.

30There is no established international system for classifying invasive species or ranking them in order of importance. A panel of experts has recently classified the 117 main invasive plants in South Africa, based on crossing four factors: the current range of the species (very large, large or localised), geographical abundance of the species (abundant, common, rare), habitats liable to be invaded (large, medium or small numbers, waterside areas) and the number of propagules (high, medium, low). For Q.B.C. Cronk and J.L. Fuller (1994), major or dominant invasive plants are species that have been introduced, have naturalised, and cause significant changes in the composition, structure and functioning of the ecosystem.

31Species with major ecological and socio-economic impacts include:

  • tropical and sub-tropical aquatic plants (Eichhornia spp., Salvinia molesta, Egeria densa) capable of invading lakes, ponds and rivers, reducing oxygen and light in the water, increasing turbidity and sedimentation, causing drying or eutrophication of watercourses and obstructing irrigation canals;
  • pyrophytic grasses (Andropogon spp., Melinis spp., Pennisetum spp.) which form dense, highly inflammable clumps, increasing the frequency and intensity of wildfires and regenerating after a fire;
  • trees that are heavy consumers of water (Acacia mearnsii, Tamarix spp., Prosopis spp.) and that exhaust water reserves in dry areas;
  • leguminous plants (Acacia spp., Paraserianthes falcataria) and Myrica faya which enrich the soil in nitrogen, disturbing the natural secondary succession;
  • climbing vines (Thunbergia spp., Passiflora spp.) capable of completely covering the canopy.

32The list of "100 of the World’s Worst Invasive Alien Species" includes 32 land plants and 2 freshwater aquatic plants presenting the above features. Nine of the 34 are present in New Caledonia: Arundo donax, Eichhornia crassipes, Imperata cylindrica, Lantana camara, Leucaena leuco-cephala, Schinus terebinthifolius and Wedelia trilobata, Miconia calves-cence, Merrenia peltata.

33As to potentially invasive plants in New Caledonia, these are determined by comparison with plants that have become invasive elsewhere. Thus of the 300 major weeds and invasive plants in tropical and sub-tropical regions and islands, 165 are present in New Caledonia, 47 of them being invasive, 66 naturalised, 12 sub-spontaneous and 40 cultivated (see paper by J.Y. Meyer et al.). The latency period between the time a species is introduced and the moment it becomes invasive can be as much as 100 years. Every biological invasion is a particular case, depending on the characteristics of the species, its origin, its history, and the characteristics of the invaded ecosystem.

34The number of introduced, naturalised and invasive species in New Caledonia, and their density per km2, seem relatively low compared to those recorded on the neighbouring tropical islands in the Pacific? Hawaii and French Polynesia? or on Réunion island in the Indian Ocean. Similarly, the proportion of New Caledonia’s total flora that consists of naturalised aliens is low: 10%, compared to 40-50% in New Zealand, for example. But New Caledonia’s economic development, with increasing trade and the influx of tourists, are likely to increase the number of intentional or inadvertent introductions, and hence increase the risk of introducing invasive or potentially invasive plants.

35Apart from introductions connected with agriculture, horticulture and industry, there are other factors that encourage the introduction of species that may become invasive: disturbance of the environment by natural events such as wildfire and cyclones or human activities such as fragmentation of forest areas, overgrazing, etc., and also interactive effects, e.g. the impact of alien animal species rendering an area vulnerable to invasion by plants. In any event, it is important to update the 1994 species census. Especially as the above assessment of the New Caledonian situation is probably biased by lack of a recent published inventory.

INTRODUCED AND POTENTIALLY INVASIVE INVERTEBRATES

36It is estimated that 25,000 invertebrate species occur in New Caledonia, only 6,000 of them being named so far. There is also no fossil record of invertebrate fauna change, even if some invertebrate species must have been introduced with plants transported by early Melanesian groups (such as bananas, Hibiscus...). According to literature, 518 taxa whose occurrence in New Caledonia can be explained only through human introduction was drawn. This list includes 1 oligocheta, 2 myriapoda, 3 crustacea, 17 nematoda, 31 mollusca, 43 arachnida and 421 insecta (see paper by H. Jourdan & C. Mille). Among these species, 511 established perennial populations in the wild: 21 species live in fresh water, 66 interact with human or animal health, 55 are biological control agents and 369 species are encountered in native or disturbed habitats. This last group includes most of the agricultural pests which cause severe damages to human food crops. Some are world trade quarantine pests and importation countries require specific treatments, such as Japan and New Zealand for the fruit fly, Bactrocera tryoni on risky shipments from New Caledonia. Most of the introductions were accidental, but 51 species were intentionally released, 47 in the context of biological control programs (42 are successful), and 4 other species to food purposes: the edible snail Cantareus aspersus and 3 varieties of the domestic bee. Every New Caledonia habitat may be invaded. The majority of invertebrate introductions are known from Main Island, but data are very scarce or missing for other islands. Moreover, the impacts of most of allochtonous species are unknown, as there is no relevant scientific study. In this context, establishing a reliable ecological or socio-economical threat ranking order is difficult, as well as identifying potentially invasive species. Anyway, one should remember that among the 14 invertebrate species included in the IUCN list of the "100 of the world worst invasive alien species", 6 are known from New Caledonia: the giant African snail Achatina fulica, the rosy wolf snail Euglandina rosea, the whitefly Bemisia tabaci, and the ants Anoplolepis gracilipes, Pheidole megacephala and Wasmannia auropunctata. Nevertheless, the Main Island appears to be the main entry point for the archipelago and the dispersal source to other islands for allochtonous invertebrates.

37As to potentially invasive species, there are hundreds if not thousands of them. From literature dealing with other tropical insular areas, a list of 541 main taxa, which may be introduced in New Caledonia, has been drawn (see paper by H. Jourdan). This list includes mostly insect species (475 taxa), mainly phytophageous ones, but also arachnida (29 taxa), mollusca (20 taxa) and nematoda (17 taxa). Threats appear to be diverse, but the examples below give some idea of the scale of possible damages.

Red imported fire ant (Solenopsis invicta)

38Also known by the acronym RIFA, this species is a native of South America. It first moved North into Alabama in the early 20th century before invading the whole of the southern United States. It has very strong venom and is renowned for the damage it causes to public health, agriculture, infrastructures, biodiversity and quality of life. In the past twenty years it has invaded the Caribbean islands, crossing from Florida, and could progress to the Pacific islands if concerted measures are not taken. One colony can contain 200,000 individuals. At a density of 150 colonies per hectare, there can be up to 3,000 individuals per square metre. They bite as soon as they feel threatened, and each ant can inflict several extremely painful bites. They are attracted by electrical equipment such as traffic light housings, airport runway lights, electricity distribution systems and communication systems. Tens of millions of US dollars are spent annually on pesticides, the only means of control found so far. An ant prevention plan for the Pacific has been proposed, but is awaiting funding (see paper by Lloyd Loope). Of all the ant species present in the Pacific region, the red fire ant, along with the little fire ant, is the greatest threat to quality of human life and biodiversity.

Glassy-winged sharpshooter (GWSS) (Homalodisca coagulata)

39The glassy-winged sharpshooter is a native of the south-eastern United States and north-eastern Mexico. It established itself in southern California in the 1980s, probably arriving on ornamental plants. It is considered a major pest there, feeding and breeding on more than 300 plant species? farm crops, urban green space ornamentals and indigenous species. The insect’s main danger is that it carries a bacterium, Xylella fastidiosa, which multiplies in the xylem of a plant, producing secretions that finally block the fluid transport canals until the host plant dries up and dies. One of the main victims of the bacterium is the grapevine? including dessert grapes, which New Caledonia plans to develop as a crop.

40The combined presence of the insect and the bacterium can be a serious danger for indigenous plants and ecosystems on Pacific islands. The glassy-winged sharpshooter breeds fast in the warm, moist climate of French Polynesia, although the Xylella bacterium has not yet been reported there. So far no successful biological control method has been found in California. In Hawaii, however, where the insect arrived in 2004, its spread is being hindered for the time being by a "spontaneous biocontrol agent" that lives as a parasite on sharpshooter eggs.

Pandanus scale insect (Thysanococcus pandani)

41On the Hawaiian island of Maui a scale insect called Thysanococcus pandani is attacking the coast-dwelling tree Pandanus tectorius, causing severe damage and sometimes death. The insect was previously known only in Java and Singapore. It first appeared in Hawaii in 1995, in the botanical garden in Hana, Maui, and then spread throughout the north coast of the island. It has not yet spread to other parts of Hawaii. In the 1920s, most Pandanus tectorius and Pandanus spurius on the island of Rarotonga in the Cook islands were apparently destroyed by Laminicoccus pandani. Similarly, it seems that vast areas planted to Pandanus tectorius on Atiu and Mangaia were destroyed by this insect in the 1980s.

42The genus Pandanus is an important source of fibre. New Caledonia has 18 species of it, of which 16 are endemic. Given the experience accrued on other Pacific islands, New Caledonia needs to protect itself from Pandanus pests. A first stage would be to draw up a list of insects and diseases known to attack Pandanus species in the Pacific.

The cycad aulacaspis scale insect (Aulacaspis yasumatsui)

43This scale insect is indigenous to Thailand and southern China and was described in 1972 from a Thai species of cycad. From 1996 it began to be found outside Southeast Asia: on ornamental cycads in Miami, then in Hawaii. In late 2003 it was detected on an ornamental cycad, Cycas revoluta, in Guam. It is easily carried on the wind, and in the two years that followed it spread across the northern two-thirds of the island of Guam, infesting and killing both ornamental and indigenous cycads. Cycas micronesica, an indigenous Micronesian cycad, seems to be particularly sensitive, with mortality rates of 100% in infested areas.

44Like many of New Caledonia’s vascular plants, cycads are a primitive group, older than most plant taxons. Of the world’s 185 known species of cycad, New Caledonia has only one indigenous species, Cycas celebica. The case of the cycad aulacaspis scale and its impact in Cycus micronesica in Guam can be interpreted as a particularly pertinent example for New Caledonia, which has several dozen species of primitive gymnosperms.

Culicoides midges (Culicoides spp.)

45Culicoides midges are mainly present in continental subtropical and tropical regions and, apart from the no-no of Polynesia, few inhabit oceanic islands. The adult females of many species suck the blood of vertebrates (humans and wild and domestic animals). Apart from the discomfort, these midges carry a certain number of viruses, protozoans and nematodes. They may also have a significant potential impact on island birds. Midges of the Culicoides genus (over 1,000 species) and three other genera in the same family (Ceratopogonidae) pose problems for human and animal health in many parts of the world.

INVASIVE FRESHWATER SPECIES

46The hydrographic network on Grande-Terre is fairly dense, although the elongated shape of the island and its mountainous relief mean that there are no large rivers. Lakes, pools and marshland cover about 4,000 hectares. The lake district in southern Grande-Terre has a particularly high rate of endemism in its flora and fauna alike. The Loyalty Islands, by contrast, have not a single permanent watercourse.

47At the present stage of prospecting, 50 to 60 species of aquatic flora have been identified (not including sub-aquatic species) of which 11 or 12 are endemic and 4 of these very rare. Benthic invertebrates are largely dominated by insects (75 of the 167 taxons identified). New Caledonia’s creeks are have 64 fish species including 11 endemics, a far wider diversity than La Réunion or French Polynesia. Among these species, Galaxias neocaledonicus is thought to be a survivor from the ancient fauna of Gondwanaland. The same species richness is to be found among the decapod crustaceans 37 species including 14 endemics). But it is the molluscs that hold the record for endemism: 65 species out of 81 (80%), while 100% of the Hydrobiidae family water snails are endemic.

48Despite the fragility of freshwater ecosystems and their high rates of endemism, many alien species have been introduced. Some dozen of them are invasive or potentially so: Pistia stratiotes, Nymphoides indica, Eichhornia crassipes, Typha domingensis, Marsilea mutica, Ipomoea aquatica, Ludwigia octovalvis, Cladium mariscus, Hydrilla verticillata, Lemna aequinoctialis, Salvinia auriculata and Azolla pinnata. Seven of these already ought to be eradicated or at least controlled (see Table 6).

49Species not yet present but which should be guarded against include Egeria densa (variously called Brazilian elodea, egeria, leafy elodea, Brazilian waterweed, anacharis) which can form a very dense carpet and eliminate the indigenous aquatic species of lakes and rivers. It is found on Easter Island and in Hawaii, New Zealand and Australia. The only elimination trials so far have used chemicals, which can scarcely be considered in New Caledonia.

50As regards fish and crustaceans, most aliens are reported to have been introduced on the initiative of the South Pacific Commission for reasons of food self-sufficiency. Examples of this are two species of crayfish and 13 fish: Mozambique tilapia (Oreochromis mossambicus), Tilapia zillii, Sarotheron occidentalis, largemouth bass (Micropterus salmoides), snakeskin gourami (Trichogaster pectoralis), chevron snakehead or striped snakehead (Channa striata), guppy (Poecilia reticulata), western mosquitofish (Gambusia affinis), swordtail (Xiphophorus hellerii), giant gouramy (Osphronemus gouramy), carp (Cyprinus carpio), goldfish (Carassius auratus) and rainbow trout (Oncorhynchus mykiss). The latter four species in the list have not acclimatised and the mosquitofish and Tilapia zillii have disappeared. Only seven species have acclimatised and could constitute a real threat to indigenous species. The largemouth bass is a particular example (see Table 4).

  • § For further information see paper by J.-Cl. Lefeuvre.

Table 6 - Seven aquatic plants already present in New Caledonia and which should be eradicated or controlled§

Table 6 - Seven aquatic plants already present in New Caledonia and which should be eradicated or controlled§

Notas

1 For greater precision in these definitions, see the papers by M. Pascal et al. and J-Y Meyer etal. Using these definitions, we will not deal here with species or varieties which, although indigenous or endemic, can become invasive. Examples in New Caledonia are Casuarina collina (Casuarinaceae) and Acacia spirobis subsp. Spirobis (Leguminosae), which behave invasively in places where plant communities have been degraded by human activity. Another example is Commersonia bartramia (Malvaceae) in Port-Bouquet and the Tchamba valley, or the creeper Mucuna platyphylla (Leguminosae), both of which can propagate rapidly or displace other indigenous plants to form single-species cover. While it is not necessary, or a priority, to eradicate them (which would anyway be impossible), it is important not to propagate them and to inform neighbouring countries and island groups of the risk of invasive behaviour by these New Caledonian species.

Notas finales

* In brackets: number of species potentially present and whose absence is not specified in the literature.

Percentage of alien species present compared to endemic + indigenous species.

For further information see paper by M. Pascal et al.

§ For further information see paper by J.-Cl. Lefeuvre.

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