Exotic species

The study of introduced species has gained popularity in recent years. A species introduced to a new area can have negative effects on the native ecosystems, as well as positive interactions with local fauna. The success of an exotic species depends on many factors. Those that are most successful at expanding possess mechanisms of reproduction, settlement, and distribution that aid in competing for space and resources. Tubastraea coccinea, also known as orange cup coral, is native to the Indo-Pacific and was introduced in Bonaire in the 1940s. Little is known about the effects T. coccinea has on the local marine community. It has a very opportunistic nature and has become a dominant scleractinian coral in the subtidal zones occupying shallow, heavy surged waters. T. coccinea is an azooxanthellate coral, which explains its ability to occupy habitats not desirable by other corals requiring sufficient nutrients and sunlight for photosynthesis. The purpose of this investigation was to determine the distribution and abundance of T. coccinea along various sites in Bonaire and observe its habitat preferences. Six sites in Kralendijk, Bonaire were surveyed by snorkelers, who counted various sized colonies and substratum occupancy. T. coccinea was found at all six surveyed sites, being most abundant at sites with very shallow shores and heavy surge. It preferred man-made pilings underneath docks as its habitat. This confirms that T. coccinea is established in Bonaire. By observing the distribution and preferences, the successful nature of T. coccinea throughout the Caribbean can be better understood.

This student research was retrieved from Physis: Journal of Marine Science XIII (Spring 2013)19: 10-16 from CIEE Bonaire.

A review of the introduced agricultural pests and animal and plant diseases and vectors for the Dutch Caribbean in which a total of 47 exotic pests, diseases, parasites and pathogens established on one or more of the Dutch Caribbean islands are listed and discussed. These include 2 species of voracious herbivorous snails, 7 species of millipedes, 8 species of invasive ants, and some 16 species of insects that infest plants. Most agricultural pests are not strongly host-specific and will typically also affect native plants and/or animals. This makes it very difficult to eradicate or control these species once established. Therefore, prevention and early eradication is key.

The most information on invasive alien pests is available for the leeward Dutch islands while the least is known for the windward Dutch islands. The principal means of entry is the importation of unsterilized soil and plant material through container shipment, import of ornamental plants and air traffic. The economic costs, both in terms of damages and control measures, as well as missed opportunities that these species cause, has not been estimated but certainly runs in the millions of dollars annually. By far the most economically costly invasive species is the yellow fever mosquito Aedes aegypti, a pest and disease vector closely associated with man. In a few cases, biological control and eradication has been successful.

Introduction of invasive pest species continues at a high rate in the Dutch Caribbean and preventive measures are urgently needed to limit future costs and risks in terms of economy and health.

Key recommendations are: a) to strongly restrict and control importation of ornamental plants, most of which can be propagated locally without risk of new introductions, b) restrict importation of unsterilized foodstuffs, c) practice tighter control and prophylactic fumigation of container shipments, d) continue strict veterinary controls on animal importations. To effectively implement such measures, will require greater awareness, supporting legislation, cooperation of customs agents and shippers and the presence of a biosecurity unit authorized and equipped to act on short notice.

Based on experiences in other Caribbean countries and existing trade patterns and taking into account which species could survive in an arid climate, it is possible to draw up a preliminary listing of “Alert” species for the Dutch Caribbean. Such a listing is a critical tool for effective prevention. The preliminary Alert list discusses 21 species to be on the look-out for, most of which are insects and most of which can be expected to cause important damage to crops and/or nature, or both, if introduced.

We here provide an overview of 72 invasive animals of the terrestrial and freshwater environments of the Dutch Caribbean, eleven of which are no longer present. All invasive animals that are principally agricultural pests and or animal and plant diseases (46 species) are excluded as these are discussed separately elsewhere. The 61 species documented and discussed here as presently living in the wild or semi-wild state on one or more of the Dutch Caribbean islands, amount to 12 exotic mammals, 16 birds, 13 reptiles, 5 amphibians, 2 freshwater fishes, 3 insects, 2 mollusks and 8 exotic earthworms. For most species, the ecology, distribution, status and current impact remains poorly known as few invasive species have been object of directed studies. Some of the most deleterious animal introductions have been mammals, particularly the grazers and the predators, most of which have been introduced in the historical past. Among these, the four key species are grazing goats, the mongoose the cat and the black rat. In most cases, such species cannot be eradicated because they are widespread and firmly established or even kept as livestock. Nevertheless, these species must urgently be controlled in sensitive areas where possible. Our review also shows that many introduced mammals and reptiles are still present in relatively small populations, making eradication still very feasible. Seven species have the status of being native in parts of the Dutch Caribbean but introduced to other parts where they are not native. The most threatening of this last category is the green iguana, as introduced to St. Maarten where it outcompetes and hybridizes with the weaker Lesser Antillean iguana.

The key priorities for successful action against invasive exotic animals are:

• the control of goats;
• control of introduced predators (rats and cats) near seabird breeding colonies;
• eradication of several small populations of exotic mammal predators and reptiles as long as this is possible before the get a strong foothold and spread; 
• eradication of introduced species from small satellite islands which serve (or served) as seabird breeding habitat.

In addition to such on-island action against species already present, it is critical to prevent further introductions. The most important pathways to focus control on are the container transport of goods, the international trade in pets and the trade in ornamental plants. Two key action points are urgently needed: a) develop the existing legislation and b) invasive species management teams (ISMTs) empowered for action. It is essential that these initiatives be firmly imbedded in a policy framework. The first step ahead in these respects should be to outline an Invasive Species Strategy and Action Plan (ISSAP). However, in the interim, the lack of an ISSAP should not hinder directed critical action at the local level (eg. against goats in the national parks and cats at seabird breeding sites).

This research is part of the Wageningen University BO research program (BO-11-011.05-004) and has been financed by the Ministry of Economic Affairs, Agriculture and Innovation (EL&I) under project number 4308202004. 

Abstract:

The Netherlands are signatories of the international Convention on Biological Diversity (CBD). This implies that the nation will protect biodiversity on its territory. This includes the protection of natural fauna and vegetation from negative impact caused by invasive alien species (see 2.1. for a definition). By 10-10-2010 the BES islands (Bonaire, St Eustatius and Saba) became ‘special municipalities’ of the Netherlands. They together form “Caribisch Nederland” (Caribbean Netherlands, Hulanda Karibe). Due to this stronger link to the Netherlands many responsibilities have moved from the Antillean government to the Netherlands. This includes important responsibilities with respect to the protection of nature.

The present study was financed by the Dutch Ministry of Economic Affairs, Agriculture and Innovation and included a literature study, a field trip and writing of the present document with main observations, conclusions and recommendations. A major part of the report consists of an alphabetical list of (known) invasives with their current status (4.1.1.). Apart from the three islands belonging to Caribisch Nederland, for completeness, some attention is given to Aruba, Curacao and St. Maarten as well (esp. in 4.1.1. and Appendix II).

Stages of invasion
In order to define the problem of invasive alien (non-native) species of plants more accurately it is relevant to recognise the following categories:

Exotic: Species that are not part of the natural indigenous vegetation are called exotics. Examples are introductions as ornamental or agricultural species. If contained within the confines of gardens and farms, these species are not considered problematic.

Established: Species that occur ‘in the wild’, i.e. outside the control of cultivation or husbandry and are able to reproduce themselves resulting in new individuals, we call established (present). Species can stay in this phase, the ‘lag phase’ (see 2.1), for quite some time. It is the stage in which the species adapts to its new environment using its genetic flexibility. At this stage complete eradication is still an option, because the number of individuals and locations is limited. This means that the costs can be relatively low, compared to eradication at a later stage.

Naturalised: If given enough time, species may start to adapt genetically to the new environment, by optimising its physiology and/or growth habit. As a result the species will start spreading more rapidly and effectively and becoming part of the natural flora. In most cases this is not considered a major problem; the plants will get their own function within the ecology of the island and will not replace indigenous species entirely. Moreover, the costs of complete eradication have become prohibitive at this stage, so only containment is an option.

Invasive: It is generally believed that about one in one thousand exotics becomes really problematic, e.g. with respect to environmental, ecological or economical impact (Williamson 1995). They start to grow out of control, massively invade natural habitats and reduce or eliminate native species. They have broken down the dispersal barrier and have become invasive. At this stage one can only try to achieve a stage of equilibrium, of mitigation, by intensive control measures. These are usually limited by financial resources, and can normally only be successful with commitment of the local society, e.g. shown by the enthusiastic support and hand labour of many volunteers.

Invasives of the Caribbean Netherlands
In this report 65 species of invasives are enumerated (4.1.1.) with their history and properties, based on a literature survey and completed with experience and findings of the authors. Four of the main problematic species are treated more extensively in 4.1.2. These are the Coral vine (Antigonon leptopus) which poses a great threat to nature, especially in St. Eustatius; the Rubber vine (Cryptostegia grandiflora) which is able to overgrow and smother shrubs and trees and is especially spreading on the Leeward Islands; the neem tree (Azadirachta indica) which is planted for shade and medicinal purposes, but is escaping on Bonaire; and ‘Donna grass’ (Bothriochloa pertusa) which is a very problematic species replacing the more palatable local grasses on the Windward Islands, most notably on St. Eustatius.

In a complementary list a further 80 species that need more investigation are mentioned (4.1.3.). This list is not complete but it enumerates species that are present on at least one of the islands. They need special attention because it is best to prevent them from entering at all or to eliminate the few plants or populations that have established themselves. Some species in this list are already present at some scale, like some of the arable weeds, but need careful monitoring to prevent them from entering nature.

A general problem are the free-roaming animals, cows, donkeys and especially goats (all non- native species) that are destroying nature in an uncontrolled way. Their presence has a detrimental effect on biodiversity, eating young seedlings and trees, and thereby preventing the natural regeneration and succession. Moreover, the bare soils that result are susceptible to water and wind erosion; material that is deposited in the surrounding seas.

Management recommendations:

Before an exotic has been introduced prevention is the most important action, i.e. keep the chance that exotic species may be introduced as low as possible. As soon as a first introduction has been realised and the exotic still occurs at low densities at few sites, eradication after first observation will be the most important action. Finally, if an exotic has already spread over different sites or even different habitats and has increased in densities, eradication might not be an achievable option anymore. Then containment and population management will be the most relevant actions to minimise the negative impact (mitigation). In general, prevention will generate the most cost-effective options to avoid problems due to invasive exotic plants (Davis 2009). The main observations are:

Prevention: Prevention plans need to be developed with regulations restricting the import of exotic species. This includes the development of ‘Black lists’ for the Leeward and Windward Islands respectively. Public awareness (customs and other officials, general public, landscapers, new inhabitants) must be raised and alternatives for imported exotics must be offered. Agricultural departments and customs offices on all islands are understaffed and not able to control the many routes through which exotics enter.

Eradication after first observation: Rapid first observation of an exotic plant after introduction into the wild is essential for the success of an eradication action. Therefore a ‘Watch list’ or ‘Grey List’ needs to be developed. Since the difference in climates, these watch lists will partly differ between islands and differ even more between the Leeward and Windward islands. Also knowledge about the natural flora and invasives must be increased through education, at schools as well as for professionals (rangers, customs personnel, agricultural department, etc.). Floras for the Windward Islands are outdated and not accessible.

Containment/population management: Management plans need to be developed for the control Antigonon, Cryptostegia and neem to be able to stop further spreading and to mitigate the impact on nature. Research on the life cycle of invasives and experiments for their control have to be carried out. The problem of roaming animals must be tackled. Small island communities are not able to do this without outside assistance. If chemical control is considered, special Dutch Caribbean regulations apply based on restricted import permissions for crop protection agents.