Invasive species

Dutch below 

More than 210 invasive alien species have been documented in the wild within the Dutch Caribbean. These species can have major ecological effects by decimating native flora or fauna. They can also cause large economic losses and impact human health. Over the next few weeks, the Dutch Caribbean Nature Alliance (DCNA) will publish several articles on “invasive alien species” to help provide context to this complex issue.  

Boa constrictor. Photo credit: Diego Marquez

Invasive alien species are animals and plants introduced by human activity – deliberately or accidentally – to a natural environment outside their native range. Invasive species can have severe environmental, economic, and social impacts to their new areas. Environmentally, invasive species can be determinantal to local flora and fauna by preying on native species, outcompeting native species for food or other resources, causing, or carrying diseases, and preventing native species from reproducing. Consequently, they can have negative economic impacts on the agriculture, tourism, fishery and industry sectors. Invasive species can also bring new pathogens which can have a societal impact by making people sick or lead to outbreaks which can affect travel to these areas. The most recent examples include Chikungunya, Zika and West Nile Viruses, all which were introduced from exotic invasive mosquitoes. 

Many scientific studies have shown that alien invasive species are one of the major causes of biodiversity loss globally and that island ecosystems are especially vulnerable. This is due to the islands’ small size (with small plant and animal populations), unique species, relatively large borders that are difficult to control and a small human population lacking the necessary capacity and resources.

Dutch Caribbean 

A report from Wageningen University and Research estimated that there are more than 210 invasive alien species within the Dutch Caribbean alone. These include 27 introduced marine species, 65 introduced terrestrial plants, 72 introduced terrestrial and freshwater animals and 47 introduced agricultural pests and diseases and the list grows longer each year. 

Coralita vine. Photo credit: Marjolijn Lopes Cardozo

Some invasive alien species are a common issue for all six islands, including rats which devastate local bird populations, or lionfish, which spread quickly and consume many local reef fish. This also includes invasive feral grazers, such as goats, which can demolish local vegetation and contribute to desertification and biodiversity loss. 

In addition, many islands have their own specific issues, such as the boa constrictors on Aruba or the vervet monkeys on St. Maarten. Some of these invasive species were brought over to the islands as pets but were released into the wild once the owner could no longer care for them.  

Managing Invasive Species 

Lionfish.  Photo credit: Rudy van Gelderen

The introduction of invasive species should be avoided in the first place. This includes following the local import and export laws, effective border controls and regular monitoring. Furthermore, it is important that there is better cooperation between the parks and Customs, for example, in training of Customs officers in CITES and invasive species detection. Even the best prevention cannot stop all invasive species, however. Once a species is introduced, early detection and rapid assessment and response can still allow the islands to control the issue. Unfortunately, management options for dealing with invasive species are frequently not optimal. Decisions need to be made whether a complete eradication is needed or that monitoring and restricting the distribution (mitigation) is the best or only option. Eradication is a complex task and never the preferred management method, nevertheless, sometimes it is the only choice. Inaction would be a crueler fate for the islands as these invasive alien species can quickly negatively impact the islands’ biodiversity, human health, and/or economy. 

For more information, see the Wageningen University Report on Alien Invasive Species . Stay tuned for the follow-up articles where we take a deeper dive into these issues on each island. 

DCNA 

 The DCNA supports science communication and outreach in the Dutch Caribbean region by making nature related scientific information more widely available through amongst others the Dutch Caribbean Biodiversity Database, DCNA’s news platform BioNews and through the press. This article contains the results from several scientific studies but the studies themselves are not DCNA studies. No rights can be derived from the content. DCNA is not liable for the content and the in(direct) impacts resulting from publishing this article.  

Meer dan 210 invasieve uitheemse soorten zijn in het wild gedocumenteerd in de Nederlandse Cariben. Deze soorten kunnen grote ecologische effecten hebben door de inheemse flora of fauna te decimeren. Ze kunnen ook grote economische verliezen veroorzaken en de menselijke gezondheid aantasten. De komende weken zal de Dutch Caribbean Nature Alliance (DCNA) verschillende artikelen publiceren over “invasieve uitheemse soorten” om context te geven aan deze complexe kwestie.

Boa constrictor. Foto: Diego Marquez

Invasieve uitheemse soorten zijn planten en dieren die door menselijke activiteit – opzettelijk of per ongeluk – zijn geïntroduceerd in een natuurlijke omgeving buiten hun oorspronkelijke verspreidingsgebied. Invasieve soorten kunnen ernstige ecologische, economische en sociale gevolgen hebben voor hun nieuwe gebieden. Vanuit milieuoogpunt kunnen invasieve soorten bepalend zijn voor de lokale flora en fauna door op inheemse soorten te jagen, inheemse soorten te overtreffen voor voedsel of andere hulpbronnen, ziekten te veroorzaken of te dragen en te voorkomen dat inheemse soorten zich voortplanten. Hierdoor kunnen ze ook negatieve economische gevolgen hebben voor de sectoren landbouw, toerisme, visserij en industrie. Invasieve soorten kunnen ook nieuwe ziekteverwekkers met zich meebrengen die een maatschappelijke impact kunnen hebben door mensen ziek te maken of tot uitbraken te leiden die het reizen naar deze gebieden kunnen beïnvloeden. De meest recente voorbeelden zijn Chikungunya-, Zika- en West-Nijlvirussen, allemaal geïntroduceerd door exotische invasieve muggen.

Veel wetenschappelijke studies hebben aangetoond dat invasieve uitheemse soorten wereldwijd een van de belangrijkste oorzaken zijn van het verlies aan biodiversiteit en dat ecosystemen op eilanden bijzonder kwetsbaar zijn. Dit komt door de kleine omvang van de eilanden (met kleine plant- en dierpopulaties), unieke soorten, relatief grote grenzen die moeilijk te controleren zijn en een kleine menselijke populatie die niet over de nodige capaciteit en middelen beschikt.

Nederlands Caribisch gebied

Een rapport van Wageningen University and Research schat dat er alleen al in Caribisch Nederland meer dan 210 invasieve uitheemse soorten zijn. Deze omvatten 27 geïntroduceerde mariene soorten, 65 geïntroduceerde terrestrische planten, 72 geïntroduceerde land- en zoetwaterdieren en 47 geïntroduceerde plagen en ziekten in de landbouw en de lijst wordt elk jaar langer.

Coralita. Foto: Marjolijn Lopes Cardozo

Sommige invasieve uitheemse soorten zijn een veelvoorkomend probleem voor alle zes de eilanden, waaronder ratten die lokale vogelpopulaties verwoesten, of koraalduivels, die zich snel verspreiden en veel lokale rifvissen consumeren. Hieronder vallen ook invasieve wilde grazers, zoals geiten, die lokale vegetatie kunnen vernietigen en bijdragen aan woestijnvorming en verlies aan biodiversiteit.

Daarnaast hebben veel eilanden hun eigen specifieke problematiek, zoals de boa constrictors op Aruba of de groene meerkatten, een apensoort, op Sint Maarten. Sommige van deze invasieve soorten werden als huisdier naar de eilanden gebracht, maar werden in het wild vrijgelaten toen de eigenaar niet langer voor ze kon zorgen.

Beheer van invasieve soorten

Koraalduivel. Foto: Rudy van Gelderen

De introductie van invasieve soorten moet in de eerste plaats worden vermeden. Dit omvat het volgen van de lokale import- en exportwetten, effectieve grenscontroles en regelmatige controles. Verder is het van belang dat er een betere samenwerking komt tussen de parken en de Douane, bijvoorbeeld bij het trainen van douanebeambten in CITES en detectie van invasieve soorten. Zelfs de beste preventie kan echter niet alle invasieve soorten stoppen. Als een soort eenmaal is geïntroduceerd, kunnen de eilanden het probleem nog steeds onder controle krijgen door vroege detectie en snelle beoordeling en reactie. Helaas zijn de beheersmethoden voor het omgaan met invasieve soorten vaak niet optimaal. Beslissingen moeten worden genomen of volledige uitroeiing nodig is of dat toezicht houden en beperking van de verspreiding (mitigatie) de beste of enige optie is. Uitroeiing is een complexe taak en nooit de geprefereerde beheersmethode, maar soms is het de enige keuze. Niets doen zou een wreder lot zijn voor de eilanden, aangezien deze invasieve uitheemse soorten snel een negatieve invloed kunnen hebben op de biodiversiteit, de menselijke gezondheid en/of de economie van de eilanden.

Zie voor meer informatie het Wageningen University Report on Alien Invasive Species. Houd ons in de gaten voor de vervolgartikelen waarin we op elk eiland dieper ingaan op deze problemen.

DCNA

De DCNA ondersteunt wetenschapscommunicatie en outreach in de Nederlandse Caribische regio door natuurgerelateerde wetenschappelijke informatie breder beschikbaar te maken via onder meer de Dutch Caribbean Biodiversity Database, DCNA’s nieuwsplatform BioNews en via de pers. Dit artikel bevat de resultaten van verschillende wetenschappelijke onderzoeken, maar de onderzoeken zelf zijn geen DCNA-onderzoeken. Aan de inhoud kunnen geen rechten worden ontleend. DCNA is niet aansprakelijk voor de inhoud en de indirecte gevolgen die voortvloeien uit het publiceren van dit artikel

Published on BioNews 62

Research conducted by the Saba Bank Management Unit and Wageningen University and Research documented the third incidence of rapid lionfish population decline within the Western Atlantic since their introduction over 30 years ago.  This local population crash could indicate that lionfish are reaching the final stage of their invasion for this area.

Lionfish. Photo credit: Rudy van Gelderen

Lionfish, a venomous fish native to the Indo-pacific, were first introduced in the Western Atlantic more than 30 years ago.  Since then, they’ve been steadily spreading throughout the Caribbean, now reaching as far south as Brazil. Although populations seemed to be expanding rapidly, several locations have actually started to see a “leveling-off” of numbers, leaving many experts to believe the Caribbean may start to see more stable or even decreasing lionfish populations moving forward.

Boom-Bust

A recent survey recorded lionfish captured in lobster and redfish (snapper) fishery traps within the Saba Bank.  Since 2010, Saba Bank has seen a rapid rise in lionfish numbers and then a subsequent population crash since 2020.  This represents the third case of boom-bust events for lionfish populations within the tropical Western Atlantic.  The first event was documented in the Bahamas in 2012, and the second event, which was associated with a high incident of skin lesions, was observed in the Gulf of Mexico in 2020.

Lobster trap. Photo credit: Hans Leijnse

Interestingly, none of the lionfish caught within the Saba Bank showed any signs of skin lesions, leaving experts uncertain to the cause of the sudden population dip. Overall, long term monitoring data shows that the lionfish caught in traps peaked between 2012 and 2015 and then steadily declined before reaching its lowest values in 2020.  Although the lionfish invasion is one of the most widely studied marine fish invasions, there is still very little known about the factors controlling these populations.  Perhaps the rapid decrease in populations within the Gulf of Mexico resulted in lower overall larval recruitment for the Caribbean. If this is the case, researchers expect to see lower lionfish populations in other areas of the Caribbean as well.

Final Stage

There are 27 exotic marine species recorded throughout the Dutch Caribbean. Research, such as this, gives local governments and park management organizations a better understanding of the fragility of local reefs. It would appear that lionfish have now reached the final stage of their invasion, firmly established on the reef with population numbers beginning to stabilize. Hopefully, local predators will soon develop resistance to the lionfish venom, allowing these fish to become integrated into the local food web.

You can learn more by finding the full report on the Dutch Caribbean Biodiversity Database.

Published in BioNews 59

New Red-billed Tropicbird data suggested declining nest survival rates may be more related to parental behavior than previously thought. A researcher from Utrecht University, along with STENAPA and CNSI staff analyzed nest characteristics, trap camera photos and historical data to better understand the driving factors to declining nest survival rates.

Seabird populations are facing unprecedented levels of threats which has resulted in nearly 70% loss of monitored seabird populations over the past fifty years.  This is faster than any other group of birds worldwide and can be linked to overfishing, habitat destruction, invasive species, increased storm events and changes in food availability.

Red-billed Tropicbird and chick. Photo credit: Michiel Boeken

Pilot Hill

The Red-billed Tropicbird are an iconic species for the northern Dutch Caribbean islands.  In fact, a small but globally significant colony of breeding pairs nests within the Boven Important Bird Areas of Sint Eustatius.  Unfortunately, this area has been experiencing high rates of nest failure over the past decade. New research, conducted by Utrecht University student Hailley Danielson-Owczynsky, analyzed a combination of previously collected information with new monitoring data from the Pilot Hill nesting area in an attempt to better understand what is causing these low success rates.

Nest Monitoring

Previously, high predation by cats, rats and crabs were blamed for declining egg survival rates.  This was partially linked to the success of predator control projects on Saba, where nest survival of one site was improved from 0 to 40% after two-seasons of cat removal. Additionally, when reviewing the 1.6 million photos taken by nest cameras between 2017 and 2022, 80.5% of monitored nests showed predator presence, leading managers to blame predators for declining numbers. Further analysis conducted by Danielson-Owczynsky found that before being consumed by predators, many of the eggs had already been left unattended by parents for a prolonged period of time.  This same study found that predators were much less likely to visit a nest when a parent was nearby. Therefore, egg failure is more likely attributed to parent behavior prior to its predation.  It is important to note that invasive predators are still a concern, these results merely give an additional factor for conservation managers to consider.

Difficult foraging conditions for Tropicbird parents could lead to decreased nest attendance.  Red-billed Tropicbird’s diet is comprised primarily of flying-fish; however, overfishing has led to a decrease in overall fish populations requiring parents to forge over greater distances for longer periods of time.

Red-billed tropicbird. Photo source: Christian König

Implications

Pelagic seabirds, such as the Red-billed Tropicbird possess many unique traits, such as long lifespans, slow development and low reproductive rates, often attributed to their limited and sporadic food supply.  Given their long-life spans and the fact that they forage across wide ranges, these birds have been used as indicators for overall marine ecosystem health.  Therefore, the rapid decline in local populations gives key insight and rising concern for overall marine environmental conditions.  Understanding the magnitude of threats facing these and other related species will be key in safeguarding a strong and resilient marine environment moving forward.

Report your sightings

Species reports by local communities and tourists are invaluable for nature conservation efforts to help increase public awareness and overall species protection.

You can report your Red-billed Tropicbird sightings and photos on the website www.Observation.org or download the free apps (iPhone (iObs) & Android (ObsMapp)). You can also send your information to research@DCNAnature.org for support. An automatic species recognition tool is in development, so stay tuned for updates.

To learn more, you can find the full report by using the link below.

More info in the Dutch Caribbean Biodiversity Database

Published in BioNews 56.

New research from Wageningen University, University of Amsterdam and Florida International University highlighted the role herbivorous fish species plays in staving off nonnative seagrass invasions.  A healthy and diverse fish population can provide top-down control by grazing on invasive seagrass species, minimizing its overall invasion.

Invasive species can pose a direct threat to native species through competition and hybridization. Species which evolved to reproduce and spread rapidly generally have a greater chance at survival, and when introduced to a new environment, can out compete slower growing native species. This is certainly the case for Halophila stipulacea, a seagrass native to the Red Sea, Persian Gulf and Indian Ocean which has been rapidly gaining habitat within the Caribbean since its first reported sighting in 2002. This species is quickly outpacing native Thalassia testudinum (turtle grass) and Syringodium filiforme (manatee grass), both of which provide critical habitat, coastal protection and foraging grounds. 

Mixed area of Halophila stipulacea (shorter blades) and Thalassia testudinum (longer blades). Photo Credit: Fee Smulders

The Study

A new study by Wageningen University and Research, the University of Amsterdam and Florida International University worked to improve overall understanding of the controlling factors in the spread of invasive seagrasses.  Researchers investigated the influences of local nutrient enrichment (nitrogen and phosphorus) as well as the impact of large herbivorous fish on the growth and expansion rates of Halophila stipulacea. The study took place between 2018 and 2019 within two seagrass meadows, Lac Bay on Bonaire and Barcadera on Aruba.

Seagrass Meadow. Photo Credit: Fee Smulders

The Results

At both sites, nutrients were added to selected seagrass plots by using slow-release fertilizer. Interestingly, only on Bonaire did these excess nutrients actually result in a reduction of H. stipulacea’s expansion into the turtle grass meadows, while native seagrass was unaffected.  This is believed to be because on Bonaire, herbivore fish abundance is 7 times greater and diversity is 4.5 times higher than on Aruba, therefore excess nutrients likely enticed more fish to graze therefore limiting the spread of the invasive seagrass.  Native seagrass is more adapted to high grazing pressures, during this study grazing pressure increased after nutrient enrichment but only the invasive species showed lower expansion rates.  In fact, the exclusion of large herbivorous fish (like parrotfish) doubled the invasive expansion rates within sandy patches on Bonaire, further strengthening this theory.

Top-Down Approach

This study highlights the importance of holistic approaches to ecosystem management.  Healthy and diverse fish communities can provide top-down control to invasive species expansion Increasing grazing pressures can help reduce the competitive advantage of fast-growing species, slowing down invasion of non-native species. The key to seagrass restoration and conservation could lie in protecting the biodiversity of these fragile areas.

To learn more, please find the full report on the Dutch Caribbean Biodiversity Database using the button below.

https://www.dcbd.nl/document/fish-grazing-enhanced-nutrient-enrichment-m...

Article published in BioNews 49

Coralita is an invasive plant species, rapidly spreading across St. Eustatius.  A recently published report highlighted the ability to use satellite imagery to systematically map Coralita’s distribution over the island.  The approach could provide key insights into how habitat and vegetation are changing over time to aid in conservationists’ efforts to minimize the negative effects of Coralita and similar invasive species.

Coralita overgrowth (Source: Achsah Mitchell)

Coralita is a fast-growing, climbing vine with beautiful pink or white flowers. Originally from Mexico, Antigonon leptopus started out as a popular garden plant, but has expanded its territory and is now aggressively invading natural areas. Its fast-growing nature means it can outcompete most native species for terrain, quickly making it the dominant species, and reducing overall diversity. This is especially the case on St. Eustatius, where ground surveys indicate the plant already appears on 15-33% of the island.

Mapping Techniques

One of the biggest issues in controlling invasive species is accurately accounting for its presence, particularly if data needs to be collected over a wide area. This is where satellite imagery can help by providing an affordable, high spatial resolution option. A new collaborative study from the Utrecht University, University of Zurich, Wageningen University, and the Technical University of Braunschweig provided key insight by using such satellite imagery to identify Coralita. The method is successful, as areas dominated by Coralita emit a relatively distinct electromagnetic signal that can be detected by satellites. Once the distribution of Coralita has been mapped using this technique, it is possible to identify the environmental conditions associated with Coralita’s presence. This approach provides a relatively low-cost solution that is powerful, accurate and repeatable; key in identifying and monitoring its spread in the future.

“In creating this map,” said Elizabeth Haber, first author of this study, “it was my hope to produce something that could be useful for those who are caring for and protecting the incredibly special nature on Statia.”

Results

Using this method, researchers sampled 162 locations across St. Eustatius and estimated that Coralita was the dominant canopy cover (>50%) on over 3% of the island (64 ha). Perhaps more importantly, this map also showed that Coralita was not randomly distributed but generally found, for example, in areas of water accumulation, near roads or near drainage channels. Furthermore, Coralita was often found in grasslands and areas of development and is relatively rare in natural forests, highlighting how human disturbances can promote the spread of Coralita. It is important to note that data filtering and physical limitations of using satellite imagery means that Coralita growing under trees or shrubs or in smaller patches is likely underrepresented in this study.

Map of the distribution of Coralita on St. Eustatius (Haber et al., 2021)

Conservation Implications

Even with the physical limitations, the fact that this study is cost effective and repeatable means that consistent comparisons of Coralita’s distribution can be made over time. These comparisons are vital in understanding how populations and habitats are shifting, granting conservationists a fantastic tool in forecasting the spread of invasive species. Arguably the greatest asset of the Caribbean is its vast biodiversity. Already threats of climate change, habitat loss, invasive species and urban development are upsetting this fragile balance. St. Eustatius, although small, is home to several endemic plant species, two of which are the Statia morning glory and Statia milkweed, along with the critically endangered Lesser Antillean Iguana which could all be threatened by the habitat alterations of Coralita growth.

To read more, please find the full report on the Dutch Caribbean Biodiversity Database using the link below.

https://www.dcbd.nl/document/high-spatial-resolution-mapping-identifies-...

Article published in BioNews 48

Wageningen University and Research and the University of Applied Sciences Van Hall Larenstein researchers have recently identified two new nonnative reptiles on Saba. The smooth-scaled tegulet and Brahminy blindsnake are both able to reproduce asexually, so their populations could expand quickly. Understanding the impact of their introduction will be key in protecting the biodiversity of Saba.

The island of Saba is home to five native species of reptiles, one snake (red-bellied racer) and four lizards (Saban anole, Saban black iguana, Saban least gecko, and the turnip-tailed gecko). Recently, two additional non-native species were identified, the smooth-scaled tegulet (Gymnophthalmus underwoodi) and Brahminy blindsnake (Indotyphlops braminus).  Exactly how these two species arrived on Saba is still unknown, however its likely they hitched a ride over from St. Maarten, since almost everything that arrives on Saba must go through St. Maarten first.

Smooth-Scaled Tegulet 

Photo credit: Thijs van den Burg

The smooth-scaled tegulet (Gymnophthalmus underwoodi) has been identified across the island and was first spotted in May 2020. Researchers from Wageningen University and Research and the University of Applied Sciences Van Hall Larenstein were able to capture five individuals from a variety of different life stages. These lizards have been observed on over 50% of the island, in habits which vary between gardens, dry forest and rocky slopes.  The wide spread dispersal of this species suggests it’s been on the island for a while.  These populations are expected to continue to increase as these lizards are very quick to reproduce.

Brahminy Blindsnake

More recently, a local resident has encountered at least two different Brahminy blindsnakes (Indotyphlops braminus) in her garden along the Windward side between May and July of 2021. Although no other observations have been made, this species is widely introduced on neighboring islands, so it’s presence on Saba is not surprising. Although there are currently no known documented native blindsnakes on Saba, it is possible for these species to go undetected, as was recently noticed on St. Eustatius with the discovery of the native blindsnake (geomotus) in 2020.

Island Impact

There had previously been two known nonnative amphibians and reptiles on Saba, so the addition of these two now doubles that list. Furthermore, currently 40% of all terrestrial reptiles and amphibians on Saba are nonnative species. Although direct competition between these two new species and native species is not expected, invasive species are considered among the top drivers of biodiversity loss and ecosystem change around the world. Understanding and addressing this issue will be key in preserving the unique biodiversity on Saba.

Report your sightings

If you happen to spot either one of these new reptiles while on Saba, you can report it on https://dutchcaribbean.observation.org. This is a free website and app which allows local citizens to report sightings of important plants and animals. These tools are available in over 40 languages and can be used by biologists and citizens and tourists alike. Species reports by local communities are invaluable for nature conservation efforts to help increase public awareness and overall species protection.

Read the full report entitled “Establishment of two nonnative parthenogenetic reptiles on Saba, Dutch  Caribbean: Gymnophthalmus underwoodi and Indotyphlops braminus” using the link below

https://www.dcbd.nl/document/establishment-two-nonnative-parthenogenetic...

Article published in BioNews 48

A new study by Wageningen Marine Research, St. Eustatius National Parks Foundation and Caribbean Netherlands Science Institute highlights the need for a continuation of the rapid response removal campaign to control the invasive green iguana population. Through displacement and hybridization, the green iguana threatens to wipe out the endemic Lesser Antillean Iguanas of St. Eustatius.  

The Lesser Antillean Iguana, , is an IUCN Red List Critically Endangered species, which has disappeared from most of its habitat, including St. Maarten. This species is endemic to St. Eustatius and is the largest native vertebrate on the island. Its main threat comes from displacement by and hybridization with the invasive species green iguana, Iguana iguana.  In fact, St. Eustatius is one of the last three major islands where this species was (until recently) still free from hybridization.  Biological invasions can create several issues which threaten biodiversity, the environment, agriculture, livelihoods, health, and local culture. 

Photo credit: Philippa King

Rapid Response 

In February of 2016, an adult female green iguana was caught in Princess Estates on St. Eustatius. Green iguanas and their hybrid offspring can be most easily distinguished from the native iguana based on their banded tail and the large scale on their cheek (see figure).  It was unknown how long this individual had been on the island and if she had already laid eggs, potentially introducing additional iguanas to the area. In response, the Ministry of Economic Affairs agreed to fund a limited Rapid Response Removal Campaign (RC) on the island.  

During the RC, three visual surveys were conducted throughout key risk areas.  In total, 409.5 hours were spent over 40 days, resulting in a single detection.  This low detection rate suggested that the RC occurred early in the invasion process and highlighted the need to stay vigilant. Luckily, local publicity via newspaper and radio programs led to a number of publicly reported sightings. Among these reports and opportunistic encounters by park management staff, an additional five green iguanas and their hybrids were captured before the campaign ended in January 2017, and an addition eight have been captures since. 

Research 

As part of the RC, a study was conducted by Wageningen Marine Research, St. Eustatius National Parks Foundation and Caribbean Netherlands Science Institute (CNSI) to learn more about this invasion. In addition to tracking population data during the surveys, they also worked to identify introduction events, points of entry and likely points of origin.  The harbor of St. Maarten was identified as the source of the most recent 2020 introductions, as this harbor serves as a major inter-island transshipment hub within the Lesser Antilles.  This recent study highlights four apparently distinct green iguana introduction events between 2013 and 2020, one of which was likely intentional and three of which were from incidental stowaways arriving on container ships. 

Photo credit: Dolfi Debrot

Moving Forward 

Luckily even four years after the RC the numbers of green iguanas and their hybrids appears to be limited.  This gives researchers hope that it is not too late to stop the invasion before it heavily interbreeds with and thus effectively wipes out the island’s critically endangered Lesser Antillean iguana.  Research alone will not be enough to control this issue. Investment both in finances and in capacity necessary to prevent introduction and spread of these iguanas will be required.  RCs are significantly lower in cost than full invasive species removal projects, so the early detection and active management provides a unique opportunity for the island to eradicate this threat while still possible and affordable.   

Report your sightings 

If you happen to spot a green iguana while on St. Eustatius, you can report it to the local park authority STENAPA (+599 318 2884) or CNSI (+599 318 2040) as well as on https://dutchcaribbean.observation.org. This is a free website and app which allows local citizens to report sightings of important plants and animals. These tools are available in over 40 languages and can be used by biologists and citizens and tourists alike. Species reports by local communities are invaluable for nature conservation efforts to help increase public awareness and overall species protection.  

Read the full report on the Case Study of a Rapid Response Removal Campaign for St. Eustatius on the Dutch Caribbean Biodiversity Database. 

https://www.dcbd.nl/document/st-eustatius-invasive-alien-green-iguana-ca...

Article published in BioNews 47

Seagrasses are marine flowering plants that can reproduce both sexually (through flowering and subsequent seed formation) and asexually (through clonal growth). Sexual reproduction increases genetic diversity, resilience and dispersal success of seagrasses. A recent study discovered that the first report of sexual reproduction of a successful invasive seagrass was incorrect, and therefore released a new field guide to improve future determination.

Photo credit: Henkjan Kievit

The invasive seagrass Halophila stipulacea originating from the Red Sea and Western Indo-Pacific, has been successfully invading the Mediterranean Sea since 1894 and the Caribbean Sea since 2002. It was shown to outcompete native seagrass species and affect local ecosystem functioning.

In this new paper, WUR PhD candidate Fee Smulders found that so far, only male flowers have been described of the successful invasive seagrass species H. stipulacea in the Caribbean Sea. Female flowers and fruits have not been reported. This means that fragmentation and fast clonal growth may be the only factors explaining its current success, without genetic adaptation capacity. This needs to be taken into account in further studies studying H. stipulacea expansion.

In-depth monitoring of reproductive structures in invaded seagrass meadows, both in the Mediterranean and the Caribbean Sea is important to assess further invasion potential.

Because the fruits and flowers of  H. stipulacea have been misidentified in the past, we have developed a field guide with a dichotomous key, to take into the field and easily identify the various structures by eye. We call upon (citizen) scientists to keep an eye out underwater when they are in the Caribbean, to be able to predict future invasion success of this species.

– Fee Smulders

The field guide can be found in the supplementary material of the paper, and reports can be made in the online global database www.seagrassspotter.org.

Or check the field guide directly in the DCBD:

https://www.dcbd.nl/sites/default/files/documents/FIeldguide_Hstipulacea...

Article published in BioNews 44

Although the La Soufrière volcano on St. Vincent saw its latest explosive eruption over a week ago, and the threat level has decreased to Orange, caution is still necessary. Uncertainty for the St. Vincent population therefore remains, as thousands of people had to evacuate their villages and stay elsewhere on the island. Further uncertainty and hardship are caused by the eruptions’ effect on local food and water supplies. Gratefully, in a region where catastrophic weather events are not uncommon, regional organizations and nations quickly mobilized relief efforts to aid Vincentians.

In a letter to the journal Science, biologists from 12 Caribbean organizations, including STENAPA on St. Eustatius, highlight the need to prioritize both humanitarian aid and biosecurity when responding to natural disasters. The authors note how bypassing biosecurity could cause additional long-term harm to both the local ecosystems and the human population. Erik Boman, Director of STENAPA, pointed out that this threat is especially grave on islands. The letter also “urge governments and aiding parties responding to catastrophes to recognize and mitigate potential risks”.

Several of the authors have been involved in invasive species control on Dominica, where during the humanitarian aid campaign that followed the passing of Hurricane Maria in 2017, several non-native species were introduced. The local NGO WildDominique is currently working hard to remove both amphibian and reptile species that established populations there. The green iguana is also a biosecurity issue for local iguana, Iguana delicatissima on St. Eustatius. Although thousands of dollars have already been invested in these eradication efforts, a complete assessment of all species that arrived with the aid supplies still awaits. In the aftermath of natural disasters, when the natural environment is heavily affected and recovering, arriving non-native species will have the opportunity to spread out further and would form a major threat to the isolated and native flora and fauna on the island.

The letter further addresses the need for wide and multi-organizational collaborations to prepare for future large-scale humanitarian aid campaigns, of which each will be unique.

Link to Letter at Science: https://science.sciencemag.org/content/372/6542/581

Article published in BioNews 43

Abstract

The Invasive Alien Green Iguana (IAGI), Iguana iguana, has spread worldwide via the pet trade, as stowaways and via other means and has become a pest species of global concern. It also represents a major threat to the endemic Lesser Antillean Iguana, Iguana delicatissima, on St. Eustatius. Following the capture of an adult female IAGI on St. Eustatius in early 2016, we conducted a Rapid Response Removal Campaign (RC) from April 2016 to January 2017. Three sets of directed visual surveys totaling 409.5 observer hours and covering a combined trajectory of 114.2 km realized only a single detection of a hybrid that was later removed. During the remainder of the campaign period, an additional four IAGI hybrids were opportunistically detected and removed thanks to park staff or community involvement. Since the end of the campaign, eight additional detections and removals have been realized, three of which were IAGIs caught while offloading freight in the harbour and five of which were hybrids caught in surrounding suburban areas. We suggest that at least four distinct IAGI introductions to St. Eustatius occurred between 2013 and 2020. Our results show the value of motivating and mobilizing stakeholders and the public at an early stage of an invasion. Since the program’s initiation, eight of the 13 iguanas detected for culling were thanks to public and key stakeholder support and involvement. Four years after our campaign, the number of IAGIs and their hybrids still appear to be limited and concentrated in and around inhabited areas. Additional removal campaigns should be initiated as soon as possible, firmly based in public outreach, motivation and engagement. New legislation is needed to prohibit the importation, possession and harbouring of IAGIs or hybrids and to provide a framework for long-term structural funding required for effective control and removal. Routine fumigation and rigorous inspection of arriving cargo to eliminate the risk of stowaway IAGIs are also recommended. Culling of IAGIs is recommended for the port of St. Maarten, which serves as a major point of dispersal of IAGIs to St. Eustatius and likely also other islands in the region.