BIOT Science Expedition 2014 - Pete Carr BIOT Science Expedition 2014 Initial Report Terrestrial Invasive Species

Monitoring the Spread of Terrestrial Invasive Species

Peter Carr, Permian Global

From a terrestrial perspective, along with the decline of certain breeding seabirds, the spread of invasive species throughout the Chagos Archipelago is of gravest concern and requires urgent practical conservation management and scientific base-lining.  Invasive species in the Chagos that require management now include native as well as introduced species.  The species of main concern are native Coconut Cocus nucifera where it has been planted as a crop in areas that were cleared of native forest and where it is detrimentally encroaching on other habitats, e.g. mangroves; native Hawaiian Dodder Cassytha filiformis where it is growing over and destroying Sooty Tern fairs (breeding sites); introduced Rat-tail Stachytarpheta sp. where it is growing over and rendering useless Sooty Tern fairs; Native Mulberry Pipturus argenteus where it is encroaching on other habitat, especially on the Bois Mangues where it is choking out new growth Pisonia grandis; introduced White Trumpet Tree Tabebuia pallida where it is choking out other species, especially on North Brother and Diego Garcia and, introduced Longhorn Crazy Ants Paratrechina longicornis to confirm they have not spread to the outer islands from Diego Garcia.

While conducting the coconut crab surveys on Vache Marine, Middle Brother and Eagle Island, the introduced house gecko, Hemidactylus frenatus, was recorded on all three islands for the first time. The ecological impact of this species on these islands is unknown. On Eagle Island, a quick site assessment was completed for one of the two mangrove forests on Chagos. While there was evidence of choking of the mangroves by coconut and other invasive species, there was also signs of mangrove recruitment which was encouraging.  

The species above require management now before their negative impact is irreversible; this is especially relevant on the rat-free Important Bird Area (and potentially Important Plant Area) islands.  This management requires funding, prioritisation, scientific base-lining and justification immediately.  Similar to the demise of the breeding Common Noddy and possibly Sooty Tern, the management of invasive species needs to be the UK FCO top priority before the loss of biodiversity through their negative impact is irretrievable.

Figure 27: Exotic species, the house gecko Hemidactylus frenatus, documented on Middle Brother