Keywords: endemic species, Caribbean, Saba, Saint Eustatius, Saint Marten, Saba Bank
Endemic species and subspecies (or “taxa” for short) having restricted geographic distributions are an extremely important feature of biodiversity and a key criterion to conservation valuation and nature management goal-setting. Saba, St. Eustatius and St. Martin (the Dutch SSS islands) form part of the Caribbean biodiversity hotspot region but up to now no systematic assessment was available on the occurrence of endemic animals and plants on these islands and in the surrounding marine areas (incl. Saba Bank). We here provide such a preliminary assessment as an aid to conservation and nature management, and to help in prioritizing future research. Our assessment shows that the SSS islands and Saba Bank together possess 223 endemic animals and plants (32 subspecies, 191 species), of which 35 are endemic to the SSS islands or Saba Bank, 15 are endemic to the Northern Lesser Antilles (Virgin Islands southwards up to and including Montserrat, including St Kitts Bank and Anguilla Bank endemics), 110 to the Lesser Antilles (Virgin Islands southwards up to and including Grenada) and 58 to the joint Antilles (Lesser and Greater Antilles). Of the 35 island endemics, 8 are marine, 26 are terrestrial and 1 is from brackish water.
The breakdown of the 223 endemic species and subspecies according to larger taxonomic groupings is as follows: Worms (Polychaeta): 1; Spiders, scorpions and pseudoscorpions (Arachnida): 23; Copepods (Hexanauplia): 2; Beetles (Coleoptera): 33; Flies (Diptera): 4; True bugs (Hemiptera):3 ; Sawflies, wasps, bees, and ants (Hymenoptera): 3; Butterflies and moths (Lipidoptera): 12; Dragonflies and damselflies (Odonata): 1; Grasshoppers, locusts and crickets (Orthoptera): 22; Amphipods: 1; Crabs, lobsters and shrimps (Decapoda): 1; Isopoda: 1; Pycnogonida: 1; Bony fish (Actinopterygii): 4; Sharks and rays (Chondrichthyes): 1; Birds: 23; Amphibians: 1; Mammals (bats): 5; Reptiles: 16; Cnidarians: 5; Bivalves: 5; Gastropods: 28; Flatworms (Platyhelminthes) 1; Red Algae: 3; Spermatophyta (Vascular plants): 22.
The breakdown of the 35 taxa that are endemic to the SSS islands or Saba Bank is as follows: Polychaeta: 1; Arachnida: 4; Hexanauplia: 2; Coleoptera: 3; Diptera: 1; Hemiptera: 1; Orthoptera: 10; Bony fish: 2; Reptiles: 3; Bivalves: 1; Gastropods: 3; Red Algae 1; Vascular plants: 3.
The breakdown in numbers of island endemics for the SSS islands and Saba Bank is:
· St. Martin: 12 island endemics (10 animal species and 2 plant species)
· St. Eustatius: 10 island endemics: (8 animals species and 2 plant species)
· Saba: 10 island endemics: (10 animals species, 0 plant species).
· Saba Bank: 3 endemics (3 animal species, 0 plant species)
The number of endemics is probably larger than reported here. Very little marine taxonomic research has been conducted in the SSS islands and many species probably remain to be described. In the past decade many new and potentially endemic species (of algae, fish, corals, sponges, etc.) have been discovered, mainly on the Saba Bank. Furthermore, additional research on specific species groups (e.g. beetles) could result in the discovery of yet more new endemic species. The IUCN assesses the conservation status of plant and animal species worldwide. Most rare and endangered island endemics are not included in the assessments due to lack of information or perceived priority. Therefore, most IUCN-listed threatened species for the SSS islands are species with much wider distributions. Assessments are only available for 42 of the endemic (sub)species of the SSS islands. The only recent endemic ground-dwelling mammal, the Nevis rice rat, is extinct. The endemic bats and bird subspecies have wider dispersal capabilities and currently carry no IUCN threatened listing, eventhough several only survive in tiny, scattered and vulnerable populations. Only
the following six endemic terrestrial reptiles currently carry a IUCN threatened status:
· Critically Endangered: Lesser Antillean Iguana (Iguana delicatissima).
· Endangered: Anguilla Bank Racer (Alsophis rijgersmaei); Spondylurus powelli.
· Vulnerable: Saba Racer (Alsophis rufiventris) and Anguilla Bank Bush Anole (Anolis pogus).
· Near threatened: St. Christopher Ameiva (Pholidoscelis erythrocephalus).
Many of the 223 endemic taxa listed here are restricted to very small populations on one or only a few small islands. This makes them very vulnerable to extinction. Indeed, in the recent past, some species may already have become extinct (e.g. two endemic plants known only from St. Martin). Therefore, assessments of the conservation status of each of the identified endemic taxa are urgently needed for the SSS islands and Saba Bank. In addition, conservation strategies need to be developed to minimize extinction risk for the most endangered endemics.