Myxomycete Biodiversity on Remote Islands of the Eastern Indian Ocean: A Comparison Between the Cocos (Keeling) and Christmas Islands

Myxomycetes are a widespread group of organisms but, given their inconspicuousness and the specialist knowledge needed to culture and identify them, there are many regions of the world where they have never been studied. The Cocos (Keeling) Islands, an Australian Territory in the Indian Ocean, are one such location. We collected substrates from islands in the Cocos archipelago and cultured 37 morphospecies of myxomycete representing 15 genera. Five substrate types were sampled; the greatest species richness was associated with aerial litter, aerial twigs, and ground litter. Eight habitat types were sampled, of which coconut forest had the greatest species richness. The main (southern) atoll of the Cocos group is dominated by (largely) anthropogenic coconut (Cocos nucifera) forest. Here, there was no relationship between myxomycete community structure and habitat, but substrate type significantly influenced community structure. In contrast, on the northern atoll of Pulu Keeling, which retains a more natural vegetation structure including large stands of Pisonia grandis forest absent from the southern atoll, there was a strong relationship between the myxomycete community and habitat type but not substrate. We also compared myxomycete diversity from the Cocos Islands with diversity from a similar study of myxomycete morphospecies recorded from Christmas Island. Although about 1000 km apart, these are the closest terrestrial habitats in a vast expanse of the eastern Indian Ocean. These islands had very different myxomycete communities and shared relatively few species in common, likely a result of their very different histories, geographies, and contrasting habitat types and substrates available to myxomycetes.