Coccolithophore assemblages and a new species of Alisphaera from the Faafu Atoll, Maldives, Indian Ocean

Abstract

Coccolithophore assemblages were investigated from the Faafu Atoll in November 2018. The surface waters were sampled around the islands of Magoodhoo and Adanga, from the coast to the open water towards both the lagoon and the ocean, as well as waters up to 40 m depth at selected stations. Coccolithophores were scarce close to the coast (0.1–4 × 103 coccospheres/l), increased in abundance towards both the lagoon and the open ocean (20–44 × 103 coccospheres/l) and showed no clear depth trend. The assemblages were dominated by Gephyrocapsa oceanica with a large contribution by species that are typically reported from the mid- to lower-photic zone, i.e., primarily Oolithotus antillarum, followed by Calciosolenia spp., Michaelsarsia adriaticus, Calciopappus rigidus, Ophiaster spp. and Algirosphaera robusta. As for other tropical settings, Emiliania huxleyi made a minor contribution. Taxa that are common in the upper layers of oligotrophic stratified settings like Umbellosphaera spp., Discosphaera tubifera and Rhabdosphaera clavigera were scarce. Overall, such assemblages displayed the characteristics of neritic settings, with high trophic resources and elevated water turbidity, even though the measured chlorophyll-a concentration was low throughout the investigated area.