Biogeographic Patterns in the Indian Ocean and their Drivers

Abstract

Marine biogeographic provinces based on species composition are taxon and method-dependant and cannot be extrapolated. Dispersal is not the first barrier to a region’s species composition in the neritic oceans. Environmental filtering does not universally dictate community composition. Using public species presence and oceanographic data, we create standardised biogeographic provinces for all data-rich faunal groups within the Indian Ocean. We find three provinces for several taxa: the Australian Bight, the Northern Indian Ocean, and the rest of the Indian Ocean. Next, we test if environmental filtering drives community composition within and across provinces. We find that environmental filtering poorly predicts community composition within the Indian Ocean. We also find that the former Tethys basin once forming a contiguous neritic region acts as a biogeographic axis within the Indian Ocean. Our results suggest that species composition in the Indian Ocean is based on past faunal patterns influenced by tectonic activity.

Plate tectonics regulates marine diversity patterns, but quantifications of the timescales involved are lacking. The former Tethys basin is an ideal system to attempt to quantify this. This is because it once formed a shallow marine basin stretching from today’s Mediterranean in the West to today’s Indo-Australian Archipelago (IAA) in the East and contained three different hotspots at different time periods within it arranged in a NW-SE direction. We create testable models of marine diversity using publicly available occurrence data incorporating hotspot location along with the oceanographic parameters dictating community composition for various present-day neritic faunal groups. We find that the present IAA hotspot regulates diversity patterns today for non-planktonic shallow marine groups, and has masked the effects of the hotspots preceding it. This allows us to place an upper bound on the timescales regulating marine diversity to when the demise of the Arabian hotspot preceding the current IAA hotspot occurred.