Biogeography of Dinoflagellate Cysts in the Indian Ocean: Environmental Filtering and Dispersal Shape Basin‐Scale Diversity Patterns
Pranoy Paul, Jagadish S. PatilABSTRACT
Aim
To test how environmental filtering and dispersal jointly shape large‐scale biogeographic patterns of dinoflagellate cyst assemblages in pelagic ocean basins, while evaluating morphometric variability as environmental proxies.
Location
Pelagic regions of the Indian Ocean, encompassing the Arabian Sea, Bay of Bengal, Equatorial Indian Ocean, and South Tropical Indian Ocean (up to 30°S latitude).
Time Period
Recent (surface sediments) collected during research cruises in January–February 2020 and March–June 2021.
Major Taxa Studied
Organic‐walled dinoflagellate cysts (~48 species), including cosmopolitan taxa ( Operculodinium centrocarpum , Nematosphaeropsis labyrinthus ), and multiple harmful algal bloom (HAB) species.
Methods
Surface sediments (113–5396 m depth) were analysed for cyst assemblage composition, diversity metrics, morphometric variability, and dispersal pathways using statistical analyses and planktondrift simulations.
Results
Productive northern regions supported higher diversity and cyst abundance, whereas oligotrophic southern regions showed reduced assemblages, indicating that productivity‐driven environmental filtering and basin‐scale dispersal jointly structure assemblage composition. Twenty‐one taxa were cosmopolitan across multiple ocean basins, while 27 were endemic to northern regions. Morphometric variations in cyst process length and body size correlated with salinity and temperature gradients, supporting their proxy value. Dispersal modelling indicated lateral cyst transport over ~420–1570 km, highlighting potential long‐distance connectivity that influences sedimentary assemblages. These findings indicate scale‐dependent structuring of assemblages, with environmental filtering dominating in tropical pelagic systems while dispersal modifies regional composition.
Main Conclusions
Our results show that productivity, environmental filtering, and dispersal jointly structure dinoflagellate cyst biogeography at ocean‐basin scales, highlighting their utility as indicators of basin‐scale biogeographic patterns in pelagic systems.