Species diversity of pelagic chaetognaths in the Indo-Pacific region

We analyzed the species composition of pelagic chaetognaths in the Indo-Pacific region as reported in published papers to demonstrate geographic variation in their species diversity and its relationships with environmental variables. The resulting latitudinal pattern in species richness (SR) was asymmetric to the equator, with a peak at 35A degrees N in the Kuroshio area and a gradual decrease to a minimum at similar to 40A degrees S. Shannon's diversity index (H') showed a similar pattern, except that it plateaued between 20A degrees N and 35A degrees S. Regression analyses and structural equation models (SEMs) showed that temperature was the most important explanatory variable, both for SR and H'. The SEM also demonstrated that chlorophyll a concentration and mixed-layer depth were the second most effective variables for SR and H', respectively. On the basis of these results, models were constructed to estimate geographical variation in SR and H'. The estimated SR was high in coastal waters in tropical to subtropical areas, while H' was high at midlatitudes in the open ocean. The present data highlight the importance of the coastal waters of Southeast Asia and the Indian Ocean, but also indicate that a gap still exists in this area, which necessitates further data mining as well as basic research.