The Arabian Sea: Physical environment, zooplankton and myctophid abundance

The Arabian Sea is one of the most productive regions of the world oceans. This productivity mainly results from coastal and open ocean upwelling in s ummer and cooling effects during winter. Earlier and more recent studies sh owed that there are considerable spatial and temporal variations in the are a in primary productivity. Nonetheless, contrary to earlier thinking, it wo uld seem that the mesozooplankton abundance in the Arabian Sea is fairly hi gh in the mixed layer all through the year. This paradox of the Arabian Sea could be partly resolved by explaining the microbial loop and a fresh set of data is presented here in support. This is because most of the herbivoro us forms are either small filter feeders like copepods or larger mucous fil ter feeders like tunicates which are able to feed on very small particles. It would seem that the Arabian Sea sustains a large biomass of mesopelagic fishes (about 100 million tonnes), mainly myctophids. They mostly live in t he core of oxygen minimum layer and ascend to the surface layers during nig ht to feed on the abundant zooplankton.