Surge in the jellyfish population of a tropical monsoonal estuary: A boon or bane to its plankton community dynamics?

Recurrent jellyfish blooms and their impacts on ecosystem deliverables of coastal habitats have become a major ecological concern. In view of this, repercussions of a surge in the jellyfish population on the plankton community were studied in Cochin estuary (CE), the largest tropical estuary along the southwest coast of India. Evaluation of hydrographic attributes and plankton community of the CE during early and late pre-monsoon revealed a marked disparity in its hydrography which favoured an increase in jellyfish abundances during late pre-monsoon, eliciting distinct impacts on the plankton community. The escalation in the jellyfish abundance and their subsequent predation on the crustacean plankton released the phytoplankton community from the grazing pressure resulting in a trophic cascade in the planktonic food web. The indiscriminate feeding of jellyfishes on the ichthyoplankton, decapod larvae, and Copepoda, the primary diet component of forage fishes evoked a potent threat to the fishery potential of CE. [Display omitted] •Impact of a surge in jellyfish abundance on plankton community was studied.•Eutrophic nature of Cochin estuary (CE) influenced its biotic community structure.•Rise in jellyfish abundance led to a trophic cascade in the pelagic food web of CE.•Zooplankton abundance dropped whereas phytoplankton showed a peak in abundance.•Jellyfish predation on ichthyoplankton evoked a threat to the fishery yield of CE.