Veli–Akkulam Estuary Degradation

Why in News?

Recently, a University of Kerala study revealed severe ecological decline in the Veli–Akkulam estuary due to invasive species and environmental stressors.

• It is a shallow, bar-built, seasonally closed estuary connected periodically to the Lakshadweep Sea.
• Location – Northwest of Thiruvananthapuram, Kerala, along the southwest coast of India.
• The Arabian Sea lies to the west of the lake system.
• Structure – Separated from the sea by an elongated sandbar.
• Partially divided by an embankment (bund) into –
  • Veli Lake (west, near sea)
  • Akkulam Lake (east, inland)
• Both are connected by a narrow channel.
• Hydrology – Inflow – Precipitation is the main inflow.
• Akkulam receives water from Kannamoola stream, while Veli receives inflow from Kulathur stream and T.S. Canal.
• Outflow and Stagnation – Outflow is episodic due to sandbar closure, with the lake mouth opening only a few times annually, causing prolonged water stagnation.
• Connectivity – Connected to Kadinamkulam and Poonthura estuaries via T.S. Canal.  
• Concern – Sandbar-induced closure and water stagnation promote eutrophication, invasive species proliferation, and deterioration of water quality.
• Key Findings – Ecological Decline – Clear trajectory of ecological degradation over three decades.
• Ecosystem Shift – Transition from a moderately organised to an invasion-dominated ecosystem with invasive Species such as 
  • Exotic species – Mozambique tilapia (Oreochromis mossambicus), Nile tilapia (Oreochromis niloticus),
  • New exotic species – Amazon suckermouth catfish (Pterygoplichthys pardalis), North African catfish (Clarias gariepinus).
• Earlier invasion by water hyacinth.
• Food Web Alteration – Restructured trophic dynamics with weakened top-down control.
• It leads to a detritus-driven system with low energy transfer efficiency and loss of native species (e.g., Karimeen) with the rise of detritivores.
• Recommendations – Adaptive wetland management includes invasive species control, native species reintroduction, wastewater treatment, ecosystem restoration and long-term monitoring.

Reference

TH | Veli–Akkulam Estuary Degradation Study