On the sea’s Indian coastline, a way of life is in trouble. The fishing community is drowning, Naresh M. Gohil, a resident of Chimbai, said on a winter morning in 2015, when I visited the settlement in the state of Maharashtra. I am the last generation of fishermen in my family, he said. In Maharashtra, fish production from the state has fallen since 2004. More than 90% of the yield in 2019 was captured by large mechanized boats. In a survey among fishers in Maharashtra and Tamil Nadu states in 2011, an overwhelming majority said their catch had shrunk, with Maharashtra fishers pegging this decline to around the turn of the century. The fishers I spoke to in Chimbai agreed with the surveyed fishers that industrial fishing was a big reason for their withering fishing fortunes. Very few fishers here see climate change as a major factor, a survey by a local NGO revealed. Seeking richer answers to poorer seas But declines in fish catches call for richer explanations, the emerging research shows. Industrial pollution and domestic sewage discharged into the sea by Mumbai is a leading cause for dwindling local fisheries, according to India’s Central Marine Fisheries Research Institute. Coastal megacities in India generate more than 6 billion liters (1.6 billion gallons) of wastewater daily. Overall, the country can treat only about a third of its sewage. That means billions of liters of untreated sewage are being flushed into the Arabian Sea every year. The water body is believed to host the world’s largest dead zone, where the oxygen concentration is so low it is not conducive to life. Its waters are naturally sluggish, preventing oxygen mixing. Sewage and agricultural runoff dumped in the sea soaks up oxygen as it decomposes, creating zones where marine species struggle to survive. Except, it seems, for N. scintillans. It doesn’t just fare better in oxygen-poor waters; the dense colonies it forms could be contributing to oxygen depletion. The outbreaks are expansive; in satellite imagery, they appear like spirals of oily green paint stretched across the entire northern Arabian Sea. When the N. scintillans cells die and sink into the ocean depths, their decay could be sucking more oxygen from deep waters that are already hypoxic. A more stratified water column, skewed nutrient availability and oxygen loss all point to profound changes in the Arabian Sea. Scientists like Gomes and Goes see the sea sparkle blooms as not just a symptom of the changing environmental conditions, but as a trigger for disruptions yet to come. Despite all the changes that Chimbai residents are witnessing, the sea remains a reassuring presence. They have a saying: The sea keeps no secrets, it keeps nothing in its stomach. It reflects a belief in the perpetual pristineness of the vast blue. No matter what humans throw at the sea, it remains unscathed. That worldview could be upended at a time when human activities are transforming the seas in unprecedented ways.