Why do thousands of seashells wash up on the shores of Karachi every monsoon?

Every year around June, Karachi’s beaches fill with people, not just people, but also seashells, hundreds of thousands of them, scattered along the coast in dense, noisy piles. The sight leaves citizens intrigued and many wondering if something is wrong. The same thing happened this June as well.

Over the past few days, there has been debate both online and offline about why this phenomenon occurs. Was it climate change or the spectacle of nature?

Science and fishermen tell a more nuanced story.

A prelude to the monsoon

The phenomenon is not new. TO Sunrise report on July 17, 2009, noted that large quantities of white and yellow seashells had appeared on Clifton Beach overnight. Other Sunrise reportdated May 21, 2016, reported that wave action dislodges shellfish, particularly Venus clams, known locally as “burgar,” from shallow subtidal habitats, carrying them to beaches where they die and leave behind empty shells.

The same event was also covered by The express PAkGazette on May 22, 2016. Both reports stated that the phenomenon is related to the arrival of the monsoon.

A Aaj News report Dated July 10, 2024, it also noted that marine experts continue to identify June and July as the recurring seasonal window for this phenomenon, although it added that rising pollution levels may be contributing to higher rates of marine mortality, leading to higher volumes of shells washed ashore in some years.

Majeed Motani, president of the Pakistan Fishermen’s Forum, who has decades of experience in fishing, confirmed this. The phenomenon was not new and was locally known as “aokar”, he said, and similar seashells can be seen along several coastal areas, including Ibrahim Hyderi and other beaches in Karachi.

“We have been witnessing this phenomenon for decades, particularly during June and July,” he said, explaining that water from the deeper parts of the sea rises to the surface and eventually pushes the shells toward the shore, where they are deposited along the coast.

what science says

Scientific research on the Arabian Sea provides a clearer explanation for why this happens. When the southwest monsoon arrives around June, strong winds push warm surface water away from the coast, carrying cold water from the depths of the ocean, a process known as upwelling.

TO study published in the Journal of Sea Research explains that this cold, deep water contains very little oxygen and, when it spreads across the seafloor, is fatal to bottom-dwelling creatures such as clams and other shellfish, which cannot move fast enough to escape. Their empty shells are washed onto the beaches by the powerful monsoon waves.

PHOTO: DAWN

a separate paper on the Arabian Sea shelf, published in Deep-Sea Research, found that cold, oxygen-depleted water begins to appear off Karachi as early as June and persists until November, precisely the months when citizens observe the highest concentrations of shells along the coast.

Other study stated that the monsoon season coincides with the period when the largest number of marine invertebrates are present in the coastal waters near Karachi. In short, shellfish populations peak near the coast just as the harshest ocean conditions arrive, which is why beaches receive so many shells.

The anomaly

But 2026 may be a different year in at least one respect. Motani told iVerify Pakistan that the number of seashells this year seems higher than usual.

Fatima Yamin, a climate change and disaster management expert, highlighted that India’s National Ocean Information Services Center issued a marine heat wave advisory in April confirming that parts of the Arabian Sea (including the coasts of India, Pakistan and Bangladesh extending towards Oman) are under high alert due to an increase in the sea surface temperature anomaly.

“Whether it affects deep water remains to be seen, but it would affect the continental shelf. This correlates with accounts from fishermen who have not seen such a large amount of seashells washed ashore before. Warmer temperatures at the sea surface can also change oxygen levels, causing marine life to die in the water and can cause marine mammals to rise to the surface in search of oxygen,” he added.

What about the shells?

Meanwhile, the shells themselves do not go to waste.

According to Motani, some people, mostly families living near the sea, collect them as part of their livelihood. The shells are cleaned using chemicals and other methods and then used to make jewelry, photo frames, decorative pieces, flower pots, and other crafts sold in the market.

Beyond crafts, seashells also have broader industrial value that researchers are increasingly exploring. A study examining sustainable waste management found that seashells can be converted into calcium biocarbonate through a high-temperature calcination process. When used as a filler in high-density polyethylene (HDPE), a common industrial plastic, the shell-derived material was found to improve the thermal stability, crystallinity, and tensile strength of the plastic, while only marginally reducing its flexibility.

This article was published by iVerify Pakistan as part of its initiative to tackle climate myths and misinformation, with the support of Irada and IMS.