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

Every year, sometime around June, Karachi’s beaches become crowded – not only with people, but also with seashells, hundreds of thousands of them, scattered along the shore in dense and clattering drifts. The sight leaves the citizens fascinated, and many wonder if something was wrong. The same thing also happened in June.

For the past few days, there has been discussion both online and offline as to why this phenomenon occurs. Was it climate change or the spectacle of nature?

The science and the fishermen tell a more layered story.

A prelude to the monsoon

The phenomenon is not new. ONE Dawn report dated July 17, 2009, noted that a large number of white and yellow seashells had appeared on Clifton Beach overnight. Another Dawn reportdated May 21, 2016, reported that wave action dislodges shellfish, especially Venus clams, locally known as “burgar,” from shallow sub-tidal habitats and carries them to beaches where they die, leaving behind empty shells.

The same event was also covered by Express Pakinomist on May 22, 2016. Both news reports stated that the phenomenon is associated with the arrival of the monsoon.

An Aaj News report dated July 10, 2024, 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 contribute to higher marine mortality, leading to greater amounts of shells washing ashore in some years.

Majeed Motani, president of Pakistan Fisherfolk Forum, who has decades of fishing experience, 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, especially in June and July,” he said, explaining that water from the deeper parts of the ocean rises to the surface and eventually pushes the seashells towards the shore, where they are deposited along the shore.

What science says

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

ONE study published in the Journal of Sea Research explains that this cold, deep water contains very little oxygen, and when it spreads over the ocean floor, it proves fatal to bottom-dwelling creatures like clams and other shellfish that can’t move fast enough to escape. Their empty shells are then washed onto the beaches by powerful monsoon waves.

PHOTO: DAWN

A separate one paper on the Arabian Sea shelf, published in Deep-Sea Research, found that cold, oxygen-poor waters begin to appear off Karachi as early as June and persist through November, the very months when citizens observe the highest concentrations of shells along the coast.

Another study stated that the monsoon season coincides with the period when the largest number of marine invertebrates are present in coastal waters near Karachi. Simply put, shellfish populations are at their peak near the coast just as the harshest sea conditions arrive, which is why the 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 clam shells this year appears to be higher than usual.

Fatima Yamin, an expert on climate change and disaster management, highlighted that the Indian National Center for Ocean Information Services issued a Marine Heatwave Advisory in April confirming that parts of the Arabian Sea – including coasts of India, Pakistan and Bangladesh stretching towards Oman – are on high alert due to a rise in sea surface temperature.

“It is yet to be seen if it affects deep water, but it will affect the continental shelf. This correlates with reports of fishermen who have not seen such large numbers of shellfish washed ashore before. Warmer sea surface temperatures can also change oxygen levels, causing marine life to die in the water and can cause marine mammals to rise to the surface of oxygen,” she added.

What happens to the shells?

Meanwhile, the shells themselves do not go to waste.

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

In addition to handicrafts, seashells also have a wider industrial value, which is increasingly being explored by researchers. A study investigating sustainable waste management found that clam shells can be converted into bio-calcium carbonate through a high-temperature calcination process. When used as a filler in high-density polyethylene (HDPE), a common industrial plastic, the seashell-derived material was found to improve the plastic’s thermal stability, crystallinity, and tensile strength, while only marginally reducing its flexibility.

This article was published by iVerify Pakistan under its initiative Tackling Climate Myths and Misinformation, supported by Irada and IMS