Crab export boom: Is it really gold or ecological loss?

To harvest as soft-shell crabs, they are kept in individual containers until they naturally shed their shells. Immediately after the moulting process. Photo: TBS

Nowadays, a new species has emerged in the export market: the soft-shell crab. In the export industry, it is often referred to as "gold" because of its high commercial value. It has become popular among farmers, while non-governmental organisations are promoting it as an income-generating project, and large investors are increasingly investing in soft-shell crab production.

In reality, this is not conventional farming but rather a fattening process, similar to cow fattening. Soft-shell crabs are collected from the Sundarbans mangrove forest and placed in baskets that float in saline water. After two to three months, the crabs reach export-ready condition.

In the Sundarbans, crabs represent the most dominant faunal biomass. More than 50 species have been recorded in the region, generally classified into four major functional and commercial groups. Among them, the most famous and economically significant are the Commercial Giants, or Mud Crabs (Scylla species). These crabs are large, powerful, and serve as a major source of income for local crab catchers.

Scylla olivacea (the Orange or Red Mud Crab) is the most commonly found species, followed by Scylla serrata (the Giant Mud Crab). They inhabit deep burrows in the mudflats and are highly valued for their meat. Although commercially abundant, these species are under increasing pressure due to overharvesting driven by export demand.

Secondly, the Engineers or Fiddler Crabs (Uca/Austruca species) are small yet vividly coloured. Common species include Uca rosea, Uca dussumieri, and Uca annulipes. They are best known for the male's single oversized claw—the "fiddle"—which he waves to attract mates. These crabs play a vital role in maintaining soil health, as their extensive burrow networks help aerate the oxygen-poor mangrove mud.

Third are the Red and Ghost Crabs. Red crabs are strikingly bright red and are often found in sandy or estuarine areas such as Dublar Char in the Sundarbans. They are extremely fast and quickly disappear into the sand when threatened. Ghost crabs (Ocypode species) are often pale or naturally camouflaged to blend with the sand. They are primarily nocturnal scavengers and are commonly found along the beach fringes of the Sundarbans.

Fourthly, other specialised mangrove crabs can be grouped into four main types: Sesarmid Crabs, Hermit Crabs, Horseshoe Crabs, and Swimming Crabs. Sesarmid crabs are commonly known as "leaf-eating crabs." They play a crucial role in nutrient cycling, as they feed on fallen mangrove leaves and help recycle organic matter back into the ecosystem.

Hermit crabs (Clibanarius species) are commonly found in intertidal zones, where they use discarded snail shells as protective homes. Horseshoe crabs are often referred to as "living fossils." Two species—Carcinoscorpius rotundicauda and Tachypleus gigas—are found in the muddy estuaries of the Sundarbans. Although they are called crabs, they are more closely related to spiders and scorpions than to true crabs.

Swimming crab species, such as the Blue Swimmer Crab (Portunus pelagicus) and the Three-spot Swimming Crab, are typically found in the deeper tidal rivers of the region.

Farmers usually collect "empty" female crabs (rejected by exporters for lacking eggs) or "soft" male crabs that have recently moulted. They rear them in small earthen ponds (ghers) or in plastic boxes floating in the water. Box culture is particularly popular because it prevents cannibalism—crabs are naturally aggressive and will eat each other if kept together in open ponds.

The crabs are fed "trash fish," low-value tilapia, or eel, typically every two to three days. Within a month, the crabs become "meaty," or, in the case of females, develop high-value orange roe (eggs).

A more specialised process involves round-the-clock monitoring. The moment a crab moults—shedding its old shell—it is harvested within hours, while the new shell is still paper-thin. These soft-shell crabs are then immediately frozen for export.

The Sundarbans mud crab (Scylla olivacea) is almost entirely an export-oriented product. There is very little domestic demand in Bangladesh due to its high price and prevailing cultural and religious preferences.

China and Hong Kong are the largest markets for live hard-shell crabs. They prefer large, live crabs—especially egg-bearing females—for traditional luxury dining. There is also strong demand for frozen soft-shell crabs in the high-end gourmet segment in the United States and the European Union, where they are commonly served whole in sandwiches or as tempura.

Japan and South Korea import both premium-sized live crabs and frozen products, but maintain very strict quality standards. They pay the highest prices for large male crabs. In South Korea, live mud crabs are especially popular and are widely known for their use in the famous "chilli crab" dishes.

Since almost 100% of crab "seeds" (juvenile crabs) are sourced from the wild Sundarbans, the forest is under immense ecological pressure. Despite several attempts, producing crab seeds in hatcheries has not yet been successful. As a result, the random and unregulated collection of juveniles is placing growing strain on the ecosystem.

Due to this practice, the Sundarbans are facing serious threats, including over-exploitation, bycatch, and rising climate and security risks. Strong international demand for soft-shell and mud crabs has encouraged some harvesters to ignore size limits, capturing juvenile crabs before they have a chance to reproduce. In some cases, non-traditional netting methods can unintentionally kill up to 30–40 other aquatic species for every single crab caught.

Crab harvesters also face significant physical dangers. They regularly risk encounters with tigers, crocodiles, and forest pirates, while extreme weather events can damage or destroy their small-scale fattening ponds, threatening both livelihoods and long-term sustainability.

In fact, crabs maintain a keystone role in the Sundarbans mangrove ecosystem. Without them, the entire system would likely collapse or look drastically different. Acting as "ecosystem engineers," crabs bridge the gap between the trees and the surrounding marine environment. They also function as natural cleaners, helping to recycle organic matter and maintain the health of the mangrove habitat.

Mangrove mud is notoriously anoxic—lacking oxygen—and high in toxic sulfides. Burrowing crabs, such as fiddler and sesarmid crabs, dig complex tunnel systems that allow oxygen to penetrate deeper soil layers. This aeration enables mangrove roots to "breathe" and supports the growth of beneficial bacteria that break down toxins. Without crabs, the soil could become too toxic for the trees to survive.

Mangroves also produce massive amounts of leaf litter, much of which would be washed away by the tide if not for the crabs. These crabs are the primary consumers of fallen leaves, dragging them into their burrows to eat or store. By processing this organic matter, they retain energy within the forest. Their waste is rich in nitrogen and phosphorus, acting as a natural fertiliser for the trees.

Crabs are surprisingly influential "gardeners," determining which trees grow where. Many species feed on the seeds (propagules) of specific trees. By selectively consuming the seeds of some species while leaving others untouched, crabs help dictate the zonation of the forest, essentially shaping which tree species dominate certain areas.

Crabs also serve as a vital link between the primary production of mangrove trees and higher-level predators. Mangrove roots provide shelter for juvenile crabs. As these crabs grow and reproduce, they produce millions of larvae that become a key food source for fish and birds. Because crabs are highly sensitive to pollution and changes in salinity, their population health is often used by scientists as an indicator of the overall health of the mangrove forest.

While all mangrove crabs contribute to the ecosystem, the fiddler crab and the mud crab represent two very different ecological "professions." One acts as a tiny gardener and soil refiner, while the other is a heavy-duty architect and top predator.

Fiddler crabs are the "maintenance crew" of the mangrove floor. Their impact is concentrated on the micro-level of the sediment. Using their small pincers, they scoop up mouthfuls of mud, sifting out bacteria, microalgae, and detritus before spitting out clean pellets of sand. Highly active burrowers, they create dense networks of tunnels. This process, known as bioturbation, brings nutrient-rich sediment from deep underground to the surface and pushes oxygen into the soil. They are so numerous—often hundreds per square metre—that they can oxygenate up to 80% of the surface sediment in some forests, preventing the accumulation of toxic sulfides that would otherwise harm mangrove roots.

Mud crabs (often called mangrove crabs) are the "heavy engineers" and "security" of the ecosystem. Their impact is focused on the macro-level of the food web. Unlike fiddler crabs, mud crabs are large and aggressive, preying on mollusks, smaller crabs—including fiddler crabs—and fish. By controlling the populations of other species, they prevent any one group from overgrazing the mangroves. Their burrows are much larger and deeper, sometimes exceeding a metre in depth. These massive tunnels act as conduits for tidal water, allowing it to penetrate deep into the soil. Mud crabs are also a "bridge" species: they spend their adult lives in the mangroves but migrate to the open ocean to spawn, transferring enormous amounts of energy in the form of larvae from the forest to the sea.

In the calendar year 2024, Bangladesh earned approximately $76 million from crab exports. In the fiscal year 2024–25, the Khulna region alone—the country's primary hub for crabbing—reported earnings of Tk 173.27 crore from the export of 1,166.89 tonnes of crabs. This represented a significant jump from the previous year (Tk 97.87 crore), a 77% increase in value for the region. Recent data from the first half of FY 2024–25 (July–December) showed crab exports worth $7.05 million, a 36.89% increase compared with the same period the year before.

Yet, in earning this foreign currency, we are exporting our ecological engineers while simultaneously degrading the mangrove ecosystem. So, can we truly call it gold?

Gouranga Nandy, Free-lance Journalist and Chairman, CEPR (Centre for Environment and Participatory Research), can be reached gouranga.nandy@gmail.com.

Disclaimer: The views and opinions expressed in this article are those of the authors and do not necessarily reflect the opinions and views of The Business Standard.