- Polychaete worms, also known as bristle worms, occur in almost all marine habitats, with some even adapting to low-salinity and inland water environments.
- They play numerous ecological roles, including breakdown of organic matter, oxygen transport, and its redistribution.
- In recent years, the booming shrimp aquaculture industry has driven large-scale harvesting of wild polychaete worms.
- Hatcheries on India’s east coast alone are estimated to require 400 kg per day as live feed for broodstock.
Polychaete worms are among the most diverse groups of marine invertebrates on Earth. According to the World Register of Marine Species, approximately 13,148 valid polychaete species are currently recognised. Some researchers even estimate that this number could rise to 16,700 by the end of the century.
“They (polychaete worms) occur in almost all marine habitats, from estuaries, mangroves, sandy shores, coral reefs, and seagrass beds to the continental shelf and deeper waters,” said Sanitha Sivadas, a marine benthic ecology expert and Scientist E at the National Centre for Coastal Research (NCCR), Visakhapatnam. “A small percentage of polychaete species have even adapted to low-salinity and inland water environments,” Sivadas added.
Polychaeta, Greek for “having much hair”, refers to the bristles on the fleshy, leg-like protrusions on their body, which also lends them their other name, bristle worms. These worms range in size from a few millimetres to more than a metre long and come in colours ranging from dull brown to neon yellow and orange-red.
In India, despite their vast diversity, polychaete worms remain understudied. Mongabay-India spoke to polychaete experts and taxonomists to learn more about the bright, bristly worms of our seas.
India’s underexplored diversity
With its extensive coastline and diverse coastal and marine habitats, India is home to a huge diversity of polychaete worms, said Sivadas. “[But] the current recorded [polychaete] diversity represents only a part of the actual diversity in Indian waters,” she added.
Pierre Fauvel laid the foundation for documenting India’s polychaete fauna. The well-known French polychaetologist’s 1953 work described 304 species from the subcontinent. Since then, polychaete knowledge has been accumulated only through scattered studies. Sivadas notes that between 2001 and 2019, researchers reported only eight new polychaete records.
In their 2020 checklist, Sivadas and co-author Russell Carvalho brought together all this scattered information and critically evaluated the taxonomic status of the reported polychaete records. “We compiled 727 marine annelid species,” she said. “But about 25% (183) of the reported records were considered questionable based on the available literature and taxonomic revisions.”
Re-evaluation is a continuous process in taxonomy, as new morphological, molecular and other evidence becomes available, Sivadas said. A 2025 NCCR study described a new polychaete species from the sandy sediments off the Tamil Nadu coast in the northern Indian Ocean. “Even areas that have been studied before can reveal species that were previously overlooked or misidentified,” Sivadas said, who was one of the paper’s authors.
Polychaete worms and their ecological role
Polychaete worms are a diverse group of marine annelids that play numerous ecological roles, according to Sivadas. Polychaete worms can be deposit feeders that consume sediment to feed on dead plant and animal matter, filter feeders that strain tiny organisms like plankton out of the water, grazers that feed on algae and other plant matter, or predators that hunt and feed on live prey.
“As detritivores (that consume detritus to obtain nutrients), polychaete worms play a major role in the breakdown of organic matter, oxygen transport, and its redistribution,” said Moumita Bhowmik, a PhD scholar at the CSIR-Central Salt & Marine Chemicals Research Institute in Bhavnagar, Gujarat. Polychaete worms are also a major food source for other benthic and pelagic organisms and therefore play an indirect role in controlling ocean fauna populations, the senior research fellow added.
Their high ecological adaptability and sensitivity to environmental stresses also make polychaetes great bioindicators of ecological health, Sivadas said. “Changes in their abundance and community composition can reflect changes in sediment quality and other environmental stresses,” she said.
For her PhD, Bhowmik is studying polychaete ecology in the mudflats of the Gulf of Khambhat, a highly polluted and ecologically disturbed habitat. “I am focusing on nereidids (a specific group of polychaete worms) and exploring their adaptability in stressful habitats,” she said.
According to Bhomwik, polychaete worms are perfect model systems for studying ecological adaptation to pollution stressors. They can also degrade harmful chemicals and utilise carbon sources from them, making them valuable for future pollution remediation strategies, she added.
Habitat changes
A 2016 study by Sivadas found that the distribution of polychaetes, gastropods and bivalves along the east and west Indian coasts was shaped by a combination of environmental conditions, habitats and oceanographic processes rather than geography alone.
“Since most of the polychaetes are small and poorly known, their conservation is closely linked to protecting their habitats and maintaining healthy benthic ecosystems,” Sivadas said. Climate-related changes add further pressure, she added.
Although Bhowmik’s research highlights their adaptability, which enables polychaete worms to persist in polluted, uninhabitable, hypoxic (low oxygen) sediments, she noted that areas with high habitat disturbances tend to show no traces of polychaete worms.
“A combination of factors such as sediment particle size, tidal exposure in intertidal areas, and physical disturbances plays a crucial role in determining their habitability,” Bhowmik said. Dredging and other human disturbances leading to shoreline changes can affect polychaete niches and their overall distribution, she added.
Cost of wild harvesting
In recent years, the rapid growth of shrimp hatcheries across India has made wild harvesting of polychaete worms a major concern.
Along the east coast alone, more than 200 shrimp hatcheries are now registered with the Coastal Agriculture Authority, according to Perumal Murugesan, an associate professor at the Centre of Advanced Study in Marine Biology at Annamalai University in Parangipettai, Tamil Nadu.
“While live feeds such as trash fish, crab meat and even beef liver are commonly used, hatchery operators prefer polychaete worms due to their rich polyunsaturated fatty acid (PUFA) content,” Murugesan said. PUFAs are scientifically proven to increase spawning rate and yield in mother shrimps, he added.
According to Murugesan, a shrimp hatchery requires, on average, two kilograms of polychaete worms a day. This puts the daily demand from hatcheries on India’s east coast alone at 400 kg.
Over the years, a huge network has emerged to meet this rising demand, Murugesan said. “Regrettably, the people who collect these polychaete worms, the Irular tribal fishing community on the Tamil Nadu Coast, receive a meagre ₹500-800 per kg,” he said. “[But] by the time it reaches the hatchery, it is sold at around ₹3,500-4,000 per kg, depending on the quality.”
Murugesan is worried we could soon run out of “natural stock” if we keep collecting polychaete worms from the wild, but then pointed out that for communities such as the Irular tribe, who dig up and handpick these worms from intertidal mudflats and mangrove backwaters, it is a matter of livelihood. “We have to see to it that the natural environment is protected, and their livelihood is also protected. It has to be a win-win situation,” he said.
On the west coast, a 2022 study assessed the harvesting of polychaete worms from Mumbai’s intertidal zones. There, the authors argued that along with better monitoring and regulation of wild harvesting, India needs to develop polychaete aquaculture to meet the growing demands of its shrimp aquaculture industry.
Murugesan and team have developed and patented a technology for the controlled aquaculture of the native Perinereis nuntia. They are currently working with hatcheries to test its potential as a sustainable live feed for shrimp.
Watch: Shrimp or mangroves? Odisha’s coastal dilemma
Future research in India
Sivadas called for more opportunities and recognition for taxonomists if marine invertebrate biodiversity research is to thrive in India. “Taxonomy is the foundation of biodiversity research, but relatively few young researchers are choosing it as a career,” she said. “We need to create an environment that encourages and supports them to take up this field.”
Sivadas also hopes for better exploration of poorly studied regions and habitats. Bhowmik, who recently received funding from the Ocean Census Species Discovery Committee, aims to do exactly that by creating a regional database for polychaete species in the Gulf of Khambhat and Gulf of Kachchh. Bhowmik also demanded better access to museum collections for polychaete taxonomists. The Indian Museum in Kolkata currently houses one of the most extensive polychaete collections, she said.
Sivadas stressed that the aim should not only be to add more species names, but to understand their distribution and how they are responding to changing environments. “Only then can we understand what may happen to [our] marine biodiversity in the future,” she said.
Banner image: Amphinomidae sp. bristle worms. Image by Moumita Bhowmik.
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