Intertidal Gastropods (Gastropoda: Mollusca): Insights on diversity and distribution in the Mumbai Metropolitan Region, India

This study utilizes a decade-long citizen science project to document the diversity and distribution of 163 gastropod species across 28 intertidal sites in the Mumbai Metropolitan Region, revealing numerous new records and rediscoveries while demonstrating the effectiveness of low-cost citizen science for addressing taxonomic data gaps.

The Gist

Imagine the coastline of Mumbai not just as a bustling city of skyscrapers and traffic, but as a giant, underwater city block where millions of tiny, shelled, and shell-less creatures live, work, and play. This paper is like a newly discovered phone book for that underwater neighborhood, finally listing the names and addresses of the residents who have been living there in the shadows for decades.

Here is the story of the paper, broken down into simple, everyday concepts:

1. The Missing Puzzle Pieces

For a long time, scientists knew Mumbai had a lot of marine life, but their knowledge was like a jigsaw puzzle with half the pieces missing. Most of the old records were written over 100 years ago by people who didn't have good cameras or modern science tools. They knew that snails existed, but they didn't know which snails, where exactly they lived, or what they looked like in detail. It was like knowing a city has "people" but not knowing if they are doctors, artists, or chefs, or where their houses are.

2. The "Citizen Science" Detective Squad

Instead of hiring a small team of expensive experts to spend years studying the coast, the authors used a massive, volunteer detective squad. They launched a project called "Marine Life of Mumbai" on a platform called iNaturalist.

Think of this like a community photo contest. Regular people—students, locals, and hobbyists—went to the beach during low tide, snapped photos of the snails and sea slugs they found, and uploaded them. Over 10 years, 13 dedicated volunteers collected 2,164 sightings. It's as if the whole city turned into a giant pair of eyes, scanning the rocks and mud for clues that professional scientists had missed.

3. The Big Reveal: 163 Species Found!

When the authors analyzed all these photos, they didn't just find a few snails; they found a whole new neighborhood.

• The Total Count: They identified 163 different species of gastropods (snails and sea slugs).
• The New Arrivals: 29 of these species were brand new to the Mumbai record books. It's like discovering that a new family of neighbors had moved in next door, but no one had ever introduced themselves before.
• The "Ghost" Residents: They also found 7 species that were thought to be extinct or lost in this area. Some hadn't been seen in Mumbai for over 100 years!
  • One snail, Lataxiena bombayana, was last seen 131 years ago. Finding it again is like finding a time traveler who walked out of a 19th-century history book and is now living on a modern Mumbai rock.
  • Another, Siphonaria bassiensis, hadn't been seen in 31 years.

4. The "Sea Slugs" vs. The "Shelled Snails"

The paper highlights two main groups of residents:

• The Shelled Snails: These are the classic snails with hard houses (shells). They are like the homeowners of the intertidal zone, clinging to rocks and mangroves.
• The Sea Slugs (Nudibranchs): These are the shell-less, colorful, and often weird-looking creatures. The paper describes them in detail, noting their bright colors, weird shapes, and how they look like underwater dragons or alien flowers. The study found that this group is incredibly diverse in Mumbai, with many species never before recorded in the region.

5. Why This Matters (The "Why Should I Care?" Factor)

You might ask, "Why do we need a list of snails?"

• The Canary in the Coal Mine: Snails and sea slugs are like canaries in a coal mine. Because they are sensitive to pollution, temperature changes, and dirty water, their presence (or absence) tells us how healthy the ocean is. If the "snail population" is thriving, the water is likely okay. If they disappear, it's a warning sign.
• The Urban Jungle: Mumbai is one of the most crowded cities on Earth. The coast is under constant pressure from construction, sewage, and oil spills. This study proves that even in a heavily damaged, concrete-heavy environment, nature is still fighting to survive. It's a reminder that biodiversity is resilient, but it needs help.
• The Power of the Crowd: The biggest lesson here is that you don't need a PhD to be a scientist. By simply taking photos and sharing them, regular people helped fill a massive gap in scientific knowledge. It shows that with enough eyes on the ground, we can map the world in ways that were previously impossible.

The Takeaway

This paper is a celebration of curiosity and community. It tells us that even in the most urbanized, "concrete" parts of the world, there is a vibrant, hidden world of tiny creatures that we are only just beginning to understand. By turning the public into citizen scientists, the authors didn't just write a list; they rewrote the history of Mumbai's coastline, proving that there is still so much to discover right under our noses.

Technical Summary

1. Problem Statement

The Mumbai Metropolitan Region (MMR), despite being a highly biodiverse coastal area on India's west coast, suffers from a critical data deficiency regarding its intertidal marine biodiversity.

• Historical Gaps: While malacological research in the region dates back nearly two centuries (e.g., Leith, 1853; Melvill, 1893), existing literature consists largely of classical natural history accounts lacking modern morphological descriptions, visual records, or fine-scale spatial data.
• Taxonomic Uncertainty: Previous studies often rely on outdated taxonomy, leading to inconsistencies in species identification. Many historical records are based on empty shells or lack diagnostic features, making it difficult to establish a robust baseline for ecological monitoring.
• Anthropogenic Pressure: The MMR is one of the world's most densely populated metropolises, subjecting its intertidal zones to severe stressors (reclamation, pollution, sewage). Without accurate baseline data, assessing the impact of these disturbances and planning conservation strategies is impossible.

2. Methodology

The study employs a citizen science approach combined with rigorous taxonomic validation to bridge these data gaps.

• Study Area: The research covers the MMR (19°18'–19°30' N, 72°42'–72°57' E), encompassing 28 intertidal sites across rocky, sandy, and muddy habitats. These sites are divided into 11 zones, ranging from Vasai in the north to Colaba in the south, including the eastern Thane Creek.
• Data Collection:
  • Duration: February 2014 to January 2024 (10 years).
  • Method: Opportunistic surveys conducted by 13 citizen scientists during low tides (<1 meter).
  • Documentation: High-resolution photography (DSLR, macro, smartphones) of gastropods in situ. For shelled species, dorsal, ventral, and lateral views were captured; for shell-less species (nudibranchs/heterobranchs), diagnostic features like rhinophores and cerata were emphasized.
  • Platform: All observations were uploaded to iNaturalist.org under the "Marine Life of Mumbai" project.
• Data Analysis & Validation:
  • Identification: Species were identified to the lowest possible taxonomic level using morphological characters visible in photos, cross-referenced with historical literature and modern databases (WoRMS, MolluscaBase).
  • Expert Verification: Identifications were validated by subject matter experts via online communities (Nudibase, Nudibranch Central, Sea Slug Forum) and reference websites.
  • Filtering: Only observations of live specimens with adequate diagnostic features were included in the final checklist. Empty shells were recorded separately.

3. Key Contributions

• First Comprehensive Checklist: The study presents the first exhaustive, georeferenced checklist of intertidal gastropods for the MMR, consolidating a decade of fragmented data.
• Taxonomic Revision: It addresses historical inconsistencies by re-evaluating species against modern taxonomic standards (WoRMS 2025), clarifying synonyms and taxonomic statuses (e.g., Glossodoris semeion).
• Rediscoveries: The study successfully located species that had not been recorded from their type localities in Mumbai for decades or even over a century.
• Methodological Demonstration: It validates citizen science as a cost-effective, scalable method for generating high-quality biodiversity data in data-deficient, urbanized ecosystems.

4. Key Results

The study documented 163 species of gastropods belonging to 112 genera, 66 families, and 5 subclasses from 2,164 observations.

• New Records:
  • 29 New Species: First records for the MMR, including Aplysia cf. rudmani, Smaragdinella sieboldi, Paromoionchis penangensis, and several nudibranchs like Herviella yatsui and Janolus mirabilis.
  • 34 New Genera: Including Ercolania, Costasiella, Berthella, and Phidiana.
  • 1 New Family: The family Limapontiidae was recorded for the first time in the region.
• Rediscoveries:
  • 7 Species were rediscovered from their type localities after long absences:
    • Lataxiena bombayana (Neogastropoda): Rediscovered after 131 years.
    • Siphonaria bassiensis (Siphonariida): Rediscovered after 31 years.
    • Five Heterobranch species (including Glossodoris poecila, Glossodoris semeion, Goniobranchus bombayanus, Goniobranchus trimarginatus, and Goniodoris kolabana) were rediscovered after 78 years.
• Distribution Patterns:
  • Heterobranchia was the most diverse subclass (79 species), while Patellogastropoda was the least diverse (3 species).
  • The family Muricidae had the highest representation (14 records).
  • Distribution varied significantly across the 11 zones, with some species restricted to specific microhabitats (e.g., mangrove creeks vs. rocky shores).
• Conservation Status: Most recorded species are not evaluated on the IUCN Red List. Seven common species (Cassidula aurisfelis, Melampus sincaporensis, etc.) are listed as "Least Concern." None are currently protected under India's Wildlife Protection Act, 2022.

5. Significance

• Baseline for Conservation: This study provides the essential baseline data required to monitor the health of the MMR's intertidal ecosystems, which are under constant anthropogenic threat.
• Ecological Indicators: By documenting the diversity of gastropods (known bioindicators), the study highlights the resilience and current state of the region's marine biodiversity despite heavy urbanization.
• Taxonomic Clarity: The detailed morphological descriptions and photographic plates serve as a critical reference for future taxonomists and ecologists, reducing identification errors in the region.
• Policy Implications: The findings underscore the urgent need for fine-scale ecological studies to understand species-habitat relationships and to inform coastal management policies in the MMR.
• Citizen Science Model: The success of the "Marine Life of Mumbai" project demonstrates that structured citizen science can effectively fill large-scale biodiversity gaps in complex urban environments, offering a replicable model for other data-deficient regions globally.

In conclusion, this paper transforms the understanding of Mumbai's intertidal gastropod diversity from a fragmented historical record into a robust, modern dataset, revealing a thriving yet understudied community that requires immediate scientific and conservation attention.