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Last Updated: 09 October 2025
Estimated Reading Time: ~7 minutes
Lead: Want a compact, exam-ready guide to sampling and identifying brachyuran crabs from the Andhra Pradesh coast? This post translates a PhD thesis into practical steps you can use in the lab and field.
- Key takeaway: The thesis recorded 46 brachyuran species across 15 families from Andhra Pradesh (important: Portunidae & Xanthidae dominated). 0
- Field window: Systematic monthly sampling ran from June 2014–May 2018 (monsoon trawl ban: 15 Apr–15 Jun). 1
- Practical tip: Trawl-bycatch 10-kg subsamples give reliable diversity snapshots for coastal surveys. 2
Introduction — why Brachyuran crab diversity Andhra Pradesh matters
Coastal crabs are both ecologically central and economically valuable: they shape mangrove sediment dynamics and support local fisheries. The thesis provides a systematic account of brachyuran diversity across 20 stations on the Andhra coast and resolves many identification ambiguities that students often face. 3
In this post you’ll learn the sampling design, quick ID checks, habitat notes and lab ideas you can use for assignments or exam revision.
Study snapshot & why this topic is best for students
One-sentence rationale: Studying trawl bycatch and mangrove sampling gives students exposure to real-world diversity, specimen handling, and the taxonomic challenges that modern molecular tools help solve. 4
Field sampling design (practical summary)
Plain-English summary: Monthly, multi-station sampling across major harbours and minor landing centres using trawl-bycatch subsamples plus targeted mangrove hand-picking. 5
“Sampling was done along with the 20 stations of the study area regularly, for a period of four years from June 2014 to May 2018.” (p. 20). 6
Explanation: pick 10-kg random sub-samples from trawl landings, wash in seawater, record carapace length/width, sex, maturity and colour. Preserve in 10% formalin (add sodium arsenate mix to retain red pigments when needed). 7
Exam tip: Memorise the preservation recipe and the 10-kg subsample rule — it’s a common methods question.
Rapid ID cues — families you will meet
Plain-English summary: Portunidae (swimming crabs) and Xanthidae (often rocky/muddy) were the most frequently recorded families in this study. 8
“The maximum crab species were recorded belonging to family Portunidae and Xanthidae.” (p. 157). 9
Explanation: Portunids usually have a broad carapace and flattened fifth pereiopods (swimmerets); Xanthids often show robust spination and bright colours. Use cheliped shape, carapace spination and first male pleopod morphology for species-level keys. 10
Student note: Draw the first male pleopod during practicals — many keys rely on it.
Seasonal & habitat notes
Plain-English summary: Species composition shifts with season — many crabs peak in pre-monsoon/post-monsoon; mud crabs (Scylla spp.) are most important in mangrove estuaries (Koringa). 11
Explanation: salinity gradient, substrate and mangrove cover drive distribution. Expect burrowing crabs in muddy creeks and swimmer crabs in sandy sublittoral zones. 12
Exam tip: For distribution questions, link habitat (substrate + salinity) → feeding mode → likely family (e.g., burrowers = Ocypodidae/Grapsidae).
Molecular confirmation (when morphology is ambiguous)
Plain-English summary: The thesis used molecular barcoding on selected Xanthidae to confirm ID and flag potential new species. 13
“Molecular taxonomy of two brachyuran crab species were identified for barcoding, confirmation was done in BLAST.” (p. 176). 14
Explanation: when morphological characters conflict (polymorphism, sexual dimorphism), sequence mitochondrial markers (COI / 16S rRNA) and compare against reference databases.
Lab note: For an undergraduate practical, prepare muscle tissue following the field-preservation notes and send to a sequencing facility — practice interpreting BLAST % identity in class.
Selected species (quick reference)
| Species | Family | Field clue |
|---|---|---|
| Scylla serrata | Portunidae | Large mud crab, robust chelae — estuaries/mangroves. 15 |
| Portunus pelagicus | Portunidae | Swimmerets present, sandy bottoms. 16 |
| Thalamita crenata | Portunidae | Distinct carapace teeth near anterolateral margin. 17 |
| Demania spp. | Xanthidae | Small, often toxic — handle with care. 18 |
| Atergatis floridus | Xanthidae | Bright patterns; poisonous species reported. 19 |
Practical / lab implications
Use the thesis’ combination of systematic morphology + selective molecular barcoding in your lab module: morphology for first-pass ID; COI/16S for ambiguous or potentially new records. 20
Visuals & infographic suggestions
Suggested diagrams:
- Map infographic: Andhra Pradesh coast with 20 sampling stations (show major harbours Visakhapatnam, Kakinada, Machilipatnam) — caption: “Study stations and trawl sampling harbours.” 21
- Identification plate: carapace shapes + key family traits (Portunidae swimmeret, Xanthidae spination, Ocypodidae burrower) — caption: “Quick ID plate for common Andhra crabs.”
Key takeaways
- 46 species, 15 families: Andhra coast supports broad brachyuran diversity — Portunidae & Xanthidae dominate. 22
- Sampling best practice: monthly 10-kg trawl subsamples + mangrove hand-picks capture useful diversity data. 23
- ID strategy: morphology first (chelae, carapace spination, pleopods), molecular barcoding for ambiguity. 24
MCQs — self-test
- Q: Which family showed the greatest species richness in the Andhra thesis survey?
A: Portunidae. Explanation: Portunidae and Xanthidae were most represented; Portunidae includes many commercial species (see results). 25 - Q: Recommended subsample weight from trawl landings for diversity assessment?
A: 10 kg. Explanation: The study used 10-kg random subsamples from trawl-bycatch. 26 - Q: Which marker is commonly used for DNA barcoding crabs?
A: COI (cytochrome oxidase I). Explanation: COI/16S are standard mitochondrial markers used for crustacean barcoding. 27
FAQs
Q: How many species did the thesis record? A: 46 brachyuran species across 15 families. 28 Q: When was sampling carried out? A: Monthly sampling between June 2014 and May 2018; monsoon trawl ban (15 Apr–15 Jun) limited sampling in that window. 29 Q: Are any species poisonous? A: Yes — some xanthid genera and Atergatis species are reported as poisonous in the study. Handle with care. 30
Conclusion
This primer distilled the thesis into field-ready steps for students studying Brachyuran crab diversity Andhra Pradesh. Use the ID tips, preservation notes and the suggested lab exercise (morphology → COI confirmation) as a ready practical module for classwork or exam prep. 31
Next read: check the full taxonomy plates (chapter 3) and the thesis’ discussion for conservation notes and newly reported records. 32
Author Bio: Researcher Ponnada Vijaya Kumar, M.Sc., M.Phil (Andhra University).
Reviewed and edited by: Professor of Zoology editorial team.
“Reviewed and edited by the Professor of Zoology editorial team. Except for direct thesis quotes, all content is original work prepared for educational purposes.”
Source & Citations
Thesis Title: Studies on the diversity and systematics of brachyuran crabs (Crustacea; Decapoda) off Andhra Pradesh coast, Bay of Bengal, India.
Researcher: Ponnada Vijaya Kumar. Guide: Prof. D.E. Babu. Co-Guide: Prof. C. Manjulatha. University: Andhra University, Visakhapatnam. Year: 2019. 33
Excerpt page numbers used: p.20 (materials & methods), p.23 (sampling notes), p.157–176 (results, species list, summary).
Other sources: None (all content derived from thesis unless explicitly stated).
Disclaimer: Disclaimer: All thesis quotes remain the intellectual property of the original author. Professor of Zoology claims no credit or ownership. If you need the original PDF for academic purposes, contact us through our official channel.
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