Brachyurans are the most prominent group of Crabs, because of their great diversity; comprising of about 6793 species, 1721 genera, and 93 families recorded globally. Brachyuran Crabs perform a significant role in the Mangrove ecosystems and are commercially valuable with high culture and fattening potential. Mangrove ecosystems warrant more attention as it is diminishing day by day, especially along Kerala coastline and its importance protecting the environment from natural catastrophes are increasing. Mangroves are fragile ecosystem having highly variable conditions of life style, which make them profusely rich in biodiversity. The ecosystem value of Mangroves overwhelms any other ecosystem as it gives very many services, including biodiversity richness. Distribution studies of Brachyuran Crabs, especially the Mangrove Crab in Indian Mangroves are scanty and the available literature generally discusses the distribution of both marine and estuarine/Mangrove Crabs together.
Literature regarding Crabs of Mangrove ecosystems of Kerala was comparatively meager apart from that of few individual report and citations of each Crab species. In 2008 Muthiah Kathirvel reported 990 species of marine Brachyuran Crabs belonging to 281 genera and 36 families from Indian waters. Thirty-six Brachyuran Crab species were identified from Pichavaram Mangroves by another study in 2008. Another study in 2013 revealed that 33 Mangrove Crab species belonging to the family Grapsidae and Ocypodidae were found in the state of Tamil Nadu. A comprehensive approach to document the diversity and abundance of true Mangrove Crabs is lacking especially fromvKerala, which is considered to be one of the Crab-rich states.
In a
paper published in the
Journal of Threatened Taxa on 26 November 2020, Kurian Mathew Abraham and Apreshgi Kolothuthara Prakasan of the Department of Aquatic Biology and Fisheries at the
University of Kerala present the results of a study which aimed to create a check list of the Brachyuran Crabs of the Mangroves of Kerala, and photo-document that diversity, along with revalidation of Crab nomenclature.
A survey of Crabs of different estuarine mangrove ecosystems along the western coastline of Kerala was carried out from June 2016 to May 2017. Crabs were collected live by handpicking, opening of burrows, bait trap and normal traditional trap kept overnight.
The sampling locations of mangrove crabs from Kerala. Abraham & Prakasan (2020).
A total of 18 species of true Mangrove Crabs under four families (Portunidae, Grapsidae, Sesarmidae, and Ocypodidae) and 11 genera were identified and documented in the present study. Highest number species was recorded from the family Sesarmidae (seven species) followed by Portunidae and Ocypodidae with four species each and Grapsidae with three species. Scylla serrata, Scylla olivacea, and Thalamita crenata were the economically valuable crab species. Parasesarma bengalense was reported for the first time from the western coast of India and Clistocoeloma lanatum was reported for the first time from Kerala Mangroves. Pseudosesarma glabrum was one of the rarer species and was recently reported from Cochin in southwestern India. Parasesarma plicatum was the most common Crab species encountered throughout west coastline Mangrove ecosystems of Kerala.
Checklist of Mangrove Brachyuran Crabs from Kerala. Abraham & Prakasan (2020).
Studiess in the 1950s reported the occurrence of Crabs from Mangrove habitats around Travancore and Bombay respectively without much of its taxonomic identity. After a long gap, a 1980s study reported the presence of 20 species of Crabs from Pichavaram Mangroves, which includes true Mangrove as well as estuarine Crabs. There are several taxonomic works on the Brachyuran Crabs of estuarine and Mangrove ecosystems of India. A total of 55 species of Brachyuran Crabs represented under 31 genera have been reported earlier from different Mangrove habitats of India. But none of the above reports exclusively documented Mangrove Crabs, in fact they included estuarine, marine forms in addition to Mangrove Crabs. Eighteen species of Brachyuran Crabs under nine genera and four families were identified exclusively from Sunderban Mangrove ecosystems. A study of the Mangrove fauna of the Andaman & Nicobar Islands listed 31 species of Crabs from Andaman Mangroves and briefly dealt with zonation and annual breeding pattern of some of the Crabs.
Mangrove Brachyuran Crabs from Kerala. Abraham & Prakasan (2020).
The nomenclature of many Crabs has been changed by different taxonomists, with the genus name of four Crabs has been changed or revalidated recently;
Perisesarma bengalense has been changed to Parasesrma, the genus
Uca has been renamed as
Austruca for
Uca annulipes and
Uca perplexa and
Uca vocans has been renamed as
Gelasimus vocans. Many taxa belonging to the genus
Perisesarma have been changed to
Parasesarma, however,
Perisesarma dussumieri, without any name changes is the type species of the genus
Perisesarma owing to its original characters of the genus. All the Crabs by Abraham and Prakasan are listed as ‘Least Concern’ status on the
International Union for the Conservation of Nature's
Red List of Threatened Species, which may be due to lack of baseline data about abundance and distribution the true Mangrove Crabs.
Mangrove Brachyuran Crabs from Kerala. Abraham & Prakasan (2020).
Abraham and Prakasan's investigation revealed 18 true Brachyuran Mangrove Crab species along estuarine mangroves of western coast of Kerala. Family Sesarmidae constitute the major diversity (seven species) followed by Portunidae (four species) and Ocypodidae (four species), and least in Grapsidae (three species) of Mangrove Crabs. Among the 18 Brachyuran Crabs, four crabs have been revalidated by change in genus or species name and provided in a checklist along with photo-documention of true Mangrove crabs of Kerala estuarine systems.
Mangrove Brachyuran Crabs from Kerala. Abraham & Prakasan (2020).
See also...
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