Johora singaporensis
Encyclopedia
Johora singaporensis, the Singapore stream crab or Singapore freshwater crab, is a critically endangered
species
of freshwater crab
endemic to Singapore
. It grows to a size of 30 millimetres (1.2 in) wide.
s running through undisturbed forest
, where it hides under rocks at the stream's edge, or inside aggregations of leaves and detritus
. It is mostly nocturnal, feeding on detritus and oligochaete worms
which live in the muddy stream bed.
, and has only ever been recorded from two locations. One of these was inside Bukit Timah Nature Reserve
, but that population is believed to have been extirpated, as recent surveys have failed to find any examples there. The second population is outside the nature reserve at Bukit Batok, partly on private land, and partly on military land. Acidification of the first stream may have caused the first population to die out, while a lowering of the water table
in the second stream threatens the second population.
J. singaporensis is one of three freshwater crabs that are endemic to Singapore. The others are Irmengardia johnsoni, and the critically endangered Parathelphusa reticulata.
are found across the Straits of Johor
on the adjacent Malay Peninsula
and some offshore islands, making J. singaporensis the southernmost species in the genus. It probably forms the sister group to a clade
comprising J. tiomanensis, J. counsilmani, J. murphyi, J. johorensis, J. gapensis and J. intermedia, from which it separated about 5 million years ago, at a time when the eustatic changes in global sea level
may have opened up a land bridge
to Singapore.
under criteria B1ab(iii)+2ab(iii), which refer to the small size of the remaining populations and the ongoing deterioration of the habitat
. The species' restriction to a single small island is likely to have increased the threat of extinction.
Critically endangered
Version 2010.3 of the IUCN Red List of Threatened Species identified 3744 Critically Endangered species, subspecies and varieties, stocks and subpopulations.Critically Endangered by kingdom:*1993 Animalia*2 Fungi*1745 Plantae*4 Protista-References:...
species
Species
In biology, a species is one of the basic units of biological classification and a taxonomic rank. A species is often defined as a group of organisms capable of interbreeding and producing fertile offspring. While in many cases this definition is adequate, more precise or differing measures are...
of freshwater crab
Freshwater crab
There are around 1,300 species of freshwater crabs, distributed throughout the tropics and subtropics, divided among eight families. They show direct development and maternal care of a small number of offspring, in contrast to marine crabs which release thousands of planktonic larvae. This limits...
endemic to Singapore
Singapore
Singapore , officially the Republic of Singapore, is a Southeast Asian city-state off the southern tip of the Malay Peninsula, north of the equator. An island country made up of 63 islands, it is separated from Malaysia by the Straits of Johor to its north and from Indonesia's Riau Islands by the...
. It grows to a size of 30 millimetres (1.2 in) wide.
Ecology
J. singaporensis lives in streamStream
A stream is a body of water with a current, confined within a bed and stream banks. Depending on its locale or certain characteristics, a stream may be referred to as a branch, brook, beck, burn, creek, "crick", gill , kill, lick, rill, river, syke, bayou, rivulet, streamage, wash, run or...
s running through undisturbed forest
Forest
A forest, also referred to as a wood or the woods, is an area with a high density of trees. As with cities, depending where you are in the world, what is considered a forest may vary significantly in size and have various classification according to how and what of the forest is composed...
, where it hides under rocks at the stream's edge, or inside aggregations of leaves and detritus
Detritus
Detritus is a biological term used to describe dead or waste organic material.Detritus may also refer to:* Detritus , a geological term used to describe the particles of rock produced by weathering...
. It is mostly nocturnal, feeding on detritus and oligochaete worms
Oligochaeta
Oligochaeta is a subclass of animals in the biological phylum Annelida, which is made up of many types of aquatic and terrestrial worms, and this includes all of the various earthworms...
which live in the muddy stream bed.
Distribution
J. singaporensis only lives in SingaporeSingapore
Singapore , officially the Republic of Singapore, is a Southeast Asian city-state off the southern tip of the Malay Peninsula, north of the equator. An island country made up of 63 islands, it is separated from Malaysia by the Straits of Johor to its north and from Indonesia's Riau Islands by the...
, and has only ever been recorded from two locations. One of these was inside Bukit Timah Nature Reserve
Bukit Timah Nature Reserve
The Bukit Timah Nature Reserve is a small 1.64 square kilometer nature reserve near the geographic centre of the city-state of Singapore, located on the slopes of Bukit Timah Hill, Singapore's highest hill standing at a height of 163.63 metres, and parts of the surrounding area...
, but that population is believed to have been extirpated, as recent surveys have failed to find any examples there. The second population is outside the nature reserve at Bukit Batok, partly on private land, and partly on military land. Acidification of the first stream may have caused the first population to die out, while a lowering of the water table
Water table
The water table is the level at which the submarine pressure is far from atmospheric pressure. It may be conveniently visualized as the 'surface' of the subsurface materials that are saturated with groundwater in a given vicinity. However, saturated conditions may extend above the water table as...
in the second stream threatens the second population.
J. singaporensis is one of three freshwater crabs that are endemic to Singapore. The others are Irmengardia johnsoni, and the critically endangered Parathelphusa reticulata.
Phylogeny
The relatives of J. sinaporensis in the genus JohoraJohora
Johora is a genus of freshwater crabs found in the Malay Peninsula and surrounding islands. It includes the following species:*Johora aipooae *Johora counsilmani *Johora gapensis...
are found across the Straits of Johor
Straits of Johor
The Straits of Johor is a strait that separates the Malaysian state of Johor to the north from Singapore to the south....
on the adjacent Malay Peninsula
Malay Peninsula
The Malay Peninsula or Thai-Malay Peninsula is a peninsula in Southeast Asia. The land mass runs approximately north-south and, at its terminus, is the southern-most point of the Asian mainland...
and some offshore islands, making J. singaporensis the southernmost species in the genus. It probably forms the sister group to a clade
Clade
A clade is a group consisting of a species and all its descendants. In the terms of biological systematics, a clade is a single "branch" on the "tree of life". The idea that such a "natural group" of organisms should be grouped together and given a taxonomic name is central to biological...
comprising J. tiomanensis, J. counsilmani, J. murphyi, J. johorensis, J. gapensis and J. intermedia, from which it separated about 5 million years ago, at a time when the eustatic changes in global sea level
Sea level
Mean sea level is a measure of the average height of the ocean's surface ; used as a standard in reckoning land elevation...
may have opened up a land bridge
Land bridge
A land bridge, in biogeography, is an isthmus or wider land connection between otherwise separate areas, over which animals and plants are able to cross and colonise new lands...
to Singapore.
Status
Johora singaporensis is listed by the International Union for Conservation of Nature as Critically EndangeredCritically Endangered
Critically Endangered is the highest risk category assigned by the IUCN Red List for wild species. Critically Endangered means that a species' numbers have decreased, or will decrease, by 80% within three generations....
under criteria B1ab(iii)+2ab(iii), which refer to the small size of the remaining populations and the ongoing deterioration of the habitat
Habitat
* Habitat , a place where a species lives and grows*Human habitat, a place where humans live, work or play** Space habitat, a space station intended as a permanent settlement...
. The species' restriction to a single small island is likely to have increased the threat of extinction.