By John Dawes

Hobbyists and people within the fish trade have taken additional interest in freshwater crustacea—specifically micro-shrimps—as nano aquarium popularity grows. While most of this sector is taken up by shrimps, there is also a subsector that consists of freshwater crabs, plus some terrestrial species, such as Cardisoma armatum from West Africa, that spend time both under and above water.

The rainbow or patriot crab (Cardisoma armatum)—shown here underwater—is one of the most commonly-seen species of freshwater/terrestrial crabs found in shops. Courtesy of John Dawes.

According to a recent study carried out by scientists from the Zoological Society of London, Northern Michigan University, National University of Singapore and other institutions, of the 1,280 species currently known, no fewer than 227 “should be considered as near threatened, vulnerable, endangered or critically endangered.” (See “Freshwater crabs ‘feel the pinch’” by Matt Walker, on the BBC - Earth News website).

Of the above,  33 are in the “critically endangered” category, while 52 are listed as “endangered” and 106 as “vulnerable,” leaving another 36 as “near threatened” and the remainder in the “least concern” and “data deficient” categories (1,053 species).

According to the study, “about one-sixth of all freshwater species have an elevated risk of extinction, only one-third are not at-risk, and although none are actually extinct, almost half are too poorly known to assess.” The scientists further report that “out of the 122 countries that have populations of freshwater crabs, 43 have species in need of protection.” No country illustrates this more forcefully than Sri Lanka, where no fewer than 40 of its 50 species of freshwater crabs are considered threatened.

This example cited is used “to underline and prioritize and develop conservation measures before species decline to levels from which they cannot recover.” Ben Collen from the Zoological Society of London, one of the scientists involved in the survey, said, “We must set clear goals to reverse these trends and ensure that our enduring legacy is not to wipe out the small things that provide us with great benefits, such as nutrient cycling.”

This last comment refers to the dietary habits of freshwater crabs, many of which feed on leaf litter, algae, detritus, fruits and even carrion. This makes them easy to keep in aquaria or terraria setups (the setup varies according to the species kept)—something that, allied to the attractive coloration of many species, is certain to ensure their niche in our industry and hobby…that is, until or unless all-encompassing legislation is formulated to protect those species that are in genuine danger of extinction. <HOME>

REFERENCE:
Neil Cumberlidge, Peter K.L. Ng, Darren C.J. Yeo, et al, Freshwater crabs and biodiversity: Importance, threats, status, and conservation challenges. Biological Conservation, Vol. 132, Issue 8, August 2009, pages 1665-1673.