Endemic predatory shrimp  (Procaris ascensionis)

This species has not yet been classified by the IUCN.

Endemic to just two small rock pools on Ascension Island, this shrimp occupies an extremely vulnerable position (3). The endemic predatory shrimp is partly translucent, with yellow colouration inside the front of its body and red colouration covering fragments of its exterior. Specialised appendages help in the trapping of prey for this ‘more than likely’ blind shrimp (4). All five pereiopods, which are appendages used for moving, feeding and defence, are extended to pull the prey in (4) (5). The victim is then trapped against the shrimp’s underside with the aid of maxillipeds, which are limbs at the front of the body that are modified to act as mouth parts (4) (5). The shrimp has then been observed swimming upside down, trapping its prey within a cage formed by the spiny pereiopods (4).

Confined to the southwest corner of Ascension Island (3).

Found in two coastal rock pools (6) set well inland from the high tide mark, but with possible underground connections with the ocean (3). The largest pool is about 5 yards in diameter and contains 18 inches of water, with its rocky bottom covered with muddy clay (3). Smaller individuals appear to spend most of their time in crevices and amongst algae, whilst larger individuals spend more time in open water (2) (4).

The endemic predatory shrimp feeds on both plant matter and crustaceans, including amphipods (small, prawn-like species) and atyid shrimp (2). Individuals can often be observed moving through the algae, extending their pereiopods, apparently searching for prey (4).

Little is known about the reproductive biology or life history of these shrimp. A sex ratio of eight females to one male has been found, but the reason for this remains unknown. A single female bore approximately 60 large, bright orange eggs in a laboratory, but no egg-bearing females have been seen in the wild (2).

The precise threats facing the endemic predatory shrimp are unknown, but its extremely restricted range is a considerable cause for concern. In 1976, three mangrove trees were found in the larger pool, in a straight line as if they had been deliberately planted. While the pools are difficult to get to, it has been noted that locals would occasionally visit them to collect shrimps to feed their aquarium fishes, and may have planted the mangroves. These were perceived to threaten the shrimp population so were promptly removed, but human disturbance and invasion by alien species remain significant threats (3). Furthermore, it has been argued that the similarities between all Procaris species, and their distribution only in obscure marine caves and pools that have changed little over time, indicate an extremely slow rate of evolution. The suggestion is that Procaris and its predecessors may have been more widely distributed in the past but can now survive only in cryptic habitats removed from the sort of human and environmental pressures that necessitate evolutionary change (2). Thus, if this species’ small, restricted habitat should change, it is unlikely that it could adapt fast enough to survive.

There are currently no conservation measures directly targeted at this species.

For more information on the endemic predatory shrimp see:

CaveBiology.com:
http://www.tamug.edu/cavebiology/fauna/shrimp/P_sp.html

Abele, L.G. & Felgenhauer, B.E. (1985) Observations on the ecology and feeding behaviour of the anchialine shrimp Procaris ascensionis. Journal of Crustacean Biology, 5(1): 15 – 24.