Sesarma Robertii

The Sesarma Robertii is a common semi-terrestrial crab of small streams, seepage zones, and wet rock faces in Dominica. It favors shaded banks with steady trickles of water from near sea level to about 300 meters. Typical spots include boulder-strewn reaches of the Layou River and stony margins along the Batalie River, where it shelters under flat rocks and buttressed roots. After rainfall, individuals fan out to graze along damp leaf litter and exposed stones on the riverbank.

Ecology and identification

Medium sized for a stream crab, with a carapace about 25 to 27 mm long that is nearly as long as it is wide. Walking legs are long and slightly flattened, which helps the crab brace beneath rocks in moving water. Ground color ranges tan to dark brown with pale straw markings, eyestalks often show deep reddish tones with greenish corneas. Diet includes algae films, soggy leaf litter, insect larvae, amphipods, and other tiny invertebrates. By shredding detritus and scraping biofilm, the species supports riverbank ecosystems, contributes to island biodiversity, and forms part of the riparian wildlife community. Females brood eggs under the abdomen; larvae are released in brackish water and juveniles later recruit back into headwater creeks.

Sightings and best viewing areas

Move slowly along shallow riffles and seepage patches on rivers after rainfall. Lift only flat stones you can replace exactly as found, then wait quietly for movement at the edges. Late afternoon is productive when humidity is high and banks remain wet. Look for tight wedging behavior under rocks rather than quick dashes into open water, which is characteristic of this species on Dominican streams.