Behavioural and physiological implications of a burrow-dwelling lifestyle for two species of upogebiid mud-shrimp (Crustacea: Thalassinidea)

Upogebia stellata and U. deltaura (Crustacea: Thalassinidea) construct burrows in nearshore sediments in U.K. waters. Burrow structure is similar in both species; the basic burrow consisting of a two-opening, U-shaped section with a vertical shaft descending from the mid-point of the U. This structure may be variously elaborated. Burrow cross-section is circular, dilations allow turning by somersaulting and surface openings are often constricted. Conditions within the burrows are usually hypoxic and hypercapnic. Burrow water PO2 in the parts normally occupied by the mud-shrimp was between 80-110 Torr, but was much lower (10-45 Torr) in the deepest, poorly-irrigated parts. Both species irrigate their burrows by episodes of pleopod beating of variable duration (mean=8.5 +/- 3.5 min and 2.8 +/- 0.5 min for U. deltaura and U. stellata, respectively), which draws oxygenated water into the burrow and also particulate food for suspension feeding. When exposed to hypoxia, U. deltaura and U. stellata were able to maintain their rates of oxygen consumption approximately constant over a wide range of PO2 (Pc=30-50 Torr). Under these conditions, there was a pronounced increase in scaphognathite beat rate but heart rate remained relatively constant. Below the Pc, however, both rates declined. (C) 1997 Academic Press Limited.