Salinity and survival in Bathyporeia pilosa Lindström and B. Pelagica (Bate)

Abstract

Experimental studies have shown that Bathyporeia pilosa has a wider salinity tolerance than B. pelagica. In both species, gravid females and juvenile males tolerate hyposalinity better than mature males, and an increase in temperature lowers the tolerance to hyposaline conditions. The differences in salinity tolerance between the species are considered to be important in determining the horizontal and vertical distribution. Field studies have shown that B. pilosa extends into areas where salinity fluctuations are pronounced, whilst B. pelagica occurs in areas of higher and more stable salinity. Seasonal changes in vertical distribution and abundance are considered to be influenced by salinity-temperature fluctuations acting in association with maturation. In both species, a silver staining technique has shown that permeable areas of the cuticle are restricted to the ventral surface. In B. pelagica oval-shaped ‘patches’ are very evident on the arthrodial membranes of the ventral surface, whilst in B. pilosa these patches are indistinct. The difference in development of these permeable areas is considered relative to the differences in salinity tolerance between the species.