Salinity influences body weight quantification in the scyphomedusa Aurelia aurita: Important implications for body weight determination in gelatinous zooplankton

Abstract

Comparisons are made between bell diameter:weights (wet, dry, ash-free dry, ash and elemental) relationships for the scyphomedusa Aurelia aurita (L.). There are significant differences in the relationships between bell diameter and dry, ash-free dry and ash weights at different salinities, with these weights increasing as the ambient salinity increases. These trends are attributable to differences in the quantity of both bound water (i.e. 'water of hydration') and ash content, both of which vary with the size of medusae. Dry, ash-free dry and ash weights change rapidly as the salinity of an individual's environment alters, and these changes are associated with changes in the individual's buoyancy. Unless salinity effects are appropriately considered, significant errors may arise in the quantification of the biomass, production, and other weight-dependent measurements of A. aurita. Similar errors arise in other gelatinous organisms, and studies of such groups must make allowances for these effects.