The effects of mercury on developing larvae of Rhithropanopeus harrisii (Gould) : I. Interactions of temperature, salinity and mercuryon larval development

Abstract

Larvae of the estuarine xanthid crab Rhithropanopeus harrisii were reared inthe laboratory from hatch through completion of metamorphosis to postlarva in 64 combinations of temperature (20–35°C), salinity (10–40‰) and mercury (0–20 parts 10 −9 Hg 2+ ). Multiple linear regression analysis and response surface methodology were used to determine and visually display the individual and interactive effects of the various constant temperature-salinity-mercury combinations on both survival and developmental rates of developing larvae throughout total larval development and for zoeae and megalopae separately, to distinguish any differential sensitivity between the two larval forms. Survival capacity of larvae under a broad range of salinities and temperatures characteristic of temperate estuarine conditions was progressively reduced upon continual exposure to mercury ranging from 5 to 20 parts 10 −9 Hg 2+ . Exposure concentrations as low as 5 parts 10 −9 Hg 2+ reduced the salinity and temperature plasciticity of the normally euryhalinic and eurythermal larvae. Larval survival from hatch to postlarva was affected by both mercury-salinity and mercury-temperature interactions with mercury toxicity increasing under suboptimal temperatures and salinities. Viability of early zoeal stages proved more sensitive to mercury exposure than the final megalopa stage. Exposure to mercury concentrations from 5–20 parts 10 −9 , Hg 2+ prolonged complete developmental duration by 3 to 4 days with zoeal developmental rates retarded more than megalopal rates. Developmental rates of the megalopa were more reduced by mercury at higher salinities, and both zoeal and megalopal developmental rates were more retarded by mercury at lower temperatures. The reduced plasticity of larvae to estuarine conditions, and retarded developmental rates by low mercury concentrations may reduce recruitment into adult benthic populations and alter the distributional patterns of pelagic R. harrisii larvae.