Effects of salinity changes on zinc uptake and regulation by the decapod crustaceans Palaemon elegans and Palaemonetes varians

Abstract

The decapod crustaceans Palaernon elegans Rathke and Palaernonetes varians (Leach) regulate their body concentrations of zinc to an approximately constant level (ca 76 to 82 and 90 to 99 11g Zng-' dry wt respectively) when exposed to a wide range of dissolved Zn concentrations, until a threshold dissolved concentration when regulation breaks down and net accumulation of body Zn begins. This threshold concentration decreases with decrease in salinity, from 100 "/u SW to 50 O/ O SW in the case of P. elegans (ca 92 to 27 pg Zn 1-' respectively) and from 100 % SW to 5% SW in the case of P. varians (ca 191 to 19 pg Zn 1-' respectively), in correlation with increased rates of Zn uptake. P. elegans showed a further increased uptake rate in 25 SW (1.054 _t 0.385 yg Zn g-' d-l in 25 ' 1 0 SW vs 0.735 f 0.077 1-19 Zn g-' d-' in 100 % SW at 10C in 56.2 pg Zn I-'), but had an atypical pattern of Zn regulation in raised Zn concentrations, probably as a result of atypically high Zn efflux caused by changes in water balance under osmotic stress. P. varians has a lower rate of Zn uptake than P elegans under identical physico-chemical conditions (1.80 2 0.61 vs 5-27 2 3.67 11g Zn g -' d-' in 100 [[g Zn 1-' in 5 0 % SW). Fifteen day acclimation of P. varians to either 50 or 25 % SW did not significantly change the subsequent mean rate of Zn uptake from 100 pg Zn 1-' in 2 5 % SW The body Zn concentration of P. varians transferred to dilute media of 25 and 5 O/O SW increased initially as a low salinity response but decreased again after 2 to 10 d to be regulated at ca 95pg Zn g-l It is concluded that Zn uptake and regulation in decapods are affected both by extrinsic physico-chemical factors and by intrinsic adaptations of the species concerned.