Seasonal densities of Eurytemora affinis, a calanoid copepod in the Ch
esapeake Bay, seem to be controlled by temperature and salinity. To ex
amine the role of osmotic stress we analyzed protein synthesis under v
arious conditions of temperature and osmotic stress. Adult females wer
e exposed in groups for 5 hours to different temperature and salinity
regimes in the presence of isotope-labelled amino acid. Newly synthesi
zed (stress) proteins could be separated and identified using polyacry
lamide gel electrophoresis and autoradiography. The protein profiles o
ccurring in copepods experiencing osmotic shock alone were different f
rom those of control animals. Copepods transferred to lower (2 and 5 p
arts per thousand) and higher (15 and 20 parts per thousand) salinitie
s showed differences in the up- and down-regulation of specific protei
ns. Concurrent heat stress changed these protein patterns. Animals exp
eriencing osmotic and heat shock at the same time exhibited enhanced e
xpression of another set of proteins. Variation in induced proteins oc
curred among individuals.