Osmoregulation and respiration in a marine chironomid larva, Paraclunio alaskensis Coquillett (Diptera, Chironomidae)

Abstract

The hemolymph of larvae acclimated in freshwater (19 mosmol/L) and seawater (897 mosmol/L) was analyzed and levels of Na+ (191 mM, 247 mM), Mg2+ (8 mM, 14 mM), Cl− (60 mequiv./L, 126 mequiv./L), and osmolarity (417 mosmol/L, 530 mosmol/L) were determined. Paraclunio alaskensis larvae were shown to be both euryhaline and hyperosmotic and hyposmotic regulators. The isotonic point of the hemolymph was 475 mosmol. Whole larvae contained 72% water and actively regulated water content (signified by changes in weight) over a wide range of external media. The basal respiration rate of larvae in seawater (0.032 μg O2∙mg dry weight−1∙h−1) indicated active cuticular respiration. The significance of these findings in relation to the intertidal habitat is discussed.