Overwintering strategies in polar copepods: Physiological mechanisms and buoyancy regulation by ammonium

• Applicants: Holger Auel, Ph.D.; Dr. Franz Josef Sartoris
• Subject Area: Oceanography
• Term: from 2010 to 2016
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 172475510

Ontogenetic seasonal migration associated with a diapause is known as an adaptation to escape temporally from an unfavourable environment in several calanoid copepod species in Polar Seas. Diapausing copepods reside for several months in greater depths where they are presumably neutrally buoyant. Ammonium buoyancy as been observed in several marine invertebrates has never been studied in diapausing copepods. Dependent on the pH, ammonia exists in solutions as both NH3 and NH4 +). Due to the toxicity and the higher diffusibility of NH3 a low haemolymph pH is required to favour the formation of ammonium (NH4 +). The trigger (onset, duration, termination) of diapause is yet unknown. In a recent study we detected ammonium values as high as 500 mmol L-1 in the haemolymph of the diapausing Antarctic copepods Calanoides acutus and Rhincalanus gigas, as well as in the diapausing calanoid copepods Calanoides carinatus and Eucalanus sp. in the Benguela Current upwelling system, indicating ammonia buoyancy in these species. In diapausing copepods metabolic depression is evident by reduced metabolic rate and reduced swim activity. We hypothesize that a low extracellular pH in the haemolymph of diapausing copepods necessary to form NH4 + and to prevent it from diffusive loss could play a fundamental role in the regulation of metabolic depression and thus in the control of diapause. This would lead to a seasonality of ammonia buoyancy with high ammonium and low pHe during diapause and high pHe and low ammonium in the active periods.

• DFG Programme: Infrastructure Priority Programmes
• Subproject of: SPP 1158: Infrastructure area - Antarctic Research with Comparative Investigations in Arctic Sea Ice Areas
• Participating Person: Professorin Dr. Sigrid Schiel