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

• Main Author: Schründer, Sabine
• Other Authors: Auel, Holger, Schiel, Sigrid
• Format: Doctoral or Postdoctoral Thesis
• Language: English
• Published: Universität Bremen 2015
• Subjects: Antarctic; copepod; C; acutus; diapause; buoyancy; ammonium; 500; 500 Science; ddc:500; Austral; Antarc*; Copepods
• Online Access: https://media.suub.uni-bremen.de/handle/elib/955; https://nbn-resolving.org/urn:nbn:de:gbv:46-00104867-18

Copepods play a vital role in marine pelagic food webs. They channel energy from primary production to higher trophic levels and, via the biological carbon pump, substantially affect biogeochemical cycles and carbon fluxes. The distinct seasonality of primary production is the most important factor influencing life-cycle adaptions of herbivorous copepods in polar ecosystems. Ontogenetic seasonal vertical migration (OVM) with a resting stage (diapause) at great depth is known as an adaption to escape food scarcity during winter. Diapause is characterised by reduced metabolic rates and the cessation of feeding. Therefore, diapausing copepods are presumably neutrally buoyant to avoid a depletion of their restricted recources by swimming movements. However, no experimental observations or density determinations had been conducted for Antarctic copepods so far and the mechanisms triggering the on- and offset of OVM and diapause, and regulating buoyancy, were still far from understood. Within the present study, novel hypotheses about the controlling factors for dormancy and OVM were established. The accumulation of ammonium (NH4 ) and the replacement of ions with a higher density is a known buoyancy regulation mechanism in several marine invertebrates. To keep ammonium in the less toxic ionised form, a low pH is required. Knowing that acidic pH conditions are a relevant factor inducing metabolic reduction, a low haemolymph pH might not only be a precondition for ammonium accumulation, but in addition trigger dormancy in copepods. Buoyancy observations of anaesthetised individuals revealed that diapausing Calanoides acutus was neutrally buoyant during austral winter, whereas actively overwintering Calanus propinquus was negatively buoyant. Diapausing and non-diapausing species differed sigificantly in their extracellular cation composition. In actively overwintering species, the cation composition of the haemolymph was similar to that of seawater. In diapausing copepods, severly elevated concentrations of up to 530 ...