Buoyancy and diapause in Antarctic copepods: The role of ammonium accumulation

Autor: Astrid Cornils, David N. Thomas, Sigrid B Schnack-Schiel, Franz Josef Sartoris
Rok vydání: 2010
Předmět:
Zdroj: Limnology and Oceanography. 55:1860-1864
ISSN: 0024-3590
DOI: 10.4319/lo.2010.55.5.1860
Popis: To test the hypothesis that copepods are able to regulate their buoyancy via altering their ionic content, we analyzed both the cation concentration in the hemolymph of Antarctic pelagic copepod species in late winter and the vertical distribution pattern and population structure. High concentrations of ammonia/ammonium (NH3/ NH z ) were measured only in the hemolymph of Calanoides acutus, an Antarctic copepod definitely known to undergo vertical ontogenetic migrations and diapause at great depth, and in Rhincalanus gigas, in which a vertical ontogenetic migration pattern associated with diapause is still under debate. None of the other investigated species showed elevated ammonium concentrations in their hemolymph. We suggest that ion replacement by ammonium contributes to neutral buoyancy in diapausing calanoid copepods in the Southern Ocean. We hypothesize that ammonium buoyancy changes with season and is associated with shifts in extracellular pH and, therefore, most likely mediates metabolic depression during diapause. Copepods are dominant members of the zooplankton biomass worldwide (Longhurst 1985), and owing to their high production:biomass ratio of 4.4 (Voronina 1998) they contribute greatly to the total zooplankton production. In Antarctic waters the dominance of copepods is mainly due to large calanoid species such as Rhincalanus gigas, Calanus propinquus, Calanoides acutus, Metridia gerlachei ,a nd Paraeuchaeta spp., which can make up more than 50% of the total zooplankton biomass (Boysen-Ennen et al. 1991). The annual production of these large copepods significantly exceeds that of the Antarctic krill Euphausia superba (Voronina 1998). In polar seas herbivorous calanoid copepod species are strongly affected by the distinct seasonality in primary production and have developed specific behavioral and life history strategy adaptations to survive long periods of food scarcity. Species belonging to the Eucalanidae and Calanidae families are known to undergo an extensive ontogenetic vertical migration: They descend out of the surface waters as late copepodite stages to greater depths ($ 500 m), where they remain in a resting stage (diapause) for several months (Conover and Huntley 1991; Dahms 1995; Schnack-Schiel 2001). During this time they have severely reduced respiration and swimming activity (Schnack-Schiel et al. 1991; Dahms 1995), suggesting that they have little active control over their vertical distribution. This invokes a rather fundamental question: How can an animal with reduced metabolism and swimming activity remain at a particular depth layer for such long periods of time? For this to happen the animal must be neutrally buoyant at that depth.
Databáze: OpenAIRE
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