Ammonium content and buoyancy in midwater cephalopods

The majority of squid families (Teuthoidea: Cephalopoda) exchange sodium for ammonium, creating a low-density fluid that imparts lift for neutral buoyancy. However, previous methods for measuring ammonium did not distinguish between NH4 + and various other amine compounds. The present study, using single column ion chromatography, reassessed the cation concentrations in several midwater cephalopod species. High NH4 + levels were confirmed for histioteuthid, cranchiid, and chiroteuthid and related squids. A strong relationship is reported between ammonium content and body mass in Histioteuthis heteropsis , suggesting a gradual accumulation of ammonium coincident with an ontogenetic migration to greater depths. The bathypelagic squids Bathyteuthis abyssicola and Bathyteuthis berryi, on the other hand, contained very little ammonium but rather contained large quantities of an as yet unidentified cation. The ecological significance of this compound is not yet known. Morphology in Bathyteuthid squids suggests that the unknown cation is contained intracellularly and so, unlike sequestered ammonia, does not diminish the space available for muscle tissue. Accordingly, protein measurements in B. berryi mantle muscle are on par with shallower-living muscular 0022-0981/$ doi:10.1016/j. * Corresp E-mail add Journal of Experimental Marine Biology and Ecology see front matter D 2004 Elsevier B.V. All rights reserved. jembe.2004.08.015 onding author. Tel.: +1 401 874 7997; fax: +1 401 874 4256. ress: [email protected] (B.A. Seibel). B.A. Seibel et al. / J. Exp. Mar. Biol. Ecol. 313 (2004) 375–387 376 squids, and in situ submersible observations reveal strong locomotory abilities relative to other deep-water squids. D 2004 Elsevier B.V. All rights reserved.