ABSTRACT
Shells and mantle tissues of six brachiopod species were analysed for elemental carbon, hydrogen and nitrogen (CHN), and ash-free dry mass, (AFDM) content. Four were punctate articulates (Liothyrella neozelanica, L. uva, Terebratulina retusa and Kraussina rubra), one was an impunctate articulate (Notosaria nigricans) and another was a punctate inarticulate (Neocrania anomala). All C:N ratios were between 3.8 and 5.8. These were low values and indicated a high protein content in all samples. Unexpectedly, elemental analysis revealed higher C:N ratios in shells than mantle tissues, suggesting that protein contents of mantle tissues were higher than shells, including the impunctate N. nigricans. Organic content assessments for shells using an HCl digest method were not significantly different from loss on ignition estimates for 2 of 3 species analysed. Similar HCl digest estimates for mantle tissue samples produced underestimates of around 50%, and the method is not appropriate for soft tissues. Shell AFDM estimates calculated from CHN assessments were lower than loss on ignition assessments in 5 of the 6 species studied (except L. neozelanica). The average estimates were 2.45% for calculations based on CHN content and 3.01% for loss on ignition. For mantle tissues the calculations based on elemental analysis produced estimates around 50% of those from the loss on ignition method. The major aim of this project, to apportion fractions of shell organic content to caeca and protein matrix was not possible because the C:N ratios obtained for mantle tissues were lower than for shell samples.
