Respiration data - a way of estimating growth rates of Antarctic sponges

Gatti, S; Brey, T; Arntz, WE

Antarctic sponges are supposed to grow very slowly because of low ambient water temperatures and scarce, seasonally strongly varying food supply. Sponges build hard structures (i. e. silicious spicules) that are possibly permanent. However, so far no method exists to use them for age analysis. It is not possible to distinguish any classes in size frequency distributions. Thus, it is currently impossible to assess growth or age via direct methods as done in molluscs, echinoderms, or fish. An indirect method provides a rough first estimate of growth rates and the age of abundant Antarctic sponges: During recent expeditions of RV Polarstern mass specific respiration rates of two species of Demospongiae (Stylocordyla borealis and Cinachyra antartica) were established. Oxygen consumption was measured as decreasing oxygen concentration in an intermittant flow system using micro-optodes (oxygen acts a quencher of luminophore fluorescence, i. e. fluorescence lifetime measured by the optodes is a function of oxygen concentration). Oxygen consumption of the very small individuals was distinctly higher than values inferred from respiration/mass relationships of boreal species, whereas values for larger individuals were comparable to boreal, tropical, or deep sea sponges. First results show a correlation between body mass (W) [mg afdw] and respiration R [ml O2 mg-1 afdw] log R = 0.0456 - 1.1083 * log W with r2 = 0.678; n=69 (for Cinachyra antarctica). To estimate the maximum capacity of oxygen consumption ETS (the activity of the electron transport system) was measured for several species of Antarctic sponges. Correlations between observed oxygen consumption and theoretically possible oxygen consumption will facilitate estimation of oxygen consumption of those species not used in respiration experiments. Production, P/B ratios and, subsequently, age can be inferred from the above data and population size frequency data using well established empirical relationships.