Early life history ofNautilus: evidence from isotopic analyses of aquarium-reared specimens

Abstract

Specimens of Nautilus species caught in the wild show a marked increase in oxygen isotopic composition between embryonic and postembryonic septa. The significance of this increase in terms of the early life history of Nautilus has been unclear. To help explain this pattern, we analyzed the isotopic composition of the septa of three specimens of Nautilus belauensis raised in aquariums under controlled temperature conditions. Our results indicate that both embryonic and postembryonic septa are secreted with the same temperature-dependent fractionation of aragonite relative to water as that of other aragonite-secreting molluscs (Grossman and Ku 1986). The δ18O values of the septa thus provide a reliable means of determining the water temperature in which the septa form. Calculated temperatures based on oxygen isotopic data from specimens caught in the wild reveal that embryonic development occurs at 22°-24° corresponding to a depth of 100-200 m depending on the location. The increase in δ18O in postembryonic septa reflects a migration into colder, deeper water after hatching. In Cretaceous nautilids, a systematic shift in δ18O is not present, indicating that these animals probably did not change their habitat after hatching. This is consistent with the likelihood that they lived in shallower environments than that of modern Nautilus.

Ammonoid Habitats and Life History

“…Sclerochronologic (i.e., hard-part measurements in chronological order) δ 13 C and δ 18 O records from numerous Nautilus species were provided by several authors (Eichler and Ristedt 1966a, b;Cochran et al 1981;Taylor and Ward 1983;Wefer 1985;Landman et al 1983Landman et al , 1994Auclair et al 2004;Zakharov et al 2006). δ 13 C and δ 18 O in Sepia cuttlebones were also measured (Longinelli 1966;Longinelli and Nuti 1973;Hewitt and Stait 1988;Bettencourt and Guerra 1999;Hobson and Cherel 2006;Rexfort and Mutterlose 2006;Cherel et al 2009).…”

“…Stable isotope analyses performed on micro-and macroconchs could help to strengthen or refute these assumptions because δ 13 C and δ 18 O data generate details on seasonality and ontogeny. Eichler and Ristedt 1966a, b;Cochran et al 1981;Taylor and Ward 1983;Landman et al 1983Landman et al , 1994Landman 1988;Oba et al 1992;Auclair et al 2004;Zakharov et al 2006;Kruta et al 2014). Due to the isochronous timing of the isotope shift from negative to positive values and the decrease in septal spacing and position of the nepionic constriction, this isotope shift is considered to represent hatching of the animal (Cochran et al 1981;Oba et al 1992).…”

“…However, the eggs analysed by Crocker et al (1985) did not contain developing embryos, so the fractionation between the egg water and embryonic shell was not evaluated. Landman et al (1994) finally succeeded to analyze the δ 18 O of shells of N. belauensis raised under controlled temperatures in the Waikiki Aquarium from embryonic and early postembryonic stages. The shells of both stages were secreted under isotopic equilibrium with the in situ water.…”

“…Adapted and extended after Lukeneder et al (2010). Maximal depth range estimates based on siphuncle strength index (SiSI) from Hewitt (1996, black stars) and Westermann (1996, white stars) Cochran et al 1981;Taylor and Ward 1983;Landman et al 1983Landman et al , 1994Landman 1988;Oba et al 1992;Moriya et al 2003;Auclair et al 2004;Lukeneder et al 2010). Similarly, if we know the local seasonal variation of ancient sea surface temperatures, which is comparable to the ontogenetic variation of isotope temperature of an analyzed ammonoid individual, we can infer habitat depth (Moriya et al 2003).…”

“…The main feature causing postmortem drift in cephalopod shells is the presence of a gas-filled phragmocone. Postmortem drift of empty cephalopod shells can be observed in Recent Nautilus (Kennedy and Cobban 1976;Saunders and Landman 1987;Ward 1987;Reyment 2008). Hamada (1964Hamada ( , 1984 and Toriyama et al (1964) report similar shell concentrations for modern Nautilus.…”