Sources of otolith carbonate: experimental determination of carbon incorporation rates from water and metabolic CO2, and their diel variations

Abstract

Although carbon isotopes in fish otoliths are widely utilized to obtain information on environmental records, uncertainty regarding the sources of otolith carbonate, either from fish diet or ambient water, limits detailed determinations. The present study experimentally determined absolute incorporation rates of carbon derived from 2 sources, metabolic CO 2 and ambient water, into otoliths using goldfish under controlled conditions. In addition, the proportions of the 2 sources in otolith daily increments were also determined by the diel variations in the rate of incorporation from the 2 sources. A group of fish was administered with D-[ 14 C-U]-glucose or was exposed to water containing NaH 14 CO 3 , and incubated for 1, 3, 6, 12 and 24 h. Another group was similarly treated with the radiocarbons at 06:00, 12:00, 18:00, 00:00 or again at 06:00 h, and were incubated for 6 h. After incubation, serum and otoliths were collected and were separated into organic and inorganic carbon fractions, and the incorporation rates from the 2 sources were determined. The rates of carbon incorporation from D-[ 14 C-U]-glucose injected and NaH 14 CO 3 water were 0.27 (25.5%) and 0.79 (74.5%) nmol mg -1 otolith h -1 , respectively. During darkness (18:00 to 06:00 h), both the incorporation rate and proportion of metabolic-CO 2 -derived carbon significantly decreased to ~50% of that during daylight. These results suggest that otolith carbonate is mainly derived from ambient water, and the ratio of carbon derived from metabolic CO 2 is lower in the D-zone than that in the L-zone of the otolith daily increments.

Influence of diet on stable carbon isotope composition in otoliths of juvenile red drum Sciaenops ocellatus

“…The results of this experiment and the experiments of others clearly demonstrate some influence of metabolically derived carbon on otolith δ 13 C value (Kalish 1991, Radtke et al 1998b, Schwarcz et al 1998, Høie et al 2003, Solomon et al 2006, Tohse & Mugiya 2008. But, in order to properly interpret carbon stable isotope results for use in ecological studies, it is necessary to know the relative contribution of DIC and diet to the observed otolith δ 13 C value.…”

“…But, in order to properly interpret carbon stable isotope results for use in ecological studies, it is necessary to know the relative contribution of DIC and diet to the observed otolith δ 13 C value. To that end, studies with various fish species have demonstrated a dietary contribution ranging from 17 to 35% (Kalish 1991, Høie et al 2003, Solomon et al 2006, Tohse & Mugiya 2008. Solomon et al (2006), in a detailed experimental study on rainbow trout, estimated fractionation factors associated with otolith formation by manipulating the ambient water DIC δ 13 C and the dietary δ 13 C and, subsequently, by measuring the δ 13 C of the otolith, the endo lymph DIC, and the blood DIC.…”

“…A poor understanding of the proportional contribution of each source and associated enrichment factors has limited the usefulness of otolith δ 13 C values in fish ecology. Several studies have quantified the proportion of each carbon source, DIC and food, and, in most cases, the δ 13 C values of the otoliths reflect ~80% DIC and ~20% food (Weidman & Millner 2000, Høie et al 2003, Solomon et al 2006, Tohse & Mugiya 2008. To our knowledge, the only study that has estimated the associated fractionation factors from the carbon sources to the otolith (Solomon et al 2006) found otoliths to be enriched by 2.7 to 3.6 ‰ relative to the fish's diet.…”

Stock structure of Grey Mackerel, Scomberomorus semifasciatus (Pisces: Scombridae) across northern Australia, based on otolith stable isotope chemistry

“…Recently, Solomon et al (2006) reported that in Rainbow Trout, Oncorhynchus mykiss greater than 80% of otolith δ 13 C was derived from DIC in ambient seawater, while 17% was metabolically derived. In addition, Tohse and Mugiya (2008) determined that in Goldfish, Carassius auratus 75% of δ 13 C in otolith carbonates is derived from DIC in ambient seawater with the remainder (25%) derived from metabolic sources. There appears to be a large amount of variation among species in the proportion of metabolically derived δ 13 C in otoliths ranging from 5 to 40% and concomitantly in that derived from DIC in ambient seawater (Solomon et al 2006).…”

Ecogeochemistry potential in deep time biodiversity illustrated using a modern deep-water case study

“…Organic tissue carbon has a much more negative d 13 C vPDB value, typically ranging between ca 230‰ and 220‰. Consequently, while there is some evidence for isotopic fractionation of carbon during membrane transfer [61], the isotopic composition of carbon in biomineral carbonates in heterotrophic organisms represents a weighted average between the isotopic compositions of the dissolved inorganic and metabolic carbon sources, and increasing metabolic rates will drive biomineral carbon isotopes towards more negative values [59][60][61][62].…”