Kinetic and Metabolic Isotope Effects in Zooxanthellate and Non-zooxanthellate Mediterranean Corals Along a Wide Latitudinal Gradient

Abstract

Many calcifying organisms exert significant biological control over the construction and composition of biominerals which are thus generally depleted in oxygen-18 and carbon-13 relative to the isotopic ratios of abiogenic aragonite. The skeletal δ 18 O and δ 13 C values of specimens of Mediterranean zooxanthellate (Balanophyllia europaea and Cladocora caespitosa) and non-zooxanthellate corals (Leptopsammia pruvoti and Caryophyllia inornata) were assessed along an 8 • latitudinal gradient along Western Italian coasts, spanning ∼2 • C and ∼37 W m −2 of annual average sea surface temperature and solar radiation (surface values), respectively. Seawater δ 18 O and δ 13 C DIC were surprisingly constant along the ∼850 km latitudinal gradient while a ∼2 and ∼4% variation in skeletal δ 18 O and a ∼4 and ∼9% variation in skeletal δ 13 C was found in the zooxanthellate and non-zooxanthellate species, respectively. Albeit Mediterranean corals considered in this study are slow growing, only a limited number of non-zooxanthellate specimens exhibited skeletal δ 18 O equilibrium values while all δ 13 C values in the four species were depleted in comparison to the estimated isotopic equilibrium with ambient seawater, suggesting that these temperate corals cannot be used for thermometry-based seawater reconstruction. Calcification rate, linear extension rate, and skeletal density were unrelated to isotopic compositions. The fact that skeletal δ 18 O and δ 13 C of zooxanthellate corals were confined to a narrower range at the most isotopically depleted end compared to non-zooxanthellate corals, suggests that the photosynthetic activity may restrict corals to a limited range of isotopic composition, away from isotopic equilibrium for both isotopes. Our data show that individual corals within the same species express the full range of isotope fractionation. These results suggest that metabolic and/or kinetic effects may act as controlling factors of isotope variability of skeleton composition along the transect, and that precipitation of coral skeletal aragonite occurs under controlling kinetic biological processes, rather than thermodynamic control, by yet unidentified mechanisms.

Photosymbiosis in Late Triassic scleractinian corals from the Italian Dolomites

“…The oxygen and carbon isotopic signatures from Alpe di Specie corals fall within the range of values measured for Late Triassic scleractinians previously recognized as symbiotic (yellow ellipse in Fig. 4; Stanley Jr & Swart, 1995;Frankowiak et al, 2016b) and do not show a clear correlation (r 2 = 0.1 for linear regression) which is consistent with similar observation for modern zooxanthellate and in contrast to azooxanthellate corals (Stanley Jr & Swart, 1995;Prada et al, 2019). These observations corroborate with photosymbiotic status of all studied herein corals.…”

“…When combined, the δ 18 O and δ 13 C parameters differ significantly between symbiotic and asymbiotic scleractinians ( Fig. 4; Swart, 1983;Stanley Jr & Swart, 1995;Cohen & McConnaughey, 2003;Adkins et al, 2003;Frankowiak et al, 2016b;Prada et al, 2019). The oxygen and carbon isotopic signatures from Alpe di Specie corals fall within the range of values measured for Late Triassic scleractinians previously recognized as symbiotic (yellow ellipse in Fig.…”

Oxygen and carbon isotope variations in Chamelea gallina shells: Environmental influences and vital effects

“…This inconsistency could be attributed to the fact that C. gallina precipitates the shell carbonate preferentially during the warm period, while considerably reducing its activity during the cold season (Cespuglio et al, 1999;Keller et al, 2002). The same seasonality of shell growth in the Adriatic Sea was found in the long-lived bivalve Glycymeris pilosa and in the venerid Callista chione and Venus verrucosa, that showed to be a promising archive for the reconstruction of summer seawater temperatures with the slowest growth during winter (Peharda et al, 2019;Purroy et al, 2018;Uvanović et al, 2021).…”

Determination of temperature-dependent otolith oxygen stable isotope fractionation on chum salmon Oncorhynchus keta based on rearing experiment

“…It should be noted that a weak correlation between the oxygen and carbon fractionation was observed for the 9°C group (see Figure 8), with a wide fluctuation of the oxygen isotopes. In biogenetic carbonates, isotopic disequilibrium is mainly attributed to metabolic and kinetic isotope effects (McConnaughey, 1989a;Cohen and McConnaughey, 2003;Daëron et al, 2019;Prada et al, 2019;Huyghe et al, 2020), and it is difficult to discriminate between them. Kinetic effects are more significant, resulting in the depletion of heavier 13 C and 18 O simultaneously, rather than the incorporation of metabolic CO 2 alone.…”