Dataset: CSIA-AA comparison between live polyps and outer proteinaceous skeletal material in three (3) taxons of deep-sea corals

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Project: 
Principal Investigator: 
Thomas Guilderson (University of California-Santa Cruz, UCSC)
BCO-DMO Data Manager: 
Amber D. York (Woods Hole Oceanographic Institution, WHOI BCO-DMO)
Version: 
1
Version Date: 
2023-03-07
Restricted: 
No
Validated: 
No
Current State: 
Preliminary and in progress

CSIA-AA comparison between live polyps and outer proteinaceous skeletal material in three taxons of North Pacific deep-sea corals
Abstract: 
Much of the recent proxy development work with proteinaceous deep-sea corals has focused on stable isotope analysis (SIA) of total (“bulk”) skeletal material, as a proxy for changes in surface ocean conditions (e.g., Heikoop et al. 2002; Sherwood et al. 2005, 2009; Williams et al. 2007; Hill et al. 2014). We conducted bulk d13C and d15N analyses on all paired polyp tissue and proteinaceous skeleton samples from the three genera of deep-sea corals. For bulk d13C analyses of skeleton, a subset of each skeleton sample was individually acid washed in 1 N HCl in glass vials for four hours, rinsed three times in Milli-Q water, and dried over night at 50°C to remove calcium carbonate and isolate the organic fraction of the skeleton. Bulk d15N analyses were conducted on non-acidified skeleton samples. Deep-sea coral polyp tissues are very lipid rich (Hamoutene et al. 2008), and therefore a subset of each polyp sample was lipid extracted three times following the conventional methanol/chloroform protocol of Bligh and Dyer (1959) prior to d13C analysis. Bulk d15N analyses were conducted on non-lipid extracted polyp samples. Bulk stable carbon (d13C) and stable nitrogen (d15N) isotopes were measured on a 0.3 mg aliquot of each sample using a Carlo Erba 1108 elemental analyzer interfaced to a Thermo Finnegan Delta Plus XP isotope ratio mass spectrometer (IRMS) at the Stable Isotope Lab, University of California, Santa Cruz. Raw isotope values were corrected for instrument drift and linearity effects, calibrated against the in house isotopic reference materials of the Stable Isotope Laboratory (http://emerald.ucsc.edu/~silab/), and reported in per mil (‰) relative to Vienna PeeDee Belemnite and air for carbon and nitrogen, respectively. Reproducibility of two lab standards was 0.05‰ and 0.15‰ for carbon and nitrogen isotopes, respectively. Bulk tissue and individual AA stable isotope offsets were calculated as the difference in isotope value (d13C or d15N) between paired polyp and skeleton samples for each specimen within each genus of deep-sea coral. Carbon isotopes have long been used to infer sources of primary producers contributing to food web architecture (Wada et al. 1991; Boecklen et al. 2011). Bulk d13C were generally more positive in Primnoa from the Gulf of Alaska and Isidella from the Sur Ridge than Kulamanamana from the NPSG (Table B.1 of McMahon et al., 2018). However, interpreting past changes in primary producer composition from these bulk carbon isotope values is challenging (Schiff et al. 2014; McMahon et al. 2015a). For example, we found large differences in the bulk d13C values (mean offset = 3.5 ± 0.5‰ averaged across all three species) and C/N ratio (mean offset = 1.9 ± 0.7) between lipid-intact coral polyp tissue and recently deposited protein skeleton within single colonies. These offsets were far greater than the differences in d13C value (1-2‰ for a given tissue) among different genera of corals collected from vastly different oceanographic regimes (Table B.1). This intra-colony offset likely reflects differences in macromolecular tissue composition (lipid, AA, carbonate) rather than environmental drivers. Once lipids were removed from the polyp tissue, there was only a small difference in bulk d13C value (mean offset = -0.4 ± 0.1‰ averaged across all three species) and C/N ratio (mean offset = 0.2 ± 0.3) between proteinaceous skeleton and polyp tissue for all species. However, even after bulk lipid extraction of polyp tissue and decalcification of skeleton material, the remaining confounding influences of primary producer source and trophic dynamics make interpreting bulk d13C variability among specimens very challenging. Stable nitrogen isotopes of consumers reflect both the source of nitrogen at the base of the food web and the number of trophic transfers between that base and the consumer (Boecklen et al. 2011). While these factors may explain the significant differences in bulk tissue d15N values among the proteinaceous deep-sea coral species (~6‰) in our study (Table B.1 of McMahon et al.,2018), we also found a moderate offset in bulk d15N value (1.9 ± 0.7‰ across all three species) between polyp tissue and proteinaceous skeleton within colonies (Table B.1 of McMahon et al., 2018). As with bulk d13C differences discussed above, such offsets between tissue types of the same individuals are likely due primarily to biochemical composition: i.e., the larger diversity of nitrogenous organic molecules in coral polyp as compared with its skeleton, as well as the highly selected AA composition of the specialized gorgonin structural protein found in proteinaceous skeleton (Goodfriend et al. 1997; Ehrlich 2010). Bulk d15N isotope data therefore can be even more challenging to interpret than bulk d13C data, given the potential differences in tissue composition within and among species, as well as the much larger influence of d15N baseline and trophic position. These data were published in an alternate format as part of the supplementary materials pdf of McMahon et al. (2018).

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