Decomposition-Induced Change in Stranded Megafauna: Decoupling Postmortem Impacts from the Isotopic Niche

Area of Science:

• Paleoecology
• Marine Mammal Ecology
• Biogeochemistry

Background:

• Stable isotope analysis of animal tissues is crucial for reconstructing lifetime diets.
• Postmortem decomposition effects on stable isotope measurements are not well understood.
• Different tissue turnover rates influence dietary reconstructions over time.

Purpose of the Study:

• To investigate the impact of decomposition on stable isotope values (δ¹³C, δ¹⁵N, δ³⁴S) in various harbor porpoise tissues.
• To assess changes in both bulk and amino acid stable isotope measurements during early decomposition.
• To understand how decomposition affects the reliability of stable isotope-based dietary studies.

Main Methods:

• Analysis of bulk δ¹³C, δ¹⁵N, and δ³⁴S values from multiple harbor porpoise tissues.
• Analysis of amino acid δ¹³C and δ¹⁵N values from the same tissues.
• Comparison of isotopic values across samples with varying states of decomposition.

Main Results:

• Decomposition led to a consistent decline in δ¹³C values across all tissues and amino acids, indicating microbial fermentation.
• δ¹⁵N and δ³⁴S values remained largely stable during early decomposition.
• Tissue-specific isotopic differences were significant, influenced by metabolism and elemental turnover.

Conclusions:

• Early decomposition causes predictable shifts in carbon stable isotope values, necessitating caution in interpreting data from degraded samples.
• Nitrogen and sulfur isotope values are more resilient to early decomposition.
• Accurate dietary reconstructions from moderately decomposed marine mammal tissues require tissue-specific discrimination factors and careful amino acid selection.