Application of the bomb radiocarbon chronometer with eye lens core Δ¹⁴C for age validation in deepwater reef fishes

Abstract

Eye lens core Δ14C of Gulf of Mexico outer shelf and upper slope reef fishes matched a regional Δ14C reference time series, but otolith cores were depleted in 14C relative to the reference series. This is due to C in eye lens protein being derived from metabolic sources, with the ultimate source being epipelagic phytoplankton. In contrast, otolith C is derived mainly (70-80%) from dissolved inorganic C, which is depleted in 14C beyond the epipelagic. Analyzing Δ14C in eye lens cores provides a novel approach for validating age estimates of deepwater (>200 m) fishes, which was unresolved in earlier applications of the bomb 14C chronometer.

Eye lens-derived Δ14C signatures validate extreme longevity in the deepwater scorpaenid blackbelly rosefish (Helicolenus dactylopterus)

“…The offset between surface reference and otolith core Δ 14 C for species living at depths > 500 m is often reported to be 100–150‰, which is in the same range as the offset between nGOM blackbelly rosefish otolith core Δ 14 C and reference series Δ 14 C values. However, data reported here, as well as for the suite of nGOM deepwater fishes 48 , suggests deriving birth year Δ 14 C signatures from eye lens rather than otolith cores may enable the bomb 14 C chronometer to be generally effective for age validation of deepwater fishes. It is currently unclear, however, if this approach has some depth threshold to its effectiveness, but to date it has been successfully applied to upper slope reef fishes that live at depths as great as 500 m. Given vertical migrants routinely (daily) transit from depths of 1,000 m or more into the epipelagic to forage 80 – 82 , it may be that the organic carbon available at those depths also has a contemporary surface bomb 14 C signature.…”

“…Additionally, eye lenses, like otoliths, are metabolically inert once formed and grow throughout a fish’s life 46 , 47 . Thus, eye lens cores may be an ideal source of birth year Δ 14 C for deepwater species 44 , and analysis of eye lens versus otolith core Δ 14 C values of nGOM deepwater (to 500 m) fishes suggests eye lens Δ 14 C does in fact match surface Δ 14 C DIC values 48 . Therefore, the objectives of this study were to conduct age validation of blackbelly rosefish via application of the bomb 14 C chronometer to eye lens Δ 14 C, as well as to estimate growth, longevity, and natural mortality from ageing data.…”