Abstract
We evaluated eye lenses as potential recorders of stable isotope histories in fish because they consist of metabolically inert optical proteins that are deposited in successive, concentric circles (laminae) much like otolith circuli and tree rings. We conducted four different tests on lenses from red snapper, red grouper, gag, and white grunt. The first test was a low-resolution screening of multiple individuals (4–5 radial groups of laminae per lens, all species except white grunt). Along the radial axis, all individuals exhibited substantial isotopic variability. Red snapper individuals separated into two groups based on δ 15N and gag separated into two groups based on δ 13C. Two gag with the greatest variation were chosen for high-resolution temporal analysis using individual laminae from their second eye lenses. The first-order patterns from the high-resolution analysis generally mimicked patterns from the low-resolution screening of grouped laminae, yet the high-resolution plots revealed early-life details that were not apparent in the low-resolution screenings. For the third test, left- versus right-eye variation was compared using high-resolution methods. White grunt left- and right-eye radial isotopic patterns were almost identical for both δ 13C and δ 15N, suggesting the variations observed among individual fish were not artifacts. The final test evaluated intra-laminar variation; multiple samples were analyzed from different parts of the same lamina. Seven laminae from three individuals of two species were analyzed in this manner; variations among laminae were found to be much higher than variations within laminae. However, nominal intra-laminar variations were comparable to nominal differences between left and right lenses, suggesting intra-laminar variation established measurement precision. Eye lens isotopes appear to be useful for reconstructing the isotopic histories of individual fish; these histories can be compared with spatially-derived isoscapes to reconstruct individual histories for site fidelity, movement and trophic position.
Highlights
Recorded stable-isotope histories can be used to recreate lifelong trends in animal diets, trophic dependences, and movement within isotopically variable landscapes [1,2,3,4,5]
Fish were obtained from surveys conducted by the Florida Fish and Wildlife Commission (FWC) and from a licensed charter-fishing vessel operating within state and federal regulatory guidelines in waters no more than 80 km distant from John’s Pass, Madeira Beach, Florida
Low-resolution screening analyses were conducted for eight red snapper, four red grouper, and three gag
Summary
Recorded stable-isotope histories can be used to recreate lifelong trends in animal diets, trophic dependences, and movement within isotopically variable landscapes [1,2,3,4,5]. Such lifelong records are difficult to obtain because most tissues undergo metabolic turnover, and this turnover places limits on the retrospective time period that can be investigated [2,3,5,6,7]. Fish scales, and vertebrae are tissues currently used to provide life-history records for fish. Some tissues can be sampled noninvasively on a regular basis to create a long-term isotopic record, but require recapture of the same animal on a regular basis [18,19]
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