Stable isotope and pen feeding trial studies confirm the value of horseshoe crab Limulus polyphemus eggs to spring migrant shorebirds in Delaware Bay

G.M. Haramis; W.A. Link; P.C. Osenton; Daniel B. Carter; R.G. Weber; N.A. Clark; M.A. Teece; D.S. Mizrahi

doi:10.1111/j.0908-8857.2007.03898.x

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Stable isotope and pen feeding trial studies confirm the value of horseshoe crab Limulus polyphemus eggs to spring migrant shorebirds in Delaware Bay

G.M. Haramis·W.A. Link·P.C. Osenton·Daniel B. Carter·R.G. Weber·N.A. Clark·M.A. Teece·D.S. Mizrahi

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Abstract

We used stable isotope (SI) methods in combination with pen feeding trials to determine the importance of eggs of the Atlantic horseshoe crab Limulus polyphemus to migratory fattening of red knots Calidris canutus rufa and ruddy turnstones Arenaria interpres morinella during spring stopover in Delaware Bay. By manifesting measurable fractionation (ca +3‰) and rapid turnover, blood plasma δ 15 nitrogen proved a functional marker for SI diet tracking during the short 3-week stopover. Blood samples from free-ranging knots (3 data sets) and turnstones (1 data set) produced similar convergence of plasma δ 15 N signatures with increasing body mass that indicated highly similar diets. Asymptotes deviated slightly (0.3‰ to 0.7‰) from that of captive shorebirds fed a diet of only crab eggs during stopover, thus confirming a strong crab egg-shorebird linkage. The plasma δ 15 N crab-egg diet asymptote was enriched ca +4.5‰ and therefore readily discriminated from that of either blue mussels Mytilus edulis or coquina clams Donax variabilis , the most likely alternative prey of knots in Delaware Bay. Crab eggs were highly palatable to captive knots and turnstones which achieved rates of mass gain (3–11 g/d) comparable to that of free-ranging birds. Peak consumption rates during hyperphagic events were 23,940 and 19,360 eggs/bird/d, respectively. The empirical conversions of eggs consumed to body mass gained (5,017 eggs/g for knots and 4,320 eggs/g for turnstones) indicate the large quantities of crab eggs required for the maintenance of these shorebird populations during stopover.

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Source-reported bounding extent: 38.777640223073355° to 39.22799807055236° latitude; -75.399169921875° to -74.90478515625° longitude. This indicates report coverage, not an exact sampling location. View area on OpenStreetMap.

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G.M. Haramis, W.A. Link, P.C. Osenton, Daniel B. Carter, R.G. Weber, N.A. Clark, M.A. Teece, D.S. Mizrahi. 2007-11-06. Stable isotope and pen feeding trial studies confirm the value of horseshoe crab Limulus polyphemus eggs to spring migrant shorebirds in Delaware Bay. https://doi.org/10.1111/j.0908-8857.2007.03898.x

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