Patterns of stable carbon isotope turnover in gag, Mycteroperca microlepis, an economically important marine piscivore determined with a non-lethal surgical biopsy procedure

Environ Biol Fish (2011) 90:243252 DOI 10.1007/s10641-010-9736-4

Patterns of stable carbon isotope turnover in gag, Mycteroperca microlepis, an economically important marine piscivore determined with a non-lethal surgicalbiopsy procedure

James Nelson & Jeffrey Chanton &

Felicia Coleman & Christopher Koenig

Received: 14 December 2009 /Accepted: 27 October 2010 /Published online: 5 November 2010 # Springer Science+Business Media B.V. 2010

Abstract To determine the feasibility of using stable isotopes to track diet shifts in wild gag, Mycteroperca microlepis, populations over seasonal timescales, we conducted a repeated measures diet-shift experiment on four adult gag held in the laboratory. Fish were initially fed a diet of Atlantic mackerel, Scomber scombrus, (mean 13C=21.30.2, n=20) for a period of 56 days and then shifted to a diet of pinfish, Lagodon rhomboids, (mean 13C=16.60.6, n=

20) for the 256 day experiment. We developed a non-lethal surgical procedure to obtain biopsies of the muscle, liver, and gonad tissue monthly from the same four fish. We then determined the 13C value of each tissue by isotope ratio mass spectrometry. For the gonad tissue we used the relationship between C/N and lipid content to correct for the influence of lipids on 13C value. We observed a significant shift in the 13C values of all of the tissues sampled in the study. Carbon turnover rates varied among the three tissues, but the shift in diet from mackerel to pinfish was clearly traceable through analysis of 13C values. The turnover rates for muscle tissue were 0.005 day1,

and for gonad tissue was 0.009 day1. Although it is generally thought that tissue turnover rates in ectotherms are driven primarily by growth, we found that metabolic rate can be a major factor driving tissue turnover in adult gag.

Keywords Biopsies . Surgery. Lipid correction . Trophic shift

Introduction

For most animals, the menu is always changing. Permanent changes in diet typically occur with ontogenetic habitat or diet shifts (Mullaney and Gale 1996; Herzka et al. 2001; Bosley et al. 2002; Post 2003; Post et al. 2007; Logan and Lutcavage 2008). Other changes in diet are temporary, occurring either during annual migrations or with seasonal changes in prey availability (Hobson 1999; Herzka 2005). Determining the timing and magnitude of diet changes can provide information on an animals life history, food...