Using otolith microchemistry to assess nursery habitat contribution and function at a fine spatial scale

Estuarine tributaries are vital links in connectivity for transient coastal fish undergoing ontogenetic habitat shifts, yet these resources are on the frontlines of anthropogenic change. Prioritizing actions to protect valuable fisheries may require fine-scale analyses of the relative value and function of tributaries as nurseries for regional populations. For sectioned otoliths from young-of-the-year (YOY) common snook Centropomus undecirnalis; snook), we used laser ablation-inductively coupled plasma-mass spectrometry and stable isotope analysis to obtain microchemical signatures distinguishing 9 tributaries (each <1.0 km(2) , <5 km apart) along a mangrove-to-saltmarsh gradient in the Little Manatee River (LMR), Florida, USA. Using canonical analysis of principal coordinates and jackknifed leave-one-out classification for 123 fish, 70 (56.9%) were classified correctly based on microchemical signatures, compared with 11.1% that would have been correctly classified by chance alone (chi(2 ), p <0.0001). Months later, 39 of 40 (98%) yr-1 snook collected from throughout the LMR were assigned to a YOY nursery tributary based on otolith core signatures. The 3 tributaries making the greatest contribution of YOY snook to the yr-1 population were in pristine, low salinity (0.5-1.5 psu) saltmarshes farthest from the estuary mouth. Since other studies have identified completely different spatial patterns in fish nursery use from year to year, this study should be replicated to assess temporal variation in snook contribution from these nurseries. Nevertheless, this fine-scale application of otolith microchemistry is encouraging for future efforts seeking to protect locations having the greatest likelihood of contributing to survival of fishes that make ontogenetic habitat shifts within coastal ecosystems.