Turnover rates of nitrogen stable isotopes in the salt marsh mummichog, Fundulus heteroclitus, following a laboratory diet switch

Author Posting. © The Authors, 2005. This is the author's version of the work. It is posted here by permission of Springer-Verlag GmbH for personal use, not for redistribution. The definitive version was published in Oecologia 147 (2006): 391-395, doi:10.1007/s00442-005-0277-z.Nitrogen stable isotopes are frequently used in ecological studies to estimate trophic position and determine movement patterns. Knowledge of tissue-specific turnover and nitrogen discrimination for the study organisms is important for accurate interpretation of isotopic data. We measured δ15 N turnover in liver and muscle tissue in juvenile mummichogs, Fundulus heteroclitus, following a laboratory diet switch. Liver tissue turned over significantly faster than muscle tissue suggesting the potential for a multiple tissue stable isotope approach to study movement and trophic position over different time scales; metabolism contributed significantly to isotopic turnover for both liver and muscle. Nitrogen diet-tissue discrimination was estimated at between 0.0 and 1.2‰ for liver and –1.0 and 0.2‰ for muscle. This is the first experiment to demonstrate a significant variation in δ15 N turnover between liver and muscle tissues in a fish species.This study was funded by NSF LTER grant OCE-9726921

Impact of salt-marsh management on fish nursery function in the bay of Aiguillon (French Atlantic coast), with a focus on European sea bass diet

International audienceThe Bay of Aiguillon is a national French Nature Reserve of great importance for birds. Recently, the managers of the Reserve (ONCFS-LPO) paid attention to the influence of saltmarshes management on the nursery function for fish feeding in creeks at high tide. A study carried out from March to July 2012 aimed to evaluate the use of saltmarshes by fish juvenile fraction according to the mowing intensity in salt marshes surrounding creeks: ceased, irregular or annual mowing. This community approach was completed by a focus on the European sea bass Dicentrarchus labrax individual diet, vacuity index and growth, and the biomass of a main potential prey (the amphipod Orchestia gammarella). Whatever the mowing intensity, the juvenile fraction was very high for the main species, which were the grey mullet Liza ramada, the European sea bass, undetermined clupeid and the European flounder Platichthys flesus. Adult and subadult for these species were anecdotic or totally absent. Despite very different biomasses of amphipods between mown and natural sites, vacuity index, prey composition and their relative abundance in the diet of European sea bass juveniles were little different, contrary to their hypothetical growth (i.e. when assuming site fidelity), which appeared higher in non-mown site. The low distance between sampling sites could allow fish exchange over time between optimal and suboptimal creeks to feed on, as a hypothesis to explain such results. Because mowing was subsidized by European Union (EU) to favour open habitats for geese and maintain an economic activity, indirect impacts on nursery for fish called into question the appropriateness of such agro-environmental measure on natural habitats, and related fish nursery function

What makes nearshore habitats nurseries for nekton? An emerging view of the nursery role hypothesis

Estuaries and other coastal habitats are considered essential for the survival of early life stages of commercial, recreational, and other ecologically important species. While early designations simply referred to habitats with higher densities of juveniles as nurseries, the definition was improved by arguing that contribution per unit area to the production of individuals that recruit to adult populations is greater, on average, in nursery habitats. However, this and related approaches typically consider critical habitats as individual, homogeneous entities that are static in nature and do not specifically incorporate important dynamics that determine nursery function. The latter include environmental variability, estuarine hydrodynamics, trophic coupling, ontogenetic habitat shifts, and spatially explicit usage of habitat patches and corridors within larger seascapes. Subsequent studies have identified important factors that regulate nursery value, and researchers working independently across the globe have not only supported the advances made in defining the processes underlying nursery function but, as set forth in this narrative, have advanced it while suggesting that much work still needs to be done to improve our understanding of the links between juvenile nekton survival and the estuarine-coastal seascape. We discuss the current nursery role hypothesis and the data supporting (or refuting) it along with the implications for management of estuarine habitats for the conservation or restoration of nursery function