2024/07/24 by Oliver N. Shipley, Bailey C. McMeans, Chris Harrod +2 · 1 voice
Environmental Science · #Isotope Analysis in Ecology #Marine Bivalve and Aquaculture Studies #Physiological and biochemical adaptations
paper · pdf · doi:10.1111/jfb.15880
openalex publication_date 2024/07/24 · openalex created_date 2025/10/10 · openalex updated_date 2026/07/15
It is over 50 years since the distribution of carbon and nitrogen stable isotopes (δ13C and δ15N) was first described in animal tissues (DeNiro & Epstein, 1978, 1981; Fry et al., 1978; Parker, 1964; Schroeder, 1983; Schoeninger & DeNiro, 1984). For fishes, this catalyzed a rich history of studies assessing trophic relationships, movement and migration, and physiological status across freshwater, brackish, and marine environments (Boecklen et al., 2011; Hansson et al., 1997; Shipley & Matich, 2020). As technological advancements continue to improve analytical capabilities, isotopic techniques will continue to transform the field of fish biology. This special issue celebrates some of these recent innovations with a focus on four broad themes: (1) constraining patterns of isotopic discrimination, (2) determining drivers of energy distribution across diverse fish communities, (3) assessing the impacts of human alteration on foraging and fitness, and (4) nontraditional stable isotope systems. The goal of this collection is to showcase state-of-the-art approaches that can improve our understanding of fish ecology and physiology in a changing world. Accurate interpretation of stable isotope values requires detailed knowledge of isotopic discrimination, defined as changes in the relative abundances of isotopes (e.g., 13/12C or 14/15N) due to some ecological (i.e., diet or habitat shift) or physiological (i.e., tissue anabolism/catabolism) process. Despite the need for ecological studies to effectively constrain discrimination (Canseco et al., 2022; Stephens et al., 2023), many aspects remain poorly examined. In elasmobranch fishes (sharks, skates, and rays) that exhibit diverse reproductive modes, it has long been proposed that the isotopic composition of neonate and YOY tissues may be influenced by isotopic discrimination associated with maternal provisioning. Therefore, neonate and YOY tissues may reflect maternal foraging (with some discrimination) rather than ambient environmental conditions experienced directly following birth. Because patterns of mother–embryo isotope discrimination have only been described for a handful of species, it remains uncertain whether correction factors can fully resolve estimates of neonate and YOY foraging and habitat use. Raoult et al. (2024) explore this issue through measuring δ13C and δ15N values in female sparsely spotted stingarees (Urolophus paucimaculatus), banded stingarees (Urolophus viridis), and Tasmanian numbfish (Narcine tasmaniensis) and their offspring sampled from Southeast Australia. They observed highly variable patterns of mother–embryo isotope discrimination that differed by individual and between species. This suggests that unique patterns of isotopic discrimination exist between each embryo and its mother, confounding the use of general correction factors. Assessing patterns of isotopic discrimination between tissues from the same individual can also help to resolve important ecological information. Due to the rising conservation concern of many species and ethical limitations to sampling, assessing patterns of discrimination between lethal (e.g., liver, muscle, and vertebrae) and non-lethally sampled tissues (e.g., fin, scales, and mucus) has become increasingly encouraged. This approach can challenge interpretation, however, because inter-tissue isotope discrimination is driven by the molecular composition of tissues and the rate at which they integrate isotopic information from the environment. To tackle this issue, Taulbee and Walther (2024) assess relationships between δ13C and δ15N values of scale exteriors and muscle tissue in estuarine red drum (Sciaenops ocellatus). They find strong, positive relationships for both isotopes, suggesting that scale exteriors offer a viable non-lethal alternative to muscle. Roberts et al. (2022) apply a similar approach in freshwater species, providing δ13C and δ15N linear conversation relationships between fin and muscle tissue in northern pike (Esox Lucius L.), yellow perch (Perca flavescens), and lake whitefish (Coregonus clupeaformis) while also assessing effects of seasonality. The authors suggest that seasonal variation in ecosystem dynamics combined with variable isotopic incorporation of available tissues may require seasonally specific conversions, at least for highly seasonal ecosystems such as temperate lakes. Finally, Walther and Torrance (2024) explore the complimentary use of stable isotopes with otolith microchemistry. A systematic literature review of 56 studies identified the strong complementarity of the two techniques for assessing diverse ecological questions. However, otolith microchemistry and tissue stable isotope values are not likely to be ecologically synonymous, evidenced by a lack of relationship between Ba:Ca ratios in the outer edge of the otolith and muscle tissue δ13C values in estuarine red drum. This collection of studies offers new insight into the drivers of isotopic discrimination and provides strategies for mitigating the growing ethical considerations associated with lethal sampling for stable isotope analysis. The distribution of energy within food webs presents a core component of fish community dynamics, yet it is unclear how this may be influenced by environmental characteristics such as seasonality and habitat type. Two papers in this collection aim to assess how environmental characteristics modulate energetic assembly in diverse fish communities. Cobain et al. (2024) assess the temporal stability of benthic-pelagic coupling across a diverse estuarine fish community sampled at a monthly resolution. Sulfur isotope values (δ34S) suggested remarkable consistency in benthic-pelagic coupling by benthic and benthopelagic fishes throughout the year, with larger individuals utilizing greater amounts of benthic energy. Monthly δ13C and δ15N values tracked seasonal pulses in productivity and nutrient dynamics associated with the onset and end of the spring bloom. Hayden et al. (2024) examine how energetic assembly across 15 species of reef fishes is governed by the use of cryptobenthic, epibenthic sand, epibenthic rock, and hyperbenthic microhabitats in Adriatic fish communities. They observed high niche segregation between species within each microhabitat, suggesting that microhabitat complexity may promote functional diversity within reef fish communities. Combined, these studies illustrate the utility of stable isotopes for inferring the drivers of energetic assembly in structurally complex ecosystems, such as temperate estuaries and reefs. Human activities and global climate change have been altering ecological communities for decades. Yet, the associated effects of environmental disturbance on the functional roles of fishes and their fitness remain poorly described for many species. Three articles in this issue address this topic through quantifying the implications of anthropogenically driven environmental disturbance on diet, habitat use, and fitness in both freshwater and marine fishes. Ripku et al. (2024) tackle concerns associated with silver nanoparticle pollution (AgNP) on benthic-pelagic coupling by yellow perch and northern pike in freshwater lakes. AgNPs are common antibacterial and anti-odor agents used in many textiles that enter aquatic ecosystems through wastewater effluent and elicit negative impacts on the productivity of benthic periphyton. Implementing Bayesian mixing models, the authors observe a 32% (P. flavescens) and 40% (E. lucius) decline in the contribution of benthic energy following AgNP introduction, illustrating how anthropogenic pollutants can drastically impact benthic-pelagic coupling facilitated by lake fishes. Two papers examine direct links between environmental variation, foraging, and fitness through integrating stable isotopes with body condition measurements. Scharnweber et al. (2024) employ hydrogen stable isotopes (δ2H) to assess the implications of iron oxide pollution associated with historical lignite mines on relative use of aquatic versus terrestrial insects by common bleak (Alburnus alburnus). Bleak residing in river areas associated with high iron oxide pollution exhibited greater reliance on terrestrial insects, which resulted in lower body condition. Feeney et al. (2024) compared body condition of Atlantic salmon (Salmo salar) with δ13C and δ15N values of scales that reflect the last season of growth prior to returning to natal rivers. Higher δ13C and lower δ15N values were associated with better body condition, suggesting that temperature and foraging variation may impact body condition, and potentially reproductive fitness and survival. Given the high dispersal capabilities of Atlantic salmon, these findings suggest that spatially proximate natal populations could elicit varied responses to ocean warming dictated by their previous foraging location and associated temperature regimes. Combined, these studies illustrate how environmental variation and human activity can impact the foraging dynamics of fishes and their associated functional roles with direct implications for fitness. The continued advancement in analytical technology and mass resolving power has increased the accessibility of non-traditional isotope systems to fish biologists, such as Calcium (Martin et al., 2015) and Zinc (δ66Zn; McCormack et al., 2022). Assemat et al. (2024) expand the application of calcium stable isotope analysis to modern shark tooth enamel, revealing distinct δ44/42Ca values of shortfin mako sharks (Isurus oxyrinchus), bluntnose sixgill sharks (Hexanchus griseus), and white sharks (Carcharodon carcharias), indicative of ontogenetic dietary preference and spatial variation in foraging. Given that tooth enamel can be extremely well preserved in the geologic record, continued application of δ44/42Ca holds great promise for uncovering the functional roles of many ancient fish lineages. The sustained evolution of isotopic tools offers an exciting future for fish biologists. Given the broad utility of isotopic approaches, we predict that studies will continue to exponentially increase and diversify in their applications. This will continue to expand ecological and physiological insights imperative for the management and conservation of global fish populations. Studies of global relevance are now supported by the development of new centralized repositories, such as IsoBank (www.isobank.org), thereby expanding collaborative efforts and the diversity of questions that can be pursued.