Phylogenetic conservatism drives nutrient dynamics of coral reef fishes

Quantifying energy and nutrient fluxes in coral reef food webs

The movement of energy and nutrients through ecological communities represents the biological 'pulse' underpinning ecosystem functioning and services. However, energy and nutrient fluxes are inherently difficult to observe, particularly in high-diversity systems such as coral reefs. We review advances in the quantification of fluxes in coral reef fishes, focusing on four key frameworks: demographic modelling, bioenergetics, micronutrients, and compound-specific stable isotope analysis (CSIA). Each framework can be integrated with underwater surveys, enabling researchers to scale organismal processes to ecosystem properties. This has revealed how small fish support biomass turnover, pelagic subsidies sustain fisheries, and fisheries benefit human health. Combining frameworks, closing data gaps, and expansion to other aquatic ecosystems can advance understanding of how fishes contribute to ecosystem functions and services.

Ontogenetic variation in the ecological stoichiometry of 10 fish species during early development

The chemical composition and stoichiometry of vertebrate bodies changes greatly during ontogeny as phosphorus-rich bones form, but we know little about the variation among species during early development. Such variation is important because element ratios in animal bodies influence which element limits growth and how animals contribute to nutrient cycling. We quantified ontogenetic variation from embryos through 2-3 months of age in 10 species of fish in six different families, ranging in adult size from 73 to 720 mm in length. We measured whole-body concentrations (percentage of dry mass) and ratios of carbon (C), nitrogen (N), and phosphorus (P) as fish developed. We also quantified whole-body concentrations of calcium (Ca), because Ca should reflect bone development, and RNA, which can be a major pool of body P. To account for interspecific differences in adult size, we also examined how trends changed with relative size, defined as body length divided by adult length. Ontogenetic changes in body composition and ratios were relatively similar among species and were more similar when expressed as a function of relative size compared to age. Body P increased rapidly in all species (likely because of bone development) from embryos until individuals were ~5%-8% of adult size. Body N also increased, while body C, C:N, C:P, and N:P all decreased over this period. Body Ca increased with development but was more variable among species. Body RNA was low in embryos, increased rapidly in young larvae, then decreased as fish reached 5%-8% of adult size. After fish were about 5%-8% of adult size, changes in body composition were relatively slight for all elements and ratios. These results reveal a consistency in the dynamics of body stoichiometry during early ontogeny, presumably because of similar constraints on the allocation of elements to bones and other body pools. Because most changes occur when individuals are <1 month old (<10% of adult size for that species), early ontogenetic variation in body stoichiometry may be especially important for growth limitation of individuals and ecosystem-level nutrient cycling.

Water column contributions to coral reef productivity: overcoming challenges of context dependence

Coral reefs are declining at an unprecedented rate. Effective management and conservation initiatives necessitate improved understanding of the drivers of production because the high rates found in these ecosystems are the foundation of the many services they provide. The water column is the nexus of coral reef ecosystem dynamics, and functions as the interface through which essentially all energy and nutrients are transferred to fuel both new and recycled production. Substantial research has described many aspects of water column dynamics, often focusing on specific components because water column dynamics are highly spatially and temporally context dependent. Although necessary, a cost of this approach is that these dynamics are often not well linked to the broader ecosystem or across systems. To help overcome the challenge of context dependence, we provide a comprehensive review of this literature, and synthesise it through the perspective of ecosystem ecology. Specifically, we provide a framework to organise the drivers of temporal and spatial variation in production dynamics, structured around five primary state factors. These state factors are used to deconstruct the environmental contexts in which three water column sub-food webs mediate 'new' and 'recycled' production. We then highlight critical pathways by which global change drivers are altering coral reefs via the water column. We end by discussing four key knowledge gaps hindering understanding of the role of the water column for mediating coral reef production, and how overcoming these could improve conservation and management strategies. Throughout, we identify areas of extensive research and those where studies remain lacking and provide a database of 84 published studies. Improved integration of water column dynamics into models of coral reef ecosystem function is imperative to achieve the understanding of ecosystem production necessary to develop effective conservation and management strategies needed to stem global coral loss.

SEED: A framework for integrating ecological stoichiometry and eco-evolutionary dynamics

Characterising the extent and sources of intraspecific variation and their ecological consequences is a central challenge in the study of eco-evolutionary dynamics. Ecological stoichiometry, which uses elemental variation of organisms and their environment to understand ecosystem patterns and processes, can be a powerful framework for characterising eco-evolutionary dynamics. However, the current emphasis on the relative content of elements in the body (i.e. organismal stoichiometry) has constrained its application. Intraspecific variation in the rates at which elements are acquired, assimilated, allocated or lost is often greater than the variation in organismal stoichiometry. There is much to gain from studying these traits together as components of an 'elemental phenotype'. Furthermore, each of these traits can have distinct ecological effects that are underappreciated in the current literature. We propose a conceptual framework that explores how microevolutionary change in the elemental phenotype occurs, how its components interact with each other and with other traits, and how its changes can affect a wide range of ecological processes. We demonstrate how the framework can be used to generate novel hypotheses and outline pathways for future research that enhance our ability to explain, analyse and predict eco-evolutionary dynamics.

Temperature, species identity and morphological traits predict carbonate excretion and mineralogy in tropical reef fishes

Anthropogenic pressures are restructuring coral reefs globally. Sound predictions of the expected changes in key reef functions require adequate knowledge of their drivers. Here we investigate the determinants of a poorly-studied yet relevant biogeochemical function sustained by marine bony fishes: the excretion of intestinal carbonates. Compiling carbonate excretion rates and mineralogical composition from 382 individual coral reef fishes (85 species and 35 families), we identify the environmental factors and fish traits that predict them. We find that body mass and relative intestinal length (RIL) are the strongest predictors of carbonate excretion. Larger fishes and those with longer intestines excrete disproportionately less carbonate per unit mass than smaller fishes and those with shorter intestines. The mineralogical composition of excreted carbonates is highly conserved within families, but also controlled by RIL and temperature. These results fundamentally advance our understanding of the role of fishes in inorganic carbon cycling and how this contribution will change as community composition shifts under increasing anthropogenic pressures.

Little-Parks like oscillations in lightly doped cuprate superconductors

Understanding the rich and competing electronic orders in cuprate superconductors may provide important insight into the mechanism of high-temperature superconductivity. Here, by measuring Bi₂Sr₂CaCu₂O_8+x in the extremely underdoped regime, we obtain evidence for a distinct type of ordering, which manifests itself as resistance oscillations at low magnetic fields (≤10 T) and at temperatures around the superconducting transition. By tuning the doping level p continuously, we reveal that these low-field oscillations occur only when p < 0.1. The oscillation amplitude increases with decreasing p but the oscillation period stays almost constant. We show that these low-field oscillations can be well described by assuming a periodic superconducting structure with a mesh size of about 50 nm. Such a charge order, which is distinctly different from the well-established charge density wave and pair density wave, seems to be an unexpected piece of the puzzle on the correlated physics in cuprates.

Understanding the rich electronic orders in cuprate superconductors provide insights into the mechanism of high-temperature superconductivity. Here, the authors report a distinct charge order with Little-Parks like resistance oscillations at magnetic fields up to 10 T and around T_c in lightly doped Bi₂Sr₂CaCu₂O_8+x.