Marine and freshwater organism energy densities integrated across previous sources

Abstract

Energy is the currency of exchange within ecosystems which defines the strength and influence of interactions, particularly between predator and prey. The ability to estimate the productivity of an ecosystem is, therefore, dependent upon the estimation of consumer diet contents and their energetic quality. To estimate growth, reproduction, and, ultimately, survival of individuals, measures of prey quality for predators are essential both at the individual level and for scaling to ecosystem-wide fluxes and pools. Among measures of prey quality, energy density (in kilojoules per gram) is the most used in ecology. Considerable efforts have established estimates of energy densities for many aquatic taxa. However, a database of aquatic organism energetics constructed by integrating and organizing across multiple sources spawning marine and freshwater habitats across the globe is needed to add both depth (more samples to measure within-taxa variation) and breadth (more taxa). To generate a comprehensive energy density database of aquatic organisms, we performed a multifaceted review to find sources from the peer-reviewed and grey literature with a broad search on Web of Science, from citations of related literature, and a haphazard recommendation from experts. Estimates of energy density of whole organism live mass (in kilojoules per gram wet mass) were prioritized to better relate to diet and energetics studies. When energy density was only provided per gram dry mass, the dry mass and percentage water were used to calculate energy density per gram wet mass. Sub-organism (i.e., tissue specific) energy density estimates are included (e.g., muscle, liver, and egg) when only these were reported. A total of 3810 records are included from 134 sources, covering 2018 unique taxa, of which 1771 (87.76%) are identified at the species level. Species or taxa-specific energy densities ranged from 0.015 to 17.949 kJ/g wet mass (WM) with a mean ± SD = 4.509 ± 1.94 kJ/g WM and median = 4.225 kJ/g WM. Among those phyla with more than three species (n phyla = 9), chordates (n taxa = 1283) had the highest average energy density (mean ± SD; 4.92 ± 1.90; 0.162–17.9 kJ/g WM) and ctenophores (n taxa = 4) had the lowest average (0.0988 ± 0.074; 0.03–0.205 kJ/g WM). Each record includes the organism taxonomy to the lowest resolution listed in the original source, energetic data available from the source including body composition and energy density data, number of replicates and methodology for measuring energetics information—primarily split between bomb calorimetry and proximate composition—as well as the source's author(s), year, and publication. Additional meta-data are included whenever possible based on details from the original source including the (1) environmental features: area, method, and timing of capture; (2) methodological features: storage method, storage duration, and tissue type measured; and (3) organismal features: mass, length, and sex as well as any additional notes about the source. This comprehensive database integrates those data discoverable by our search and which met inclusion criteria identified above in a taxonomic and spatial organization framework to facilitate modeling trophic interactions, bioenergetics, growth, productivity, and energy fluxes through marine and freshwater ecosystems. The data and code are released under the Creative Commons Attribution 4.0 license.