Taxonomic identity best explains variation in body nutrient stoichiometry in a diverse marine animal community

Temporal and spatial differences in nitrogen and phosphorus biogeochemistry and ecosystem functioning of a hypertrophic lagoon (Curonian Lagoon, SE Baltic Sea) revealed via Ecological Network Analysis

In coastal lagoons, eutrophication and hydrology are interacting factors that produce distortions in biogeochemical nitrogen (N) and phosphorus (P) cycles. Such distortions affect nutrient relative availability and produce cascade consequences on primary producer's community and ecosystem functioning. In this study, the seasonal functioning of a coastal lagoon was investigated with a multielement approach, via the construction and analysis of network models. Spring and summer networks, both for N and P flows, have been simultaneously compiled for the northern transitional and southern confined area of the hypertrophic Curonian Lagoon (SE Baltic Sea). Ecological Network Analysis was applied to address the combined effect of hydrology and seasonality on biogeochemical processes. Results suggest that the ecosystem is more active and presents higher N and P fluxes in summer compared to spring, regardless of the area. Furthermore, larger internal recycling characterizes the confined compared to the transitional area, regardless of the season. The two areas differed in the fate of available nutrients. The transitional area received large riverine inputs that were mainly transferred to the sea without the conversion into primary producers' biomass. The confined area had fewer inputs but proportionally larger conversion into phytoplankton biomass. In summer, particularly in the confined area, primary production was inefficiently consumed by herbivores. Most phytoplanktonic N and P, in the confined area more than in the transitional area, were conveyed to the detritus pathway where P, more than N, was recycled, contributing to the unbalance in N:P stoichiometry and favouring N-fixing cyanobacteria over other phytoplankton groups. The findings of this study provide a comprehensive understanding of N and P circulation patterns in lagoon areas characterized by different hydrology. They also support the importance of a stoichiometric approach to trace relative differences in N and P recycling and abundance, that promote blooms, drive algal communities and whole ecosystem functioning.

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.

Species trait diversity sustains multiple dietary nutrients supplied by freshwater fisheries

Species, through their traits, influence how ecosystems simultaneously sustain multiple functions. However, it is unclear how trait diversity sustains the multiple contributions biodiversity makes to people. Freshwater fisheries nourish hundreds of millions of people globally, but overharvesting and river fragmentation are increasingly affecting catches. We analyse how loss of nutritional trait diversity in consumed fish portfolios affects the simultaneous provisioning of six essential dietary nutrients using household data from the Amazon and Tonlé Sap, two of Earth's most productive and diverse freshwater fisheries. We find that fish portfolios with high trait diversity meet higher thresholds of required daily intakes for a greater variety of nutrients with less fish biomass. This beneficial biodiversity effect is driven by low redundancy in species nutrient content profiles. Our findings imply that sustaining the dietary contributions fish make to people given declining biodiversity could require more biomass and ultimately exacerbate fishing pressure in already-stressed ecosystems.

Consumer-driven nutrient recycling of freshwater decapods: Linking ecological theories and application in integrated multitrophic aquaculture

The Metabolic Theory of Ecology (MTE) and the Ecological Stoichiometry Theory (EST) are central and complementary in the consumer-driven recycling conceptual basis. The understanding of physiological processes of organisms is essential to explore and predict nutrient recycling behavior, and to design integrated productive systems that efficiently use the nutrient inputs through an adjusted mass balance. We fed with fish-feed three species of decapods (prawn, anomuran, crab) from different families and with aquacultural potential to explore the animal-mediated nutrient dynamic and its applicability in productive systems. We tested whether body mass, body elemental content, and feeds predict N and P excretion rates and ratios within taxa. We also verified if body content scales allometrically with body mass within taxa. Finally, we compared the nutrient excretion rates and body elemental content among taxa. N excretion rates of prawns and anomurans were negatively related to body mass, emphasizing the importance of MTE. Feed interacted with body mass to explain P excretion of anomurans and N excretion of crabs. Body C:N content positively scaled with body mass in prawns and crabs. Among taxa, prawns mineralised more N and N:P, and less P, and exhibited higher N and C body content (and lower C:N) than the other decapods. Body P and N:P content were different among all species. Body content and body mass were the main factors that explained the differences among taxa and influence the role of crustaceans as nutrient recyclers. These features should be considered to select complementary species that efficiently use feed resources. Prawns need more protein in feed and might be integrated with fish of higher N-requirements, in contrast to crabs and anomurans. Our study contributed to the background of MTE and EST through empirical data obtained from decapods and it provided insightful information to achieve more efficient aquaculture integration systems.

Phylogenetic conservatism drives nutrient dynamics of coral reef fishes

The relative importance of evolutionary history and ecology for traits that drive ecosystem processes is poorly understood. Consumers are essential drivers of nutrient cycling on coral reefs, and thus ecosystem productivity. We use nine consumer "chemical traits" associated with nutrient cycling, collected from 1,572 individual coral reef fishes (178 species spanning 41 families) in two biogeographic regions, the Caribbean and Polynesia, to quantify the relative importance of phylogenetic history and ecological context as drivers of chemical trait variation on coral reefs. We find: (1) phylogenetic relatedness is the best predictor of all chemical traits, substantially outweighing the importance of ecological factors thought to be key drivers of these traits, (2) phylogenetic conservatism in chemical traits is greater in the Caribbean than Polynesia, where our data suggests that ecological forces have a greater influence on chemical trait variation, and (3) differences in chemical traits between regions can be explained by differences in nutrient limitation associated with the geologic context of our study locations. Our study provides multiple lines of evidence that phylogeny is a critical determinant of contemporary nutrient dynamics on coral reefs. More broadly our findings highlight the utility of evolutionary history to improve prediction in ecosystem ecology.

Nitrogen and phosphorus enrichment cause declines in invertebrate populations: a global meta-analysis

Human-driven changes in nitrogen (N) and phosphorus (P) inputs are modifying biogeochemical cycles and the trophic state of many habitats worldwide. These alterations are predicted to continue to increase, with the potential for a wide range of impacts on invertebrates, key players in ecosystem-level processes. Here, we present a meta-analysis of 1679 cases from 207 studies reporting the effects of N, P, and combined N + P enrichment on the abundance, biomass, and richness of aquatic and terrestrial invertebrates. Nitrogen and phosphorus additions decreased invertebrate abundance in terrestrial and aquatic ecosystems, with stronger impacts under combined N + P additions. Likewise, N and N + P additions had stronger negative impacts on the abundance of tropical than temperate invertebrates. Overall, the effects of nutrient enrichment did not differ significantly among major invertebrate taxonomic groups, suggesting that changes in biogeochemical cycles are a pervasive threat to invertebrate populations across ecosystems. The effects of N and P additions differed significantly among invertebrate trophic groups but N + P addition had a consistent negative effect on invertebrates. Nutrient additions had weaker or inconclusive impacts on invertebrate biomass and richness, possibly due to the low number of case studies for these community responses. Our findings suggest that N and P enrichment affect invertebrate community structure mainly by decreasing invertebrate abundance, and these effects are dependent on the habitat and trophic identity of the invertebrates. These results highlight the important effects of human-driven nutrient enrichment on ecological systems and suggest a potential driver for the global invertebrate decline documented in recent years.