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Schiettekatte, N. M. D., Barneche, D. R., Villeger, S., Allgeier, J. E., Burkepile, D. E., Brandl, S. J., et al. (2020). Nutrient limitation, bioenergetics and stoichiometry: A new model to predict elemental fluxes mediated by fishes. Funct. Ecol., 34(9), 1857–1869.
Résumé: Energy flow and nutrient cycling dictate the functional role of organisms in ecosystems. Fishes are key vectors of carbon (C), nitrogen (N) and phosphorus (P) in aquatic systems, and the quantification of elemental fluxes is often achieved by coupling bioenergetics and stoichiometry. While nutrient limitation has been accounted for in several stoichiometric models, there is no current implementation that permits its incorporation into a bioenergetics approach to predict ingestion rates. This may lead to biased estimates of elemental fluxes. Here, we introduce a theoretical framework that combines stoichiometry and bioenergetics with explicit consideration of elemental limitations. We examine varying elemental limitations across different trophic groups and life stages through a case study of three trophically distinct reef fishes. Further, we empirically validate our model using an independent database of measured excretion rates. Our model adequately predicts elemental fluxes in the examined species and reveals species- and size-specific limitations of C, N and P. In line with theoretical predictions, we demonstrate that the herbivoreZebrasoma scopasis limited by N and P, and all three fish species are limited by P in early life stages. Further, we show that failing to account for nutrient limitation can result in a greater than twofold underestimation of ingestion rates, which leads to severely biased excretion rates. Our model improved predictions of ingestion, excretion and egestion rates across all life stages, especially for fishes with diets low in N and/or P. Due to its broad applicability, its reliance on many parameters that are well-defined and widely accessible, and its straightforward implementation via the accompanyingr-packagefishflux, our model provides a user-friendly path towards a better understanding of ecosystem-wide nutrient cycling in the aquatic biome. A freePlain Language Summarycan be found within the Supporting Information of this article.
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Villeger, S., Brosse, S., Mouchet, M., Mouillot, D., & Vanni, M. J. (2017). Functional ecology of fish: current approaches and future challenges. Aquat. Sci., 79(4), 783–801.
Résumé: Fish communities face increasing anthropogenic pressures in freshwater and marine ecosystems that modify their biodiversity and threaten the services they supply to human populations. To address these issues, studies have been increasingly focusing on functions of fish that are linked to their main ecological roles in aquatic ecosystems. Fish are indeed known to control other organisms through predation, mediate nutrient fluxes, and can act as ecosystem engineers. Here for each of the key functions played by fish, we present the functional traits that have already been used to assess them. We include traits measurable from observations on living individuals, morphological features measured on preserved organisms or traits categorized using information from the literature, and we discuss their respective advantages and limitations. We then list future research directions to foster a more complete functional approach for fish ecology that needs to incorporate functional traits describing, food provisioning and cultural services while accounting more frequently for intraspecific variability. Finally, we highlight ecological and evolutionary questions that could be addressed using meta-analyses of large trait databases, and how a trait-based framework could provide valuable insights on the mechanistic links between global changes, functional diversity of fish assemblages, and ecosystem services.
Mots-Clés: biodiversity; centrarchid fishes; coral-reef fishes; dietary-morphological relationships; ecosystem processes; Ecosystem services; fish; food-web; fresh-water fish; functional trait; global change; labrid fishes; life-history strategies; ocean; phosphorus-limitation; population regulation; river
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Zilius, M., Bartoli, M., Bresciani, M., Katarzyte, M., Ruginis, T., Petkuviene, J., et al. (2014). Feedback Mechanisms Between Cyanobacterial Blooms, Transient Hypoxia, and Benthic Phosphorus Regeneration in Shallow Coastal Environments. Estuaries and Coasts, 37(3), 680–694.
Résumé: We investigated the dissolved oxygen metabolism of the Curonian Lagoon (Baltic Sea) to assess the relative contributions of pelagic and benthic processes to the development of transient hypoxic conditions in shallow water habitats. Metabolism measurements along with the remote sensing-derived estimates of spatial variability in chlorophyll a were used to evaluate the risk of hypoxia at the whole lagoon level. Our data demonstrate that cyanobacterial blooms strongly inhibit light penetration, resulting in net heterotrophic conditions in which pelagic oxygen demand exceeds benthic oxygen demand by an order of magnitude. The combination of bloom conditions and reduced vertical mixing during calm periods resulted in oxygen depletion of bottom waters and greater sediment nutrient release. The peak of reactive P regeneration (nearly 30 mu mol m(-2) h(-1)) coincided with oxygen depletion in the water column, and resulted in a marked drop of the inorganic N:P ratio (from > 40 to < 5, as molar). Our results suggest a strong link between cyanobacterial blooms, pelagic respiration, hypoxia, and P regeneration, which acts as a feedback in sustaining algal blooms through internal nutrient cycling. Meteorological data and satellite-derived maps of chlorophyll a were used to show that nearly 70 % of the lagoon surface (approximately 1,000 km(2)) is prone to transient hypoxia development when blooms coincide with low wind speed conditions.
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