We present the state of the art of the development of dynamic energy budget theory, and its expected developments in the near future within the molecular, physiological and ecological domains. The degree of formalization in the set-up of the theory, with its roots in chemistry, physics, thermodynamics, evolution and the consistent application of Occam's razor, is discussed. We place the various contributions in the theme issue within this theoretical setting, and sketch the scope of actual and potential applications.Keywords: dynamic energy budget theory; biology; metabolism; ecology; evolution; energetics REACHING OUT FOR GENERALITYIn physics, there is a quest for a unified theory. Physical theories have a broad spectrum of application, a strong mathematical background and are subject to numerous empirical tests. By contrast, in biology, mathematical theory has played a secondary role because biology is frequently seen as a science of exceptions and particular cases, with little interest in abstraction and generalization. Exceptions are the research being done in the fields of theoretical biology and mathematical biology. However, theoretical and mathematical biology have frequently been carried out without a concern for empirical testing. When this concern appears, models are of narrow application, reducing their theoretical breadth. The dynamic energy budget (DEB) theory starts from the Dutch tradition of theoretical and mathematical biology, but couples it with a fundamental concern in producing general theory that is subjected to careful empirical testing.DEB theory aims to capture the quantitative aspects of metabolism at the individual level for organisms of all species. It builds on the premise that the mechanisms that are responsible for the organization of metabolism are not species-specific (Kooijman 2001(Kooijman , 2010. This hope for generality is supported by (i) the universality of physics and evolution and (ii) the existence of widespread biological empirical patterns among organisms . Table 1 synthesizes the essential criteria for any general model for the metabolism of individuals. We explore the links between DEB theory and each of the proposed criteria in the following paragraphs. DEB theory is explicitly based on the conservation of mass, isotopes, energy and time, including the inherent degradation of energy associated with all processes. So it complies to criteria 1, table 1.The DEB theory is biologically implicit, so it applies to all species. Species-specific restrictions of DEB models are explained and predicted by the theory (criterion 5, table 1). For example, consider the most important difference between DEB models, the number of reserves (biomass components that fuel metabolism) and structures (biomass components that have maintenance needs) that are delineated. This depends on the degree of coupling of the various substrates an organism needs. Animals feed on other organisms, which couples uptake of the various substrates (proteins, carbohydrates, lipids, nutrients) tightly and ex...

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A mechanistic model has been developed to characterize and quantify sediment-mixing due to macrobenthic organisms that construct gallery systems. The mixing model is time-and spacedependent and employs ordinary differential equations. It uses (1) biological parameters -the size of the bioturbated zone, rate of biodiffusion and rate of biotransport; (2) physical parametes -output to the water-column coefficient and rate of physical mixing due to local water currents; and (3) biogeochemical parameters -decay rate of the tracer. This gallery-diffusor model is based on a combination of 2 processes: biodiffusion in the sediment layer containing very dense gallery systems, and biotransport in the region of tube bottoms. The performance of this gallery-diffusor model is compared with that of the biodiffusor model classically used to describe mixing of such organisms. Both models are applied to conservative tracer profiles measured in laboratory experiments with the polychaete Nereis diversicolor. Our new model provides mechanisms to describe and explain the tracer-profile shapes observed in sediments. It includes rapid particle transport from the upper layer of the sediment to the tube bottom zone, which is not taken into account with the biodiffusor model but which is of great importance in understanding the processes of organic matter degradation in the sedimentary column. It also makes possible the accurate quantification of the different components of the mixing process of an organism (in this study, the polychaete N. diversicolor). The gallery-diffusor model constitutes 1 of 5 elementary components in a global bioturbation model that allows the study, quantification and prediction of sediment reworking by macrobenthic communities according to their functional group and composition and/or to the specific characteristics of the individual organisms. KEY WORDS: Bioturbation · Nereis diversicolor · Model · Functional groups · MacrobenthosResale or republication not permitted without written consent of the publisher

Temperature-induced variations in bioturbation could affect sediment mixing processes in the marine benthic environment. In this study, sediment reworking by Neanthes virens (Sars), a widely distributed polychaete in muddy sand communities of northern temperate latitudes, was studied under different temperature conditions representing winter (1°C), spring and fall (6°C), summer (13°C), and tide pool (18°C) temperatures in the lower St. Lawrence Estuary, Québec, Canada. Sediment reworking was quantified using inert fluorescent particles (luminophores) deposited at the sediment surface. Based on the 1-D luminophore distributions obtained after 5 and 30 d, the use of the specific 'gallery-biodiffusor' model allowed us to quantify both biodiffusion (D b ) and biotransport (V b ) due to the organisms. Our results showed temperature effects on sediment transport. The lowest biotransport and biodiffusion coefficients were measured at 1 and 6°C and did not change with time. The highest biodiffusion occurred at 13°C for both sampling periods. At 18°C, biodiffusion was intermediate while biotransport was maximal. Differences between the 13°C biodiffusive transport and the other temperatures increased with time. Low transport values at 1 and 6°C suggest that a quiescent stage exists for this species at these temperatures, with sediment mixing occurring mostly during burrow construction. On the other hand, sediment mixing resulted from both the burrow construction and maintenance phases at higher temperatures (13 and 18°C).