Regional variability in the trophic requirements of shelf sea fisheries in the Northeast Atlantic, 1973-2000

Hydrographic, plankton, benthos, fisheries landings, and fish diet data from shelf sea areas in the Northeast Atlantic have been combined into an analysis of the foodweb structure and secondary production requirements of regional fisheries. Fish landings from the Baltic and North Sea are shown to be taken from a lower trophic level and are shown to be overall more planktivorous than those from shelf edge regions. The secondary production required per unit of landed fish from the North Sea was approximately half that for landings from the southwest approaches to the UK, referred to as the Celtic Seas, where zooplankton production accounted for only a small fraction of the secondary production demands of the fisheries. In the North Sea, variability in zooplankton production seems to have exerted a bottom-up effect on fish production, which in turn has exerted a top-down effect on the benthos. Conversely, Celtic Seas benthos production has been a bottom-up driver of fish production, which seems to have been independent of variability in plankton production.Thus, climate and fishing pressures can be expected to influence these regional fisheries in very different ways. Overall, the results indicate very strong spatial patterns in the fish foodweb structure and function, which will be important considerations in the establishment of regional management plans for fisheries

Reconciling end-to-end and population concepts for marine ecosystems

Author Posting. © The Author(s), 2010. This is the author's version of the work. It is posted here by permission of Elsevier for personal use, not for redistribution. The definitive version was published in Journal of Marine Systems 83 (2010): 99-103, doi:10.1016/j.jmarsys.2010.06.006.The inherent complexities in the structure and dynamics of marine food webs have led to two major simplifying concepts, a species-centric approach focused on physical processes driving the population dynamics of single species and a trophic-centric approach emphasizing energy flows through broad functional groups from nutrient input to fish production. Here we review the two approaches and discuss their advantages and limitations. We suggest that these concepts are complementary: their applications involve different time scales and distinct aspects of population and community resilience, but their integration is necessary for ecosystem-based managementWe acknowledge NOAA-CICOR award NA17RJ1233 (J.H. Steele) and NSF award OCE0217399 (D.J. Gifford)

Modeling Plankton Mixotrophy: A Mechanistic Model Consistent with the Shuter-Type Biochemical Approach

Mixotrophy, i.e., the ability to combine phototrophy and phagotrophy in one organism, is now recognized to be widespread among photic-zone protists and to potentially modify the structure and functioning of planktonic ecosystems. However, few biogeochemical/ecological models explicitly include this mode of nutrition, owing to the large diversity of observed mixotrophic types, the few data allowing the parameterization of physiological processes, and the need to make the addition of mixotrophy into existing ecosystem models as simple as possible. We here propose and discuss a flexible model that depicts the main observed behaviors of mixotrophy in microplankton. A first model version describes constitutive mixotrophy (the organism photosynthesizes by use of its own chloroplasts). This model version offers two possible configurations, allowing the description of constitutive mixotrophs (CMs) that favor either phototrophy or heterotrophy. A second version describes non-constitutive mixotrophy (the organism performs phototrophy by use of chloroplasts acquired from its prey). The model variants were described so as to be consistent with a plankton conceptualization in which the biomass is divided into separate components on the basis of their biochemical function (Shuter-approach; Shuter, 1979). The two model variants of mixotrophy can easily be implemented in ecological models that adopt the Shuter-approach, such as the MIRO model (Lancelot et al., 2005), and address the challenges associated with modeling mixotrophy

Experimental strategies to assess the biological ramifications of multiple drivers of global ocean change-A review

Marine life is controlled by multiple physical and chemical drivers and by diverse ecological processes. Many of these oceanic properties are being altered by climate change and other anthropogenic pressures. Hence, identifying the influences of multifaceted ocean change, from local to global scales, is a complex task. To guide policy-making and make projections of the future of the marine biosphere, it is essential to understand biological responses at physiological, evolutionary and ecological levels. Here, we contrast and compare different approaches to multiple driver experiments that aim to elucidate biological responses to a complex matrix of ocean global change. We present the benefits and the challenges of each approach with a focus on marine research, and guidelines to navigate through these different categories to help identify strategies that might best address research questions in fundamental physiology, experimental evolutionary biology and community ecology. Our review reveals that the field of multiple driver research is being pulled in complementary directions: the need for reductionist approaches to obtain process-oriented, mechanistic understanding and a requirement to quantify responses to projected future scenarios of ocean change. We conclude the review with recommendations on how best to align different experimental approaches to contribute fundamental information needed for science-based policy formulation

Linear understanding of a huge aquatic ecosystem model using a group-collecting sensitivity analysis

Huge complex ecosystem models with several hundred parameters andlarge input data sets escape standard attempts at integral assessment.We introduce the concept of group-collecting sensitivity analysisin which related model parameters or forcing coefficients are combinedinto subsets. Since means and standard deviations of subsets are variedinstead of individual coefficients, the method is numerically efficient andproduces a condensed amount of results. Application to the AquaticEcosystem Model (AQEM) is presented. AQEM is a descendantof the European Regional Seas Ecosystem Model (ERSEM) with a finerprocess and spatial resolution with respect to the Wadden Sea. Atwo-dimensional sub-structured sensitivity table, which is the major resultof this approach, enables an immediate perception of sensitive functionalrelationships and dependencies between individual parameters and therelevant characteristics of a near-shore aquatic ecosystem. Specialemphasis is placed on differences in average and seasonal behaviour.The response of selected result variables to the variations of the majorityof group parameters is correlated, i.e. result variables show a similarsensitivity to variations in a specific parameter group. We show thatexceptions to this rule lead to a deeper insight into the model system

Modelling Zostera marina and Ulva spp. in a coastal lagoon

We have implemented new modules of seagrass and macroalgae in the European Regional Seas Ecosystem Model (ERSEM). The modules were tested using a version of ERSEM coupled with the General Ocean Turbulence Model (GOTM) in San Quintin Bay (SQB), a coastal lagoon in Baja California, Mexico. As we are working in a region where horizontal advective transport of nutrients is important, we have included the horizontal nutrient gradients which result in nutrient advection when combined with the local currents. The addition of the Zostera marina and Ulva spp. modules to ERSEM, and the inclusion of advection results in a better simulation of the seasonal and interannual trends in nutrient concentrations and macrophyte biomasses in SQB. The differences between the simulations with and without advection are particularly apparent during the upwelling periods. Therefore, by increasing the horizontal gradients of nitrate in the model during the strong upwelling seasons a stronger advection results in higher nitrate concentrations from May to July in 2004 and 2005. The difference in the seasonal trend in biomasses between both macrophytes, with Ulva spp. reaching its seasonal maximum in June–July and Z. marina reaching it in September–October reflects the different response to the various factors controlling their primary production. Z. marina is particularly sensitive to variations in the photosynthetically active radiation (PAR) and the light limitation factor, while Ulva spp. is more sensitive to changes in the maximum uptake rates of nitrate. The model was forced using field data from the lagoon collected in 2004 and 2005