Lower Trophic Level Ecosystem Model Research Articles

Controlling factors of large-scale harmful algal blooms with Karenia selliformis after record-breaking marine heatwaves

Unprecedented, large-scale harmful algal blooms (HABs) dominated by Karenia selliformis occurred off the southeastern coast of Hokkaido, Japan, from late September to early November 2021, about a month after intense and extensive marine heatwaves (MHWs) had subsided. The aims of the present study were to understand the mechanism of development, maintenance, and decay of the HABs as well as to investigate the effect of the MHWs on the HABs. We developed a one-dimensional, lower trophic-level ecosystem model (NEMURO+) to simulate the HABs. The model successfully simulated the 2021 HABs and indicated that their development, maintenance, and decay were controlled primarily by changes of water temperature. Nitrate supply from subsurface layers by seasonal vertical diffusion in autumn also helped to maintain the HABs. Vertical diffusion following MHWs in 2021 contributed to the long duration of the preferred temperature for K. selliformis and the occurrence of pre-bloom of K. selliformis, resulting in preconditioning and accelerating the HABs. However, simulations for normal years (i.e., the climatological mean during 2003–2018) showed that HABs could have occurred, even in the absence of MHWs. The simulations indicated that massive blooms of other phytoplankton species (e.g., diatoms) would not have occurred in 2021, even in the absence of a K. selliformis bloom. The implication was that the HABs in 2021 were the species-specific responses of K. selliformis. The proposed mechanism of the HABs was peculiar to our study area and differed from that previously reported for other K. selliformis blooms. Specifically, the preferred temperature for the HABs of K. selliformis was clearly lower than the previously reported preferred temperature of K. selliformis; thus, the physiological characteristics of the K. selliformis that bloomed in our study area differed from those of other K. selliformis strains. These discoveries provide the first evidence to explain how MHWs affect HABs, and to understand how inter-regional dissimilarities of K. selliformis can lead to large-scale, devastating outbreaks under different oceanographic conditions.

Quantitative estimation of the ecosystem services supporting the growth of Japanese chum salmon

Chum salmon (Oncorhynchus keta) are distributed widely in the subarctic North Pacific. The Japanese stock is maintained by artificial release procedures. Chum salmon, including the Japanese stock, provide important ecosystem services for humans that are related to provisioning, culture and support. These ecosystem services are supported by the supply of prey and habitat that the fish use. We regard the supply of prey and habitat as supporting services for salmon. We developed a procedure to estimate supporting services quantitatively, based on the prey biomass consumed by individual salmon, by coupling a bioenergetics model and a lower trophic level ecosystem model. Using this procedure, we estimated the prey biomass consumed by a cohort of Japanese chum salmon released in a single year. The phytoplankton biomass indirectly consumed by a cohort was also estimated and considered to be the primary production supporting the fish. The Japanese chum salmon cohort was estimated to consume ca. 4.2–4.7 × 109 kg wet weight of zooplankton, of which more than half is eaten in the Bering Sea. The Japanese chum salmon cohort is supported by an estimated primary production of 2.0–2.2 × 109 kg C, which amounts to 0.17%–0.19% of primary production in the areas and periods through which the fish migrate. We also attempted to calculate the monetary value of supporting services for the growth of Japanese chum salmon.

Numerical experiments based on a coupled physical–biochemical ocean model to study the Kuroshio-induced nutrient supply on the shelf-slope region off the southwestern coast of Japan

Abstract We developed a triply nested 1/50° ocean model coupled with a NPZD-type lower trophic level ecosystem model and used it to conduct numerical experiments to identify the major processes that supply nutrients on the shelf-slope region north of the Kuroshio. Tosa Bay, an open-type bay facing the Kuroshio, was selected for our experiment. Comparisons of numerical simulations using different grid sizes revealed that a grid size no larger than 1/50° was essential to reproduce a time-independent density structure related to the Kuroshio jet that uplifted nitrate from subsurface waters into the euphotic zone north of the Kuroshio front. The monthly mean budget of nitrate within the euphotic zone on the shelf showed that primary production was nearly balanced by physical advection and the biochemical supply of nitrate via mechanisms such as remineralization of detritus. Eddy advection of nitrate based on Reynolds decomposition, attributable primarily to submesoscale variations, had both positive and negative values within the bay, the indication being that eddy advection functioned regionally to supply or remove nitrate. Lagrangian particle-tracking experiments were performed to examine the major pathways of the nitrate used for primary production in Tosa Bay during the summer, when subsurface maxima of primary production typically appeared. The experiments revealed that when the Kuroshio took a stable nearshore path, nitrate was frequently uplifted around the Kuroshio front and horizontally transported along the front and into the bay via the counterclockwise circulation within the bay; it was sometimes further uplifted onto the shelf.

Ecosystem model-based approach for modeling the dynamics of <sup>137</sup>Cs transfer to marine plankton populations: application to the western North Pacific Ocean after the Fukushima nuclear power plant accident

Abstract. Huge amounts of radionuclides, especially 137Cs, were released into the western North Pacific Ocean after the Fukushima nuclear power plant (FNPP) accident that occurred on 11 March 2011, resulting in contamination of the marine biota. In this study we developed a radioecological model to estimate 137Cs concentrations in phytoplankton and zooplankton populations representing the lower levels of the pelagic trophic chain. We coupled this model to a lower trophic level ecosystem model and an ocean circulation model to take into account the site-specific environmental conditions in the area. The different radioecological parameters of the model were estimated by calibration, and a sensitivity analysis to parameter uncertainties was carried out, showing a high sensitivity of the model results, especially to the 137Cs concentration in seawater, to the rates of accumulation from water and to the radionuclide assimilation efficiency for zooplankton. The results of the 137Cs concentrations in planktonic populations simulated in this study were then validated through comparison with the data available in the region after the accident. The model results have shown that the maximum concentrations in plankton after the accident were about 2 to 4 orders of magnitude higher than those observed before the accident, depending on the distance from FNPP. Finally, the maximum 137Cs absorbed dose rate for phyto- and zooplankton populations was estimated to be about 5 × 10−2 µGy h−1, and was, therefore, lower than the predicted no-effect dose rate (PNEDR) value of 10 µGy h−1 defined in the ERICA assessment approach.

The predictive potential of early life stage individual-based models (IBMs): an example for Atlantic cod Gadus morhua in the North Sea

Using a spatially explicit individual-based model (IBM), we examined the potential larval survival (PLS) and growth of early life stages of Atlantic cod Gadus morhua in the North Sea ecosystem in response to changes in physical and biological forcing. We employed a 3-dimensional coupled model system that includes a hydrodynamic model, a physiologically based IBM and the lower trophic level ecosystem model ECOSMO, to provide related prey fields. The statistical analysis of a long-term (1949 to 2008) hindcast integration and the comparison to a set of 30-yr-long scenario experiments revealed a strong impact of atmospheric forcing on changes in PLS, where variations in transport processes and in the prey field are equally as important as temperature-dependent processes. Furthermore, the scenario experiments show that the different impacting environmental factors interact non-linearly and are non-homogeneous in time and space. A correlation analysis between estimated PLS and observed Atlantic cod recruitment in the North Sea indicated that time periods of high correlation alternate with periods of low or negative correlation. In the 1960s and from the end of the 1980s onwards, we identified high correlations between estimated PLS and recruitment and concluded that the model exhibits a significant predictive potential for cod recruitment during these periods. However, we also identified contrasting periods, e.g. during the 1970s and 1980s, for which we conclude that recruitment variability during these periods was significantly influenced by alternative processes, such as top-down or bottom-up controls during post-larval life stages.

Winter mixed layer depth and spring bloom along the Kuroshio front: implications for the Japanese sardine stock

Recruitment of Japanese sardine Sardinops melanostictus is related to interannual variability in the winter mixed layer depth (MLD) near the Kuroshio axis (line of maximum cur- rent), possible because MLD may influence the feeding environment of sardine larvae through phytoplankton productivity. However, a relationship between the winter MLD and phytoplankton productivity has not been shown. Particle release experiments with quasi-observed current fields from ocean reanalysis products and satellite-observed phytoplankton (chlorophyll a) density from 1998 to 2006 showed that deeper waters of the winter mixed layer flowing 0° to 0.5° north of the Kuroshio axis led to a greater bloom in the subsequent spring, although such a relationship was not detected south of the Kuroshio axis. By using the output of a 3-dimensional, high-resolution lower trophic level ecosystem model that reproduced the MLD−phytoplankton relationship, we found that entrainment of deeper nutrient-rich subsurface water leads to abundant nutrients in the early spring and enhances the subsequent spring bloom along the northern side of the Kuroshio axis. On the southern side, where mode water develops in winter, the deeper winter mixed layer does not necessarily contain higher nutrient contents, because nutrient vertical profiles often have inversions. These results support the hypothesis that sardine larvae that are distributed in the deeper winter mixed layer north of the Kuroshio axis (called the Kuroshio frontal zone) encounter a higher phytoplankton density, which yields favorable feeding conditions, resulting in recruit- ment success.

Coupling of an individual-based model of anchovy with lower trophic level and hydrodynamic models

Anchovy (Engraulis japonicus), a small pelagic fish and food of other economic fishes, is a key species in the Yellow Sea ecosystem. Understanding the mechanisms of its recruitment and biomass variation is important for the prediction and management of fishery resources. Coupled with a hydrodynamic model (POM) and a lower trophic level ecosystem model (NEMURO), an individual-based model of anchovy is developed to study the influence of physical environment on anchovy’s biomass variation. Seasonal variations of circulation, water temperature and mix-layer depth from POM are used as external forcing for NEMURO and the anchovy model. Biomasses of large zooplankton and predatory zooplankton which anchovy feeds on are output from NEMURO and are controlled by the consumption of anchovy on them. Survival fitness theory related to temperature and food is used to determine the swimming action of anchovy in the model. The simulation results agree well with observations and elucidate the influence of temperature in over-wintering migration and food in feeding migration.

Impacts of climate change on growth, migration and recruitment success of Japanese sardine (Sardinops melanostictus) in the western North Pacific

We developed a multi-trophic level ecosystem model by coupling physical, biogeochemical-plankton and fish models. An oceanic general circulation model was coupled with a lower trophic level ecosystem model and a Japanese sardine migration model, and applied to the western North Pacific. To investigate the impact of global warming on the pelagic fish ecosystem, such as Japanese sardine, we conducted numerical experiments of growth and migration of Japanese sardine using physical fields for the present day and future with a global warming scenario simulated by a high-resolution climate model. The model results demonstrated possible impacts of global warming on the growth and migration pattern of Japanese sardine. The growths of fish in the current main spawning region under the global warming scenario were significantly slower than those under the present climate scenario. Fish in this region will be at disadvantage for their recruitment under the global warming condition. Prey conditions in the spawning region were projected not to markedly change under global warming condition while water temperature increased. As a result sardine spawning ground was projected to shift towards more north areas. During the feeding migration period in summer, geographical distribution of juveniles fish was projected to shift northwards by one to two degrees latitude under the global warming condition following the change in the distribution of optimal temperature region for feeding. However, this northwards shift of the optimal temperature for feeding was minimized adjacent to the western North Pacific by the cooler water supply by the intensification of the Oyashio.

Application of a bioenergetics growth model for European anchovy (Engraulis encrasicolus) linked with a lower trophic level ecosystem model

A bioenergetics model is implemented for European anchovy (Engraulis encrasicolus) and applied to the north-eastern Aegean Sea (eastern Mediterranean Sea). The model reproduces the growth of anchovy in a one-way linked configuration with a lower trophic level (LTL) ecosystem model. The LTL model provides densities for three zooplankton functional groups (heterotrophic flagellates, microzooplankton and mesozooplankton) which serve as available energy via consumption for the anchovy model. Our model follows the basic structure of NEMURO.FISH type models (North Pacific Ecosystem Model for Understanding Regional Oceanography for Including Saury and Herring). Several model parameters were specific for the Mediterranean or the Black Sea anchovy and some others were adopted from related species and NEMURO.FISH due to lack of biological information on E. encrasicolus. Simulation results showed that the fastest growth rate occurs during spring and the slowest growth rate from August to December. Zooplankton abundance during autumn was low implying that decreased prey density lead to a reduction in anchovy weight, especially for the age-3 class. Feeding parameters were adjusted to adequately fit the model growth estimates to available weight-at-age data. A detailed sensitivity analyses is conducted to evaluate the importance of the biological processes (consumption, respiration, egestion, specific dynamic action, excretion and egg production) and their parameters to fish growth. The most sensitive parameters were the intercept and exponent slope of the weight-dependent consumption and respiration process equations. Fish weight was fairly sensitive to temperature-dependent parameters.

Influence of cross-shelf water transport on nutrients and phytoplankton in the East China Sea: a model study

Abstract. A three dimensional coupled biophysical model was used to examine the supply of oceanic nutrients to the shelf of the East China Sea (ECS) and its role in primary production over the shelf. The model consisted of two parts: the hydrodynamic module was based on a nested model with a horizontal resolution of 1/18 degree, whereas the biological module was a lower trophic level ecosystem model including two types of phytoplankton, three elements of nutrients, and biogenic organic material. The model results suggested that seasonal variations occurred in the distribution of nutrients and chlorophyll a over the shelf of the ECS. After comparison with available observed nutrients and chlorophyll a data, the model results were used to calculate volume and nutrients fluxes across the shelf break. The annual mean total fluxes were 1.53 Sv for volume, 9.4 kmol s−1 for DIN, 0.7 kmol s−1 for DIP, and 18.2 kmol s−1 for silicate. Two areas, northeast of Taiwan and southwest of Kyushu, were found to be major source regions of oceanic nutrients to the shelf. Although the onshore fluxes of nutrients and volume both had apparent seasonal variations, the seasonal variation of the onshore nutrient flux did not exactly follow that of the onshore volume flux. Additional calculations in which the concentration of nutrients in Kuroshio water was artificially increased suggested that the oceanic nutrients were distributed in the bottom layer from the shelf break to the region offshore of the Changjiang estuary from spring to summer and appeared in the surface layer from autumn to winter. The calculations also implied that the supply of oceanic nutrients to the shelf can change the consumption of pre-existing nutrients from rivers. The response of primary production over the shelf to the oceanic nutrients was confirmed not only in the surface layer (mainly at the outer shelf and shelf break in winter and in the region offshore of the Changjiang estuary in summer) but also in the subsurface layer over the shelf from spring to autumn.

Interannual spring bloom variability and Ekman pumping in the coastal Gulf of Alaska

A lower trophic level ecosystem model is coupled to a three‐dimensional coastal ocean circulation model for the northwestern coastal Gulf of Alaska (CGOA) to investigate regional ecosystem dynamics on seasonal and interannual timescales. By including explicit growth limitation by light, nitrate, ammonium, silicic acid, and iron, the ecosystem model provides a comprehensive framework to investigate the combined role of macronutrients and micronutrients in shaping phytoplankton community structure. On the basis of comparisons with available in situ and remotely sensed observations for 1998 through 2002, the model reproduces the dominant modes of variability associated with the northwestern CGOA ecosystem dynamics. An empirical orthogonal function (EOF) analysis of biological and surface forcing fields suggests that, for the 5‐year period, interannual variability in peak chlorophyll concentrations during the spring bloom is related to interannual variability in the wind stress curl over the northern CGOA during the previous winter. Positive wind stress curl anomalies during winter result in enhanced Ekman pumping and, thus, nutrient upwelling on the shelf and at the shelfbreak. Since phytoplankton growth is severely light‐limited when Ekman pumping occurs, nutrient upwelling associated with the wind stress curl acts as a priming mechanism for the CGOA shelf, leading to higher peak chlorophyll concentrations during the following spring bloom. Enhanced wind stress curl and Ekman pumping are associated with the presence of a low‐pressure system in the northern CGOA, and potentially connected to the large‐scale variability of the Aleutian Low in the North Pacific.

Modeling the effect of ENSO on the lower trophic level ecosystem of the Cold Tongue and the Warm Pool regions in the equatorial Pacific

The effects of El Niño-Southern Oscillation (ENSO) processes on the lower trophic levels of Cold Tongue (140°W) region were examined with eight-year simulations for a time, 1991–1999, that included three ENSO cycles. As a comparison, simulations were done for a region in the western Pacific at 165°E at the equator, which is known as the Warm Pool. A one-dimensional multi-component lower trophic level ecosystem model that includes detailed algal physiology is used, which is forced by an eight-year time series of spectrally-dependent light, temperature, and water column mixing obtained from a Tropical Atmosphere-Ocean (TAO) Array mooring. Autotrophic growth is represented by five algal groups, which have light and nutrient utilization characteristics of low-light adapted Prochlorococcus, high-light adapted Prochlorococcus, Synechococcus, autotrophic eukaryotes, and large diatoms. The simulated response of the lower trophic levels in the two regions of the equatorial Pacific to ENSO cycles differs in community structure and level of production. For the Cold Tongue region, the ENSO warm phase results in a shift to small algal forms (e.g., Prochlorococcus spp. and Synechecoccus) and low primary productivity (25 mmol C m − 2 d − 1 versus an annual average of 75 mmol C m − 2 d − 1 ). For the Warm Pool region, the phytoplankton community is dominated by larger algal forms (e.g., autotrophic eukaryotes) and primary production increases (150 mmol C m − 2 d − 1 versus an annual average of 59 mmol C m − 2 d − 1 ). Also, during ENSO events carbon production and export in the Cold Tongue are limited by iron, whereas the relative abundance of iron and macronutrients (i.e. nitrate, silicate) limits production and export in the Warm Pool. Model results suggest that the occurrence of the large bloom following the 1997 El Niño at 140°W cannot be explained by local processes and that resolving the so called “barrier layer” is critical to simulate the biological dynamics at 165°E. Inclusion of diurnally varying mixed layer depths did not greatly affect the simulated carbon export. This suggests that pumping of particulate material out of the euphotic zone due to mixed layer shoaling during the day and redistribution of particulate material throughout the mixed layer due to mixed layer deepening during the night can be counter balanced.

Population dynamics model of Copepoda ( Neocalanus cristatus) in the northwestern subarctic Pacific

A population dynamics model (PDM) was developed for Neocalanus cristatus, which is the dominant large copepod in the northwestern subarctic Pacific, to simulate the increase of production with developmental stage and the transfer of production by vertical migration. The PDM was coupled with a lower trophic level ecosystem model, North Pacific Ecosystem Model Used for Regional Oceanography (NEMURO, developed by the North Pacific Marine Science Organization (PICES)), by replacing the large zooplankton component (ZooL) in NEMURO with the PDM. Ecological effects in the coupled model were compared to those in the original NEMURO. In the simulations, the annual cycle of copepodite stages begins during the spring bloom, followed by a decrease in biomass during summer, then migration of Neocalanus to the deep water where they diapause during autumn and winter, and finally the simulation ends with egg production in winter. The PDM successfully described the annual life cycle of Neocalanus. During early copepodite stages (during the spring bloom), they graze small phytoplankton (PhyS) without consuming large phytoplankton (PhyL). Therefore, PhyL biomass increases greatly in spring. In summer, during the last copepodite stage, they begin to prey mostly on PhyL, causing a decrease in the PhyL biomass, while the PhyS biomass increases. Production of PhyL remains higher than that of PhyS because predatory pressure by Neocalanus gradually weakens as the last copepodite stage, near the surface, approaches its end in summer. These simulations suggest that in addition to Neocalanus we should include PDMs for the other large copepods, which consume PhyL during the summer, in order to reproduce the lower trophic ecosystems of the northwestern subarctic Pacific.

Influence of nutrient utilization and remineralization stoichiometry on phytoplankton species and carbon export: A modeling study at BATS

The primary objective of this research is to understand the underlying mechanisms of the time-varying flux of carbon in the Sargasso Sea. To address this objective, a one-dimensional multi-component lower trophic level ecosystem model that includes detailed algal physiology as well as nutrient cycles is used at the Bermuda Atlantic Time-series Study (BATS, 31 ∘ 40 ′ N , 64 ∘ 10 ′ W ) site. In this model autotrophic growth is represented by three algal groups and the cell quota approach is used to estimate algal growth and nutrient uptake. This model is tested and evaluated for year 1998 using the bimonthly BATS cruise data. Results show that phosphorus and dissolved organic matter (DOM) are necessary compartments to correctly simulate organic elemental cycles at the BATS site. Model results show that autotrophic eukaryotes and cyanobacteria (i.e. Prochlorococcus and Synechococcus) are the most abundant algal groups and are responsible for 63% and 33% of carbon production in the region, respectively. Sensitivity analyses show that the annual contribution of nitrogen fixation and atmospheric nitrogen deposition to new production is approximately 9% and 3%, respectively. However, the recycled nitrogen and phosphorus are important components of the ecosystem dynamics because sustained growth of algal groups depends on remineralized nutrients which accounts for 75% of the annual carbon production. Nutrient uptake and remineralization stoichiometry can play an important role in determining the surface ocean nutrient distribution. Model results suggest phosphate limitation even during the spring bloom. Phosphate may thus limit the growth of all algal groups throughout the year.

Simulations of phytoplankton species and carbon production in the equatorial Pacific Ocean 2. Effects of physical and biogeochemical processes

A one-dimensional multi-component lower trophic level ecosystem model that includes detailed algal physiology is used to investigate the response of phytoplankton community and carbon production and export to variations in physical and biochemical processes in the Cold Tongue region of the equatorial Pacific Ocean at 0N, 140W. Results show that high-frequency variability in vertical advection and temperature is an important mechanism driving the carbon export. Filtering out low frequency physical forcing results in a 30% increase in primary production and dominance of high-light adapted P rochlorococcus and autotrophic eukaryotes. Sensitivity studies show that iron availability is the primary control on carbon export and production; whereas, algal biomass concentration is largely regulated by zooplankton grazing. Recycled iron is an important component of the ecosystem dynamics because sustained growth of algal groups depends on remineralized iron which accounts for 40% of the annual primary production in the Cold Tongue region. Sensitivity studies show that although all algal groups have a considerable effect on simulated phytoplankton carbon biomass, not all have a strong effect on primary production and carbon export. Thus, these sensitivity studies indicate that it may not be necessary to represent a broad spectrum of algal groups in carbon cycle models, because a few key groups appear to have a large influence on primary production and export variability. Combining the low-light adapted P rochlorococcus, high-light adapted P rochlorococcus and Synechococcus groups as a single group and using a three algal group model may be sufficient to simulate primary production and export variability in the tropical Pacific waters. The results from this modeling study suggest that the net effect of increased stratification and temperature conditions is a decrease in carbon export in the Cold Tongue region and a shift in the phytoplankton community towards smaller algal forms (e.g., P rochlorococcus spp. and Synechecoccus). Increased stratification can result in decreased iron concentration and reduced vertical velocities, both of which contribute to decreased carbon export. Also, stratified conditions enhance the remineralization rate of nutrients (e.g., iron), which enhances carbon production. Thus, inclusion of iron dynamics in climate models may be needed to fully represent the effect of climate variability on equatorial Pacific ecosystems.

Simulations of phytoplankton species and carbon production in the equatorial Pacific Ocean 1. Model configuration and ecosystem dynamics

The primary objective of this research is to investigate phytoplankton community response to variations in physical forcing and biological processes in the Cold Tongue region of the equatorial Pacific Ocean at 0N, 140W. This research objective was addressed using a one-dimensional multicomponent lower trophic level ecosystem model that includes detailed algal physiology, such as spectrally-dependent photosynthetic processes and iron limitation on algal growth. The ecosystem model is forced by a one-year (1992) time series of spectrally-dependent light, temperature, and water column mixing obtained from a Tropical Atmosphere-Ocean (TAO) Array mooring. Autotrophic growth is represented by five algal groups, which have light and nutrient utilization characteristics of low-light adaptedProchlorococcus, high-light adaptedProchlorococcus,Synechococcus, autotrophic eukaryotes, and large diatoms. The simulated distributions and rates are validated using observations from the 1992 U.S. Joint Global Ocean Flux Study Equatorial Pacific cruises. The modeldata comparisons show that the simulations successfully reproduce the temporal distribution of each algal group and that multiple algal groups are needed to fully resolve the variations observed for phytoplankton communities in the equatorial Pacific. The 1992 simulations show seasonal variations in algal species composition superimposed on shorter time scale variations (e.g., 8–20 days) that arise from changes in the upwelling/downwelling environmental structure. The simulated time evolution of the algal groups shows that eukaryotes are the most abundant group, being responsible for half of the annual biomass and 69% of the annual primary production and organic carbon export.

NEMURO—a lower trophic level model for the North Pacific marine ecosystem

The PICES CCCC (North Pacific Marine Science Organization, Climate Change and Carrying Capacity program) MODEL Task Team achieved a consensus on the structure of a prototype lower trophic level ecosystem model for the North Pacific Ocean, and named it the North Pacific Ecosystem Model for Understanding Regional Oceanography, “NEMURO”. Through an extensive dialog between modelers, plankton biologists and oceanographers, an extensive review was conducted to define NEMURO's process equations and their parameter values for distinct geographic regions. We present in this paper the formulation, structure and governing equations of NEMURO as well as examples to illustrate its behavior. NEMURO has eleven state variables: nitrate, ammonium, small and large phytoplankton biomass, small, large and predatory zooplankton biomass, particulate and dissolved organic nitrogen, particulate silica, and silicic acid concentration. Several applications reported in this issue of Ecological Modelling have successfully used NEMURO, and an extension that includes fish as an additional state variable. Applications include studies of the biogeochemistry of the North Pacific, and variations of its ecosystem's lower trophic levels and two target fish species at regional and basin-scale levels, and on time scales from seasonal to interdecadal.

Initial design for a fish bioenergetics model of Pacific saury coupled to a lower trophic ecosystem model

AbstractA fish bioenergetics model coupled with an ecosystem model was developed to reproduce the growth of Pacific saury. The model spatially covers three different oceanographic spatial domains corresponding to the Kuroshio, Oyashio, and interfrontal (mixed water) regions. In this coupled model, three (small, large, and predatory) zooplankton densities which were derived from the lower trophic level ecosystem model were input to the bioenergetics model of saury as the prey densities. Although certain model parameters were imposed from other species’ bioenergetics, several model parameters were estimated from observational data specific to Pacific saury. The integrated model results reproduced appropriate growth rates of Pacific saury. Model sensitivities to water temperature and prey density are examined and observational methods to evaluate the model parameters are discussed.