Plankton biodiversity along a gradient of productivity and its mediation by macrophytes

We studied the effect of aquatic vegetation on the process of species sorting and community assembly of three functional groups of plankton organisms (phytoplankton, seston-feeding zooplankton, and substrate-dwelling zooplankton) along a primary productivity gradient. We performed an outdoor cattle tank experiment (n = 60) making an orthogonal combination of a primary productivity gradient (four nutrient addition levels: 0, 10, 100, and 1000 microg P/L; N/P ratio: 16) with a vegetation gradient (no macrophytes, artificial macrophytes, and real Elodea nuttallii). We used artificial plants to evaluate the mere effects of plant physical structure independently from other plant effects, such as competition for nutrients or allelopathy. The tanks were inoculated with species-rich mixtures of phytoplankton and zooplankton. Both productivity and macrophytes affected community structure and diversity of the three functional groups. Taxon richness declined with increasing plankton productivity in each functional group according to a nested subset pattern. We found no evidence for unimodal diversity-productivity relationships. The proportional abundance of Daphnia and of colonial Scenedesmus increased strongly with productivity. GLM analyses suggest that the decline in richness of seston feeders was due to competitive exclusion by Daphnia at high productivity. The decline in richness of phytoplankton was probably caused by high Daphnia grazing. However, partial analyses indicate that these explanations do not entirely explain the patterns. Possibly, environmental deterioration associated with high productivity (e.g., high pH) was also responsible for the observed richness decline. Macrophytes had positive effects on the taxon richness of all three functional plankton groups and interacted with the initial productivity gradient in determining their communities. Macrophytes affected the composition and diversity of the three functional groups both by their physical structure and through other mechanisms. Part of the macrophyte effect may be indirect via a reduction of phytoplankton production. Our results also indirectly suggest that the often reported unimodal relationship between primary productivity and diversity in nature may be partially mediated by the tendency of submerged macrophytes to be most abundant at intermediate productivity levels.     

Study of the nutrient and plankton dynamics in Lake Tanganyika using a reduced-gravity model

An eco-hydrodynamic (ECOH) model is proposed for Lake Tanganyika to study the plankton productivity. The hydrodynamic sub-model solves the non-linear, reduced-gravity equations in which wind is the dominant forcing. The ecological sub-model for the epilimnion comprises nutrients, primary production, phytoplankton biomass and zooplankton biomass. In the absence of significant terrestrial input of nutrients, the nutrient loss is compensated for by seasonal, wind-driven, turbulent entrainment of nutrient-rich hypolimnion water into the epilimnion, which gives rise to high plankton productivity twice in the year, during the transition between two seasons. Model simulations predict well the seasonal contrasts of the measured physical and ecological parameters. Numerical tests indicate that the half saturation constant for grazing by zooplankton and the fish predation rate on zooplankton affect the zooplankton biomass measurably more than that of phytoplankton biomass. This work has implications for the application of this model to predict the climatological biological productivity of Lake Tanganyika.     

The effects of seston food quality on planktonic food web patterns

In planktonic food webs, the conversion rate of plant material to herbivore biomass is determined by a variety of factors such as seston biochemical/elemental composition, phytoplankton cell morphology, and colony architecture. Despite the overwhelming heterogeneity characterizing the plant–animal interface, plankton population models usually misrepresent the food quality constraints imposed on zooplankton growth. In this study, we reformulate the zooplankton grazing term to include seston food quality effects on zooplankton assimilation efficiency and examine its ramifications on system stability. Using different phytoplankton parameterizations with regards to growth strategies, light requirements, sinking rates, and food quality, we examined the dynamics induced in planktonic systems under varying zooplankton mortality/fish predation, light conditions, nutrient availability, and detritus food quality levels. In general, our analysis suggests that high food quality tends to stabilize the planktonic systems, whereas unforced oscillations (limit cycles) emerge with lower seston food quality. For a given phytoplankton specification and resource availability, the amplitude of the plankton oscillations is primarily modulated from zooplankton mortality and secondarily from the nutritional quality of the alternative food source (i.e., detritus). When the phytoplankton community is parameterized as a cyanobacterium-like species, conditions of high nutrient availability combined with high zooplankton mortality led to phytoplankton biomass accumulation, whereas a diatom-like parameterization resulted in relatively low phytoplankton to zooplankton biomass ratios highlighting the notion that high phytoplankton food quality allows the zooplankton community to sustain relatively high biomass and to suppress phytoplankton biomass to low levels. During nutrient and light enrichment conditions, both phytoplankton and detritus food quality determine the extent of the limit cycle region, whereas high algal food quality increases system resilience by shifting the oscillatory region towards lower light attenuation levels. Detritus food quality seems to regulate the amplitude of the dynamic oscillations following enrichment, when algal food quality is low. These results highlight the profitability of the alternative food sources for the grazer as an important predictor for the dynamic behavior of primary producer–grazer interactions in nature.     

宁波市某人工泻湖浮游生物变化特征及影响因素分析

以宁波市北仑区梅山水道形成的人工泻湖为研究对象,在不同季节进行水质及浮游生物调查,分析其浮游生物时空分布特征与水质的关系。4个采样点共检出浮游植物66种,以硅藻为绝对优势种,检出浮游动物25种,主要为桡足类、少量轮虫及网纹虫;拦坝后水道内浮游生物密度有了数量级增长,各项生物评价指数降低,但各采样点仍处于中污染水平。监测理化参数表明,研究水域在拦坝后盐度下降、悬浮物浓度下降,氮磷含量无明显变化;水域大部分点位处于中度富营养化水平。结合浮游生物分布与理化参数进行分析,发现堤坝合龙后,水道内侧海水淡化、悬浮物含量下降,导致浮游生物密度上升、生物多样性下降、出现淡水优势种群;营养盐含量不是浮游生物生长的限制因子,对浮游生物分布无显著影响。     

贫营养型水库中罗非鱼对浮游植物的影响:围隔实验

于2009年9～11月在贫营养型的大型深水水库(流溪河水库)中进行了围隔(体积约为85 m3)实验,分析了罗非鱼对浮游植物的影响.根据水库中现有鱼类的生物量,设置加鱼处理组(2 g/m3)和无鱼对照组两组.每组有3个重复,实验开始后每周采样一次,测定水质与采集浮游生物定性和定量样品.实验结果表明,加鱼处理组和对照组的总氮、可溶性无机氮没有明显差别,实验后期的总磷与正磷有一定差别,处理组略高于对照组.加鱼处理组浮游植物丰度及生物量、叶绿素a的含量显著高于对照组(P<0.05),且透明度低于对照组,个体小于30μm的浮游植物种类的丰度与生物量较明显增加,浮游动物丰度显著低于对照组(P<0.05),但是生物量差异不显著(P>0.05).总的来说,在贫营养条件下,低生物量的罗非鱼对水库浮游植物群落结构仍有着明显的影响,罗非鱼排泄产生的上行效应大于摄食产生的下行效应.     

Ecotoxicological effects of Trichloroethene upon plankton

A case study in an experimental pond was performed to evaluate the ecotoxic effects of Trichloroethene (TRI) upon the population density and productivity of phyto‐ and zooplankton. TRI was continuously released into two pond enclosures over 11 weeks (mean concentrations 1.5 and 7.5 mg/l). The chronic chemical treatment showed distinctive toxic influences upon the biota. Following the high TRI concentration, the phytoplankton density slightly increased; the productivity per single cells, however, was significantly reduced compared to the controls and the low TRI concentration. Cryptophyceae were the most sensitive algae taxa. The density and reproductivity of Daphniae and Phyllopodae decreased by the high TRI concentration. Most of the Rotatoriae were not negatively influenced. With increasing TRI concentrations two different bacteria forms showed a mass development. Small amounts of Trichloroacetic acid were detected in both enclosures as a conversion product of TRI (～3 μg/l after 80 days treatment).     

Effets eutrophiques au débouché d'un grand fleuve (Grand Rhône)

A study of hydrographical and biological parameters has been undertaken in surface waters near the mouth of the Rhône. Salinity, temperature and nutrient salts have been recorded, and the phytoplankton, as well as the zooplankton, quantitatively and qualitatively analyzed. Furthermore, the concentrations of chlorophyll a, seston, and organic matter have been determined. The hydrographical structure near the Rhône is heterogenous. The biological results are diffcult to explain on the basis of hydrographical parameters. The numerical data of zooplankton in the investigated area are 10 times higher than those of the Mediterranean Sea. There is a great abundance of brackish and freshwater phytoplankton in the dilution zone, but these cells are dead or almost dead; these observations coincide with the low concentrations of chlorophyll a.     

Influence of the organophosphorus insecticide phosphamidon on lentic water

The inland freshwater resources are being increasingly subjected to heavy stress as a result of indiscriminate dumping of industrial wastes, domestic sewage and agricultural run-off causing deterioration of the water quality and adverse impact on aquatic biota. Pesticides drained to the aquatic environment are primarily of agricultural origin. Phosphamidon (widely used organophosphate pesticide in paddy field) significantly reduced dissolved oxygen (DO) at 1.8 mg/l exposure and reduced alkalinity at 0.9 and 1.8 mg/l. Hardness also reduced gradually but not significantly. Free carbondioxide was increased significantly at 1.8 mg/l of the insecticide compared to control. The insecticide had no influence on pH and temperature. There was maximum reduction of phytoplankton and zooplankton population at 1.8 mg/l of phosphamidon. Though gradual reduction of plankton community was also noticed at different lower concentrations of pesticides but in case of phytoplankton an abrupt reduction (about 50% of the control) was observed. The normal behaviour and feeding rate of air breathing teleost, Channa punctatus was also hampered. Therefore, phosphamidon even at low concentrations may create disorders in the aquatic ecosystem.     

Modeling the seasonal autochthonous sources of dissolved organic carbon and nitrogen in the upper Chesapeake Bay

In this paper we investigate the seasonal autochthonous sources of dissolved organic carbon (DOC) and nitrogen (DON) in the euphotic zone at a station in the upper Chesapeake Bay using a new mass-based ecosystem model. Important features of the model are: (1) carbon and nitrogen are incorporated by means of a set of fixed and varying C:N ratios; (2) dissolved organic matter (DOM) is separated into labile, semi-labile, and refractory pools for both C and N; (3) the production and consumption of DOM is treated in detail; and (4) seasonal observations of light, temperature, nutrients, and surface layer circulation are used to physically force the model. The model reasonably reproduces the mean observed seasonal concentrations of nutrients, DOM, plankton biomass, and chlorophyll a. The results suggest that estuarine DOM production is intricately tied to the biomass concentration, ratio, and productivity of phytoplankton, zooplankton, viruses, and bacteria. During peak spring productivity phytoplankton exudation and zooplankton sloppy feeding are the most important autochthonous sources of DOM. In the summer when productivity peaks again, autochthonous sources of DOM are more diverse and, in addition to phytoplankton exudation, important ones include viral lysis and the decay of detritus. The potential importance of viral decay as a source of bioavailable DOM from within the bulk DOM pool is also discussed. The results also highlight the importance of some poorly constrained processes and parameters. Some potential improvements and remedies are suggested. Sensitivity studies on selected parameters are also reported and discussed.     

Spring phenological responses of marine and freshwater plankton to changing temperature and light conditions

Shifts in the timing and magnitude of the spring plankton bloom in response to climate change have been observed across a wide range of aquatic systems. We used meta-analysis to investigate phenological responses of marine and freshwater plankton communities in mesocosms subjected to experimental manipulations of temperature and light intensity. Systems differed with respect to the dominant mesozooplankton (copepods in seawater and daphnids in freshwater). Higher water temperatures advanced the bloom timing of most functional plankton groups in both marine and freshwater systems. In contrast to timing, responses of bloom magnitudes were more variable among taxa and systems and were influenced by light intensity and trophic interactions. Increased light levels increased the magnitude of the spring peaks of most phytoplankton taxa and of total phytoplankton biomass. Intensified size-selective grazing of copepods in warming scenarios affected phytoplankton size structure and lowered intermediate (20–200?μm)-sized phytoplankton in marine systems. In contrast, plankton peak magnitudes in freshwater systems were unaffected by temperature, but decreased at lower light intensities, suggesting that filter feeding daphnids are sensitive to changes in algal carrying capacity as mediated by light supply. Our analysis confirms the general shift toward earlier blooms at increased temperature in both marine and freshwater systems and supports predictions that effects of climate change on plankton production will vary among sites, depending on resource limitation and species composition.     

How does cod (Gadus morhua) cope with variability in feeding conditions during early larval stages?

Response of mesocosm-reared cod (Gadus morhua L.) larvae to different feeding conditions was investigated in 1988 in two mesocosms: a large basin and a smaller bag enclosure within the basin. The basin was filled with seawater, and a community of naturally occurring plankton developed. Plankton concentrations were monitored, and cod larvae stocked in the enclosures were sampled for determination of growth, survival, and gut content. In the bag, insufficient amounts of energetically favourable prey, as copepod nauplii, led to non-selective ingestion of plankton from a broad range of sizes, including considerable amounts of protozoans (tintinnid and oligotrich ciliates). Growth of larvae from the bag was low, with daily specific growth rates (SGR) less than 2.8% the first 3 wk post-hatch. This was followd by rapid increase of SGR to 21.7%, which coincided with a large increase in availability of copepod nauplii. In the basin, high nauplii concentrations led to SGR of 13.7 to 21.7% from onset of feeding to 16 d post-hatch, respectively. Under such conditions, the larvae were highly selective feeders. At 3 wk post-hatch, survival was 36.7 and 38.3% in the basin and bag enclosure, respectively. To cope with variations in the feeding conditions, the cod larvae were shown to be opportunists when nauplii were scarce, and included plankton from several trophic levels in their diet. When nauplii were abundant, cod larvae realized their high potential for growth. Both opportunism and realization of a high growth potential may enhance survival of the larvae.     

渭河浮游生物群落结构特征及其与环境因子的关系

渭河是黄河第一大支流,是黄河流域生态保护与高质量发展的重要研究区域.为了掌握渭河浮游生物组成结构及生态环境现状,于2018—2019年分两个季节在渭河开展4次水生态调查,研究分析了渭河浮游生物群落结构特征及其影响因子.调查结果显示,浮游植物有8门53种,以绿藻门和硅藻门为主,占比分别为43.4％、33.9％;浮游动物4...     

Natural diet of larval Penaeus merguiensis (Decapoda: Penaeidae) and its effect on survival

The relationship between Penaeus merguiensis protozoea larvae and their phytoplankton diet was examined using seasonal plankton surveys and in situ rearing experiments. Larval abundance, phytoplankton community structure, and chlorophyll a concentration in Albatross Bay, Gulf of Carpentaria, were monitored monthly for 2 yr. Larval abundance peaked in November (spring) and March (autumn), at which times diatoms were the most abundant group in net samples of phytoplankton and in the guts of larvae. During November 1989 and March 1990, larvae were reared in nylon mesh enclosures positioned throughout the water column at three depths: 0 to 3 m, 3 to 6 m and 6 to 9 m. Overall, larval survival and gut fullness were both higher in November than in March. In both months, larval survival was lower at the surface than at other depths. This correlated with lower chlorophyll a concentrations, but lower total cell densities were not detected. During the in situ experiments, diatoms were the most abundant phytoplankton group in the water column and in the guts of larvae and, therefore, appeared to be the principal diet of larvae. Pigment analysis demonstrated that while gut contents generally reflected the composition of the phytoplankton community, the larvae were not feeding exclusively on diatoms. They also ingested green algae and possibly seagrass detritus. The in situ experiments demonstrated that the predominantly diatom flora in Albatross Bay can provide a nutritionally adequate environment for prawn larvae even at seasonally low levels. It is unlikely, therefore, that starvation is a major cause of mortality of P. merguiensis larvae during either of the biannual peaks in their abundance in Albatross Bay, Gulf of Carpentaria.     

Characteristics of plankton Hg bioaccumulations based on a global data set and the implications for aquatic systems with aggravating nutrient imbalance

• Hg bioaccumulation by phytoplankton varies among aquatic ecosystems. • Active Hg uptake may exist for the phytoplankton in aquatic ecosystems. • Impacts of nutrient imbalance on food chain Hg transfer should be addressed. The bioaccumulation of mercury (Hg) in aquatic ecosystem poses a potential health risk to human being and aquatic organism. Bioaccumulations by plankton represent a crucial process of Hg transfer from water to aquatic food chain. However, the current understanding of major factors affecting Hg accumulation by plankton is inadequate. In this study, a data set of 89 aquatic ecosystems worldwide, including inland water, nearshore water and open sea, was established. Key factors influencing plankton Hg bioaccumulation (i.e., plankton species, cell sizes and biomasses) were discussed. The results indicated that total Hg (THg) and methylmercury (MeHg) concentrations in plankton in inland waters were significantly higher than those in nearshore waters and open seas. Bioaccumulation factors for the logarithm of THg and MeHg of phytoplankton were 2.4–6.0 and 2.6–6.7 L/kg, respectively, in all aquatic ecosystems. They could be further biomagnified by a factor of 2.1–15.1 and 5.3–28.2 from phytoplankton to zooplankton. Higher MeHg concentrations were observed with the increases of cell size for both phyto- and zooplankton. A contrasting trend was observed between the plankton biomasses and BAF_MeHg, with a positive relationship for zooplankton and a negative relationship for phytoplankton. Plankton physiologic traits impose constraints on the rates of nutrients and contaminants obtaining process from water. Nowadays, many aquatic ecosystems are facing rapid shifts in nutrient compositions. We suggested that these potential influences on the growth and composition of plankton should be incorporated in future aquatic Hg modeling and ecological risk assessments.     

Effects of ocean acidification, temperature and nutrient regimes on the appendicularian Oikopleura dioica: a mesocosm study

Increasing pCO₂ is hypothesized to induce shifts in plankton communities toward smaller cells, reduced carbon export rates and increased roles of gelatinous zooplankton. Appendicularians, among the most numerous pan-global “gelatinous” zooplankton, continuously produce filter-feeding houses, shortcutting marine food webs by ingesting submicron particles, and their discarded houses contribute significantly to carbon fluxes. We present a first mesocosm-scale study on the effects of temperature, pCO₂ and bloom structures on the appendicularian, Oikopleura dioica. There were effects of temperature and nutrients on phytoplankton communities. No shifts in functional phytoplankton groups, nor changes in particle sizes/morphotypes, known to impact appendicularian feeding, were observed under manipulated pCO₂ conditions. However, appendicularian abundance was positively correlated with increased pCO₂, temperature and nutrient levels, consistent with hypotheses concerning gelatinous zooplankton in future oceans. This suggests appendicularians will play more important roles in marine pelagic communities and vertical carbon transport under projected ocean acidification and elevated temperature scenarios.     

Warming modifies trophic cascades and eutrophication in experimental freshwater communities

Climate warming is occurring in concert with other anthropogenic changes to ecosystems. However, it is unknown whether and how warming alters the importance of top-down vs. bottom-up control over community productivity and variability. We performed a 16-month factorial experimental manipulation of warming, nutrient enrichment, and predator presence in replicated freshwater pond mesocosms to test their independent and interactive impacts. Warming strengthened trophic cascades from fish to primary producers, and it decreased the impact of eutrophication on the mean and temporal variation of phytoplankton biomass. These impacts varied seasonally, with higher temperatures leading to stronger trophic cascades in winter and weaker algae blooms under eutrophication in summer. Our results suggest that higher temperatures may shift the control of primary production in freshwater ponds toward stronger top-down and weaker bottom-up effects. The dampened temporal variability of algal biomass under eutrophication at higher temperatures suggests that warming may stabilize some ecosystem processes.     

Nutrient cycling by fish supports relatively more primary production as lake productivity increases

Animals can be important in nutrient cycling in particular ecosystems, but few studies have examined how this importance varies along environmental gradients. In this study we quantified the nutrient cycling role of an abundant detritivorous fish species, the gizzard shad (Dorosoma cepedianum), in reservoir ecosystems along a gradient of ecosystem productivity. Gizzard shad feed mostly on sediment detritus and excrete sediment-derived nutrients into the water column, thereby mediating a cross-habitat translocation of nutrients to phytoplankton. We quantified nitrogen and phosphorus cycling (excretion) rates of gizzard shad, as well as nutrient demand by phytoplankton, in seven lakes over a four-year period (16 lake-years). The lakes span a gradient of watershed land use (the relative amounts of land used for agriculture vs. forest) and productivity. As the watersheds of these lakes became increasingly dominated by agricultural land, primary production rates, lake trophic state indicators (total phosphorus and chlorophyll concentrations), and nutrient flux through gizzard shad populations all increased. Nutrient cycling by gizzard shad supported a substantial proportion of primary production in these ecosystems, and this proportion increased as watershed agriculture (and ecosystem productivity) increased. In the four productive lakes with agricultural watersheds (>78% agricultural land), gizzard shad supported on average 51% of phytoplankton primary production (range 27-67%). In contrast, in the three relatively unproductive lakes in forested or mixed-land-use watersheds (>47% forest, <52% agricultural land), gizzard shad supported 18% of primary production (range 14-23%). Thus, along a gradient of forested to agricultural landscapes, both watershed nutrient inputs and nutrient translocation by gizzard shad increase, but our data indicate that the importance of nutrient translocation by gizzard shad increases more rapidly. Our results therefore support the hypothesis that watersheds and gizzard shad jointly regulate primary production in reservoir ecosystems.     

Post-bloom grazing byCalanus glacialis,C. finmarchicus andC. hyperboreus in the region of the Polar Front,Barents Sea

The plankton community in the Polar Front area of the Barents Sea was investigated during a cruise from 14 to 28 July 1987. The colonial algaePhaeocystis pouchetii andDinobryon pellucidum dominated the phytoplankton. Depth integrated carbon assimilation rates varied from 190 to 810 mg C m^–2 d^–1. A high carbon:chlorophyll ratio (which varied from 123 to 352) prevailed at the three stations investigated, which may relate to facultative heterotrophic behaviour byD. pellucidum. The herbivorous zooplankton community was dominated byCalanus glacialis, C. finmarchicus, andC. hyperboreus. Maximum zooplankton biomass was found in the same depth strata as phytoplankton chlorophyll maximum. The herbivorous copepod populations did not display consistent day-night vertical migration patterns. Phytoplankton consumption rates of the various life stages were estimated from the turnover rate of plant pigments in the gut. The gut defecation rate constant (R) varied from 0.014 to 0.027 min^–1 at 0°C in copepodites (Stage II to adult female) ofC. glacialis, independent of developmental stage.Calanus spp. community carbon ingestion rates calculated from particulate carbon:chlorophyll ratios, were 10, 65 and 400% of daily phytoplankton carbon fixation rates at Stations 1, 2 and 3, respectively.     

Production and respiration of overall plankton and ultraplankton communities at the entrance to the Gulf of Finland in the Baltic Sea

Primary productivity and respiration of the overall plankton community and of ultraplankton (organisms passing through a 3-m Nuclepore filter) were studied at the entrance to the Gulf of Finland during the growth season in 1982. Data of the respiration measurements from previous years are also presented. During the development of a diatom spring bloom, the algal component could be successfully separated from the bacterial component by size fractionation with a 3-m Nuclepore filter and thus the algal respiration could be approximated, being on the order of 10 to 20% of the gross production. After the phytoplankton spring maximum, bacteria played an important role in mediating the energy flow from phytoplankton exudates to higher trophic levels. Maximum values of 1 230 and 740 mg O₂ m^-2 d^-1 were recorded for overall and for ultraplankton respiration, respectively, during late July. High productivity values coupled with low phytoplankton biomass and low inorganic nutrient values were also recorded in late July, indicating effective nutrient regeneration and rapid turnover of the plankton community. During late summer, a considerable fraction (over 30%) of phytoplankton production was released as exudates, suggesting that much of the energy is channeled to higher trophic levels via bacterial pathways rather than by direct herbivorous grazing during this season. The summer development of phytoplankton community structure and functioning is strongly controlled by hydrographic conditions, i.e. by nutrient inputs via upwelling and by water temperature. A carbon budget for late summer indicated that bacteria may contribute only up to 50% of the overall respiration of the plankton community, which suggests that heterotrophs other than bacteria play an important role in nutrient regeneration. The present study stresses the importance of energy flow via the phytoplankton exudatebacteria-micrograzer pathway in relatively oligotrophic, brackish water ecosystems.     

A simple plankton model for the Oregon upwelling ecosystem: Sensitivity and validation against time-series ocean data

Simple plankton models serve as useful platforms for testing our understanding of the mechanisms underlying ecosystem dynamics. A simple, one-dimensional plankton model was developed to describe the dynamics of nitrate, ammonium, two phytoplankton size-classes, meso-zooplankton, and detritus in the Oregon upwelling ecosystem. Computational simplicity was maintained by linking the biological model to a one-dimensional, cross-shelf physical model driven by the daily coastal upwelling index. The model sacrificed resolution of regional-scale and along-shore (north to south) processes and assumed that seasonal productivity is primarily driven by local cross-shelf Ekman transport of surface waters and upwelling of nutrient-rich water from depth.Our goals were to see how well a simple plankton model could capture the general temporal and spatial dynamics of the system, test system sensitivity to alternate parameter set values, and observe system response to the effective scale of potential retention mechanisms. Model performance across the central Oregon shelf was evaluated against two years (2000-2001) of chlorophyll and copepod time-series observations. While the modeled meso-zooplankton biomass was close in scale to the observed copepod biomass, phytoplankton was overestimated relative to that inferred from the observed surface chlorophyll concentration. Inshore, the system was most sensitive to the nutrient uptake kinetics of diatom-size phytoplankton and to the functional grazing response of meso-zooplankton. Meso-zooplankton was more sensitive to alternate parameter values than was phytoplankton. Reduction of meso-zooplankton cross-shelf advection rates (crudely representing behavioral retention mechanisms) reduced the scale of model error relative to the observed seasonal mean inshore copepod biomass but had little effect of the modeled meso-zooplankton biomass offshore nor upon phytoplankton biomass across the entire shelf.