Effects of freshwater flow and phytoplankton biomass on growth, reproduction, and spatial subsidies of the estuarine copepod Pseudodiaptomus forbesi

Kimmerer, Wim; Ignoffo, Toni R.; Kayfetz, Karen; Slaughter, Anne M.

doi:10.1007/s10750-017-3385-y

Cited by 26 publications

(55 citation statements)

References 88 publications

(114 reference statements)

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“…Finally, our post hoc evaluation of the model and data highlighted that the copepod prey of juvenile smelt are also impacted by whole‐Delta outflow (Kimmerer et al. , ), indicating that water management could indirectly impact smelt abundances through decoupling trophic linkages, a consequence which needs to be explicitly explored (see Merz et al. for further treatment).…”

Section: Discussionmentioning

confidence: 98%

“…We assumed that both development and movement contributed to the observed abundance and future research should work to determine relative inputs from both sources. Finally, our post hoc evaluation of the model and data highlighted that the copepod prey of juvenile smelt are also impacted by whole-Delta outflow (Kimmerer et al 2018(Kimmerer et al , 2019, indicating that water management could indirectly impact smelt abundances through decoupling trophic linkages, a consequence which needs to be explicitly explored (see Merz et al 2016 for further treatment). For example, pairing model simulations with appropriate field studies could help elucidate how locally enhanced copepod production might affect delta smelt independent of outflow effects on salinity.…”

Section: Discussionmentioning

confidence: 99%

“…However, it is possible that large densities of smelt could depress copepod density via predator–prey interactions (Kimmerer et al. ), in which case we might see a more complex relationship between smelt and calanoid densities (Ives et al. , Simonis ).…”

Section: Introductionmentioning

confidence: 99%

“…Given their (primarily) annual life-history, there is strong selective pressure for juvenile smelt to consume large quantities of prey resources quickly to be able to mature and reproduce successfully. However, it is possible that large densities of smelt could depress copepod density via predator-prey interactions (Kimmerer et al 2018), in which case we might see a more complex relationship between smelt and calanoid densities (Ives et al 2003, Simonis 2013.…”

Section: Introductionmentioning

confidence: 99%

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Prey availability, environmental constraints, and aggregation dictate population distribution of an imperiled fish

Simonis¹,

Merz

2019

Ecosphere

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Accelerated global loss of fish species underscores an urgent need to elucidate constraints on spatial and temporal population patterns and to mitigate human‐mediated impacts accordingly. We analyzed 20 yr of trawl data using a spatiotemporally explicit, hierarchically Bayesian model to define density distributions of an imperiled anadromous fish—the delta smelt, Hypomesus transpacificus—in the heavily modified and highly used San Francisco Estuary. To reduce management reliance on an estuary‐wide annual population index that minimizes data resolution and ignores uncertainty, our model took a spatiotemporal approach and explicitly accounted for sampling and observation variation through both stochastic and deterministic elements. Our model demonstrated that juvenile smelt density has decreased over annual time and displays a distinct seasonal pattern (the combination of growth into the sampled size class, mortality, and movement into and out of the sampling frame) of increases in March–June followed by decreases in June–August. Smelt density was highly spatiotemporally autocorrelated and strongly tracked prey availability yet was also constrained by local hydrological factors (salinity, turbidity, velocity). Specifically, juvenile smelt preferred slightly saline, turbid, generally slow‐moving water with ample copepod prey. However, poor swimming capabilities reduced the capacity of juvenile smelt to mix throughout the estuary and find optimal habitat, emphasizing the importance of accounting for spatiotemporal autocorrelation in species distribution models. Further, whole‐estuary outflow appeared to influence the spatial distribution of covariates and juvenile smelt, such that smelt densities tended to peak closer to the marine zone at a lower maximal value when outflow was high. The predictions of our model accurately matched observed patterns of juvenile delta smelt catch while embracing uncertainty (although the predictions tended to exaggerate the total smelt catch variation via over‐predicted tail values). These results highlight that data‐driven improvements can be made to the analytical methods currently used to guide delta smelt management and lay the groundwork for mitigating the impacts of water use, flow regimes, habitat alteration, and climate change on an endangered species in a highly impacted and economically consequential habitat.

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Section: Discussionmentioning

confidence: 98%

Section: Discussionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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Prey availability, environmental constraints, and aggregation dictate population distribution of an imperiled fish

Simonis¹,

Merz

2019

Ecosphere

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“…Calanoid copepodites were more abundant in some model period years than in historical years because between these periods several copepod species were introduced to the SFE, including P. forbesi , which had variable overlap with Delta Smelt in the low‐salinity habitat (Kimmerer et al. ).…”

Section: Discussionmentioning

confidence: 99%

Individual‐Based Modeling of Delta Smelt Population Dynamics in the Upper San Francisco Estuary III. Effects of Entrainment Mortality and Changes in Prey

Kimmerer

Rose

2018

Trans Am Fish Soc

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We used an individual‐based model, developed previously for the endangered, endemic Delta Smelt Hypomesus transpacificus, to investigate two factors widely believed to affect its abundance in the San Francisco Estuary: entrainment in large water diversion facilities and declines and species shifts in their zooplankton prey. Previous analyses suggested that these factors had substantial effects on the Delta Smelt population, although evidence is accumulating that other factors, such as contaminants and predation, are also having effects. Simulations were performed for 1995–2005 with either entrainment mortality set to zero or zooplankton biomasses replaced with values sampled from pre‐decline years. The detailed individual‐based and spatial model output was summarized as the annual finite population growth rate (λ). Eliminating entrainment mortality increased the geometric mean λ by 39% through increased survival of larvae and adults. Substituting historical food for present‐day food resulted in variable annual λ values with a geometric mean that was 41% greater than the baseline value (14–81% across 10 alternative food scenarios). Historical food caused higher juvenile consumption and growth rates, leading to larger recruits, earlier maturity, and higher individual fecundity. These results were robust to four sets of simulations using alternative formulations for density dependence, mortality, maturity, and larval growth.

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Copepod egg production estimates are biased by female mortality

Kimmerer,

Slaughter,

Ignoffo

2024

Limnology & Oceanography

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Egg production rate (EPR, eggs ♀−1d−1) is a key measure of the nutritional state of metazoans such as copepods. Chlorophyll concentration is most often used to index responses of copepod vital rates to ambient food, but the fits to EPR are often poor. A known but unexplored bias in EPR estimates is the interaction between lifetime reproductive schedules of adult females and their mortality. We examined this interaction for Pseudodiaptomus forbesi, an abundant sac‐spawning calanoid copepod, in the San Francisco Estuary (SFE), USA. The reproductive schedule of P. forbesi comprises a latent period followed by a generally steady rate of clutch production. We used a Bayesian approach to analyze data from two studies which included 141 individual estimates of proportion ovigerous, eggs per clutch, and mortality from 28 sampling events. Proportion ovigerous contributed 95% of the variation in EPR. Mortality was 0.01–0.73 d−1 by one method and ~ 20% higher by another. When mortality was high, most females were young, few were past the latent stage, and ~ 25% were ovigerous. Proportion ovigerous up to 75% occurred only with mortality > ~0.1 d−1. Adjusting for mortality increased estimates of proportion ovigerous by 3%–88% (median 36%) and allowed for a relationship with chlorophyll, which could not be fitted to the raw data. However, the adjustments increased uncertainty. Given the large effort required, we recommend that others investigate this phenomenon for other species and environments before this adjustment should be recommended for estimating copepod egg production.

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Effects of freshwater flow and phytoplankton biomass on growth, reproduction, and spatial subsidies of the estuarine copepod Pseudodiaptomus forbesi

Cited by 26 publications

References 88 publications

Prey availability, environmental constraints, and aggregation dictate population distribution of an imperiled fish

Prey availability, environmental constraints, and aggregation dictate population distribution of an imperiled fish

Individual‐Based Modeling of Delta Smelt Population Dynamics in the Upper San Francisco Estuary III. Effects of Entrainment Mortality and Changes in Prey

Copepod egg production estimates are biased by female mortality

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