Detritus fuels ecosystem metabolism but not metazoan food webs in San Francisco estuary's freshwater delta

Sobczak, William V.; Cloern, James E.; Jassby, Alan D.; Cole, Brian E.; Schraga, Tara S.; Arnsberg, Andrew J.

doi:10.1007/bf02732759

Cited by 82 publications

(85 citation statements)

References 47 publications

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“…However, in order for emergent, terrestrial, or floating aquatic vegetation to be incorporated by zooplankton and other suspension feeders, it would have to be routed through a detrital microbial loop. However, experimental work shows that the detrital-derived energy is of minor significance to pelagic pathways compared to phytoplankton, which is far more bioavailable (Sobczak et al 2002(Sobczak et al , 2005 and nutritious for zooplankton (Mueller-Solger et al 2002). This study and others in the estuary have demonstrated, using different approaches, that phytoplankton is the dominant energy source for pelagic consumers (Canuel et al 1995;Jassby and Cloern 2000;Mueller-Solger et al 2002;Sobczak et al 2002Sobczak et al , 2005.…”

Section: Pelagic Food Websmentioning

confidence: 65%

“…However, experimental work shows that the detrital-derived energy is of minor significance to pelagic pathways compared to phytoplankton, which is far more bioavailable (Sobczak et al 2002(Sobczak et al , 2005 and nutritious for zooplankton (Mueller-Solger et al 2002). This study and others in the estuary have demonstrated, using different approaches, that phytoplankton is the dominant energy source for pelagic consumers (Canuel et al 1995;Jassby and Cloern 2000;Mueller-Solger et al 2002;Sobczak et al 2002Sobczak et al , 2005. Contributions of detrital material to pelagic consumers cannot be ruled out entirely, but for the purposes of our study phytoplankton is assigned as the basal source of food for pelagic food webs (i.e., consumers with depleted d 13 C signatures) based on its likely dominance in assimilation to upper trophic levels.…”

Section: Pelagic Food Websmentioning

confidence: 99%

“…These studies have demonstrated the importance of in situ phytoplankton production as the primary source of available organic carbon for pelagic consumers in the tidal freshwater region of the estuary (Canuel et al 1995;Jassby and Cloern 2000;Mueller-Solger et al 2002;Sobczak et al 2002Sobczak et al , 2005. However, the relative importance of phytoplankton as an energy source for consumers in other habitats is unclear.…”

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confidence: 99%

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Dietary Segregation of Pelagic and Littoral Fish Assemblages in a Highly Modified Tidal Freshwater Estuary

2009

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Estuarine food webs are highly variable and complex, making identification of their trophic pathways difficult. Energy for the food web of the San Francisco Estuary is thought to be based largely on in situ phytoplankton production, but little attention has been paid to littoral habitats, where other energy sources may be important. We analyzed the stomach contents of over 960 juvenile fishes and the stable carbon and nitrogen isotope ratios of these fishes and their potential food resources in pelagic and littoral habitats from the tidal freshwater area of the estuary. The mixing model IsoSource was used to examine energy sources important to consumers. Our results show evidence of two predominant food web pathways. Pelagic fishes and some littoral fishes showed strong dependence on a zooplankton–phytoplankton trophic pathway. However, the majority of fishes in littoral habitats had diets and carbon isotope ratios consistent with energy arising from submerged aquatic vegetation and epiphytic macroalgae. IsoSource revealed that the overall majority of nutrition of littoral fishes originated from consumption of grazer amphipods. Examining both stable isotopes and stomach contents allowed us to identify a food web with contributions to resident fishes that had been previously underestimated in the estuary. This study provides insight to how estuarine food webs have changed over the last few decades and highlights why the functions of habitats must be understood for effective restoration planning.

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Section: Pelagic Food Websmentioning

confidence: 65%

Section: Pelagic Food Websmentioning

confidence: 99%

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confidence: 99%

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Dietary Segregation of Pelagic and Littoral Fish Assemblages in a Highly Modified Tidal Freshwater Estuary

2009

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“…Sommer et al, 2007). Studies have concluded that most levels of the food web above the primary producers are food limited (Müller-Solger et al, 2002;Kimmerer et al, 2005;Sobczak et al, 2005;Greene et al, 2011). The estuary has chronically low primary production (Kimmerer et al, 2012) near the bottom of estuaries listed in order of annual primary production (Boynton et al, 1982;Nixon, 1988).…”

Section: Introductionmentioning

confidence: 99%

A biogeochemical model of phytoplankton productivity in an urban estuary: The importance of ammonium and freshwater flow

Dugdale

Wilkerson

Parker

2013

Ecological Modelling

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a b s t r a c tIncreased discharge of ammonium (NH 4 ) to the San Francisco Estuary (SFE), largely in treated domestic sewage effluent, has been linked to chronically food-limited conditions and to reduced fish abundance. Elevated chlorophyll concentrations at phytoplankton bloom levels are rarely observed if the ambient NH 4 concentrations are above 4 mol L −1 -the NH 4 paradox. In both field samples and water held in enclosures for one week, an inverse relation was observed between NH 4 concentrations and nitrate (NO 3 ) uptake by phytoplankton, likely a result of inhibition of NO 3 uptake by NH 4 . A simple model was constructed to examine the interaction between NH 4 and NO 3 inputs to the estuary, with varying freshwater river flow (hereafter termed flow) conditions. Sensitivity analyses were made and initial model parameters taken from an existing oceanic biogeochemistry model. Experiments were made with the model, and showed that initial NH 4 concentrations largely controlled the length of time to peak NO 3 uptake and NO 3 exhaustion. The model parameters were then tuned using observations from a set of enclosure experiments, and validated with results from a series of independent enclosure experiments with a variety of initial conditions. The model was run in three flow modes: (1) with no (zero) flow, (2) with flow, a fully mixed water column and a uniform light field, and (3) with flow, a fully mixed water column but with light attenuation and depth integrated values of N uptake. In the zero flow mode the model simulated enclosure experiments and when compared with enclosure results indicated the basic NH 4 -NO 3 interactions to be correctly represented in the model. In the modes with flow, the model simulations reproduced a sharp transition from high phytoplankton productivity using both NO 3 and NH 4 to low productivity using only NH 4 , simulating the historical effects of increasing NH 4 inputs to the SFE. With vertical integration to incorporate effects of irradiance, sharp boundaries at specific combinations of varying flow and NH 4 inputs were observed. The model could be embedded into three dimensional models of the SFE/Delta currently being implemented for management purposes such as regulating estuarine nutrients as required by the State of California and evaluating the effects of water management decisions on salmon and protected species of fish.

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“…Cross-system differences and seasonal variation in physical forces are important determinants of the quantity and composition of suspended particulate matter available for consumers. Food quality (edibility, digestibility, nutritional sufficiency) is determined in large part by the relative contributions from allochthonous sources (terrestrial inputs) and autochthonous production (Findlay et al 2001;Sobczak et al 2005). The former is detrital material of low nutritive value, whereas the latter (algal fraction) is enriched in mineral nutrients and important biochemicals (fatty acids, amino acids, etc.)…”

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confidence: 99%

Consumer growth linked to diet and RNA—P stoichiometry: Response of Bosmina to variation in riverine food resources

Acharya

Bukaveckas

Jack

et al. 2006

Limnology & Oceanography

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Feeding experiments were performed with riverine Bosmina to investigate how their somatic growth rate responded to variation in food resources arising from changing hydrodynamic conditions. Experimental manipulations of food quality and quantity were achieved by diluting riverine suspended particulate matter (seston) to obtain a range of food concentrations and by amending natural seston with laboratory-grown Scenedesmus acutus. Bosmina experienced food limitation during periods of elevated discharge when the P content of seston was low (C : P . 600). Growth rates covaried with body RNA and P contents (R 2 5 0.96 and 0.86, respectively; content expressed as percent of dry mass), which is consistent with the hypothesis that high growth rates require increased allocation to P-rich ribosomal RNA and that high seston C : P induces P limitation in riverine Bosmina. P limitation arises in riverine consumers of riverine seston when hydrologic conditions favor terrestrial inputs, sediment resuspension, and low algal productivity, thereby resulting in seston fractions dominated by P-poor materials. During low discharge, riverine seston was P-rich relative to Bosmina requirements and growth rates were decoupled from body P content. Bosmina RNA content was strongly and linearly related to growth over a broad range of resource conditions, suggesting that it may be a useful surrogate to assess dietary sufficiency of food resources in natural settings.Hydrodynamic environments range from relatively still (wind-driven mixing) in lentic waters to turbulent (fluvialand tidal-driven mixing) in streams, rivers, and estuaries. Cross-system differences and seasonal variation in physical forces are important determinants of the quantity and composition of suspended particulate matter available for consumers. Food quality (edibility, digestibility, nutritional sufficiency) is determined in large part by the relative contributions from allochthonous sources (terrestrial in-

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Detritus fuels ecosystem metabolism but not metazoan food webs in San Francisco estuary's freshwater delta

Cited by 82 publications

References 47 publications

Dietary Segregation of Pelagic and Littoral Fish Assemblages in a Highly Modified Tidal Freshwater Estuary

Dietary Segregation of Pelagic and Littoral Fish Assemblages in a Highly Modified Tidal Freshwater Estuary

A biogeochemical model of phytoplankton productivity in an urban estuary: The importance of ammonium and freshwater flow

Consumer growth linked to diet and RNA—P stoichiometry: Response of Bosmina to variation in riverine food resources

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