Effects of Zooplankton Grazing on Phytoplankton Size-Structure and Biomass in the Lower Hudson River Estuary

Lonsdale, D; Cosper, Elizabeth M.; Doall, Michael H.

doi:10.2307/1352304

Cited by 32 publications

(33 citation statements)

References 47 publications

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“…For example, inhibitory interactions between Raphidophyceae and diatoms have previously been observed, likely due to allelopathy by both groups (Yamasaki et al 2007). Furthermore, studies have shown that both copepods and microzooplankton preferentially graze on different size classes, and each can potentially be a topdown control on phytoplankton community structure in some systems (Lonsdale et al 1996, Loder et al 2011.…”

Section: Shifting Planktonic Conditions In Western Lismentioning

confidence: 99%

Phytoplankton assemblage changes during decadal decreases in nitrogen loadings to the urbanized Long Island Sound estuary, USA

Suter¹,

Lwiza²,

Rose³

et al. 2014

Mar. Ecol. Prog. Ser.

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Despite reductions in nitrogen loadings from wastewater treatment plants (WWTPs) discharging into Long Island Sound (LIS) over the last 15 yr, eutrophication and hypoxia remain a severe problem. Here we used time series of hydrography, meteorology, nutrients, and phytoplankton pigments to explore the relationships between planktonic biomass, nutrient stocks, and physical regimes in LIS. With the exception of the most eutrophied station in the west, dissolved inorganic nitrogen (DIN) decreased between 1995 and 2009, likely resulting from WWTP upgrades. However, total dissolved nitrogen increased during this period, primarily driven by rising organic nitrogen pools. Simultaneous increases in inorganic phosphorus, silicate, and chlorophyll a (chl a) were also observed. Starting in 2002, pigment-based phytoplankton community composition revealed systematic declines in diatom abundances coincident with increases in dinoflagellates and other flagellated phytoplankton groups. Despite this, bottom water dissolved oxygen concentrations did not improve. The apparent paradox between increasing DIN limitation and escalating chl a concentrations in LIS suggests a shifting nutrient stoichiometry and an altered phytoplankton community in which phytoflagellates have increased in abundance relative to diatoms. Despite these changes, diatoms remained the most abundant algal group by the end of the study. In addition, a shift in chl a stocks in the year 2000 coincided with decreases in temperature, increases in salinity, and the proliferation of several algal groups. These results reveal the complex nature of eutrophied estuaries and indicate that policies targeting only inorganic nitrogen loadings may be insufficient to mitigate eutrophication in systems such as LIS.

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Section: Shifting Planktonic Conditions In Western Lismentioning

confidence: 99%

Phytoplankton assemblage changes during decadal decreases in nitrogen loadings to the urbanized Long Island Sound estuary, USA

Suter¹,

Lwiza²,

Rose³

et al. 2014

Mar. Ecol. Prog. Ser.

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“…The solid line is the empirically derived, maximum phytoplankton-growth rate as a function of temperature, from Eppley (1972) of the > 5 µm fraction (μ n ), rather than to low grazing pressure. The oft-observed dominance of large diatoms in nutrient-rich waters may have more to do with differential gross-growth rates than with size-selective grazing (see Lonsdale et al 1996a).…”

Section: Comparisons Between Phytoplankton Fractionsmentioning

confidence: 99%

Interactions between nutrients, phytoplankton growth, and microzooplankton grazing in a Gulf of Mexico estuary

Juhl¹,

Murrell²

2005

Aquat. Microb. Ecol.

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Dilution grazing experiments were conducted on 9 dates over a 16 mo period in Santa Rosa Sound (Florida, USA) measuring microzooplankton grazing (m) and phytoplankton grossgrowth rates under in situ (μ 0 ) and replete (μ n ) nutrient concentrations. The rates were measured on 4 phytoplankton fractions: bulk, > 5 µm, < 5 µm, and cyanobacteria. Many similarities existed among phytoplankton fractions: grazing rates were positively correlated with both μ 0 and μ n , the relationship between μ 0 and m was nearly 1:1, and μ n always exceeded m. The 1:1 relationship between μ 0 and m implied that microzooplankton grazing accounted for essentially all in situ phytoplankton growth, allowing no net accumulation under ambient nutrient concentrations. Despite this strong grazing pressure, μ 0 < μ n for all phytoplankton fractions, indicating persistent nutrient limitation. Because μ n always exceeded m, additional nutrient influx to the sound would generate a disparity between microzooplankton-grazing and phytoplankton-growth rates, resulting in increased biomass in all phytoplankton fractions. However, grazing would remain a major loss term for phytoplankton such that quantitative prediction of the biomass increase would have to incorporate grazing rates. This study therefore provides a useful example of simultaneous 'top-down' and 'bottom-up' control of phytoplankton biomass. We additionally observed that increased nutrient availability led to greater dominance by larger eukaryotic phytoplankton, due to differences in gross-growth rates between the phytoplankton fractions rather than differential grazing. Grazing rates on and gross-growth rates of cyanobacteria, but not the other phytoplankton fractions, were strongly correlated to temperature.

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“…), or heterotrophic dinoflagellates (H. dino; Oxyrrhis marina). Dissolved metal concentrations (C w ) are from Sañudo-Wilhelmy and Gill (1999) for the Hudson River Estuary, the ingestion rate (IR) was taken from Lonsdale et al (1996) as calculated by Wang and Fisher (1998), the uptake (k u ) and efflux (k ew ) rate constants for dissolved metals, as well as the growth rate (g) and the diatom assimilation efficiencies (AE ) are from Wang and Fisher (1998). The concentrations of metals in prey (C f ) were calculated from C w using volume concentration factors (VCF) for phytoplankton from Fisher and Wente (1993) ) and Fisher and Reinfelder (1995) (Cd: 1 ϫ 10 3 ).…”

Section: Subcellular Distribution Of Metals In Prey-mentioning

confidence: 99%

“…For example, while animals ingesting phytoplankton will only accumulate 33% of their total Ag body burden from food, copepods feeding on protozoa will accumulate an average of 64% from prey. Given the higher sensitivity of invertebrate zooplankton to metals accumulated from food (Hook and Fisher 2001a,b), copepods living in the Hudson River estuary may experience a heightened risk of sublethal toxicity (i.e., reduced egg production, hatching rate, ovary development, and egg protein content)-particularly from Ag-in the summer, when protozoa may be an important food source for copepods (Lonsdale et al 1996).…”

Section: Subcellular Distribution Of Metals In Prey-mentioning

confidence: 99%

Trophic transfer of trace metals from protozoa to mesozooplankton

Twining

Fisher

2004

Limnology & Oceanography

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Radiotracer techniques were used to quantify the assimilation and subsequent efflux of silver, cadmium, iron, mercury, thallium, and zinc by mesozooplankton fed ciliates, heterotrophic dinoflagellates, or heterotrophic flagellates, and the results were compared with published values measured for phytoplankton prey. The subcellular distribution of the metals within the prey cells was also determined and related to their bioavailability. Marine copepods assimilated 59-82% of Ag, 83-92% of Cd, 32-66% of Fe, 14-49% of Hg, and 71-78% of Zn ingested with protozoan prey. Higher Ag, Cd, Fe, and Hg assimilation efficiencies were observed for at least one of the species of protozoa than reported in the literature for phytoplankton. Significant differences in assimilation were not observed for Zn or for Tl fed to freshwater Ceriodaphnia in either protozoa or phytoplankton. The higher assimilation efficiencies of protozoan metals, when observed, were matched by higher fractions of metals in the cytoplasm of protozoa. A biokinetic model used to calculate steady-state metal concentrations in copepods indicates that copepods may contain 119% more Ag and 44% more Zn when feeding on ciliates instead of diatoms, possibly resulting in sublethal toxic effects at Ag and Zn concentrations reported for the Hudson River estuary. Further, higher assimilation and efflux rates of protozoan Fe may enhance remineralization of this limiting nutrient by mesozooplankton in high nutrient, low chlorophyll regions.Aquatic animals can accumulate metals both directly from their aqueous environment and from the prey they ingest, but metals accumulated through these two routes can have different physiological effects and geochemical fates. Food is often the dominant uptake pathway for metals in crustacean zooplankton (Munger and Hare 1997;Wang and Fisher 1998), and zooplankton can be more sensitive to metals accumulated through this pathway (Hook and Fisher 2001a,b). In addition to having greater physiological effects, metals that are ingested and assimilated by zooplankton can build up in food chains or be biologically recycled; these metals generally display longer residence times in surface waters than unassimilated metals, which get packaged into fecal pellets and sink out of surface waters (Fowler and Knauer 1986;Fisher et al. 1991). Metals bound to the exoskeleton may also be exported with molts (Fowler 1977).Most studies that have examined the assimilation of metals by zooplankton grazers have focused on phytoplankton prey (e.g., Sick and Baptist 1979;Fisher et al. 1991;Wang et al. 1996), but heterotrophic protists can also serve as an important food source for mesozooplankton. As the dominant grazers of heterotrophic and autotrophic picoplankton in many aquatic systems (Sherr and Sherr 1994), protozoa are an important trophic link between the microbial loop and the metazoan food web (Stoecker and Capuzzo 1990). Mi-

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Effects of Zooplankton Grazing on Phytoplankton Size-Structure and Biomass in the Lower Hudson River Estuary

Cited by 32 publications

References 47 publications

Phytoplankton assemblage changes during decadal decreases in nitrogen loadings to the urbanized Long Island Sound estuary, USA

Phytoplankton assemblage changes during decadal decreases in nitrogen loadings to the urbanized Long Island Sound estuary, USA

Interactions between nutrients, phytoplankton growth, and microzooplankton grazing in a Gulf of Mexico estuary

Trophic transfer of trace metals from protozoa to mesozooplankton

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