Interactions between nutrients, phytoplankton growth, and micro- and mesozooplankton grazing in the plume of the Mississippi River

Liu, Hongbin; Dagg, M.

doi:10.3354/meps258031

Cited by 90 publications

(71 citation statements)

References 37 publications

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“…This evidence thus supports our conclusion that (42 mm) eukaryotes, particularly diatoms, were responsible for the carbon fixation and CO 2 drawdown we and others (Cai, 2003;Lohrenz and Cai, 2006) have observed in the MRP, and not picoplankton such as Synechococcus or picoeukaryotes which exist in much greater numbers throughout the plume area. Our findings also support the existing paradigm of MRP phytoplankton community dynamics, which dictates that production led by diatoms is prevalent in the mid-salinity plume where river water mixes with the Gulf of Mexico (Bode and Dortch, 1996;Lohrenz et al, 1999;Liu and Dagg, 2003;Liu et al, 2004;.…”

Section: Discussionsupporting

confidence: 74%

Phytoplankton carbon fixation gene (RuBisCO) transcripts and air-sea CO2 flux in the Mississippi River plume

et al. 2007

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River plumes deliver large quantities of nutrients to oligotrophic oceans, often resulting in significant CO 2 drawdown. To determine the relationship between expression of the major gene in carbon fixation (large subunit of ribulose-1,5-bisphosphate carboxylase/oxygenase, RuBisCO) and CO 2 dynamics, we evaluated rbcL mRNA abundance using novel quantitative PCR assays, phytoplankton cell analyses, photophysiological parameters, and pCO 2 in and around the Mississippi River plume (MRP) in the Gulf of Mexico. Lower salinity (30-32) stations were dominated by rbcL mRNA concentrations from heterokonts, such as diatoms and pelagophytes, which were at least an order of magnitude greater than haptophytes, a-Synechococcus or high-light Prochlorococcus. However, rbcL transcript abundances were similar among these groups at oligotrophic stations (salinity 34-36). Diatom cell counts and heterokont rbcL RNA showed a strong negative correlation to seawater pCO 2 . While Prochlorococcus cells did not exhibit a large difference between low and high pCO 2 water, Prochlorococcus rbcL RNA concentrations had a strong positive correlation to pCO 2 , suggesting a very low level of RuBisCO RNA transcription among Prochlorococcus in the plume waters, possibly due to their relatively poor carbon concentrating mechanisms (CCMs). These results provide molecular evidence that diatom/pelagophyte productivity is largely responsible for the large CO 2 drawdown occurring in the MRP, based on the cooccurrence of elevated RuBisCO gene transcript concentrations from this group and reduced seawater pCO 2 levels. This may partly be due to efficient CCMs that enable heterokont eukaryotes such as diatoms to continue fixing CO 2 in the face of strong CO 2 drawdown. Our work represents the first attempt to relate in situ microbial gene expression to contemporaneous CO 2 flux measurements in the ocean.

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Section: Discussionsupporting

confidence: 74%

Phytoplankton carbon fixation gene (RuBisCO) transcripts and air-sea CO2 flux in the Mississippi River plume

et al. 2007

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“…A major proportion of mesozooplankton filtering-feeder species exhibit sizeselective feeding behavior and prefer large-sized phytoplankton, determined by limits of feeding appendages. Our results showed that large-sized phytoplankton (>20 µm) (mainly diatoms and dinoflagellates) were generally cleared by mesozooplankton with high rates, which had also been reported by many field studies in coastal and estuarine waters (e.g., Liu and Dagg, 2003;Liu et al, 2010). Therefore, the general role of mesozooplankton in natural seawaters was to directly consume large-sized phytoplankton (mostly diatoms and autotrophic dinoflagellates), which made the consumers important in the classic food chain, in addition to regulating microbial food web.…”

Section: The Effect Of Mesozooplankton Size-selective Feedingsupporting

confidence: 53%

“…Generally, small-sized phytoplankton (<5 µm) were the preferential food items for microzooplankton, while they were generally too small to be directly ingested by the majority of mesozooplankton species (Calbet and Landry, 1999;Froneman, 2002;Liu and Dagg, 2003;Liu et al, 2005a and this study). A parallel study of our research through HPLC pigment analysis also showed that the clearance rates of mesozooplankton on small-sized phytoplankton, green algae and Synechococcus, were generally negative due to trophic cascades (Liu et al, 2010).…”

Section: The Effect Of Mesozooplankton Size-selective Feedingmentioning

confidence: 99%

Seasonal Variability of Mesozooplankton Feeding Rates on Phytoplankton in Subtropical Coastal and Estuarine Waters

2017

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In order to understand how mesozooplankton assemblages influenced phytoplankton in coastal and estuarine waters, we carried out a monthly investigation on mesozooplankton composition at two contrasting stations of Hong Kong coastal and estuarine waters and simultaneously conducted bottle incubation feeding experiments. The assemblage of mesozooplankton was omnivorous at both stations with varying carnivory degree (the degree of feeding preference of protozoa and animal food to phytoplankton) and the variations of carnivory degree were significantly associated with microzooplankton biomass (ciliates for the coastal station, both ciliates and dinoflagellates for the estuarine stations) and physical environmental parameters (primarily salinity). High carnivory was primarily due to high composition of noctilucales, Corycaeus spp., Oithona spp. and Acartia spp. Results of feeding experiments showed that grazing impacts on phytoplankton ranged from −5.9 to 17.7%, while the mean impacts were just <4% at both stations. The impacts were size-dependent, by which mesozooplankton consumed around 9% of large-sized phytoplankton while indirectly caused an increase of 4% of small-sized phytoplankton. Mesozooplankton clearance rate on phytoplankton, calculated from the log response of chlorophyll a concentrations by the introduction of bulk grazers after 1-day incubation, was significantly reduced by increasing carnivory degree of the mesozooplankton assemblage. The mechanism for the reduction of mesozooplankton clearance rate with increasing carnivory degree was primarily due to less efficient of filtering feeding and stronger trophic cascades due to suppression of microzooplankton. The feeding rates of mesozooplankton on microzooplankton were not obtained in this study, but the trophic cascades indirectly induced by mesozooplankton carnivorous feeding can be observed by the negative clearance rate on small-sized phytoplankton. Overall, the main significance of this study is the empirical relationship between carnivory degree and clearance rate, which allow researchers to potentially predict the herbivory of mesozooplankton in the nature without conducting feeding experiments.

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“…During the experiment both techniques were tested with a 200 mm net for pre-screening. Pre-screening is routine in dilution experiments and excludes mesozooplankton grazers ensuring that only the microzooplankton grazing is measured (Liu & Dagg, 2003;Fonda Umani et al, 2005;Sakka Hlaili et al, 2007).…”

Section: Methodsmentioning

confidence: 99%

Conserving original in situ diversity in microzooplankton grazing set-ups

Löder¹,

Aberle²,

Klaas

et al. 2010

Mar. Biodivers. Rec.

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Grazing experiments targeting the determination of in situ grazing rates are standard. In two separate experiments the effect of the frequently used siphon filling technique on the abundance of microzooplankton during the set-up of grazing experiments was investigated and compared to results from an alternative filling method. Hereby, water containing natural communities from Helgoland Roads, Germany (54811.3 ′ N 7854.0 ′ E), was transferred into incubation bottles using a funnel system (funnel-transfer technique (FTT)). The impact of pre-screening with a 200 mm net for excluding larger mesozooplankton grazers from the incubations was evaluated. Results show that the ciliate community was strongly affected by siphoning and pre-screening, leading to significant differences in abundance and Margalef diversity. The most affected ciliates were Lohmanniella oviformis and Myrionecta rubra, both important species in the North Sea. Dinoflagellates did not show any significant response to either siphoning or pre-screening with the exception of one athecate species. Such artificial bias in ciliate assemblages is very problematic for biodiversity consideration and grazing investigations. Simply changing the method of filling during the experimental set-up can ensure the measurement of accurate grazing rates of field abundances of microzooplankton. We thus recommend using conservative filling approaches like the FTT in experiments, especially when sensitive species are present, in order to avoid shifts in the overall microzooplankton community. Furthermore, we recommend introducing a control to evaluate the degree of changes in the target community due to the experimental set-up.

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Interactions between nutrients, phytoplankton growth, and micro- and mesozooplankton grazing in the plume of the Mississippi River

Cited by 90 publications

References 37 publications

Phytoplankton carbon fixation gene (RuBisCO) transcripts and air-sea CO2 flux in the Mississippi River plume

Phytoplankton carbon fixation gene (RuBisCO) transcripts and air-sea CO2 flux in the Mississippi River plume

Seasonal Variability of Mesozooplankton Feeding Rates on Phytoplankton in Subtropical Coastal and Estuarine Waters

Conserving original in situ diversity in microzooplankton grazing set-ups

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