Use of a diatom inhibitor reveals contribution to seagrass ecosystem in experiments conducted using seagrass cores from 1m depth in Grand Bay in 2017.

Website: https://www.bco-dmo.org/dataset/819932
Data Type: experimental
Version: 1
Version Date: 2020-08-10

Project
» The biotic and abiotic controls on the Silicon cycle in the northern Gulf of Mexico (CLASiC)
ContributorsAffiliationRole
Krause, Jeffrey W.Dauphin Island Sea Lab (DISL)Principal Investigator
Cebrian, JustMississippi State University (MSU)Co-Principal Investigator
Cox, ErinUniversity of New Orleans (UNO)Contact
Haskins, ChristinaWoods Hole Oceanographic Institution (WHOI BCO-DMO)BCO-DMO Data Manager

Abstract
We report an assessment for determining the contribution by diatoms to community productivity and respiration within a coastal benthic ecosystem with multiple autotrophs. During summer, cores of open sediment and seagrass habitat were collected from a lagoon within the Northern Gulf of Mexico. Cores were maintained in an outdoor mesocosm. Germanic acid, an inhibitor of diatom cell division, was added to half the cores and quantification of production and respiration was done. Inhibition of diatoms reduced benthic productivity within the seagrass habitat. 71 to 83% of production was attributable to diatoms and this contribution moved the benthic system into net autotrophy. Diatom contribution to production in other habitat-community components was more variable (varied from 0 to 86%). Findings underscore the ecological importance of diatoms as producers in seagrass beds, the role of seagrasses in maintaining productivity, and infer that diatoms may have similar contributions in other aquatic vegetated habitats.


Coverage

Spatial Extent: Lat:30.383174 Lon:-88.312561
Temporal Extent: 2017-06-28 - 2017-07-31

Methods & Sampling

Three repeated experimental trials were done in summer months. Thirty-two cores (27 cm diameter, 14 cm depth) were collected from 50 m2 area of seagrass bed at 1 m depth on: June 28, July 12 and July 26, 2017 for trials 1-3, respectively. On each date, 16 cores were collected from seagrass habitat in pairs. Another 16 cores were collected from open sediment (OS) habitat. Extracted, paired cores were placed upright into an open-top plastic tub (49 x 33 x 42 cm) to produce eight tubs of each habitat.

Tubs were transported to Dauphin Island Sea Lab (~30-minute drive) filled with seawater (to core depth of 16 cm) pumped from Mobile Bay (20 km, east of site) and arranged in four blocks within an outdoor mesocosm. Each block contained two tubs of each habitat. After two days, a diatom-specific inhibitor (3 µM solution of germanic acid, i.e. Ge treatment) was randomly added to water, i.e. two tubs per block, one of each habitat type. Germanium (Ge) at high Ge/Si ratios (> 0.01) prevents formation of siliceous cell wall (Azam and Chisholm 1976). We added 3 µM solution and allowed two days for Ge incorporation.

Metabolism measurements:

Two days after, we quantified productivity and respiration from changes in oxygen content within 2-3 hour incubations of chambers and bottles following methods in Anton et al. (2009). Oxygen content was measured with a meter (HQ30d, Hach, Loveland, Colorado, USA) and, this was initial oxygen content for both chamber and bottle incubation. After incubation, we measured final oxygen content in bottles and chambers.

To compare rates between treatments, net community production (NCP) and respiration were assessed in mg O2 m–2 h–1 and mg O2 L-1 h-1 for benthic and water-column (WC) communities, respectively. Equations were:

WC NCP = (Fcb – Icb) t-1 (1)

WC respiration = (Fdb – Idb) t-1 (2)

Benthic NCP = [(Fcc – Icc) – (Fcb – Icb)] V t-1 A-1 (3)

Benthic respiration = [(Fdc – Idc) – (Fdb – Idb)] V t-1 A-1 (4)

where capital letters are for initial (I) or final (F) oxygen content (mg L-1) for clear (c) and dark (d) incubations (first letter in subscript) in chambers (c) or bottles (b) (second letter in subscript); t is incubation time (h), V is volume (L) and A is area (m2) of chamber. Gross primary productivity (GPP) was calculated as sum between NCP and absolute respiration for each tub.

To compare GPP between communities, control values were expressed in mg O2 m-2 h-1 after WC metrics of NCP and respiration were integrated over a 1 m depth (x 1000 L). System GPP was obtained by summing WC and benthic GPP.

Environmental measurements:

Salinity and temperature were measured at time of oxygen measurements using the same meter. Surface photosynthetic active radiation (PAR) (from environmental station 30°15.075' N, -88°04.670' E Dauphin Island, Alabama, USA; http://arcos.disl.org) was averaged over incubation duration and integrated over a 48 hour-period prior to incubations (Photosynthetic Photon Flux Density, PPFD). 48 hours reflects a short-term measure of light history.

Statistical analyses:

A series of two-way ANOVAs with trial and treatment as fixed factors were used to test for differences in producer biomass in both habitats and were used to test for differences in rates with and without diatom metabolism. Differences in rates were attributed to diatom metabolism and percent contribution to GPP was calculated based off mean GPP for each trial (n=4) with Ge rate as a proportion of control rate, expressed as a change from 100%.

 


Data Processing Description

Excel, Sigma Plot

BCO-DMO Data Manager Processing Notes:
* added a conventional header with dataset name, PI name, version date
* modified parameter names to conform with BCO-DMO naming conventions
* blank values in this dataset are displayed as "nd" for "no data."  nd is the default missing data identifier in the BCO-DMO system. Added ND as a missing data identifier.
* removed all spaces in headers and replaced with underscores
* removed all units from headers
* converted dates to ISO Format yyyy-mm-dd
* set Types for each data column 


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Data Files

File
benthic_gpp.csv
(Comma Separated Values (.csv), 21.78 KB)
MD5:26b2c9d0d40a5eecf8c7a4d3b79c9501
Primary data file for dataset ID 819932

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Supplemental Files

File
Cox etal Percent Contribution to GPP
filename: Coxetal_pct_contribution_to_GPP.csv
(Comma Separated Values (.csv), 306 bytes)
MD5:4d6e034a4663e9764a0ad591e97263d0
Percent contribution to gross primary production from lab incubation experiments.
Cox etal Rates Summarized
filename: Coxetal_rates_summarized.csv
(Comma Separated Values (.csv), 17.66 KB)
MD5:9db6620c2decbb6ee615b2020fbb41d9
Summarized Rates from Incubation Experiments.
Cox etal System GPP
filename: Coxetal_System_GPP.csv
(Comma Separated Values (.csv), 1.11 KB)
MD5:5c5152a5c2df5d933a6cee18b75889ff
System gross primary production from incubation experiments.

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Related Publications

Anton, A., J. Cebrian, K. L. H. Jr, and J. Goff. 2009. Low impact of Hurricane Katrina on seagrass community structure and functioning in the Northern Gulf of Mexico. Bull. Mar. Sci. 85: 16
Methods
Azam, F., & Chisholm, S. W. (1976). Silicic acid uptake and incorporation by natural marine phytoplankton populations1. Limnology and Oceanography, 21(3), 427–435. doi:10.4319/lo.1976.21.3.0427
Methods
Dzwonkowski, B., Greer, A. T., Briseño-Avena, C., Krause, J. W., Soto, I. M., Hernandez, F. J., … Graham, W. M. (2017). Estuarine influence on biogeochemical properties of the Alabama shelf during the fall season. Continental Shelf Research, 140, 96–109. doi:10.1016/j.csr.2017.05.001
Methods
Krause, J. W., Nelson, D. M., & Lomas, M. W. (2009). Biogeochemical responses to late-winter storms in the Sargasso Sea, II: Increased rates of biogenic silica production and export. Deep Sea Research Part I: Oceanographic Research Papers, 56(6), 861–874. doi:10.1016/j.dsr.2009.01.002
Methods
Welschmeyer, N. A. (1994). Fluorometric analysis of chlorophyll a in the presence of chlorophyll b and pheopigments. Limnology and Oceanography, 39(8), 1985–1992. doi:10.4319/lo.1994.39.8.1985
Methods

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Parameters

ParameterDescriptionUnits
Sample_Codecode used to identify samples unitless
Collection_Datedate the core of seagrass habitat or sediment habitat was collected yyyy-mm-dd
Ge_Addition_Datedate Ge was added yyyy-mm-dd
Experimental_Trial_Datedate the incubation trial was done yyyy-mm-dd
Trial_Numberthe number of repeated trials (1-3) that was done unitless
Paired_core_numbernumber 1-8 for cores placed in A-D locations (or block) within the outside mesocosm unitless
Block_A_to_Dthe block the core was placed in unitless
Ge_Control_treatmentidentifies whether Ge was added or whether it was a control unitless
Seagrass_Sediment_habitatidentifies whether the core was from seagrass or sediment habitat unitless
Light_Dark_Incubationidentifies whether the core was incubated in a clear or dark container unitless
Seagrass_Above_Ground_Biomassthe dry weight of the above-ground seagrass in the core g dw
Seagrass_Below_Ground_Biomassthe dry weight of the below-ground seagrass in the core g dw
Sediment_Chlorophyllchlorophyll concentration in the sediment mg/m2
Water_Column_Chlorophyllchlorophyll concentration in the water ug/L
Salinitysalinity of the sample at the start of the incubation psu
Start_Timestart time of the incubation; logged in CST timezone hh:mm
Temptemperature of the water at the start of the incubation degrees Celcius
O2_startoxygen content at the start of the incubation mg/L
O2_saturationoxygen content at the start of the incubation %
Salinity_2salinity of the water column within jars at the end of the incubation psu
JARS_End_Timetime at the end of the incubation of the water column; logged in CST timezone hh:mm
Temp_2temperature of the water column within jars at the end of the incubation degrees Celcius
O2_end_jarsoxygen content at the end of the incubation within jars which enclosed the water column mg/L
O2_saturation_2oxygen content at the end of the incubation within jars which enclosed the water column %
End_Time_jars_minus_Start_Timelength of the incubation of the water column in jars hh:mm
Decimal_Timelength of the incubation in decimal time of the water column in jars hours
Water_Column_NCP_and_respiration_Ratesnet community production or respiration rates of the water column enclosed in jars mg L m2 hr-1
Water_Column_NCP_and_respiration_Rates_1mnet community production or respiration rates of the water column enclosed in jars over 1 m depth mg L m2 hr-1
Water_Column_Gross_Primary_Productiongross primary production of the water column enclosed in jars mg L m2 hr-1
Salinity_3salinity of the water within the benthic chambers at the end of the incubation psu
Chambers_End_Timethe time at the end of the incubation of the benthic chambers; logged in CST timezone hh:mm
Temp_3temperature of the water within the benthic chambers at the end of the incubation degrees Celcius
O2_end_chambersoxygen content within the benthic chambers at the end of the incubation mg/L
O2_saturation_3oxygen content within the benthic chambers at the end of the incubation %
End_Time_chambers__minus_Start_Timeduration of the incubation of benthic community hh:mm
Decimal_Time_2duration of the incubation of benthic community in decimal time hours
NCP_and_Respiration_Benthic_Ratesnet community production or respiration rates of the benthic community mg L m2 h-1
Benthic_Gross_Primary_Productiongross primary production of the benthic community enclosed in chambers mg L m2 h-1


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Instruments

Dataset-specific Instrument Name
Skalar autoanalyzer
Generic Instrument Name
Nutrient Autoanalyzer
Generic Instrument Description
Nutrient Autoanalyzer is a generic term used when specific type, make and model were not specified. In general, a Nutrient Autoanalyzer is an automated flow-thru system for doing nutrient analysis (nitrate, ammonium, orthophosphate, and silicate) on seawater samples.

Dataset-specific Instrument Name
HQ30d, Hach, Loveland, Colorado, USA
Generic Instrument Name
Multi Parameter Portable Meter
Generic Instrument Description
An analytical instrument that can measure multiple parameters, such as pH, EC, TDS, DO and temperature with one device and is portable or hand-held.


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Project Information

The biotic and abiotic controls on the Silicon cycle in the northern Gulf of Mexico (CLASiC)

Coverage: Northern Gulf of Mexico, specifically the Louisiana Shelf region dominated by the discharge of the Mississippi River on the western side of the delta


NSF Award Abstract:
The Louisiana Shelf system in the northern Gulf of Mexico is fed by the Mississippi River and its many tributaries which contribute large quantities of nutrients from agricultural fertilizer to the region. Input of these nutrients, especially nitrogen, has led to eutrophication. Eutrophication is the process wherein a body of water such as the Louisiana Shelf becomes enriched in dissolved nutrients that increase phytoplankton growth which eventually leads to decreased oxygen levels in bottom waters. This has certainly been observed in this area, and diatoms, a phytoplankton which represents the base of the food chain, have shown variable silicon/nitrogen (Si/N) ratios. Because diatoms create their shells from silicon, their growth is controlled not only by nitrogen inputs but the availability of silicon. Lower Si/N ratios are showing that silicon may be playing an increasingly important role in regulating diatom production in the system. For this reason, a scientist from the University of South Alabama will determine the biogeochemical processes controlling changes in Si/N ratios in the Louisiana Shelf system. One graduate student on their way to a doctorate degree and three undergraduate students will be supported and trained as part of this project. Also, four scholarships for low-income, high school students from Title 1 schools will get to participate in a month-long summer Marine Science course at the Dauphin Island Sea Laboratory and be included in the research project. The study has significant societal benefits given this is an area where $2.4 trillion gross domestic product revenue is tied up in coastal resources. Since diatoms are at the base of the food chain that is the biotic control on said coastal resources, the growth of diatoms in response to eutrophication is important to study.

Eutrophication of the Mississippi River and its tributaries has the potential to alter the biological landscape of the Louisiana Shelf system in the northern Gulf of Mexico by influencing the Si/N ratios below those that are optimal for diatom growth. A scientist from the University of South Alabama believes the observed changes in the Si/N ratio may indicate silicon now plays an important role in regulating diatom production in the system. As such, understanding the biotic and abiotic processes controlling the silicon cycle is crucial because diatoms dominate at the base of the food chain in this highly productive region. The study will focus on following issues: (1) the importance of recycled silicon sources on diatom production; (2) can heavily-silicified diatoms adapt to changing Si/N ratios more effectively than lightly-silicified diatoms; and (3) the role of reverse weathering in sequestering silicon thereby reducing diffusive pore-water transport. To attain these goals, a new analytical approach, the PDMPO method (compound 2-(4-pyridyl)-5-((4-(2-dimethylaminoethylamino-carbamoyl)methoxy)phenyl)oxazole) that quantitatively measures taxa-specific silica production would be used.



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Funding

Funding SourceAward
NSF Division of Ocean Sciences (NSF OCE)

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