2003 Progress Report: Macrobenthic Process Indicators of Estuarine Condition for the Northern Gulf of Mexico

EPA Grant Number: R829458C008
Subproject: this is subproject number 008 , established and managed by the Center Director under grant R829458
(EPA does not fund or establish subprojects; EPA awards and manages the overall grant for this center).

Center: EAGLES - Consortium for Estuarine Ecoindicator Research for the Gulf of Mexico
Center Director: Brouwer, Marius
Title: Macrobenthic Process Indicators of Estuarine Condition for the Northern Gulf of Mexico
Investigators: Rakocinski, Chet
Institution: University of Southern Mississippi
Current Institution: University of Mississippi Main Campus
EPA Project Officer: Hiscock, Michael
Project Period: December 1, 2001 through November 30, 2005 (Extended to May 20, 2007)
Project Period Covered by this Report: December 1, 2002 through November 30, 2003
RFA: Environmental Indicators in the Estuarine Environment Research Program (2000) RFA Text |  Recipients Lists
Research Category: Water , Ecosystems , Ecological Indicators/Assessment/Restoration


The objectives pursued in Year 2 of this 4-year project were to: (1) conduct integrated field sampling along with the other Consortium for Estuarine Ecoindicator Research for the Gulf of Mexico (CEER-GOM) subgroups; (2) analyze and interpret the macrobenthic indicator data from the Grand Bay National Estuarine Research Reserve (GBNERR) case study; (3) obtain and process 2002 and 2003 macrobenthic indicator data; (4) pursue extramural collaborative efforts; and (5) disseminate CEER-GOM macrobenthic findings.

Progress Summary:

Objective 1: Conduct Integrated Field Sampling Along With Other CEER-GOM Subgroups

As an outcome of CEER-GOM collaborative meetings and recommendations by the Science Advisory Board, it was decided that in 2003 the CEER-GOM integrative field sampling efforts should be concentrated in the Pensacola Bay estuarine system, in East Bay, FL. At a joint meeting of CEER-GOM and U.S. Environmental Protection Agency Gulf Ecology Division (EPA GED) scientists held at the University of West Florida on May 13, 2003, field plans were developed for the 2003 sampling period in Pensacola Bay, including selection of sites and general sampling periods. The five 2002 stations on the Garcon Point transect were retained for development of a time course at stations PB1 (P12), PB2, PB3, PB4, and PB5. Two of these stations, PB1 (P12) and PB5, also were adopted for integrative sampling involving concurrent crustacean hypoxia, biofilm, and macrobenthic indicator sampling. Three other stations in East Bay were added to the list of integrative stations, including EPA GED stations P13, P14, and P15; these stations were sampled concurrently by the three CEER-GOM subprojects. The five integrative stations in East Bay, P12 (PB1), PB5, P13, P14, and P15, cover the lower portion of East Bay and provide varied depths and bottom conditions for the study. For example, stations P14 and P15 are relatively deep and occur in areas that are characteristically hypoxic, whereas station PB5 occurs in a shallow normoxic area. In addition, integrative sampling, including benthic sampling was conducted at two salt marsh stations on Garcon Point: Marsh Pond and Marsh Creek (MP and MC). Besides the macrobenthic component, crustacean hypoxia, Fundulus reproduction, and microbial biofilms CEER-GOM components were characterized at these two sites. Targeted samples usually comprised 10 stations, including the 7 integrated stations where biofilm and crustacean subgroups also overlapped, as well as the three remaining macrobenthic transect stations. Between July 19 and July 23, 2003, the 10 sites were targeted, although one of the transect sites (PB4) was not sampled due to rough weather. Datasondes were deployed for 2-week periods in connection with biofilm samplers at the integrated stations during the 2003 sampling periods. Integrative sampling took place at three times during the summer index and recovery periods in 2003 (July, August, and November). Two additional sampling trips were completed between August 25 and August 28 and November 4 and November 7, 2003. Both of these sampling trips coincided with CEER-GOM integrative sampling efforts. Targeted samples comprised 12 sites in August and 10 stations in November, including the 7 integrated stations with biofilm and crustacean subgroups, as well as 3 additional macrobenthic transect stations. In August, two additional stations in Santa Rosa Sound near a wastewater treatment plant also were sampled by biofilm, crustacean, and macrobenthic CEER-GOM subprojects. In addition, benthic sampling was conducted May 19-20, 2003, at the five original benthic transect stations. Salinities were low at this time and remained so throughout most of the summer. The November sampling trip also coincided with sampling for croaker by the fish reproductive endocrinology subgroup. All targeted stations were sampled successfully for macrobenthic indicators during these two periods.

Objective 2: Analyze and Interpret Macrobenthic Indicator Data From the GBNERR Case Study

We conducted a case study in the GBNERR to develop and assess the use of macrobenthic process-indicators. Four specific objectives of this study were to: (1) apply procedures to effectively characterize macrobenthic process-indicators; (2) examine spatial variation in macrobenthic process-indicators within two parallel Bayou systems; (3) determine whether the macrobenthic process-indicators were sensitive to moderate differences in levels of presumed nutrient loading; and (4) evaluate the hypothetical nonlinear macrobenthic response to eutrophication.

Study Design. Field work for the GBNERR case study was conducted from July 18-20, 2002, during the summer index period of the Mississippi National Coastal Assessment Program. A 7.5 km transect was established within each of two bayou systems, Bayou Heron and Bayou Cumbest (see Figure 1). Five sites were located along each transect, and sites were placed at distance octaves proceeding from the upper bayous to the adjoining bays (i.e., 0.5, 1.0, 2.0, and 4.0 km between sites). Sites were spaced closer in the upper regions of the systems, where organic loading and dissolved oxygen (DO) stress were more likely to occur. Bayou Heron is in a relatively pristine area, but this system exhibits relatively low DO in the uppermost portion. Bayou Cumbest is thought to be affected by moderate residential wastewater runoff due to poor septic facilities (MSU-CREC, 2000). The latter system also is subject to considerable land use as evidenced by altered shorelines in its upper reaches. Bayou Cumbest is a larger less dendritic system with higher flow rates than Bayou Heron. Combined differences in both land use and geomorphology should contribute to generally higher levels of nutrient loading in Bayou Cumbest relative to Bayou Heron. Three pairs of benthic grabs were taken at each site for macrofauna and sediments; water quality profiles as well as other information also were obtained.

Figure 1. Map of the Grand Bay National Estuarine Research Reserve (GBNERR) Study Area Showing Transects as Defined By Five Sites Within Each of the Two Bayou Systems, Bayou Cumbest and Bayou Heron

Hypothesis. Given the kinds of changes that are known to occur in abundances and body-size distributions of benthic organisms with increasing organic enrichment (Pearson and Rosenberg, 1978), one might hypothesize a nonlinear response in macrobenthic function along a gradient of increasing eutrophication (see Figure 2). More specifically, a hypothetical response might be defined by an initial linear increase in macrobenthic function up to peak levels, followed by an eventual exponential decrease in function as levels of nutrient loading intensify. Such a decline would reflect the impaired capacity of the ecosystem to process available resources at high stress levels (Xu, et al., 1999). For example, relatively low rates of production should occur at low nutrient levels due to nutrient limitation, followed by enhancement of production at moderate levels of nutrient enrichment; however, production should decline at high nutrient levels due to stress imposed by eutrophication. Stressors would include various detrimental effects associated with excessive nutrient loading and hypoxia.

Figure 2. Hypothetical Nonlinear Response in Macrobenthic Function Along a Gradient of Increasing Eutrophication

Spatial Patterns in Process-Indicators. Estimates of three macrobenthic process-indicators were examined in the case study: macrobenthic production, P:B values, and parameters of standardized biomass-size spectra. Interesting spatial variation in these three indicators was evident within the GBNERR system (see Table 1; Figure 3), and both longitudinal and cross-system patterns were apparent in these indicators. Overall, macrobenthic production increased from upestuary to downestuary sites, whereas P:B values were higher at upestuary sites, reflecting the tendency for downestuary sites to contain macrobenthic communities consisting of larger and longer lived organisms. Moreover, macrobenthic production was clearly higher within Bayou Cumbest than in Bayou Heron. Values ranged over one order of magnitude, from 8,248 to 85,308 µg m-2 d-1 in the Bayou Cumbest system and only from 95 to 15,192 µg m-2 d-1 in the Bayou Heron system. This difference was congruent with the moderate nutrient enrichment hypothesis. Ironically, the lowest production value occurred at the uppermost site in Bayou Heron, which was located near the upper limit of the main channel.

Table 1. Spatial Variation in Daily Secondary Production, Annual P:B, and Numbers of Organisms Sampled Within Three Benthic Grabs Totaling 0.124 m2 at Each of 10 Sites Within the GBNERR Study Area. Daily prod = daily production in µg m-2 d-1. Annual P:B values = the number of inferred faunal turnover periods per year based on the daily production rate.

BC Site 1
BC Site 2
BC Site 3
BC Site 4
BC Site 5
Daily prod
Annual P:B
Number org
BH Site 6
BH Site 7
BH Site 8
BH Site 9
BH Site 10
Daily prod
Annual P:B
Number org

Figure 3. Spatial Variation Standardized Biomass-Size Spectra in the Form of Linear Relationships for Each of the 10 Sites Within the GBNERR Study Area

Linear relationships were significant for 8 of the 10 standardized biomass-size spectra from the GBNERR sites; reasonable biomass-size spectrum parameters were readily obtained for the other two sites. The intercept for the uppermost Bayou Heron site was estimated by assuming the same slope as that observed for the corresponding uppermost site in Bayou Cumbest. Fitted linear relationships had negative slopes, reflecting the overall effect of diminishing biomass, when scaled to the magnitude of the size category, with increasing body size. As observed for macrobenthic production, longitudinal and cross-system differences in biomass-size spectra were evident. Slopes and intercepts reflected underlying properties of the biomass-size spectra: higher biomass, especially of small organisms, raised the intercepts; whereas, the presence of larger organisms lowered the slopes. The longitudinal pattern in biomass-size spectra reflected shifts in abundances of organisms and in the body-size composition of the macrobenthic community, ranging from high biomass of small sizes and narrow size distributions at upper sites to lower biomass of small sizes and broad size distributions at downestuary sites. Biomass-size spectra at Bayou Cumbest sites tended to have higher intercepts and steeper declining slopes than those at Bayou Heron sites.

Linking Macrobenthic Process-Indicators. Although linkages among the three macrobenthic process-indicators were not readily apparent, relationships among these indicators should exist. Furthermore, interpreting biomass-size spectra can be difficult because their slopes and intercepts are interrelated and inherently variable. However, when the intercepts of the standardized biomass-size spectra were regressed against the corresponding slopes for the 10 GBNERR sites, a significant general relationship was defined (r = -0.83; P < 0.001) (see Figure 4). Moreover, for each site the relative deviation of the intercept from the general relationship, or the standardized residual, reflected the degree to which biomass was higher or lower than expected for a biomass-size spectrum with a known slope. Notably, standardized residuals from the general biomass-size spectrum parameter-relationship were positively related to logarithm (base 10) production (r = 0.95; P < 0.0005), reflecting a connection between biomass-size spectra and production. Furthermore, when plotted within a third dimension, P:B values varied inversely in relation to production and residual biomass-size spectrum parameter values. Presumably, the three process-indicators reflected different facets of macrobenthic function; thus, a single composite factor was derived from a Principal Component Analysis (PCA) of the three indicators, which all loaded at 0.9 or higher on the same component (i.e., 0.95 log production; -0.906 P:B; 0.983 spectrum residual). This single PCA component accounted for 89.46 percent of the overall variation in the three indicators.

Figure 4. Linkages Among the Three Macrobenthic Process-Indicators. (A) General relationship between intercepts and slopes of standardized size-spectra for the 10 GBNERR sites. (B) Significant relationship between standardized residuals from Panel A and log macrobenthic production estimates. (C) P:B values align well in the third dimension relative to the two variables in Panel B.

Relating Macrobenthic Process-Indicators and Ecosystem Function. When characterized as a composite variable based on the three process-indicators, site scores for the first PCA component provided a succinct measure of macrobenthic function. Site PCA scores in turn were significantly related to several functional environmental variables, including concentrations of pore water ammonia and pore water total phosphorous, as well as surface chlorophyll and bottom DO (see Figure 5).

Figure 5. Relationships Between Macrobenthic function as Characterized by a Composite PCA Variable Based on the Three Process-Indicators and Four Functional Environmental Variables

Although the relationship with DO was relatively weak, the link was surprising given that the DO values were only point measures of a labile variable measured at different times of the day. Overall, these results suggest that the macrobenthic process-indicators did reflect ecosystem function.

Objective 3: Obtain and Process 2002 and 2003 Macrobenthic Indicator Data

Processing of 2002 Macrobenthic Samples. Sixty macrobenthic samples were obtained during the 2002 sampling period and included 30 samples from 10 stations sampled in July 2002, from the GBNERR, and two sets of 15 samples sampled in August and November 2002, from 5 stations in East Bay. All of the 2002 samples have been processed, including sorting and quality control for the removal of macrobenthic organisms, size fractionation of macrobenthic invertebrates, identification of size-taxon fractions, and volumetric determinations. QA/QC procedures also have been completed for these samples.

Processing of 2003 Macrobenthic Samples. One hundred and eight samples from 36 stations were obtained from East Bay from May to November 2003. All of these samples have been sorted and quality controlled for the removal of macrobenthic organisms. These samples also have been size fractionated in preparation for taxonomic identification and volumetric determination. Taxonomic identification and volumetric determination currently are underway; organisms from 50 percent of the 2003 samples have been identified and volumetrically determined, including data from 4 stations (12 samples) prioritized during the 2004 CEER-GOM annual meeting for inclusion in the upcoming CEER-GOM data analysis workshop.

Sediment Composition Determinations. The processing of sediment samples for sediment composition and grain size parameters has been completed for all 20 sediment samples from 2002, and for the 36 sediment samples taken in 2003.

Sediment Total Organic Carbon (TOC) Determinations. Sediment TOC determinations have been completed for all of the 2002 samples; sediment samples from 26 of the 36 stations sampled have been processed for TOC content. Ten remaining TOC samples from the November 2003, sampling trip are awaiting custody transfer and TOC analysis.

Pore Water Determinations. All 20 pore water samples from 2002 as well as the 36 samples from 2003 have been analyzed by the University of West Florida Center for Environmental Diagnostics and Bioremediation.

Preparations for the 2004 Field Season. Considerable time and effort have been spent on making an inventory of supplies and reordering items in short supply for the upcoming 2004 sampling season, including jars, vials, reagents, and other necessary supplies.

Data Management. Data management activities have involved continued entry of macrobenthic taxonomic and volumetric data into spreadsheets, continued expansion of the reference list in Procite for the trophic classification database, and continued expansion of the taxonomic image library for eventual incorporation into the project taxonomic database. All available 2002 and 2003 collection and sediment data have been entered. More than 200 taxonomic images representing more than 75 taxa have been obtained for the taxonomic image library. Post-processing of macrobenthic detail data files for East Bay from 2002 and 2003 is underway.

Relational Database Development. Relational database file structures are being developed using Microsoft Access; where appropriate, companion data entry forms also are being devised. Preliminary file structures have been developed for collection record files, detail files (i.e., macrobenthic data), water-column profile data, and sediment data. An eight-character taxon code system is being developed as a key field for the taxonomic database.

Data Analysis. Data files from the 10 collections representing two sampling events taken in 2002 from East Bay and from the 36 sampling events from East Bay in 2003 are being postprocessed to derive indicator information, including production, turnover, and biomass size-spectra parameters. These indicators have been obtained and interpreted from the 10 collections taken earlier in 2002 from the GBNERR during the project development phase. Four sample events from East Bay in 2003 have been prioritized for processing so that data from these events are available for a trial synthesis at an upcoming CEER-GOM Data Workshop in summer 2004.

Objective 4: Pursue Extramural Collaborative Efforts

Collaboration With EPA GED. Discussions have taken place with Michael C. Murrell, an ecologist with the EPA GED, regarding possible collaborations involving determinations of macrobenthic production estimates, biomass-size spectra, and P:B ratios for samples from throughout Pensacola Bay taken by the GED in 2003, to examine benthic pelagic coupling. It was agreed that this would be a mutually beneficial cooperative arrangement between GED and CEER-GOM. This possibility will be pursued once the macrobenthic subgroup has processed the CEER-GOM samples.

Collaboration With Other EaGLe Groups. Potential collaborative efforts between the CEER-GOM macrobenthic subgroup and other EaGLe groups have been discussed, including the possibility of collaboration with Dr. E. Houde of the Atlantic Coast Environmental Indicators Consortium, who is working with pelagic biomass-size spectra as an estuarine indicator; and with Dr. L. Johnson of the Great Lakes Environmental Indicators Project, who also is working with macrobenthic indicators.

Provide Macrobenthic Detail Data From GBNERR to EPA STAR Metadata Team. We worked with Dr. P. Noble of CEER-GOM to develop a prototype macrobenthic detail metadata file structure based on data obtained during the GBNERR case study conducted in 2002.

Objective 5: Disseminate CEER GOM Macrobenthic Subgroup Findings

To date, we have conducted a number of professional activities to disseminate the findings from the CEER-GOM macrobenthic subproject. We have disseminated the results of our work through various means, including presentations at scientific meetings and workshops as well as in publications.


MSU-CREC 2000. http://www.deq.state.ms.us/MDEQ.nsf/pdf/TWB_BayouCumbast&BangsMy00/$File/CoastalSBBayouCumbast-BangsLakeWSMy00.pdf?OpenElement Exit

Pearson TH, Rosenberg R. Macrobenthic succession in relation to organic enrichment and pollution of the marine environment. Oceanography and Marine Biology: An Annual Review 1978;16:229-311.

Xu F-L, Jørgensen SE, Tao S. Ecological indicators for assessing freshwater ecosystem health. Ecological Modeling 1999;116:77-106.

Future Activities:

The macrobenthic subgroup vision of the CEER-GOM working hypothesis is to jointly develop an integrated suite of coherent indicators representing multiple levels of biological organization that will provide a robust assessment tool for diagnosing eutrophication within coastal estuaries. This suite of coherent indicators should provide a more rigorous approach for assessing ecosystem "health" than any individual indicator. Functional indicators are needed for integrated assessments of ecosystem-level changes in marine and estuarine environmental quality resulting from multiple stresses, including eutrophication and resultant hypoxia. In the future, we plan to extend our research efforts to integrate with other CEER-GOM subgroups by: (1) relating the functional macrobenthic indicators to traditional (benchmark) macrobenthic indicators, such as the EPA Benthic Index developed for the Gulf of Mexico; (2) contributing to the integration of macrobenthic indicators with novel indicators being developed at various levels of organization by the other CEER-GOM subprojects; (3) collaborating across centers to examine macrobenthic indicators with respect to other indicators and at wider geographic scales; (4) transferring indicator technology to state and regional monitoring programs; and (5) calibrating macrobenthic indicators with respect to management criteria, such as state mandated total maximum daily load requirements for nutrients and DO. How are effects of low DO manifested at genetic, population, and ecosystem levels? Do response thresholds of indicators at different levels of organization provide early warning signals? These questions can be answered and connections among indicators validated only through integrated studies involving coordinated sampling and subsequent analyses of related data sets.

Journal Articles on this Report : 1 Displayed | Download in RIS Format

Other subproject views: All 13 publications 2 publications in selected types All 1 journal articles
Other center views: All 171 publications 54 publications in selected types All 48 journal articles
Type Citation Sub Project Document Sources
Journal Article Niemi G, Wardrop D, Brooks R, Anderson S, Brady V, Paerl H , Rakocinski C, Brouwer M, Levinson B, McDonald M. Rationale for a new generation of indicators for coastal waters. Environmental Health Perspectives 2004;112(9):979-986. R829458C003 (2003)
R829458C008 (2003)
R829458C008 (2004)
R828675 (2004)
R828675 (Final)
R828677C001 (Final)
R828684 (Final)
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  • Supplemental Keywords:

    population, community, ecosystem, watersheds, estuary, estuaries, Gulf of Mexico, nutrients, hypoxia, innovative technology, biomarkers, water quality, remote sensing, geographic information system, GIS, integrated assessment, risk assessment, fisheries, conservation, restoration, monitoring/modeling, Apalachicola Bay, Consortium for Estuarine Ecoindicator Research for the Gulf of Mexico, CEER-GOM, Environmental Monitoring and Assessment Program, Galveston Bay, Mobile Bay, benthic indicators, ecoindicator, ecological exposure, ecosystem monitoring, environmental indicators, environmental stress, estuarine ecoindicator, estuarine integrity., RFA, Scientific Discipline, Geographic Area, ECOSYSTEMS, Ecosystem Protection/Environmental Exposure & Risk, Aquatic Ecosystems & Estuarine Research, Ecosystem/Assessment/Indicators, Aquatic Ecosystem, Aquatic Ecosystems, Environmental Monitoring, Ecological Monitoring, Ecological Risk Assessment, Ecology and Ecosystems, Biology, Gulf of Mexico, Ecological Indicators, monitoring, ecoindicator, ecological exposure, estuaries, estuarine integrity, ecosystem monitoring, CEER-GOM, estuarine ecoindicator, benthic indicators, environmental indicators, environmental stress, water quality

    Relevant Websites:

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    Progress and Final Reports:

    Original Abstract
  • 2002 Progress Report
  • 2004 Progress Report
  • 2005 Progress Report
  • 2006
  • Final

  • Main Center Abstract and Reports:

    R829458    EAGLES - Consortium for Estuarine Ecoindicator Research for the Gulf of Mexico

    Subprojects under this Center: (EPA does not fund or establish subprojects; EPA awards and manages the overall grant for this center).
    R829458C001 Remote Sensing of Water Quality
    R829458C002 Microbial Biofilms as Indicators of Estuarine Ecosystem Condition
    R829458C003 Individual Level Indicators: Molecular Indicators of Dissolved Oxygen Stress in Crustaceans
    R829458C004 Data Management and Analysis
    R829458C005 Individual Level Indicators: Reproductive Function in Estuarine Fishes
    R829458C006 Collaborative Efforts Between CEER-GOM and U.S. Environmental Protection Agency (EPA)-Gulf Ecology Division (GED)
    R829458C007 GIS and Terrestrial Remote Sensing
    R829458C008 Macrobenthic Process Indicators of Estuarine Condition for the Northern Gulf of Mexico
    R829458C009 Modeling and Integration