Grantee Research Project Results

1999 Progress Report: Developing a New Monitoring Tool for Benthic Organisms in the Gulf of Mexico: Loss of Genetic Variability in Meiofaunal Populations

EPA Grant Number: R825355
Title: Developing a New Monitoring Tool for Benthic Organisms in the Gulf of Mexico: Loss of Genetic Variability in Meiofaunal Populations
Investigators: Montagna, Paul A. , Kennicutt, Mahlon C.
Institution: The University of Texas at Austin , Texas A & M University
EPA Project Officer: Hahn, Intaek
Project Period: December 1, 1996 through November 30, 1998
Project Period Covered by this Report: December 1, 1998 through November 30, 1999
Project Amount: $243,469
RFA: Exploratory Research - Environmental Biology (1996) RFA Text |  Recipients Lists
Research Category: Aquatic Ecosystems , Biology/Life Sciences

Objective:

The overall goal of this study is to develop a direct scientific linkage between exposure to contaminants and changes in genetic diversity and ecological integrity. These linkages then could be used as an early warning indicator of sublethal population responses to contaminants in the environment. To achieve this goal, we must discover the cause of genetic variability loss in benthic invertebrates near offshore hydrocarbon production platforms, and how this loss is linked to measures of community change, which indicates ecological integrity. The thesis of this study is that selection, founders effects, or genetic drift can occur by exposure to chronic, sublethal levels to contaminants, and this can cause populations to lose genetic variability. Therefore, as populations decline and communities change, ecological integrity is compromised. Validating these hypotheses would support the measurement of population structure at the molecular level as an ecological monitoring tool to indicate stressed populations before acute declines could be detected. To achieve the goal, there were two objectives: to carry out laboratory and field experiments to isolate confounding factors of contaminant and reef effects that could explain population subdivision found in previous studies.

The goal of the laboratory experiment was to link exposure and genetic response. The objectives in the laboratory experiment were to expose organisms to specific contaminants (e.g., heavy metals that exist at high levels at production platforms) in cultures over three generations, and measure survival and genetic diversity in offspring. Genetic diversity is indicated by an index of haplotype diversity calculated from restriction fragment length polymorphisms of mitochondrial DNA. The test organisms are harpacticoid copepods, which were the subject of the original studies linking genetic diversity loss to exposure to contaminants.

The goal of the field experiment was to link reduced genetic diversity, ecological integrity, and contaminants and distinguish this from natural background in marine ecosystems. The field experiment was composed of four treatments: artificial reefs (sunken ships and inactive platforms without contamination), sites where platforms were removed (no reef, but contaminants still exist), operating platforms (reef and contaminant effects), and control sites (normal shelf sediments at least 3 km away from natural or artificial structures). Objectives of the field experiment are to measure contaminants, ecological integrity as indicated by population size and community structure, and genetic diversity.

Progress Summary:

The laboratory exposure experiment was completed in December 1998. This study was carried out in conjunction with Dr. John Fleeger (Louisiana State University). Approximately 300 adult female Nitocra lacustris were collected from the field for the experiment. Previously, we had identified levels of metal contaminants that were associated with reduced genetic variability around offshore platforms. Therefore, the organisms were cultured in a mixture of 50 gl-1 Zn, 37.5 Pb, and 0.25 gl-1 Cd. Organisms were fed a mix of MicroFest and algae each time the culture was set up. There were two treatments (metals and 25 ppt sea water) and two replicates per treatment (four cultures). The initial cultures are identified as the parents (P generation), and three generations of offspring (F1?F3) were cultured and collected. Subsamples of 50 individuals were collected and preserved in alcohol for each generation. The genetic analyses begun in February 1999 are complete, and data analysis is underway.

The field experiment was very carefully planned and successfully carried out in August 1997. Locations were obtained for artificial reefs from the Texas Parks and Wildlife Department and for platforms and platform removal sites from the U.S. Minerals Management Service. The northwestern Gulf of Mexico was divided into three regions and a platform, reef, removal, and control site were sampled in each of the three regions. Therefore, we have a correctly replicated design at the treatment level with a total of 12 stations (3 sites ? 4 treatments). Six replicates were taken at each station for meiofaunal community structure, harpacticoid diversity, and levels of sediment contaminants.

The sediment chemistry analyses were completed by Texas A&M University. Chemical contaminant backgrounds followed expected trends as illustrated by the average concentrations (in ppm) for all samples of the following tracers of hydrocarbon exploration and production (see Table 1). Both the platform and removal sites had elevated levels of total petroleum hydrocarbons (TPH), barium (Ba), and cadmium (Cd). Reef sites were lower and similar to control sites.

Table 1: Results of Sediment Chemistry Analyses

Treatment "Site"	Total Petroleum Hydrocarbons	Barium	Cadmium
Control	3.3	432	<0.01
Reef	3.6	283	<0.01
Removal	5.0	641	0.03
Platform	5.4	563	0.06

Ecological analyses also have been completed (see Table 2). Here the trend is different from that expected. We had expected that the ecological integrity of the removal sites would be similar to platforms due to the contaminant gradient illustrated above, and reefs would be similar to background. The opposite is apparent. There are nearly twice as many meiofauna in featureless environments (2,157 in control and removal sites) than near reef habitats (1,175 in platform and reef sites). Harpacticoid density and diversity also are higher in featureless environments (61 and 1.8 in control and removal sites) than near reef habitats (60 and 1.7 in platform and reef sites), but it is not statistically significant. In general, it appears as if degraded ecological integrity is associated with habitats and not contamination.

Table 2: Results of Ecological Analyses

Treatment "Site"	Total Meiofauna Density (n 10 cm-2)	Harpacticoid Density (n 10 cm-2)	Harpacticoid Diversity (H')
Control	2509	83	1.9
Removal	1804	39	1.8
Platform	1392	74	1.8
Reef	958	45	1.6

The last objective of the field study was to measure genetic diversity at all sites. The original samples (collected in August 1997) did not preserve well, and DNA degraded. We plan on resampling in spring 2000 to complete the project.

Future Activities:

Resampling of all field sites in spring 2000 to obtain fresh material for the genetic analyses will allow us to complete the project. Manuscripts will be prepared.

Journal Articles:

No journal articles submitted with this report: View all 7 publications for this project

Supplemental Keywords:

water, marine, ecological effects, sensitive populations, genetic polymorphisms, PAH, heavy metals, indicators, EPA Region 6, Gulf of Mexico, petroleum., RFA, Ecosystem Protection/Environmental Exposure & Risk, Scientific Discipline, Geographic Area, Waste, Water, Ecological Indicators, Ecosystem Protection, Ecology, Biology, Environmental Chemistry, Ecosystem/Assessment/Indicators, Contaminated Sediments, Monitoring/Modeling, Ecological Effects - Environmental Exposure & Risk, Genetics, Gulf of Mexico, ecosystem health, heavy metals, hydrocarbons, benthic organisms, meiofaunal populations, contaminated sediment, environmental monitoring, genetic damage, monitoring, genotypes, ecological exposure, benthic organism

Relevant Websites:

http://www.utmsi.utexas.edu/staff/montagna

Progress and Final Reports:

Original Abstract

1997 Progress Report

Final Report