Grantee Research Project Results
Final Report: Developing a New Monitoring Tool for Benthic Organisms in the Gulf of Mexico: Loss of Genetic Variability in Meiofaunal Populations
EPA Grant Number: R825355Title: 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 Amount: $243,469
RFA: Exploratory Research - Environmental Biology (1996) RFA Text | Recipients Lists
Research Category: Biology/Life Sciences , Aquatic Ecosystems
Objective:
The overall objective of this research project was to demonstrate a link between exposure to contaminants and changes in genetic diversity and ecological integrity. This link could be used as an early warning indicator of sublethal population responses to contaminants in the environment. This goal was based on an earlier discovery that ecological integrity and genetic diversity declined in benthic invertebrate populations and communities near offshore hydrocarbon production platforms in the Gulf of Mexico. The offshore platform environment is an ideal model system to develop the link between contaminants, genetic diversity, and ecological integrity. However, before this application could be made, we had to make other preparations. Although concentrations of sediment contaminants are high near offshore platforms, there also is a reef effect near platforms. The legs of platforms support a hard-bottom fouling community of algae and invertebrates and a pelagic community of herbivorous and carnivorous fish. The main objective of this research was to distinguish between contaminant and reef effects on genetic and ecological responses. We analyzed genetic effects with an amphipod species. Also, we used meiofaunal communities to analyze ecological responses.
Summary/Accomplishments (Outputs/Outcomes):
The hypothesis of this research project is that selection, founders effects, or genetic drift can occur by exposure to chronic, sublethal levels to contaminants. 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 this goal, our main objective was to measure ecological integrity and genetic response in a field experiment to isolate confounding factors of contaminant and reef effects that could explain population subdivision found in previous studies.
We performed a field experiment to link reduced genetic diversity, ecological integrity, and contaminants, and distinguished this from natural background in marine ecosystems. The field experiment was composed of four treatments: (1) artificial reefs (sunken ships and inactive platforms without contamination); (2) sites where platforms were removed (no reef but contaminants still exist); (3) operating platforms (reef and contaminant effects); and (4) control sites (normal shelf sediments at least 3 km away from natural or artificial structures). The objectives of this field experiment were to measure three responses: contaminants, ecological integrity, and genetic diversity. Contaminant concentrations indicate the level of human activities. Ecological integrity is indicated by population size and community structure. Genetic diversity is indicated by an index of haplotype diversity calculated from restriction fragment length polymorphisms of the cytochrome c oxidase subunit I gene (COI) from mitochondrial DNA. The test organism for the genetic study was the amphipod Ampelisca agassizi (Judd, 1896), which has been considered an indicator of environmental quality. In the past, harpacitocid copepods were used as test organisms. An amphipod was used here because it shares important characteristics with harpacticoids (i.e., they both brood eggs, have limited dispersal, live in sediment their whole lives, and are abundant and diverse) but are much larger, making it easier to extract DNA.
The field experiment was very carefully planned and successfully conducted in August 1997. We selected locations 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. We sampled the platform, reef, removal, and control site 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). We also extracted six replicates at each station for meiofaunal community structure, harpacticoid diversity, and levels of sediment contaminants. Additional samples for genetic studies were collected at one of the sites in September 2000.
The sediment chemistry analyses were completed by Texas Agricultural and Mechanical University (M.C. Kennicutt, Principal Investigator). Chemical contaminant background levels followed expected trends as illustrated by the average concentrations (in ppm) for samples of tracers of hydrocarbon exploration and production (see Table 1). Sediment contaminant concentrations were consistent with patterns found in previous studies around offshore platforms. Higher concentrations of metals and higher sand content near platforms than at control sites. Both the platform and removal sites had elevated levels of total petroleum hydrocarbons (TPH), barium (Ba), and cadmium (Cd), which are indicators of exploration and production activities. Reef sites had lower sediment contaminant concentrations and were similar to levels at control sites. Sand and organic carbon content at reef sites were similar to control and removal sites without structures.
Treatment "Site" |
TPH (µg/g) |
Alkanes (µg/g) |
PAH (µg/g) |
Barium (ppm) |
Zinc (ppm) |
Cadmium (ppm) |
Sand (%) |
TOC (%) |
Control |
3.3 |
0.19 |
63 |
432 |
71 |
<0.01 |
27 |
81 |
Reef |
3.6 |
0.21 |
80 |
283 |
68 |
<0.01 |
24 |
82 |
Removal |
5.0 |
0.26 |
68 |
641 |
77 |
0.03 |
25 |
92 |
Platform |
5.4 |
0.59 |
78 |
563 |
653 |
0.06 |
58 |
53 |
We also have completed ecological analyses. Here, the trend is different from what we expected, we expected that ecological integrity of the removal sites would be similar to platforms, due to the contaminant gradient illustrated above. In addition, reefs would be similar to background, the opposite is apparent. There were nearly twice as many meiofauna found in featureless environments (2,157 individuals 10 cm-2 in control and removal sites) than near reef habitats (1,175 individuals 10 cm-2 in platform and reef sites). Harpacticoid density and diversity also is higher in featureless environments (61 individuals 10 cm-2 and H' of 1.8 in control and removal sites) than near reef habitats (60 individuals 10 cm-2 and H' of 1.7 in platform and reef sites), but it is not statistically significant. In general, degraded ecological integrity is associated with habitats, not contamination.
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 |
We conducted the genetic diversity study on the amphipod, A. agassizi, at the Matagorda Island site (see Table 3). Genetic diversity of each population was measured using polymerase chain reaction (PCR), gene clone sequences, and restriction fragment length polymorphism (RFLP). A large amount of genetic diversity was revealed among all populations. The haplotype diversity and fragment frequency at most loci were always higher in the control populations (h' = 0.65) than in others, even though the four collection sites were geographically close to each other. We found significantly lower fragment frequency in the platform and in artificial reef populations (h' = 0.38) than in the control and removal populations (h' = 0.56), but only two individuals were sampled at the reef site. The results indicate that the main environmental impact on genetic diversity might be caused by habitat differences rather than contaminant differences for amphipod populations among those locations. The differences in amphipod genetic diversity between platform and control sites results were nearly identical to those found earlier using five harpacticoid species.
Treatment "Site" (n) |
Restriction Enzymes Haplotype Diversity (h') |
Average Haplotype Diversity (h') |
||
Mse I |
Rsa I |
Taq I |
||
Control (20) |
0.77 |
0.46 |
0.72 |
0.65 |
Removal (11) |
0.59 |
0.30 |
0.53 |
0.47 |
Platform (9) |
0.57 |
0.20 |
0.49 |
0.42 |
Reef (2) |
0.50 |
0 |
0.50 |
0.33 |
The overall finding of this research project is that environmental effects attributed to contaminants near hydrocarbon platforms in the Gulf of Mexico are most likely confounded with habitat effects. This is apparent at the community and population levels of biological organization. At the community level, meiofauna abundance and harpacticoid species diversity was lowest at platform and reef sites. Contaminated sites were more similar to control sites. At the population level, amphipod genetic diversity also was lowest at platform and reef sites. Future studies of environmental effects near structures should include appropriate controls for the habitat effects of the structures themselves.
The current finding extends our body of knowledge in several important ways. Future field studies will have improved experimental designs to distinguish between habitat and contaminant effects. The finding that amphipods also lose genetic diversity, as with harpacticoids, confirms that genetic diversity is useful as a monitoring tool for subtle, population level effects. In addition, the finding that lower genetic diversity occurs in large macrofauna and small meiofauna indicates that the effect is occurring at different levels of the food web. Finally, the habitat effects associated with reefs has important implications for basic research. We now know that population subdivision can occur over very small spatial scales (<100 meters) in the ocean. This is direct evidence that habitat fragmentation caused by natural events or human activities can drive microevolutionary processes. This has implications for understanding species invasions and endangered species, as well as for environmental biology.
The benefit of this research project is that it provides new understanding that can be used to protect environmental health. Production of energy is important, but it must be accomplished in the least harmful way possible. The results presented here question the harm to environmental health by offshore activities because structures without contaminants appear to have the same ecological effects. However, the results could be interpreted to mean that artificial reefs are as harmful as offshore hydrocarbon production activities. Thus, we must perform new experiments to determine the mechanism responsible for the reef effects.
The potential practical application of the current research is that molecular studies can be used in monitoring programs. Using harpacticoids in molecular studies is difficult because they are small (0.1 - 0.5 mm in length) and contain little DNA. In contrast, amphipods are several mm in length and contain more DNA, making the genetic analyses much easier. Current research shows that loss of genetic diversity is coincident with smaller population sizes. This implies that lower genetic diversity in an area suspected of impacts by human activities can indicate that the population in that area is threatened.
Journal Articles on this Report : 1 Displayed | Download in RIS Format
Other project views: | All 7 publications | 1 publications in selected types | All 1 journal articles |
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Type | Citation | ||
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Montagna P, Jarvis SC, Kennicutt MC. Distinguishing between contaminant and reef effects on meiofauna near offshore hydrocarbon platforms in the Gulf of Mexico. Canadian Journal of Fisheries and Aquatic Sciences 2002;59(10):1584-1592. |
R825355 (Final) |
not available |
Supplemental Keywords:
water, marine, ecological effects, sensitive populations, genetic polymorphisms, zoology, polycyclic aromatic hydrocarbon, PAH, total petroleum hydrocarbon, TPH, heavy metals, EPA Region 6, Gulf of Mexico, petroleum., RFA, Scientific Discipline, Waste, Water, Geographic Area, Ecosystem Protection/Environmental Exposure & Risk, Ecology, Ecosystem/Assessment/Indicators, Ecosystem Protection, Contaminated Sediments, Environmental Chemistry, Genetics, Ecological Effects - Environmental Exposure & Risk, Monitoring/Modeling, Biology, Ecological Indicators, Gulf of Mexico, ecological exposure, monitoring, environmental monitoring, fish kills, benthic organism, contaminated sediment, meiofaunal populations, ecosystem health, hydrocarbons, genotypes, genetic damage, benthic organismsRelevant Websites:
http://www.utmsi.utexas.edu/people/staff/montagna.htm Exit
Progress and Final Reports:
Original AbstractThe perspectives, information and conclusions conveyed in research project abstracts, progress reports, final reports, journal abstracts and journal publications convey the viewpoints of the principal investigator and may not represent the views and policies of ORD and EPA. Conclusions drawn by the principal investigators have not been reviewed by the Agency.