Coral Relocation Mitigates Habitat Effects From Pipeline Construction Offshore Qatar
The Barzan Gas Project is a critical program to deliver natural gas to Qatar’s future industries. The project was expected to affect shallow coral communities during pipeline construction from Qatar’s North field to onshore. To partially meet the state’s environmental clearance for the project while supporting the state’s national vision, RasGas developed a project-specific coral-management, -relocation, and -monitoring plan that incorporated proven methodologies to relocate at-risk coral colonies to a suitable location.
In addition to natural-gas reserves, coral-reef communities are regarded as a significant and highly productive natural resource in Qatar, providing refuge and nursery areas for many commercially important fish and shellfish species during portions of their life cycle. Corals off the coast of Qatar grow in one of the more thermally stressed environments in the world. Elevated sea temperature and other coastal pressures such as overfishing, port development, and construction have led to a decrease in local coral-reef communities. Recognizing the importance of these habitats, Qatar included measures in the Qatar National Development Strategy 2011–16 calling for the protection, conservation, and sustainable management of marine and coastal habitats and associated biodiversity.
The RasGas Barzan Gas Project off eastern Qatar (Fig. 1) is a critical program for the state, delivering natural gas from Qatar’s North field to the onshore processing plant through export pipelines. As part of the construction phase, the Barzan project was expected to affect shallow coral communities through the direct physical removal of coral colonies from trenching activities and through sedimentation and a general deterioration of the habitat immediately adjacent to the trench.
To partially meet the state’s environmental clearance conditions for the project, RasGas developed a project-specific coral-management, -relocation, and -monitoring plan that incorporated proven methodologies to relocate at-risk coral colonies to a suitable location away from both present and future development to minimize potential harm.
Benthic Environmental Survey
In order to document the status of environmentally sensitive resources within the pipeline corridor and delineate coral and seagrass habitat, a benthic environmental survey was conducted along two predetermined parallel transects within the pipeline corridor from the shoreline (pipeline landfall) to 2 km offshore. Following the habitat delineation, quantitative data were also collected to estimate the number and species of corals within each habitat type.
Survey results showed there were four distinct areas of hard-coral habitat, differentiated by substrate type (e.g., sand, hard bottom) and coral density. By use of the areas of the four characterized hard-coral-habitat types and the estimated coral densities, it was determined that approximately 40,000 coral colonies with a diameter >10 cm were present within the hard-coral-habitat impact footprint.
Hard-Coral Recipient-Site Selection
In order to identify an acceptable recipient for the hard-coral colonies to be relocated from the pipeline corridor, several areas offshore northeast of Qatar were surveyed to assess their suitability for reattaching hard-coral colonies. Sites were selected primarily for their location outside of potential future pipeline construction and depth through a review of environmental-sensitivity maps provided by the Qatar Ministry of Environment and satellite imagery along the northeast coast. Site surveys were conducted at 21 sites within two larger areas to assess their suitability on the basis of the substrate type and topographic relief, dominant biota, coral presence/absence, and urchin presence/absence. Where hard corals were present, coral coverage was assessed qualitatively. An additional eight sites were assessed within an area closer to the project site for the potential deployment of limestone boulders to act as substrate for reattachment if a suitable natural substrate site was not identified.
A review of the survey data indicated that only two natural hard-bottom sites were suitable with the exception of water depth, which was shallower (<2 m) than the original depth of the corals to be relocated (7–8 m), potentially exposing them to an extreme thermal change. Because of the lack of available hard substrate, it was recommended that native quarried limestone boulders of composition similar to that of the natural substrate be used to create exposed hard-bottom habitat.
Approximately 550 limestone boulders, each nearly 1 m in diameter, were power washed to remove excessive sediment, transported from Ras Laffan, Qatar, and deployed into a predetermined recipient site that had been deemed suitable for habitat creation because of its proximity to a healthy reef, water depth, and distance from Ras Laffan. The relatively shallow sand veneer (≤11 cm) overlying a hard-bottom substrate indicated no risk of subsidence.
The rocks were deployed off the side deck of a barge, allowing for varying densities of rock patches and a configuration that would mimic the naturally divergent rocky outcrops. The newly created habitats not only provided a suitable substrate for the reattachment of hard-coral colonies, but additionally provided vertical and horizontal subsurfaces, interstitial spaces, crevices, and voids to create a complex habitat for a wide range of other marine life.
Corals were removed from the areas of highest coral density within the pipeline corridor by divers using hammers and chisels to separate the coral from its substrate and lift it intact to the extent possible. Corals were transported carefully to the recipient site onboard a survey vessel and were temporarily cached in metal trays on the seabed directly adjacent to the boulders until they were ready for reattachment.
Monitoring of Relocated Hard Corals
In order to assess the relative success of the Barzan coral relocation, a monitoring program was designed to permit the detection of and response to significant changes in habitat and community structure because of external disturbances (e.g., thermal extremes). Monitoring surveys will be conducted twice yearly for a minimum of 5 years to
- Evaluate the attachment status (presence/absence) of reattached hard corals
- Evaluate relative health of reattached hard corals
- Assess habitat features to evaluate temporal ecological trends
- Conduct water-quality monitoring twice yearly
- Acquire and log on-site-temperature data
Summary and Conclusions
In 2012, more than 1,600 hard-coral colonies were relocated into a newly created habitat of limestone boulders because of the lack of hard bottom. Baseline monitoring of the relocated corals was conducted 3 months post-relocation. Monitoring-survey results showed that the relocated corals exhibited health comparable to that of the reference communities and exhibited comparable signs of stress. Future monitoring surveys conducted twice yearly for a minimum of 5 years will provide data to evaluate the overall success of the project and for comparison with other coral-relocation projects in the region.
This paper presents the composite monitoring results from Surveys II (January 2013), III (July 2013), and IV (January 2014), which were assessed for reattached-colony bonding status, colony health, benthic characterization, reef-fish assemblage, sediment accumulation, sea-urchin density, and water-column data.
Reattached-Coral-Colony Bonding Status. The substrate-augmentation approach with quarried limestone boulders is deemed to be successful, with fewer coral-colony detachments at the reattachment site than reported during previous monitoring surveys.
Coral-Colony-Health Assessment. The number of coral colonies with more than 10% of the coral tissue affected by one or more conditions decreased at the reattachment and shallow reference sites from Survey III to Survey IV, indicating increased overall health at these sites.
Benthic Characterization. Lowprofile filamentous benthic algae continued to account for the greatest benthic cover within the reattachment site. The algal cover increased not only on the limestone boulders but also the surfaces of the coral colonies, resulting in a decrease in percentage of coral tissue and increase in coral-health stress ranking.
Reef-Fish Assemblage. Although the number of reef-fish observations decreased during Survey III compared with Survey II, it increased in Survey IV to the highest for the monitoring period. But the number of fish species stayed the same for the last two surveys. The assemblage composition recorded during Survey IV was more similar to those of Surveys II and III than to that of Survey I. An analysis revealed that the differences were because of increased numbers of dory snappers, yellowfin seabream, and Persian cardinalfish recorded during the latter surveys relative to pearly goatfish, a numerical dominant during Survey I. Although not observed in high abundance during the first three surveys, the yellowstripe scad was recorded in high abundance during Survey IV. The Persian cardinalfish, however, has continued to be an abundant member of the assemblage since Survey I. Overall, the assemblage was generally typical of the geographic region and habitat (Fig. 2).
Sea-Urchin Density. With the increase of algal cover, the presence of sea urchins may provide a means to reduce competition for space between the coral recruits and algae. It has been encouraging to observe an increased presence of sea urchins during Survey III compared with Survey II because these herbivores contribute positively to the dynamics of coral recruitment rates and potential survivorship in the reattachment site.
Water-Column Data. Sediment accumulation on and around the boulders has been negligible during Surveys II through IV, validating the selection of the coral-reattachment site. The hydrographic water-column profile data have been as expected in this portion of the Arabian Gulf, with anticipated temporal changes from seasonal fluctuations.
This article, written by Special Publications Editor Adam Wilson, contains highlights of paper SPE 170359, “Coral Relocation as Habitat Mitigation for Impacts From the Barzan Gas Project Pipeline Construction Offshore Eastern Qatar: Survey IV Update,” by Kaushik Deb, RasGas, and Anne McCarthy, CSA Ocean Sciences, prepared for the 2014 SPE Middle East Health, Safety, Environment, and Sustainable Development Conference and Exhibition, Doha, Qatar, 22–24 September. The paper has not been peer reviewed.