Potential Impacts of the Monterey Accelerated Research System (MARS) Cable on the Seabed and Benthic Faunal Assemblages
- Summary to Date
- Monitoring Trends
- Figs. & Images
- Jim Barry
Monterey Bay Aquarium Research Institute
- Linda Kuhnz
Monterey Bay Aquarium Research Institute
- National Science Foundation
- Monterey Bay Aquarium Research Institute
The Monterey Accelerated Research System (MARS) includes an undersea cable 51 km in length that connects the Monterey Bay Aquarium Research Institute (MBARI) to a science ‘node’ at a depth of 891 m on the continental slope just outside Monterey Bay, California (Figure 1). MARS was installed in March 2007, and the cable provides power and high data bandwidth for science instruments connected to the node via additional, thin ‘extension’ cables deployed on the seabed by remotely operated vehicles (ROVs). MARS is one of a few cabled ocean-observing systems that enable continuous, long-term science capabilities for ocean science with real-time communication, control, and data capture from offshore subsea sensor systems.
The cable connecting MARS to MBARI does not lay on top of the sea floor where it could be snagged by other human activities. Instead, the cable was buried in a thin trench, protecting it from becoming a hazard or becoming damaged by fishing activities. Digging the trench required an environmental impact report to determine the impact of both the trench and the presence of the cable on benthic and demersal biota.
Prior to MARS cable installation, an environmental impact report was prepared, including characterization of seabed biological communities along the cable route and initial sampling for future environmental impact assessment (2004). This survey included characterization of the megafaunal animals (organisms identifiable in video recordings) and macrofaunal organisms (worms, crustaceans, etc., captured from sieved sediment samples) along the cable route. Subsequent to MARS cable installation, a Post-Lay Inspection and Burial (PLIB) survey of the entire route was conducted (March 16 to March 22, 2007 and June 7, 2007) and environmental impact assessments are required at ~18 month to 5-year intervals, including observations of the condition of the cable and potential effects on biological communities. This monitoring project presents data from environmental impact assessment surveys performed prior to cable installation, in 2007-2008 following cable installation, and again in 2010.
Summary to DateInspection of the MARS cable in 2010 (Fig. 2), coupled with a sampling program to evaluate changes in geological and biological conditions on local and regional scales with respect to the installation of the cable indicate little detectable influence of the cable. The most conspicuous evidence of cable installation is the cable exposed on the seabed for a short distance where it could not be buried (Fig. 3). Analyses of the geological and biological sampling program indicate the following:
- Over most of its length, the cable remains buried, with little evidence of change since installation (Fig. 4).
- Changes in mean grain size were undetectable in relation to the MARS cable (Fig. 5).
The percent organic carbon content of sediments increased near the MARS cable at some locations, possibly due to natural variation or the effects of the cable or both (Fig. 6).
- Local variation in benthic megafaunal communities (Fig. 7A-C) within 50-100 m of the MARS cable is minor or undetectable. The abundances of most animals observed did not differ between the area over the cable route and 50 m away. Longnose skates (Raja rhina) were significantly more abundant in one area where the MARS cable is suspended over topography (~300 m depth) in 2008. These animals may have responded to weak electromagnetic fields generated by the cable. During 2010, when the cable was energized, the numbers of R. rhina were near background levels near and distant from the cable.
- The MARS cable has little effect on the distribution and abundance of macrofaunal (Fig. 7D-F) and megafaunal assemblages on a regional scale (e.g. kilometers). Megafauna and macrofauna compared before and after cable installation among 3 control stations and 1 cable station at each of 3 depth zones (Shelf - <200 m, Neck – 200-500 m, Slope - >500 m) indicated relatively few potential changes in benthic biological patterns due to the MARS cable (Fig. 8). Natural spatial and temporal variation in the abundance and distribution of benthic macrofauna and megafauna appears to be greater than any detectable effects of the MARS cable.
DiscussionThe sampling program was designed to: • Observe the condition of the cable or cable trench along the cable route (51 km), • Assess the potential impacts of the MARS cable on geological characteristics and biological assemblages on a local scale (0-100 m from the cable) and a regional scale (km), using remotely operated vehicle (ROV) video transects and sediment samples.
The major conclusion of the study is that the MARS cable has had little detectable impact on seabed geomorphology, sediment conditions, or biological assemblages.
- Substrate characterization
- Habitat association
Study MethodsCable position and condition assessed by ROV surveys
Video Transects used to estimate densities of seabed organisms and objects
Sediment core sampling using ROV manipulator arms and pushcores
Figures and Images
Figure 1. View of the MARS cable, node, and potential science instruments over exaggerated bathymetry of Monterey Bay, Monterey Canyon, and the continental slope. The science node is indicated as “MARS site.” Map credit: MBARI.
Figure 2. Map of MARS cable (black line) environmental studies sites. Colored circles represent regional sites for impact studies at Shelf (green), Neck (yellow), and Slope (blue) depths. Red box indicates location for Skate transects. Brown plus symbols (A-J) indicate transect locations for localized megafaunal studies. Map credit: MBARI.
Figure 3. Depth of burial of the MARS cable. These observations were made during the 2007 survey. Map credit: MBARI.
Figure 4. Images of the seabed along the cable route. A. Sand ripples at 31 m depth, cable not visible (2008). B. Cable on seabed at 226 m depth (2010). C. Skate (Raja rhina) aggregation at 303 m depth (2008). D. Far fewer skates were present in 2010. E. Cable trench sediment infilling at 447 m depth (2010). F. Cable trench is filled near the MARS node at 867 m depth (2010). Photo credits: MBARI.
Figure 5. Mean sediment grain size (+/- SD) at control and cable (impact) stations for cable depth zones. *= significant difference between control and impact areas. Figure credit: MBARI.
Figure 6. Mean percent organic carbon in surficial sediments for control and cable sites at three cable depth regions (+/- SD). Comparisons of control vs. cable (impact) sites within each depth were nonsignificant (Shelf, p>0.6, Slope (p>0.3) and marginally significant at the Neck depth (p<0.05). *= significant difference between control and impact areas. Figure credit: MBARI.
Figure 7. Common megafaunal and macrofaunal animals along the MARS Cable route. A-C: Megafauna: A. Rathbunaster californicus (sea star). B. Funiculina sp. (sea pen). C. Stronglylocentrotus fragilis, (urchin). D-F: Macrofauna: D. Cossura sp. (polychaete). E. Oligochaeta. F. Prionospio sp. (polychaete). These taxa are some of the most abundant organisms observed in video (megafauna) or collected in sediment cores (macrofauna). Photo credits: MBARI.
Figure 8. Variation in abundance of megafaunal groups along the cable route. Paired transects show little variation in densities of megafauna over 10 sites along the cable (p = 0.96). Cable = directly over the cable route. Control = 50 m away from and parallel to the cable. Figure credit: MBARI.