Introduction
The Acoustic Thermometry of Ocean Climate (ATOC), also known as the Pioneer Cable, is a submarine cable system deployed between Pioneer Seamount and Pillar Point Air Force Station in Half Moon Bay, California. This pioneer cable, utilized for transmitting data from a hydrophone array on Pioneer Seamount, largely resides within the Monterey Bay National Marine Sanctuary. A permit (MBNMS-2001-031) was granted for its operation until December 31, 2003. This report details comprehensive surveys conducted by the Monterey Bay Aquarium Research Institute (MBARI) during 2002-2003 to evaluate the condition of this pioneer cable and analyze its effects on the seabed and the marine life inhabiting it.
Survey Objectives and Methodology
This research was a collaborative effort between MBARI, NOAA-OAR (National Oceanic and Atmospheric Administration – Oceanic and Atmospheric Research), and NOAA-NOS (National Ocean Service). MBARI’s primary interest was in documenting the broader environmental consequences of submarine cables, a subject with limited publicly available research. NOAA-OAR, responsible for the pioneer cable, needed to assess its state prior to permit expiration. NOAA-NOS aimed to understand the general environmental impact of submarine cables and characterize the seafloor within the Monterey Bay National Marine Sanctuary.
Installed in October 1995 for the ATOC project, the pioneer cable became the responsibility of NOAA-OAR in December 2001. Its presence has been referenced in numerous scientific publications and presentations. Notably, the pioneer cable suffered damage and ceased transmitting data from Pioneer Seamount in September 2002.
Surveys were conducted at 13 sites along the 95 km pioneer cable route during February and July-August 2003. MBARI’s ROVs Ventana and Tiburon, equipped with cable-tracking technology, were used. Quantitative comparisons between cable locations and control sites were made at nine stations. Site selection was based on substrate and habitat types, points of interest, and logistical feasibility, aided by side-scan sonar data collected in October 2002. The surveys resulted in 42 hours of video footage and 138 push core samples across 15.1 km of seafloor, with approximately 12.1 km of the pioneer cable visually examined.
Findings on Cable Condition and Interaction with Seafloor
Video analysis revealed how the pioneer cable interacts with the seabed. In areas with sediment, particularly on the continental shelf in shallower waters, much of the pioneer cable has become buried over time.
Alt text: Map showing the Pioneer cable route across the seafloor, highlighting survey locations and the cable’s path from the coast to Pioneer Seamount.
However, in rocky nearshore zones exposed to strong wave action, the pioneer cable showed clear signs of damage. Abrasion was evident in the form of frayed and unraveled armor. Notably, the pioneer cable had created vertical grooves in the rock, with incisions ranging from 6.6 cm to 45 cm wide. The most severe damage occurred on ledges in uneven rocky terrains. Entangled kelp was also observed with the frayed pioneer cable in these nearshore areas.
Significant cable suspensions were observed in rocky areas with irregular bathymetry, particularly at both ends of the pioneer cable route. Suspensions reached up to 40 meters in length and over 1 meter in height near the shore, and up to 25 meters long and 2 meters high on Pioneer Seamount. Unlike the nearshore region, neither the rocks nor the pioneer cable showed damage at Pioneer Seamount outcrops. Smaller (~10 cm) suspensions were also common in sediment areas, bridging minor depressions. Loops of excess pioneer cable, resulting from a 1997 repair, were found lying flat at 950 m depths. Sharp kinks were observed at 240 m depth in an area with heavy trawling activity. Cable crossings were also documented at 13 m and 344 m water depths.
Biological Impacts of the Pioneer Cable
The primary biological difference observed between areas with and without the pioneer cable was the presence of organisms directly associated with the cable. Anemones were found to colonize the pioneer cable and were more prevalent in cable transects in most soft sediment locations. The linear arrangement of anemones effectively indicated the pioneer cable‘s position where it was buried. Extrapolating from transect data, it is estimated that over 50,000 anemones may inhabit the modified environment created by the pioneer cable. Echinoderms and sponges were also observed living on the pioneer cable. At three of the nine surveyed stations, flatfish and rockfish were seen congregating near the cable.
Alt text: Underwater image showing anemones colonizing the Pioneer cable on the seafloor, illustrating the cable as a substrate for marine life.
However, the pioneer cable appeared to have no significant impact on infaunal abundance. Other variations between cable and control sites were likely due to natural variations in animal distribution. Megafauna and macrofauna were carefully counted, and few statistically significant differences were found at the 95% confidence level between cable and control sites. The pioneer cable may have subtle effects on local water flow, potentially concentrating shell debris and drifting kelp nearby.
Conclusion
This comprehensive survey of the pioneer cable provides valuable insights into the environmental effects of submarine cables. While the pioneer cable has experienced physical damage in high-energy nearshore environments and has altered benthic habitat by providing a substrate for colonization, particularly by anemones, its broader impact on seafloor communities appears to be minimal. The findings suggest that while submarine cables like the pioneer cable do interact with the marine environment, their overall ecological footprint, especially in deeper, sedimented areas, may be limited. Further research and long-term monitoring are recommended to fully understand the cumulative effects of submarine cable installations in sensitive marine ecosystems.
