Research Technical Report

Potential Impacts of the Monterey Accelerated Research System (MARS) Cable on the Seabed and Benthic Faunal Assemblages 2015

Kuhnz, L.A., K. Buck, C. Lovera, P.J. Whaling, and J.P. Barry (December 2015)

Monterey Bay Aquarium Research Institute, MBNMS Permit Report. 58 pp.

SUMMARY

In addition to an initial biological assessment (2004) and an early 2007 Post-Lay Inspection and Burial Survey, a geological and biological sampling program to assess the condition of the MARS cable and its potential effects on seabed geology and biology was performed in late 2007 through 2008, in 2010, and again in late 2014 through 2015. The most recent study was conducted eight years after the cable was installed. The 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 at 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. Specific conclusions include the following:

• Over most of its length, the cable remains buried, with little evidence of change since installation.
  • The cable remains buried along shallow areas of the cable route
  • Sediment has filled the cable trench in deeper areas, which is now nearly invisible in most locations
  • In the limited areas where the cable was not buried, only minor suspensions of the cable are present
• No differences in mean grain size were detected in relation to the MARS cable.
• The percent organic carbon content of sediments increased near the MARS cable at some depths, possibly due to natural variation or the effects of the cable or both.
• Local variation in benthic megafaunal communities near (within 50–100 m) 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.
  • In 2008, before the cable was powered, Longnose skates (Raja rhina) were significantly more abundant along a short section at ~300 m depth, near minor (2–10 cm) suspensions of the cable above the seabed. R. rhina may have responded to mild electromagnetic fields generated by components of the cable. In 2010, when the cable was powered, there was no significant difference in the abundance of skates near the cable compared to 50 m away. Normal abundances were observed again in 2015.
• The MARS cable has little or no detectable effect on the distribution and abundance of macrofaunal and megafaunal assemblages on a regional scale (i.e. kilometers).
  • Megafauna and macrofauna compared before and after cable installation among three control stations and one cable station at each of three depth zones (Shelf: <200 m, Neck: 200–500 m, Slope: >500 m) indicated very few potential changes in benthic biological patterns due to the MARS cable.
  • 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.

NOTE: 2020 Report available at: https://montereybay.noaa.gov/research/techreports/trkuhnz2020.html