Impacts of marine seismic surveying on the plankton community

A recent study by McCauley et al. (2017) describes the fascinating and worrying observation that the noise produced during marine seismic surveys, commonly used to map geology, may severely impact the plankton community which underpins the entire marine trophic structure and food web 1.

Noise pollution is often an overlooked impact of human activity on the oceans, but it may be having severe and unseen consequences for marine wildlife. One activity that appears to generate excessive amounts of noise is seismic surveying which is used regularly during: exploration for gas and oil deposits, marine engineering work, and, geological research. Typically, an array of air guns is towed just under the surface of the water, firing, repeatedly, a pulse towards the sea floor. The vibrations reflecting up from the sea floor, or objects in the water column, is measured using sonar technology and discrepancies in the returning signal is used to accurately map features on the sea floor 2.

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Much of the previous research into the consequences of seismic surveying have focused on its impacts on taxa such as sea turtles, fish and especially cetaceans. Little attention however has been given to the impacts of seismic surveying on the plankton community.

 

McCauley et al’s. (2017) research shows how the use of a single air gun can reduce plankton abundance in the area immediately surrounding the test location. The researchers in-situ experiment off the south coast of Australia involved towing an active air gun like those used in seismic surveying along a transect, and using sonar to measure the returning backscatter, which alongside vertical plankton-net tows, was used to measure zooplankton abundance. Following exposure to the air gun, and after accounting for water drift, there were significantly less plankton individuals per m3 at all distances measured from the air gun transect. Interestingly, the sonar backscatter analysis also demonstrated a ‘hole’ appearing the returning signal which expanded over time following air gun exposure, indicating a reduction in plankton abundance 1.

The vertical plankton-net tows also indicated that airgun exposure may significantly increase the risk of plankton mortality. More dead plankton individuals were found following exposure compared to the control, and like abundance, this pattern was found at all distances measured from the transect. Interestingly, some taxa appeared more susceptible than others. All Krill larvae were found dead following exposure, and smaller Copepods were also particularly vulnerable. Given the delicate balance that the different marine trophic levels are in, even the slightest change in specific taxa abundance may have severe consequences on the entire marine ecosystem.

These worrying findings were observed after the use of only one air gun. Perhaps future research in the field could try to investigate the realistic impacts that an entire array of airguns would have on the plankton community. The experiment was replicated on two consecutive days and, whilst similar patterns were found on each day, it would be interesting to investigate the long-term impacts continuous seismic surveying may be having on the marine ecosystem. The mechanism by which seismic surveying kills and reduces the abundance of zooplankton is currently unclear and should be an immediate candidate for future research. The authors however hypothesise that the intense shock-waves produced by functioning air guns may damage the sensitive organs of individual plankton, specifically sensory organs imperative for locomotor ability. This may have even changed their orientation in the water, producing the characteristic ‘hole’ present in their backscatter analysis 1.

Though research into the impacts of noise on plankton appears in its infancy, this initial finding by McCauley and colleagues should be of immediate concern. Questions remain, how widespread is the damage, is it reversible, what are the consequences and how do we stop it? Answers which cannot come soon enough.

The long-awaited Blue Planet 2 series presented by Sir David Attenborough has recaptured the public’s fascination with the marine ecosystem (okay, maybe I’ve been slightly optimistic), and since our oceans are under immediate threat from human activity, what better time is there to push marine conservation issues further into the public consciousness. With recent geopolitical events, especially the governmental attitudes of some powerful nations towards internationally agreed environmental pledges, one ‘could’ be forgiven for resigning themselves to ignoring the depressing state of our planet’s natural ecosystems. We in the community however have a moral responsibility to communicate scientific findings to the wider audience to ensure that they are not continuously ignored.

  1. McCauley, R. D. et al. Widely used marine seismic survey air gun operations negatively impact zooplankton. Nat. Ecol. Evol. 1, 0195 (2017). https://www.nature.com/articles/s41559-017-0195.pdf
  2. Gisiner R. C. Sound and Marine Seismic Surveys. Acoustics Today: Winter 2016 10 – 18. http://acousticstoday.org/wp-content/uploads/2016/12/Seismic-Surveys.pdf