Featured Image Credit: OceanCare
By Eva Gruber
Sounds travel much faster underwater than they would in air – this is one of the primary physical characteristics of our oceans that marine life deal with. It’s how whales can communicate with each other from very far away – up to 100 miles or more. Many marine animals transmit sound through water and rely on it as a medium crucial to their natural history. Some animals even use bursts of sound to drive and confuse their prey while hunting, such as sperm whales.
However, a new threat has recently entered the underwater realm – noises created from human activity. In the last 60 years, underwater noise across all frequencies has increased by orders of magnitude. The sounds from shipping, offshore drilling, ocean floor mapping, and construction are permeating the furthest reaches of the ocean. And due to the extraordinary conductive nature of water, sounds generated in one location can travel and be detected from thousands of miles away!
We all know that sounds can be unpleasant, even harmful. But few people are aware of the fact that the sounds of our activities can be enough to alter animal behavior in significant ways. This is a burgeoning area of research as human maritime activities increase and the resulting sounds become more pervasive. Major sources of anthropogenic underwater sound can be unintentional such as ship traffic, or purposeful, such as oil and gas exploration or ocean floor mapping.
Marine mammals are especially at the forefront of the issues surrounding noise pollution in the ocean, as it is revealed often that many stranded and beached animals suffer from symptoms such as burst eardrums and internal bleeding. However, there is marine life that suffers in silence, and a recent study aims to reveal the damage that noise causes to the tiniest of marine life: plankton.
Researchers at Curtin University and University of Tasmania (both in Australia) report that blasts from a seismic airgun caused a two-to-threefold increase in dead zooplankton within 24 hours of exposure, as compared to control groups. In addition, abundance decreased by half in more than 50 percent of the species observed.
These results are hugely significant and terrifying – they prove that the seismic process (the first step in oil and gas exploration) poses not only a known risk to marine mammals, but also a previously unacknowledged risk to the entire marine ecosystem starting at the very base of the food web. With such huge impacts that the sounds have on plankton, there are more indirect consequences of noise pollution than we previously were aware of – and that these impacts need to be mitigated if we want to conserve marine life.
This study is especially pertinent as the results come two weeks after the National Marine Fisheries Service approved permits to allow the first step in offshore drilling – seismic surveys in the Atlantic seaboard to search for offshore pockets of hydrocarbons. The Trump administration has pledged to expand offshore drilling, which signals serious concern for Atlantic ecosystems and eastern fisheries. This is also extraordinary considering most Atlantic communities oppose offshore drilling.
The researchers recorded effects of seismic airgun blasts from a single airgun over the course of only 24 hours – it can only be extrapolated what effects translate to in a seismic survey, where multiple vessels towing 20-40 airguns which would blast every 10 seconds for months on end. Such an intense and thorough blasting would decimate zooplankton populations and the effects would be far-reaching and long-lasting as the building blocks of the food web are blasted out of the ecosystem.