Beneath the surface of the sea, a vast invisible world is at work.
Billions of microscopic organisms drift with the water, turning sunlight into organic matter, releasing oxygen and becoming food for the next links in the chain of oceanic life. They have no ears, but that does not mean the surrounding soundscape passes them by without a trace.
Even plankton exists within a shared physical space — among currents, pressure, light, chemical signals and vibrations of the water.
A new study has shown that the low-frequency hum of operating offshore wind farms can alter processes within a natural plankton community. After just 22 hours of exposure, phytoplankton began to grow faster, and the water's oxygen balance changed.
The ocean responded to a human sound where scientists had hardly expected to hear an answer.
An experiment among Norwegian waters
The study was conducted by an international team led by Justine Courboules and marine bioacoustician Ana Širović of the Norwegian University of Science and Technology — NTNU. Specialists from the University of Montpellier, CNRS, Ifremer, the Royal Belgian Institute of Natural Sciences and the University of Hamburg also took part in the work.
The project was funded by the Research Council of Norway under the programme PURE WIND, devoted to the effects of offshore wind energy sound on ecosystems.
How to reproduce the hum of a wind farm at sea
The researchers wanted to bring the experiment closer to a real ocean environment. So instead of cultivating a single laboratory species under sterile conditions, they used a natural community from a coastal lagoon, including phytoplankton and the zooplankton that feeds on it.
The samples were placed in experimental containers — microcosms — located directly in the marine environment. Then, underwater, real recordings of an operating offshore wind farm were played back.
The experiment included three sound regimes:
- a control group that heard only the natural background of the lagoon — about 80 dB relative to 1 µPa;
- a medium noise level — about 94 dB;
- an elevated level — about 106 dB.
The exposure covered frequencies from 50 to 2400 hertz and lasted 22 hours.
Underwater decibels cannot be directly compared with the familiar noise values in air: in water a different reference value is used, and sound itself propagates differently. Therefore the figures given characterise the differences between the experimental conditions, but do not mean that the plankton was near a source comparable in loudness to household appliances or a concert.
The scientists measured the growth rate of phytoplankton, the intensity of its consumption by zooplankton, and the change in oxygen concentration.
What changed over 22 hours
In the groups exposed to playback of the wind farm's noise, phytoplankton grew statistically significantly faster than under the control conditions.
At the same time, a more positive oxygen balance was observed in the water. The authors believe this may indicate an increase in primary production — the process in which microscopic algae and cyanobacteria use light to create organic matter and release oxygen.
At the same time, the rate at which zooplankton consumed phytoplankton did not differ significantly between the three groups.
The result is an unusual picture: the production of plant biomass changed, while its consumption during the short experiment remained roughly the same.
But this cannot be considered proven benefit from noise.
The accelerated growth of one link can disrupt the previous balance of processes. If the production and consumption of organic matter begin to diverge, over time this may affect the oxygen regime, the cycling of nutrients, the transparency of the water and the distribution of energy in the food web.
For now these are only possible consequences. The work demonstrated a short-term response, but did not trace where it will lead after weeks, months or years.
How plankton can respond to sound
The word “heard” here is a figure of speech.
Phytoplankton does not perceive sound the way a human, a whale or a fish does. But sound is physical movement: pressure waves and vibrations of water particles. They can act on microscopic organisms directly or change the conditions around them.
There are several possible mechanisms. Vibrations can influence the mixing of water, the contact of cells with nutrients, their position relative to light, their physiological state and the interaction between members of the community.
However, the new study does not establish which particular mechanism caused the acceleration of growth. It records the very fact of a response by a natural community to a certain short-term acoustic regime.
To understand the causal chain, additional experiments will be needed: with individual species and mixed communities, with different durations of exposure, frequencies, signal levels and environmental conditions.
The foundation of ocean life
Phytoplankton are easy to overlook. A single cell may be invisible to the naked eye, but together these organisms perform work on a planetary scale.
They form the basis of many marine food webs. They are eaten by zooplankton, which in turn becomes food for fish, birds and marine mammals. Phytoplankton participate in producing a significant share of the biosphere's oxygen and bind carbon, part of which over time is carried into the deep layers of the ocean.
Therefore a change in its growth is not a small event confined to an experimental vessel. It is a signal of a possible impact on the beginning of a chain on which far larger forms of life depend.
Previously, research on underwater noise was mainly focused on whales, dolphins, fish and other animals that use sound for communication, orientation and finding food. The new work broadens the question: what happens if industrial sound reaches organisms that do not possess a familiar auditory system but exist within the same physical environment?
Green energy also has a sound
Offshore wind power is necessary for reducing dependence on fossil fuels. However, an environmentally cleaner source of energy does not become completely invisible to nature.
Construction work can be especially loud — for example, pile driving when installing turbine foundations. But already operating installations also create constant low-frequency vibrations: the rotation of the blades, the movement of mechanisms and the vibrations of the structure are transmitted through the foundation into the water and the seabed.
The study does not prove that offshore power plants destroy plankton communities. Nor does it assess a specific operating wind farm as a whole. The scientists reproduced its recordings in a controlled microcosm experiment.
But the work shows that when designing offshore energy, it is not enough to take into account only visible animals. Underwater sound can propagate through different levels of the ecosystem, including its microscopic foundation.
Perhaps future turbines will need to be assessed not only by the amount of energy produced, but also by the acoustic footprint they leave in the sea.
What did the ocean remind us of today?
That in a living system there are no truly minor participants and no isolated impacts.
A human installs a turbine to convert the movement of air into electricity. The mechanism creates vibrations. The vibrations enter the water. The water transmits them to microscopic cells — and within the invisible community the course of life changes.
Even the quietest technological hum becomes part of the ocean space. It joins the common score together with currents, the movement of animals, the rustle of sediments and the natural vibrations of the water itself.
The ocean has reminded us: every technology created by humans enters into a relationship with life that already exists. Therefore true environmental friendliness begins not only with a clean source of energy, but also with the ability to hear the response of the entire system — down to its very smallest inhabitants.
Plankton has no ears. But the ocean passed our sound on to it — and life responded by changing its rhythm.
