Larger sea creatures are known to have a problem ringing in their ears - but the very small ones are apparently also affected by marine noise pollution, according to a study: When the noise of ship's propellers and the like can be heard in the water, plankton crabs eat significantly less food, show the experiments. Since the tiny creatures are part of the basis of the food chain in the sea, this disruptive effect could have far-reaching significance, the scientists say.
It was never quiet in the seas - physical effects such as waves, sounds from living beings and the wide spread of sound create a complex background noise in the underwater world. But in the kingdom of Poseidon it is also becoming increasingly unnaturally loud: ship traffic, construction projects and many other man-made noise sources cause a roar in the water in many places. Experts have long warned that marine animals can be disturbed by this. Because many species of fish, marine mammals or crustaceans produce and use sound for their navigation, reproduction or prey hunting. In some cases, interference from underwater noise has already been proven. But the extent of the problem remains unclear.
How does zooplankton react to underwater noise?
Above all, little is known about how smaller marine animals react to anthropogenic changes in the soundscape. The scientists around Saskia Kühn from the Christian-Albrechts-University in Kiel (CAU) have now devoted themselves to this research question. Her focus was on the copepods (copepods).
They are only a few millimeters in size, but due to their gigantic total mass, they represent a significant factor in global marine ecosystems. They form the basis of the food web and are an important prey for commercial fish species such as herring. They also influence the climatically important carbon cycle in the sea. This means: Anything that affects these important little things can have far-reaching consequences.
The scientists used copepods of the species Acartia tonsa to investigate the extent to which underwater noise affects the crabs. For this purpose, the animals were kept in laboratory aquariums and given specific amounts of their natural food: tiny seaweed (phytoplanton). Some of the containers were only exposed to the natural ambient sounds of the sea. In others, on the other hand, the noise of shipping traffic, which can occur in some areas of the sea today, also roared. In concrete terms, this is an increase in the noise level of more than 30 decibels above the level of the natural background noise.
Less food intake when there is a noise
As the researchers report, the comparative studies showed that the underwater noise is clearly a stress factor for the tiny creatures: "We found that the food intake of copepods was significantly reduced compared to normal ambient noise in the aquarium," says Kühn. Rather than spoiling the shrimp's appetite, the noise appears to make the crabs less effective at catching their food, the team reports. What the exact cause could be, however, remains unclear so far, say the researchers. The noise may irritate the copepods or mask hydromechanical signals from the prey. According to the scientists, however, the unnatural sound exposure could also lead to physical changes in the crabs that are associated with the changed eating behavior.
Kühn and her colleagues emphasize that the study now shows a need for further research: "Now it is important to repeat the experiments in field studies in order to investigate the influence of noise on the feeding behavior of copepods under realistic noise conditions. In this way, we can better assess the consequences of noise on the entire ecosystem,” says Kühn. Senior author Katja Heubel from the CAU goes on to say: “Noise-related effects have the potential to change the composition of communities. We need to know exactly the effects of such stressors on the ecosystem in order to be able to adapt the strategies that contribute to a good and healthy state of the marine environment," says the scientist.
Source: Christian-Albrechts-University of Kiel, Specialist article: Front. Mar.Sci, doi:10.3389/fmars.2023.1134792