In the early years of the ocean noise discussion there were heated debates about whether or not introduced noise was really harmful to marine life. Our understanding was shallow and the tools blunt. Even when animals washed ashore deafened, dead, or dying there was usually some denial that noise might be the cause. We’ve come a long way since then (although denial is still a common first response), but our understanding is getting deeper and our tools more precise.
Initially the discussion (and research) was driven by the big things happening – like hundreds of dolphins or dozens of whales washing up on the beach after some acoustical assault. But as research looks deeper into biological systems we’re finding that noise exposures can have impacts at a subtler level, both behavioral and physiological.
It stands to reason that crabs would be fearful of the sound of their predators, but eels can be less responsive to predation cues when subjected to shipping noise. This could be due to the noise masking the more delicate sounds of a predator, or a distraction response due to stress caused by the noise. Different fish species respond differently to shipping noise. Both minnows and sticklebacks were more nervous and jumpy when exposed to shipping noise, but the minnows became more social while the sticklebacks foraged more (albeit with less success than without the noise).
There are also some troubling data on the physiological impacts of noise, with seismic airgun noise correlated to high deformation rates in scallop larvae, and shipping noise arresting embryonic development and increasing larval mortality in sea hares. Many of these studies also indicate increased metabolic rates in the subjected animals– indicating stress.
Most acoustical studies of these little critters are performed in small lab aquariums for practical reasons, so the sound sources are fairly close to the subjects and the dimensions of the confinement are not equivalent to what would be found (and heard) in the open ocean. But what they do demonstrate is that noise can have negative impacts on many different animals in many different ways, perturbing the complex animal interrelationships upon which we all depend.
Scallop larvae, sea hares, eels, minnows, and crabs are not as charismatic as dolphins and whales, but they are no less important to the fabric of life within which we are all woven. What is alarming here is that the noises in these studies are increasingly ubiquitous in the ocean: Shipping noise, and airgun impulses. And because of all of the other factors in play in the ocean it will be hard to determine the actual impacts of any specific stressor.
This should not be a basis of denial, rather it should be a call for precaution.