We, humans, are terrestrial beings and often complain about our busy, noisy life. It makes us wonder how life would be underwater. We fantasise it to be calm and serene. However, a study conducted by the researchers at Northeastern University’s Marine Science Centre proves the noisy world of underwater creatures and how underwater noise affects marine life. The leading researcher of this study was Randall Hughes, an assistant professor of Marine and Environmental Sciences at Northeastern University.
We assume fishes to be calm and silent creatures. However, there is a veritable symphony of sound echoing under the sea. The mating calls of the black drum fish were waking up the local people, and this was the subject of many phone calls to the Miami police in 2005. Attracting mates isn’t the only reason for noise by fishes; it is also to find prey, relay stress, and defend their nests. These noises became the reason for this study. Hughes began to wonder how the prey hears the voices of fishes and their reactions to those sounds.
First, David Mann (Expert in Marine Acoustics based at Loggerhead Instruments in Sarasota, Florida) and David Kimbro (Assistant Professor of Marine and Environmental Sciences at Northeastern University) put crabs into mesocosms to imitate their natural surrounding with juvenile clams as food. Second, they submerged a microphone to transmit a variety of sound recordings of fishes like the black drum fish, oyster toadfish, and hardhead catfish. They found that marine crabs are capable of hearing. This auditory ability helps them in responding to fish predators.
Hughes said, “We pretty quickly saw that the crabs weren’t feeding as much in response to the predator sounds.” Further, the team wanted to confirm that this change in behaviour of crabs was due to their ability to hear and not due to any hidden variable. They also wished to know if this ability was available to mud crabs as well.
Thus, they implanted electrodes into the “statocyst” at the base of the antennae of mud crabs. The statocyst is a small organ vital for the balance of marine animals as it contains a mineral mass of thousands of sensory hairs. This organ responds to sound pressure or particle accelerations. The electrode signals showed a correlation with particle acceleration when the crabs were exposed to fast pulses of noise.
This study was the first one to show that crabs can hear too and respond to underwater noise. It has also given rise to many questions, and the team is enthusiastic about conducting more studies regarding the same.