1. Cardiac Assays
A cardiac assay was used to determine if sounds caused changes in heart activity. Lobster hearts are very sensitive to novel stimuli and will briefly stop or dramatically slow in response to sensed changes in the environment. Therefore cardiac assay is a good method for determining if lobsters can detect a certain stimulus and has been used before to examine lobsters response to temperature, salinity and sound.
We tested the response of 31 lobsters in response to sounds of 20-10,000 Hz and sounds produced by other lobsters and found that there was no difference in the detection abilities of lobsters of different ages and sexes. While a percentage of lobsters responded to each frequency tested, lobsters were most sensitive to the lower frequency sounds between 20-300 Hz. Lobster responded to sound produced by other lobsters in a similar fashion.
2. Behavioral Response
We conducted multiple experiments to try to determine the behavioral uses of sound production and sound detection, however, so far our attempts to either elicit consistent behavioral responses to the playback of lobster sounds, or to record natural, uninduced sounds, have been unsuccessful and currently the role of lobster sounds is unknown. Almost all of the sounds we recorded were elicited by grasping or threatening a lobster and, in most instances, sound production was accompanied by a defensive posture, such as meral spreading. Thus, our working hypothesis is that the primary role of shell vibrations in the American lobsters is to startle predators that are grasping them (vibrations) or about to grasp them (sound). Whether these sounds also serve some type of secondary role in terms of communication between lobsters remains to be determined.
Behavior movie – While we did not find and clear, stereotyped response of lobsters to low frequency and conspecific playback sounds, we did observe some interesting behavioral responses to sounds. Some of these responses are demonstrated in this video clip. Note that sound are produced by the underwater speaker on the right of the tank for first 2 minutes of every hour. In all of the examples except the last a light will come on at the top right of the screen when sounds are being introduced into the tank.