An interesting characteristic of spiny lobsters is their gregarious nature. This dynamic is mediated through a chemical cue released in their urine which can be detected by the antennae of other lobsters. This cue is believed to have evolved as a means to quickly find shelter, thereby limiting predation risk. This new paper provides convincing evidence that this entire signaling system may be breaking down over time. The authors used a”Y-maze” design, where lobster have a choice of moving down an arm of the Y that either has another lobster or one that does not (without being able to see the other lobster). The main finding is that lobster choose to move in the direction of the other lobster much less frequently than they did in the same experiment conducted in past years. In other words, lobsters are tending to be less gregarious than they once were.
The authors proffer a couple of potential explanations for this trend. Most intriguing are those related to natural selection – favoring those individuals that are not attracted to other lobsters. With increasing fishing pressure on spiny lobster, perhaps individuals that aggregate are more likely to be taken. Also, lobsters are susceptible to the PaV1 virus that is transmitted by close contact with infected individuals. In both cases, lobsters that choose solitary hiding places may be more likely to survive than those that shelter in groups. These patterns are important to explore further in a broader management context for this important fishery.
Here is the full Abstract…
Caribbean spiny lobsters are one of the most commercially important fisheries due in large part to their highly gregarious nature that facilitates their harvest by the use of traps or aggregation devices containing conspecifics. Aggregation in this species has been shown to be due to strong attraction to conspecific chemical cues that influence movement rates, discovery of crevice shelters, and den sharing behaviours. Although aggregation has been shown to have many potential benefits (reduction in exposure time and predation risk), it may also have significant costs as well (increase in predator encounters, disease transmission, and fishing mortality). We compared the results of three published and three unpublished Y-maze chemical cue choice experiments from 1996 to 2012 to determine if there has been a decrease in conspecific attraction by early benthic juvenile Caribbean spiny lobsters (15–55 mm carapace length, CL). We found that attraction to conspecific chemical cues decreased since 2010 and was significantly lower in 2012. Lobsters showed individual variation in conspecific attraction but this variation was unrelated to size, sex, or dominance status. We also found localized regional variation in conspecific attraction with lobsters from high shelter/high disease areas showing significantly lower conspecific attraction than those from low shelter/low disease areas. Given that conspecific attraction varies among individuals and potentially increases mortality through either natural (increased disease transmission) or fishery-induced (attraction to traps) mechanisms, we should play close attention to this loss of conspecific attraction in juvenile lobsters. Future studies should investigate both the causation and the ecological significance of changes in conspecific attraction in regions that vary in intensity of disease (PaV1) and fishing pressure.