Aspects of Antipredation in Panulirus Argus and Panulirus Guttatus

Spiny lobsters (Family Palinuridae) are large, diverse, and abundant marine crustaceans, which have conquered tropical, subtropical, and temperate coastal waters around the globe despite strong predation pressure. The mechanisms and function of antipredation strategies for most species in this highly successful taxon, encompassing behavior, morphology, and life-history characteristics, are poorly understood, particularly against natural predators. I investigate mechanisms of antipredation in spiny lobster Panulirus argus in the open during the day, at night, and while sheltering diurnally in natural dens. I also examine the function of putatively defensive acoustic signals produced by P. argus during diurnal attacks by piscine predators and while escaping octopuses at night. I also compare and contrast the mechanism and survival value of antipredator behavior and morphology between sympatric Panulirus argus and P. guttatus. Finally, I investigate ontogenetic changes in defensive behavior by diurnally sheltered P. argus to chemically-mediated predator cues. Nearly 40 species of spiny lobsters produce a characteristic sound (termed stridulation), speculated to deter predation. The occurrence and efficacy of stridulation has not been documented quantitatively during encounters with natural predators. I examined sound production in the sympatric spiny lobsters Panulirus argus and P. guttatus during attacks by their common predator, gray triggerfish Balistes capriscus, to determine if lobsters produce sound during defense, how stridulation integrates with behavioral and morphological defenses, and how interspecific differences in sound production relate to efficacy in repelling predators. Both lobster species stridulated coincident with specific defensive actions during triggerfish attack. In P. argus, stridulation occurred both during antennal lunging and during escape attempts (rapid retreat by tailflips). Panulirus guttatus stridulated only coincident with tailflips and did not lunge. Same-sized individuals of P. guttatus were subdued ~3 times more quickly on average than P. argus. The two species differed also in the relative size of the primary defensive weapons, the spinose 2nd antennae, which were far more robust in P. argus, particularly at larger body sizes. These results suggest that stridulation is an integral component of aggressive defense and escape behavior in spiny lobsters. The timing of sound production during aggressive, retaliatory defensive behavior (lunging) by P. argus suggests an aposematic role for stridulation against triggerfish. Using staged encounters of P. argus with B. capriscus, I examined whether stridulation, coincident with thrusting spines during aggressive defense, functions aposematically or simply renders a defending lobster more difficult to subdue without playing an aposematic role. I demonstrate, by disabling the stridulating organ in some lobsters (muting), that sound plays a vital role in defense against inexperienced (naïve) triggerfish, resulting in fewer successful attacks in subsequent encounters. Choice experiments with triggerfish that previously bypassed defenses and consumed lobsters show that experienced attackers do not choose muted lobsters over stridulating individuals. I propose that stridulation by P. argus against triggerfish is aposematic, as part of a multi-modal display, advertising the lobster's spiny defenses to predators. It is widely documented that sound production in P. argus and other spiny lobsters accompanies grasping of the carapace or other disturbance by human captors. Additionally, stridulation accompanies tailflip escape attempts during attacks by triggerfish. Although sound production during daytime attacks does not appear to increase survival against triggerfish, stridulating during escape may be more effective against grasping predators like octopus. Here, I investigate P. argus defensive behavior during nighttime encounters with Caribbean reef octopus Octopus briareus to determine whether P. argus stridulate during octopus attacks, how stridulation is used along with other defensive behavior (e.g. tailflips), and whether sound production improves survival in stridulating individuals. Lobsters stridulate both during grasping attacks by octopus and during escape attempts after being captured. Stridulating lobsters are also more likely to escape from attacking octopuses and remain uncaptured longer during encounters. I suggest that improving the efficacy of tailflip escapes against octopus may have been the function for which the stridulating organ initially evolved in the Stridentes clade of the Palinuridae. Benthic stages of P. argus reside in shelters during the day as a primary means of antipredation. However, when an active predator approaches and/or successfully attacks a nearby conspecific, these individuals must decide whether to emigrate quickly from the area or remain in shelter (dens or macroalgae) and rely on crypticity, defensive behavior, or the presence conspecifics to avoid attack, injury, or death. In this study, I examine how the three benthic juvenile phases of Caribbean spiny lobster Panulirus argus respond to exposure to fresh conspecific body fluid and how antipredator behavior, particularly the decision to stay or leave the area, changes during ontogeny. Additionally, I examined how the presence of conspecifics affects the decision to stay or leave in gregarious juvenile stages of P. argus. Although all size classes of P. argus respond to alarm odor, the decision to stay or leave dens changes unexpectedly with increasing body size and in the presence of conspecifics. Once shelters were abandoned, body size was a strong indicator of distance traveled in response to alarm odor. This indicates that Panulirus argus undergo an ontogenetic shift in defensive behavior, more frequently leaving dens in response to alarm odor and traveling across open substrate during the day, but only after reaching a body size at which they can effectively defend against predators.