Avoiding disease vs avoiding predation: testing the trade-off in Panulirus argus

Caribbean spiny lobsters, Panulirus argus (Latreille, 1804), usually avoid sheltering with conspecifics exhibiting the PaV1 viral disease, yet commonly cohabit with them in large, low-lying artificial shelters called "casitas" that are deployed in shelter-poor habitats in certain fisheries. We tested two hypotheses proposed to explain this finding: (A) that in shelter-poor habitats, healthy lobsters make a trade-off between avoiding disease and avoiding predation; and (B) that the large size of casitas allows segregation between healthy and diseased lobsters. We conducted eight experiments in seawater tanks fitted with two casitas, one empty and one harboring either a healthy or a diseased tethered lobster ("resident"), or both harboring a healthy or a diseased resident. We then introduced six healthy, free-ranging lobsters (FR-lobsters) into each tank (three replicates per experiment) and recorded their location after approximately 40 hrs. Experiments were conducted with and without a predatory triggerfish. Without predators, FR-lobsters used empty casitas and those harboring healthy residents, but avoided casitas harboring diseased residents, preferring to remain in the open. With a predator present, FR-lobsters used empty casitas and those harboring healthy but also diseased residents, suggesting that disease avoidance depends to some degree on availability of alternate shelter and immediacy of predation risk. In larger casitas deployed in a reef lagoon, co-occurrence of wild diseased and healthy lobsters was relatively high, but the probability of finding diseased lobsters segregated from healthy lobsters decreased with increasing number of lobsters. Overall, the results support both hypotheses, reflecting the complex but flexible behavior of P. argus under different ecological contexts.