The Ecological Ramifications of Disease and Density in the Caribbean Spiny Lobster, \u3ci\u3ePanulirus argus\u3c/i\u3e

In 1999, I discovered the first virus known to be pathogenic to any species of lobster. HLV-PA is a pathogenic herpes-like virus that infects juvenile Caribbean spiny lobster, Panulirus argus, in the waters off south Florida (USA), and it alters the behavior and ecology of this species in fundamental ways. Gross signs of HLV-PA infection are lethargy, morbidity, cessation of molting, and discolored, “milky” hemolymph that does not clot. HLV-PA infects the hemocytes of host lobsters, specifically the hyalinocytes and semi-granulocytes, but not the granulocytes. When hemolymph from infected donors was injected into healthy juvenile lobsters, 90% of the healthy individuals became infected within 80 days. In another set of laboratory trials, 40% of the juvenile lobsters that ingested conspecific tissue infected with HLV-PA developed the disease, and in a third experiment wherein transmission by contact or waterborne means was tested, 63% of the lobsters(CL), 33% of lobsters 30–40 mm CL and 10% of lobsters 40–50 mm CL became infected within 80 days. In field surveys from 2000–2001, up to 40% of the juveniles at each of twelve sites (mean = 8%) had the disease. The disease was most prevalent (mean = 16%) among the smallest juveniles (i.e.,CL) and, thus far, appears limited to juveniles. However, all of the surveys of disease prevalence are based on gross, visual signs of late stages of infection, and are, therefore, conservative estimates. A diagnostic tool to assess infection at earlier stages has not yet been developed. Field observations and laboratory experiments indicate that healthy juvenile lobsters avoid diseased conspecifics, which is only the second report of such behavior in any animal. The prevalence of the disease in wild lobster populations is not correlated with population density, even when lobsters were experimentally concentrated at sites with artificial shelters. Moreover, enhanced density does not appear to have a detrimental effect on population dynamics such as nutritional condition and short-term residency, likely due to their normal gregariousness. Thus, juvenile spiny lobsters appear to have developed remarkable contradictory behaviors, avoidance of infected conspecifics and gregariousness, both of which may ultimately enhance survival of uninfected lobsters