Nutritional indices of juvenile Caribbean spiny lobsters in a Mexican reef lagoon: Are changes over a 10-year span related to the emergence of Panulirus argus Virus 1 (PaV1)?

We compared two indices of nutritional condition, the relative weight of the digestive gland (RWDG) and the ratio of weight to carapace length (weight/CL ratio), of the first three benthic phases, algal juveniles (7–25 mm CL), postalgal juveniles (25–45 mm CL), and subadults (45–79 mm CL) of Caribbean spiny lobster (Panulirus argus) dwelling in a shelter-poor reef lagoon before (1995) and after (2005) deployment of large artificial shelters (“casitas”) in 1998. To provide an experimental baseline, in 2005 we also conducted a laboratory experiment to assess the effect of starvation on both nutritional indices. Through 25-day trials, starvation significantly decreased the mean RWDG of all three juvenile phases, but did not affect their weight/CL ratios. In the field, casitas significantly enhanced juvenile lobsters relative to control sites and to prior values, but between 1995 and 2005 there was a significant decrease in condition of algal juveniles (both indices) and postalgal juveniles (only the RWDG), but not of subadults. These results would appear to counter previous findings that, for P. argus, food is not limiting and nutritional condition is not density-dependent. However, in 2000, a new pathogenic virus that has a distinct predilection for small juveniles, Panulirus argus Virus 1 (PaV1), emerged in the reef lagoon. Among other effects, this lethal virus causes a marked atrophy of the digestive gland. Through the laboratory trials and in the field, prevalence of visibly diseased individuals was highest in algal juveniles and lowest in subadults. These individuals were excluded from statistical analyses, but the disease progression may affect the digestive gland progressively given that newly infected lobsters take several weeks to become visibly diseased. Up to 2006, PaV1 had not significantly impacted lobster density on casita sites, but because P. argus is highly gregarious and transmission of PaV1 appears to be mainly by contact, futher investigation is required. These issues are relevant to enhancement of spiny lobsters and assessment of ecological impacts of marine diseases.