Effects of population density and body size on disease ecology of the European lobster in a temperate marine conservation zone

Marine conservation zones (MCZs) are a form of spatial marine management, increasingly popular since the move towards ecosystem-based fisheries management. Implementation, however, is somewhat contentious and as a result of their short history, their effects are still widely unknown and understudied. Here, we investigate the population and health of the European lobster (Homarus gammarus) in the Lundy Island Marine Conservation Zone, Bristol Channel, UK. Using the fished refuge zone (RZ) as a control area, catch per unit effort was calculated for both the no-take zone (NTZ) and RZ and binomial logistic regression models were used to examine the effects of site, sex, landing size, and loss of chelae on the probability of shell disease and injury presence in individuals. Lobsters were also tested for the causative agent of gaffkaemia, Aerococcus viridans var. homari, and white spot syndrome virus (WSSV). The analysis revealed a higher lobster density and larger lobsters in the NTZ compared with the RZ. Shell disease was present in 24% of lobsters and the probability of shell disease occurrence increased notably for individuals over the minimum landing size (MLS) of 90 mm carapace length. Shell disease was also more prevalent in lobsters displaying injury, and in males. Injury was present in 33% of lobsters sampled and prevalence was higher in lobsters in the NTZ compared with the RZ, and in lobsters >MLS. Aerococcus viridans var. homari was detected in <1% of individuals, but WSSV was absent from all sampled lobsters. Overall, the study demonstrates both positive and potentially negative effects of NTZs, methods for effective non-lethal sampling of disease agents, and highlights the need for more comprehensive, long-term monitoring within highly protected MCZs, both before and after implementation.