Alteration of burrow‐related behaviour of the norway lobster, nephrops norvegicus during infection by the parasitic dinoflagellate hematodinium

Abstract

This study has used time‐lapse video recordings to analyze the burrow‐related behaviour of N. norvegicus under a 12 h light: dark regime in aquarium conditions, and compared this with the behaviour of lobsters infected by the parasitic dinoflagellate Hematodinium. Uninfected lobsters performed a higher number of burrow departures, of longer duration, during the hours of darkness than during the light. Infected lobsters performed a relatively constant number of departures of similar‐duration in the light and the dark periods. However, the mean number of departures per day performed by infected lobsters (70 day‐1) was more than double that of uninfected lobsters (30.1 day‐1), while the mean duration of burrow departures performed by infected lobsters (258.5s departure‐1) was more than six times greater than in uninfected lobsters (38.7s • departure‐1). This led to a more than ten‐times increase (from 1.7 to 19.4%) in the percentage of the day spent out of the burrow by infected lobsters. This altered burrow‐related behaviour could be due to the nutritional demands of the parasites on infected lobsters, causing an increased requirement to forage, or alternatively to a ‘functional hypoxia’, due to the additional respiratory demands of the parasite, causing the host to emerge from the burrow onto the sediment surface to seek oxygen. Implications for the increased time spent out of the burrow are discussed in relation to availability of infected lobsters by trawlers and predators, and to the use of infection prevalence data from trawl‐caught samples in stock assessment models for N. norvegicus.