Archival electronic tagging of a predatory sea star — Testing a new technique to study movement at the individual level

Sea stars are important marine predators, and their feeding often controls the distribution of associated species. Therefore, quantifying their activity at an individual level is important in further understanding how they structure marine communities. Sea stars are difficult to tag, so there is little information on activity of sea stars in their natural environment over extended periods of days to weeks. We tagged the New Zealand sea star Coscinasteriasmuricata with small archival electronic tags that recorded water temperate and depth every 5 min for up to 2 weeks. The tagging was undertaken to test the viability of using electronic tags in research on the ecology of the sea stars in a New Zealand fiord, where their vertical distribution is influenced by the presence of low-salinity layers. The effects of the tagging were tested in the laboratory and in the field, with tagging having no detectable influence on invitro survival, feeding rate, and righting time, or on their insitu movement and depth distribution. Laboratory experiments testing the salinity tolerance of C.muricata showed they could tolerate salinities as low as 25 PSU for at least a 20-day period. Tagging of sea stars in their natural environment provided information on depth distributions, vertical migrations and the influence of the physical environment on their behaviour. The tagging also revealed a large variation in activity at the individual level. This study represents one of the first to utilise electronic tagging to study the ecology of a mobile invertebrate such as a sea star. The success of this initial study suggests that we could gain valuable quantitative insight into the ecology of these animals in future tag deployments.