Insights into jellyfish distribution and abundance provided by a platform of opportunity

摘要: It is well established that jellyfish have many negative socio-economic impacts on society. What is less clear is whether jellyfish are increasing in response to human and/or environmental perturbations (eg eutrophication, overfishing and climate change). Critical to answering such questions is the development of an effective jellyfish monitoring tool. In this study visual surveys from a platform of opportunity (a passenger ferry) were used to estimate jellyfish abundance, seasonality and distribution across a regional sea (the Irish Sea) during April–August 2010. Abundance: Two species of scyphomedusae (Aurelia aurita and Cyanea capillata) were observed in high abundances (> 18,000 jellyfish identified and enumerated). Both species were frequently encountered, A. aurita in 52% of 5-min. samples and C. capillata in 53% of 5-min samples. Aurelia aurita was by far the more abundant reaching> 500 individuals in 11% of 5-min. samples. Only on one occasion was there~ 500 individuals of C. capillata per 5-min. sample. Abundances were normally 5-20 individuals per 5-min. sample. Seasonality: Both species displayed a classic seasonal cycle, with lower numbers observed in May/June and peak abundances occurring in August. However A. aurita peaked earlier than C. capillata. The results suggest that A. aurita and C. capillata have similar yet distinct seasonal growth patterns. Distribution: Jellyfish were found throughout the survey route, but there was evidence of a seasonal shift of mean abundance from coastal sections to open water sections as the season progressed. Insights from camera usage: SLR camera derived counts showed …