Coastal aggregations of the jellyfish Pelagia noctiluca (Scyphozoa) in Maltese coastal waters during 1980-1986

Abstract

The temporal and spatial distributions of coastal aggregations of the scyphomedusa Pelagia noctiluca around the Maltese Islands during the period 1980 to 1986 were investigated by means of sighting reports from volunteers as well as by periodic monitoring at fixed stations both offshore and onshore. The available data indicate that the outbreaks of coastal aggregations of this species started in 1980 and reached maximum densities during 1981-1983. During the period 1984 to 1985, these occurrences decreased both in duration and population density, with coastal aggregations being more frequent during March and April. Such aggregates were characterized by large numbers of small medusae, probably of recent spawning. Sexually mature medusae as well as ephyrae were however present in coastal waters almost throughout the year for the period 1981-1982. The geographic distribution of such aggregates of jellyfish in the coastal areas indicate that they are passive accumulations, the pattern of which is largely determined by the prevalent wind direction.