Pirosomatida, the only colonial order within the class Thaliacea, is still a little-known group of marine gelatinous animals inhabiting warm and temperate waters of all oceans that may form immense swarms. Pyrosoma atlanticum is the most widespread and common species of pyrosomid between 50º N and 50º S and the only species recorded so far in the Mediterranean Sea. Fresh individuals of this species were collected in different planktonic and benthic oceanographic cruises, carried out from 1991 to 2015, covering the whole Mediterranean Sea, and more intensely in the Catalan coast. A total of 475 planktonic and 342 benthic samples were analysed. Planktonic samples were taken by means of Bongo (300 μm mesh size), neuston (800 μm) and Mocness (330μm) nets, from a maximal depth of 600 m to the surface. Benthic samples were taken by single warp Otter-trawl Maireta System (6 mm), Agassiz trawl (6 mm) and other commercial-trawl nets in bottoms depths from 300 to 2800 m. Maximum abundances of 19 and 2 ind. 1000m-3 were found in the water column and in the bottom, respectively. The presence of pyrosomes was more frequent in benthic samples (38%) than in planktonic ones (13%). The highest planktonic abundances were related to open-ocean areas and night hours (in surface, 0-60 m). No pattern was detected for benthic abundances related either to day and night hours or to the different bottom depths sampled. This is the first large-scale and extensive study on P. atlanticum in the Mediterranean Sea and the first integrating planktonic and benthic data in the same area and time

5th International Jellyfish Bloom Symposium, 30 May to 3 June 2016, Barcelona.-- 1 page. 7 figures

Peer Reviewed