Scientific diving in cephalopod research: A systematic review and future perspectives

In situ observation of cephalopods is crucial for understanding their behaviour, ecology, and natural interactions. Scientific diving offers a minimally invasive approach to studying these elusive organisms, especially in shallow waters. This systematic review evaluates the application of scientific diving in cephalopod research over the past five decades, analysing trends, methodologies, and global representation. An initial database search was conducted, followed by a second, more targeted search to improve accuracy and coverage. This two-stage process significantly increased the capture rate of relevant studies, from an estimated 28% to 57%, of 225 publications meeting inclusion criteria since 1973. In total, 83 different species were studied, with Octopus cf vulgaris being the most recurrent complex species. Most studies were conducted within recreational and non-decompression diving limits, resulting in a higher representation of orders typically found within these depth ranges: Octopoda (52.7%), Sepiida (19.8%), and Myopsida (18.7%). Orders often inhabiting greater depths, such as Nautilida (4.9%) and Oegopsida (3.8%), were studied primarily through video recordings, egg collections, or specimen release. Manual collection (44%) and direct observations (35%) were the primary goal for diving uses. Publications concentrated in regions such as the West Coast of North and South America and the Mediterranean, with the United States leading contributions (21.2%). The initial under-representation of studies was largely due to inconsistent terminology and lack of direct reference to diving methods in titles, abstracts, or keywords. These findings highlight the need for standardized reporting to fully leverage scientific diving's potential in cephalopod research.