Moon jellyfish aggregations observed by a scientific echo sounder and an underwater video camera and their relation to internal waves

• Published in: Journal of oceanography Vol. 75; no. 4; pp. 359 - 374
• Main Authors: Mano, Takashi, Guo, Xinyu, Fujii, Naoki, Yoshie, Naoki, Tsutsumi, Eisuke, Saito, Rui
• Format: Journal Article
• Language: English
• Published: Singapore Springer Singapore 01.08.2019; Springer Nature B.V
• Subjects: Aurelia aurita; Backscattering; Bays; Biological activity; Camcorders; Cameras; Cnidaria; Earth and Environmental Science; Earth Sciences; Echo sounding; Echoes; Ecological aggregations; Freshwater & Marine Ecology; Internal waves; Marine invertebrates; Oceanography; Original Article; Particle tracking; Polls & surveys; Regression coefficients; Scyphozoa; Surveys; Swimming; Swimming behavior; Underwater; Echo sounder; Passive particle tracking; Moon jellyfish; Aggregations; Internal waves; Underwater video camera
• ISSN: 0916-8370; 1573-868X
• DOI: 10.1007/s10872-019-00507-8

We found a good linear relation between the mean volume backscattering strength measured using a scientific echo sounder and the distribution density of moon jellyfish recorded simultaneously by an underwater video camera in small bays (Hokezu Bay and Mikame Bay) in Japan. This relation held in all of the surveys carried out in recent years (2013–2016), although the regression coefficient varied slightly from year to year due to the existence of ambient organisms. Using this relation and high-resolution echo sounder scan surveys across the bay, we obtained the spatial structures of moon jellyfish aggregations and categorized them into either patchy, layered, or wavy aggregations. We also examined possible physical mechanisms responsible for the moon jellyfish aggregations. In particular, passive particle tracking simulations of several idealized internal wave fields suggest that the formation of wavy aggregations is closely related to the presence of internal waves. However, internal waves alone cannot induce patchy and layered aggregations, indicating that particular biological processes (e.g., swimming behavior) are also necessary for such aggregations to form.