Comparative ROV surveys reveal jellyfish blooming in a deep-sea caldera: the first report of Earleria bruuni from the Pacific Ocean

Mitsuko Hidaka-Umetsu,Dhugal J Lindsay

doi:10.1017/s0025315417001540

Abstract

Large numbers of the leptomedusa Earleria bruuni were observed inside a semi-closed deep-sea caldera during a comparative survey of the macrozooplankton fauna inside and outside the Kurose Hole, Izu-Ogasawara Islands, by the remotely operated vehicle (ROV) ‘Dolphin-3K’, on 24 September 2000. The Kurose Hole is an inactive volcanic caldera of 790 m bottom depth, located within the Izu-Bonin island arc, south of Tokyo. Archived video and audio data from a dive by the human-occupied vehicle (HOV) ‘Shinkai 2000’, carried out 3 weeks after the ROV dives, was also analysed. During all dives within the caldera, E. bruuni was present in large numbers and, during the HOV dive, two specimens for morphological analysis were obtained. Herein, we report E. bruuni from the Pacific Ocean for the first time. The vertical profiles of environmental factors and the vertical distributions of gelatinous macrozooplankton taxa such as salps, ctenophores, hydromedusae, siphonophores and scyphomedusae, were extremely different inside and outside the caldera. Inside the caldera the water temperatures were warm and dissolved oxygen levels were high compared with outside. For each taxon, their distributions were characterized and compared between the inside and outside of the caldera, and with previous literature reports.

Highlights

Gelatinous macrozooplankton such as jellyfishes have been reported to bloom in response to anthropogenic eutrophication, climate change and/or human activities such as overfishing (Purcell, 2012)
Comparative remotely operated vehicle (ROV) dives revealed that semi-closed systems such as deep-sea calderas can have unique environmental factors and gelatinous macrozooplankton communities
In the Kurose Hole, Izu-Ogasawara Islands, extremely low taxon diversity was found inside the caldera, and large numbers of the leptomedusa Earleria bruuni were observed inside the caldera, being the predominant species

Summary

Introduction

Gelatinous macrozooplankton such as jellyfishes have been reported to bloom in response to anthropogenic eutrophication, climate change and/or human activities such as overfishing (Purcell, 2012). Recent research using submersibles and remotely operated vehicles (ROVs) has revealed that gelatinous macrozooplankton are ubiquitous and predominant taxa in the deep sea In the deep sea, a new anthropogenic risk to the marine environment through seafloor mining has arisen and it has been predicted that impacts will extend not just to the seafloor but to all marine environments including the water column (Boschen et al, 2013). Pre-emptively, proposed requirements for Environmental Impact Assessments (EIAs) related to these activities have been investigated (Boschen et al, 2013).

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Conclusion