Instruments and Methods
Live capture of megafauna from 2300 m depth, using a newly designed Pressurized Recovery Device

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Abstract

The deep sea is an extremely diverse habitat, which is now threatened by human activity. Means for evaluating the response of deep-sea creatures to environmental perturbation are limited because of lethal decompression effects during sampling. The addressing of this issue requires that target species be (i) captured at depth, (ii) recovered at natural pressure, (iii) submitted to in vivo investigations. Although a single container may meet these requirements, we believe that using several dedicated cells greatly expands experimental possibilities. Accordingly, we have designed a new sampling system which has been named PERISCOP and which has accounted for the selective capture and recovery of live animals from depths exceeding 2000 m. Three hydrothermal vent shrimp species were sampled on the Mid-Atlantic Ridge, from depths of 1700 and 2300 m. In addition, a fish caught at 2300 m depth reached the surface in very good condition. This is by far the deepest record for the pressurized recovery of a live deep-sea fish. Our prototype aims at making pressurized recovery a more efficient and practical process. Finally, future evolutions of sampling methods are discussed based on the present design of the PERISCOP.

Introduction

The last 30 years have seen the discovery of several deep-sea ecosystems (hydrothermal vents, cold seeps, whale-falls, sunken woods, and seamounts (Tyler, 1995)) which have modified our vision of the deep sea. Once considered as a homogeneous biological desert (Menzies, 1965), it is now seen as a patchwork of habitats where life may show diverse forms, with locally high biomasses (Van Dover et al., 2002). At the same time, the interest for fishing resources in the deep sea has grown to an alarming degree (Devine et al., 2006; Glover and Smith, 2003), pointing to the risk of severe ecosystem perturbation. Several other forms of human activity are threatening the largest habitat of the biosphere, such as CO2 sequestration projects, waste dumping, mineral prospecting, and their impact on deep-sea fauna has barely been evaluated (Glover and Smith, 2005). It is therefore a matter of urgency to learn more about the ecology and the biology of deep-sea species, especially concerning their response to environmental changes. Although in situ experiments have yielded some interesting results (Bailey et al., 2002; Vardaro et al., 2007), laboratory studies of live animals are a precious tool here, since they allow physiological investigation at various levels, from genetic expression to organismal, physiological, and behavioural responses. Unfortunately, while some organisms may be studied in pressurized aquaria (Childress et al., 1993; Shillito et al., 2001; Girguis and Lee, 2006), many deep-living creatures preclude in vivo investigation because of lethal decompression effects upon sampling (MacDonald, 1997). The addressing of these issues requires that target species be (i) captured at depth, (ii) recovered at their natural pressure, and (iii) studied in vivo at the laboratory. In most previous attempts involving pressurized recovery (MacDonald and Gilchrist, 1972; Yayanos, 1978; Drazen et al., 2005; and references herein), a single container fulfilled these three tasks. This may lead to contradicting technical requirements and we believe that experimental possibilities would be greatly expanded by using dedicated cells for each of these tasks. Here we give account of the recovery of live animals from depths exceeding 2000 m, using a new Pressurized Recovery Device (PRD) named PERISCOP (Projet d’Enceinte de Remontée Isobare Servant la Capture d’Organismes Profonds). This prototype aims at making pressurized recovery a more efficient and practical process. Additionally, its present design is adapted to future evolutions: the transfer of freshly caught animals, without decompression, towards larger ship-based pressure aquaria.

Section snippets

General principle

The PERISCOP system is composed of: (1) an in situ sampling cell (Fig. 1) and (2) a PRD, designed to maintain in situ pressure during recovery (Fig. 2). The PRD is installed on a “shuttle” device, which is moored and recovered away from the submersible. Once fauna have been confined inside the sampling cell, the latter is stored inside the PRD, which is then sealed and later recovered after ascent through the water column. In addition, the main aperture of the PRD is designed to permit future

The sampling process (Fig. 4)

During the MOMARETO cruise in August 2006 (Mid-Atlantic Ridge), we made six attempts at recovering hydrothermal vent organisms at their native pressure (Table 1), by using the Remotely Operated Vehicle (R.O.V.) Victor 6000 (Ifremer). Two additional “control” attempts were made using the PRD, but with no pressure retention (i.e. V4 had been left open, see Fig. 2). Three shrimp and one fish species were sampled, at depths of 1700 (Mirocaris fortunata and Chorocaris chacei) and 2300 m (Rimicaris

Sampling efficiency and specificity, normal and safe operation

There have been previous successful attempts to recover deep-sea organisms at their native pressure, despite the difficulties involved in achieving this task (Yayanos, 1978; MacDonald and Gilchrist, 1982; Jannasch et al., 1982; Wilson and Smith, 1985; Bianchi et al., 1999; Koyama et al., 2002; Drazen et al., 2005). With regard to megafauna, the first challenge is to manage efficient capture. Most existing devices act as baited traps. One main drawback here is that the target species must be

Conclusion

The success of the PERISCOP provides a new step towards allowing biologists normal and practical access to live deep-sea megafauna. Three major improvements are proposed, with respect to previous devices. Their aim is to: (i) allow choice of sampling by a submersible, without requiring exclusive dedication of the dive towards this task; (ii) improve safety and simplicity of pressure compensation, as well as recording pressure and temperature history during recovery; and (iii) propose a system

Acknowledgements

We are indebted to Captains and crews of N/O “Pourquoi Pas ?” and ROV “Victor 6000” (Ifremer). This research was funded by the European Community program EXOCET/D (FP6-GOCE-CT-2003-505342). We are also grateful to P. Gavaia, E. Bonnivard, and S. Halary for their help, and to the chief scientists of previous cruises (D. Jollivet for Biospeedo 2004 and A. Godfroy for Exomar 2005), along with the Captains and crews of the manned submersible “Nautile”, and N/O “Atalante” (Ifremer) for participating

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