The supergiant amphipod Alicella gigantea (Crustacea: Alicellidae) from hadal depths in the Kermadec Trench, SW Pacific Ocean

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Abstract

Here we provide the first record of the ‘supergiant’ amphipod Alicella gigantea Chevreux, 1899 (Alicellidae) from the Southern Hemisphere, and extend the known bathymetric range by over 1000 m to 7000 m. An estimated nine individuals were observed across 1500 photographs taken in situ by baited camera at 6979 m in the Kermadec Trench, SW Pacific Ocean. Nine specimens, ranging in length from 102 to 290 mm were recovered by baited trap at depths of 6265 m and 7000 m. Mitochondrial and nuclear DNA sequences obtained indicate a cosmopolitan distribution for the species. Data and observations from the study are used to discuss the reason for gigantism in this species, and its apparently disjunct geographical distribution.

Introduction

Alicella gigantea Chevreux, 1899 (Alicellidae) is the largest known amphipod, measuring up to 340 mm total body length (Harrison et al., 1983 in Barnard and Ingram, 1986). These ‘supergiant’ amphipods (sensu Barnard and Ingram, 1986) have previously only been recorded in the Northern Hemisphere (Chevreux, 1899, Barnard and Ingram, 1986, Hasegawa et al., 1986, De Broyer and Thurston, 1987, Hessler et al., 1972) and remain somewhat enigmatic given such a low frequency of observations despite a seemingly enormous bathymetric and geographic range. The species is hitherto known to inhabit the deep abyssal plains of the Northern Hemisphere in the North Atlantic Ocean (off the Canaries, Cape Verde and in the Demerara Basin) and in the vicinity of the Hawai'i Islands in the North Pacific Ocean (Barnard and Ingram, 1986, Hasegawa et al., 1986, De Broyer and Thurston, 1987). These two localities are approximately 12,800 km (6900 nm) apart and separated by the American continental land mass. Furthermore, in both these known areas of occurrence, the specimens have been captured (albeit in low numbers) multiple times but never at more frequently studied areas around the associated ocean rims. Limited observations of A. gigantea are also surprising given an apparent vast bathymetric range. Although the majority of samples have been recovered from the lower abyssal plains (4850–6200 m), a single juvenile female was captured at 1720 m in the central North Pacific Ocean (Barnard and Ingram, 1986). This record provides the bathymetric range for A. gigantea of around 4480 m, which this study extends by 1000 m. The question then arises as to why a relatively large deep sea animal with such a large bathymetric and geographic range is so infrequently found whilst other, smaller amphipods, with similarly large extents are so frequently caught in high abundance (e.g. Eurythenes gryllus; 184–7800 m; Barnard, 1961, Thurston et al., 2002, De Broyer et al., 2004, Stoddart and Lowry, 2004, and Abyssorchomene spp.; France, 1994, Havermans et al., 2010, Jamieson et al., 2011).

Here we report on the recovery of specimens and in situ images of A. gigantea in the Southern Hemisphere (Kermadec Trench, SW Pacific Ocean) and at hadal depths (6265–7000 m). We use these observations to address questions about the distribution patterns of A. gigantea. We also provide mitochondrial and nuclear DNA sequences to facilitate analysis of the phylogenetic relationships of A. gigantea with other amphipod species in the future, and as a reference DNA barcode for future species identification.

Section snippets

Sampling equipment

Two autonomous deep-submergence vehicles were used in this study. The first was a free-fall baited camera lander (Hadal-Lander B; Jamieson et al., 2009a, Jamieson et al., 2011) and a new free-fall fish and invertebrate trap (Latis). The Hadal-Lander B camera was a five megapixel still image camera (OE14-208, Kongsberg Maritime, Norway) programmed to take one picture every 60 s during deployment with a field of view of 0.31 m−2 (665×498 mm) of seafloor. Approximately 500 g of Jack Mackerel (

Results

The supergiant amphipod Alicella gigantea was found at three sites; 32°38.190′S 177°15.001′W (Hadal-Lander), 32°22.59′S, 176°50.90′W, and 32°33.428′S, 177°14.594′W (Latis). Two and seven individuals were recovered by the Latis sites, respectively (Table 1), and an estimated nine individuals were observed at the Hadal-Lander site (Fig. 2).

The Hadal-Lander recorded salinity, temperature and pressure which provided mean bottom values of 34.69 ppt, 1.31 °C and 7145 dbar respectively. The temperature

Discussion

Details of all recorded samples of A. gigantea found previously, including body size, sex, depth and location, are listed in Table 3. The known size range of A. gigantea is ∼40 to 340 mm. The largest specimen was an adult female regurgitated by an albatross on Laysan Island (Hawai'i) estimated at 340 mm (Barnard and Ingram, 1986). There is also a report of 61 individuals recovered by baited traps at 6200 m off the coast of Japan which weighed a combined 1.1 kg, but no other information is available

Acknowledgments

We thank the captain and crew of the R.V. Kaharoa KAH1109 and KAH1202, and the NIWA Vessels Management Company. This study was funded by the Total Foundation (France) and the National Institute for Water and Atmospheric Research (NIWA), New Zealand. AJJ and NCL are funded by the MASTS pooling initiative (The Marine Alliance for Science and Technology for Scotland) and their support is gratefully acknowledged. MASTS is funded by the Scottish Funding Council (Grant reference HR09011) and

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