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First findings of decapod crustacea in the hadal zone


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Since the first major hadal sampling efforts in the 1950s, crustaceans of the order Decapoda have been thought absent from the hadal zone (6000–11,000 m) with no representatives documented >5700 m. A baited video lander deployed at 6007, 6890 and 7966 m in the Kermadec Trench, 8798 and 9729 m in the Tonga Trench (SW Pacific), 6945 and 7703 m in the Japan Trench and 5469 m in the Marianas region (NW Pacific) has now revealed a conspicuous presence of the Benthesicymid prawn Benthesicymus crenatus Bate 1881. Decapods were observed at all sites except at 7966 m in the Kermadec Trench and the two Tonga Trench sites, making the deepest finding 7703 m in the Japan Trench, 2000 m deeper than previously thought. These natantian decapods were readily attracted to fish bait and, rather than feeding on the bait itself, were observed preying upon smaller scavenging amphipods. These are the first observations of predation in the hadal zone. In less than 10 h of bottom time, 12 observations of 10 individuals were documented at 6007 m and 5 observations of 3 individuals were documented at 6890 m in the Kermadec Trench. In the Japan Trench at 6945 m 29 observations of 20 individuals were documented whilst only one individual was seen at 7703 m. Two individuals were observed in the abyssal Marianas Region (5575 m). Also, in the Kermadec Trench, individual caridean prawns (Acanthephyra spp.) were observed at 6007 and 6890 m, proving categorically that the crustacean order of Decapoda is represented in the hadal zone.
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First findings of decapod crustacea in the hadal zone
A.J. Jamieson
, T. Fujii
, M. Solan
, A.K. Matsumoto
, P.M. Bagley
, I.G. Priede
Oceanlab, University of Aberdeen, Main Street Newburgh, Aberdeenshire AB41 6AA, UK
Ocean Research Institute, University of Tokyo, 1-15-1, Minamidai, Tokyo 164-8639, Japan
article info
Article history:
Received 21 July 2008
Received in revised form
30 October 2008
Accepted 6 November 2008
Available online 17 November 2008
Benthesicymus crenatus
Hadal zone
Pacific Ocean
Since the first major hadal sampling efforts in the 1950s, crustaceans of the order
Decapoda have been thought absent from the hadal zone (60 00–11,000 m) with no
representatives documented 45700 m. A baited video lander deployed at 60 07, 6890
and 7966 m in the Kermadec Trench, 8798 and 9729 m in the Tonga Trench (SW Pacific),
6945 and 7703 m in the Japan Trench and 5469 m in the Marianas region (NW Pacific)
has now revealed a conspicuous presence of the Benthesicymid prawn Benthesicymus
crenatus Bate 1881. Decapods were observed at all sites except at 7966m in the
Kermadec Trench and the two Tonga Trench sites, making the deepest finding 7703 m in
the Japan Trench, 2000 m deeper than previously thought. These natantian decapods
were readily attracted to fish bait and, rather than feeding on the bait itself, were
observed preying upon smaller scavenging amphipods. These are the first observations
of predation in the hadal zone. In less than 10h of bottom time, 12 observations of 10
individuals were documented at 6007 m and 5 observations of 3 individuals were
documented at 6890 m in the Kermadec Trench. In the Japan Trench at 6945 m 29
observations of 20 individuals were documented whilst only one individual was seen
at 7703 m. Two individuals were observed in the abyssal Marianas Region (5575 m).
Also, in the Kermadec Trench, individual caridean prawns (Acanthephyra spp.) were
observed at 6007 and 6890 m, proving categorically that the crustacean order of
Decapoda is represented in the hadal zone.
&2008 Elsevier Ltd. All rights reserved.
1. Introduction
Decapod crustaceans have long been considered
to have no representatives in the hadal zone
(6000–11,000 m), a conclusion based largely on the
returns of a series of hadal trawls during the Galathea
and Vitjaz expeditions in the 1950s (Wolff, 1960, 1970).
Although 4700 species of invertebrates and fish were
described from the 33,000 individuals that were recov-
ered from 80 hadal trawls on the Galathea, not a single
decapod was found (Wolff, 1970). The apparent absence of
the decapods was considered to be due to the physiolo-
gical limitations of hydrostatic pressure; the deepest
decapod (Parapagurus sp.) was recorded at 5160 m. Since
then, the deepest findings of decapods are 4785, 4986,
5060, 5413, 5440, 5700 m (Tiefenbacher, 2001;Haedrich
et al., 1980;Gore, 1985b;Bouvier, 1908;Domanski, 1986;
Kikuchi and Nemoto, 1991, respectively). There are how-
ever some tentative reports of natantian decapods at
hadal depths (Peres, 1965;Hessler et al., 1978), but it is
still generally agreed that decapods have no hadal
representatives (Blankenship et al., 2007; Herring, 2002).
In contrast to the wealth of information on shallow
water decapod crustaceans, little is known about the
vertical and horizontal spatial distribution of decapods at
abyssal depths (Tiefenbacher, 2001). At these depths the
scavenging community primarily comprises of lysianas-
soid amphipods and macrourid fishes, both highly
efficient necrophages often observed to rapidly intercept
and consume simulated carrion falls (Ingram and Hessler,
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Corresponding author. Tel.: +44 1224 274410; fax: +44 1224274402.
E-mail address: (A.J. Jamieson).
Deep-Sea Research I 56 (2009) 641–647
1983;Priede et al., 1991). Amongst these more conspic-
uous abyssal scavengers, decapod crustaceans are often
observed, albeit less frequently and perhaps less predic-
tably (Henriques et al., 2002;Janßen et al., 2000;Kemp
et al., 2006). The galatheid crab Munidopsis spp., for
example, is often observed in relatively high numbers at
large carrion falls, such as cetacean carcasses, although
they do not appear for several days (Jones et al., 1998;
Kemp et al., 2006). On shorter time scales, where smaller
baits are consumed within 24 h, the highly active and fast
moving natantian decapod Plesiopenaeus sp., thought to be
a facultative scavenger, is frequently observed but in
lower numbers and often during periods of low fish
activity (Henriques et al., 2002;Thurston et al., 1995).
The aim of this paper is to describe the first observa-
tions of highly active decapod crustaceans in the hadal
trenches of the Pacific Ocean.
2. Methods
2.1. Lander operations
A hadal-rated baited video lander was deployed in the
Southern Hemisphere in the Kermadec trench (at 6007,
6890, 7966 m) and in the Tonga Trench (at 8798 and
9729 m) during July 2007. In the Northern Hemisphere it
was deployed in the Japan Trench (6945 m) and abyssal
Marianas Region (5469 m) during October–November
2007. One further deployment was made in the Japan
Trench (7703 m) in October 2008. The lander was pre-
programmed to record 1min of video every 5 min in
MPEG2 format (704 576 pixels) using a custom-built
video camera (12kCAM-V-1; Oceanlab, UK; NETmc Marine
Ltd., UK). The video system was positioned 1 m off the
seafloor with the camera and twin 50 W lamps facing
vertically down and focussed on an area of seafloor
68 cm 51 cm (0.35 m
). One kilogram of bait (blue-fin
tuna, Thunnus thynnus) was secured on a stainless-steel
bar in the centre of the field of view. Pressure (decibars)
and temperature (degree Celsius) were recorded every
30 s throughout using an SBE-39 sensor (Seabird Electro-
nics, USA). Pressure was converted to depth following
Saunders (1981).
As there are presently no current meters available with
sufficient operational depth ratings, it was not possible to
accurately measure current velocity, but estimates were
made by tracking of particles in the water resuspended by
activity of bottom-fauna.
2.2. Study sites
The Japan and Kermadec/Tonga Trench systems exhibit
the characteristic V-shaped topography of many trench
systems with soft sediment on the Oceanic plate side
(to the East) and rockier steep slopes on the continental
plate side (to the West). The Kermadec and Tonga trenches
are open to the incursion of cold, deep Antarctic water and
bottom temperatures are between 1.2 and 1.8 1C making
this trench one of the coldest in the world (Belyaev, 1989).
These trenches are oligotrophic as they lie under the
South Pacific Subtropical Gyre (SPSG) province which has
an average primary production rate of 87gC m
(Longhurst et al., 1995). The low export of primary
production to the seafloor is likely to increase the
significance of carrion falls as sources of food for
the benthic food web (Blankenship and Levin, 2007). In
contrast to the Kermadec and Tonga trenches, the Japan
Trench, situated in the Kuroshio Province (KURO), which
has higher surface primary production rate (193 g C m
(Longhurst et al., 1995) and has generally higher
bottom temperatures. The Abyssal Marianas Region site
(5469 m), situated to the east of the Southern Marianas
Trench, is the most oligotrophic of the three sites (primary
production rate ¼82 g C m
;Longhurst et al., 1995).
2.3. Data analysis
Each minute of MPEG2 video sequence was manually
analysed. Individual decapods were identified using still
images obtained from the MPEG2 sequence in conjunction
with the video sequences. Differences in body size, shape
and carapace markings were sufficient to unambiguously
distinguish each conspecific. Body lengths were measured
in cm by comparison with the in situ scale bar in the field
of view. Over ground swimming speeds were recorded in
cm per second (cm s
) and converted to body lengths per
second (BL s
). To test the statistical significance for
differences, one-way ANOVA was conducted to compare
the measurements for body length (cm) and swimming
speed (cm s
and BL s
) across three regions (Japan
6945 m; Kermadec 6007 and 68 90 m; Marianas 5469 m).
All the statistical analyses were performed using SPSS
(SPSS Inc., USA) and the ‘R’ statistical and programming
environment (R Development Core Team, 2005).
3. Results
During deployments at 5469 m in the Marianas Region,
6007 and 6890 m in the Kermadec Trench and 6945 and
7703 m in the Japan Trench, the Benthesicymid prawn
Benthesicymus crenatus Bate 1881 was readily attracted to
bait and apparently undeterred by lander structures or
illumination (Fig. 1). On video, its appearance is similar to
that of the common deep-sea Aristaeid prawn Plesiope-
naeus armatus, perhaps more commonly seen at baits
(Janßen et al., 2000;Thurston et al., 1995). However, the
resolution of the camera was sufficiently high to allow
B. crenatus to be distinguished from P. armatus (shorter
rostrum), although we recognise that both species are
known to co-inhabit in deeper areas of the South Pacific
Ocean (Poupin, 1998).
At 60 07 m in the Kermadec Trench, 12 sightings of
B. crenatus were recorded during 4 h 27 min bottom time.
Based on the length and carapace markings, these were
of 10 individuals, mean (7S.D.) body length 2273.9 cm.
From 6890 m, 4 sightings were recorded between 2 h
42 min and 6 h 02 min post touchdown of 2 individuals
(mean body length ¼22.4 cm72.6 S.D.). At 6945 m in the
Japan Trench, 29 sightings of 20 individual B. crenatus
were made (mean body length 15.3 cm72.9 S.D.) during
A.J. Jamieson et al. / Deep-Sea Research I 56 (2009) 641–647642
the 9 h 26 min bottom time (first arrival ¼10 min). On the
Abyssal Marianas location, amongst a succession of the
scavenging marcrourid fish Coryphaenoides yaquinae, two
sightings were made of one individual decapod (body
length ¼23.5 cm, arrival time 1 h 02 min). At 7703 m in
the Japan Trench, one individual was briefly observed
traversing the field of view of the camera at 4h 01 min
after touchdown. The individual was swimming too close
to the camera to determine body length or swimming
speed with confidence. The mean body length for the
Kermadec Trench decapods (n¼14) was significantly
larger than that of the Japan Trench decapods (n¼20)
(one-way ANOVA, F
(1, 32)
¼40.1, po0.0001; Fig. 3).
Single Caridean prawns were observed approaching
the bait up-current towards the end of the 6077 and
6890 m deployments in the Kermadec Trench (Fig. 1).
The individual in deployment 1 (body length ¼13.2 cm)
arrived at 3 h 40 min post touchdown and in deployment 2
the individual (14 cm) arrived at 5 h 50 min. Because
of their small body size, however, it was not possible
to confirm their identity with confidence beyond that
of the family Acanthephyra. Other than swimming speeds
of 5.7 and 6.6 m s
, respectively, no other information
was obtained and they are simply mentioned here for
No further sightings of decapods were made beyond
6890 m in the Kermadec Trench (7966 m) or at the Tonga
Trench locations (8798 and 9729 m). A summary of these
observations and environmental characteristics is given in
Table 1.
The presence of scavenging amphipods was recorded
at all sites and increased in numbers with depth. The
resolution of the video camera did not permit positive
identification, however, Blankenship et al. (2006) docu-
mented 4 species captured in traps, from the Kermadec
and Tonga Trenches (Eurythenes gryllus,Scopelocheirus
schellenbergi,Hirondellea dubia and Uristes sp. nov.).
The three deepest sites from the Kermadec and Tonga
Trench deployments (where decapods were absent) were
dominated by extremely large numbers of amphipods.
Based on the large numbers of H. dubia reported by
Blankenship et al. (2006) these can be assumed with some
confidence to be H. dubia. The species of amphipods from
the Japan Trench and Marianas Region are not known.
3.1. Decapod swimming speeds
At the Kermadec 6007 and 6 890 m sites, the typical
behaviour of B. crenatus was to approach the bait at mean
over ground swimming speeds of 7.4 cm s
71.8S.D. and
6.9 cm s
71.6S.D., respectively (translating as 0.34 BL
70.08 S.D. and 0.35 BL s
70.11 S.D.), stopping
abruptly once in close proximity to the bait, temporarily
interacting with the bait, and leaving the immediate
vicinity. Of the 12 sightings at 6007m, 7 individuals were
seen approaching the bait against the current. Of those
that were observed leaving (10 ind.), 7 left cross-current,
2 drifted back down-current and 1 continued swimming
up-current. Of these 12, each stopped at the bait (never
away from or off the bait) for a mean (7S.D.) duration of
22.8720.2 s. At 6890 m, 3 of the 4 observations showed
individuals approaching the bait from upstream. Only one
was observed leaving (backwards and down-current),
stopping at the bait for 9 s. The general behaviour of
B. crenatus in the Japan Trench was similar to that in the
Kermadec Trench, approaching the bait up-current, stop-
ping in close proximity to the bait and leaving. Of the
18 approaches recorded, 17 were up-current and 1 down-
current. They approached the bait at a mean (7S.D.)
swimming speed of 6.972.0 cm s
(0.49 BL s
S.D.). Seventeen approaches were seen to stop on the
bait, but for a shorter time (6.8 s73.8 S.D.) compared to
those in the Kermadec Trench. However, in contrast to the
Kermadec sites, in the Japan Trench individuals showed
a strong tendency to leave the bait and exited the field of
Fig. 1. The natantian decapod Benthesicymus crenatus (A) and caridean prawns (B and C) in the Kermadec Trench 46000 m (scale bar ¼20 cm).
A.J. Jamieson et al. / Deep-Sea Research I 56 (2009) 641–647 643
view up-current; of the 20 exits observed, 15 exited up-
current, 4 cross-current and 1 down-current. On physical
contact with the bait during approach, one individual
B. crenatus initiated a tail-flip escape response at a speed
of 82.7 cm s
. The single individual seen twice in the
Marianas region approached the bait up-current both
times with a mean swimming speed of 7.7cm s
72.0 S.D.
(0.33 BL s
) and one occasion stayed at the bait for 7 s. On
the second occasion it responded to a large macrourid
with a tail-flip escape response, exiting the area at a burst
swimming speed of 147.1 cm s
. Although no statistically
significant difference was found when the mean swim-
ming speeds (cm s
;Fig. 4a) were compared, there is a
significant difference when expressed in body lengths per
second (BL s
;Fig. 4b).
3.2. Decapod predation behaviour
The decapods preyed upon on scavenging amphipods
already present on the bait, rather than the bait itself.
The presence of amphipods at the bait was consistent
throughout all the locations with first arrival times
of 20 min or less at all locations. In the Kermadec Trench
at 6007 and 6890 m, Japan Trench at 6945 m and the
Marianas Region at 5469 m sites the maximum density of
actively swimming amphipods was 40ind. m
(3 h 50 min),
102.9 ind. m
(5 h 45 min) 28.6 ind. m
(2 h 58 min) and
94.3 ind. m
(7 h 47 min), with corresponding bait cover-
age of 60%, 410%, 410% and 410%, respectively. At the
next deepest site in the Kermadec Trench (7966 m) 100%
bait coverage was reached in 2 h 35 min with the density
of actively swimming amphipods reaching 1028 ind. m
Amphipod densities within the field of view increased
further at the deeper sites at 8798 and 9729m in the
Tonga trench, with peak swimming amphipod densities of
1542.9 and 2914.3 ind. m
, respectively and 100% bait
coverage at 1 h 15min and 0 h 45min post touchdown.
The confirmation of predation of amphipods by
B. crenatus was made difficult because the mouth is ventrally
located and seldom in view. In one instance, however,
an individual was observed removing and handling a large
lysianassoid amphipod (20 mm body length). The dec-
apod, 20 cm in length, approached the bait up-current
with its pereiopods trailing below and outwards (Fig. 2A).
It rapidly decelerated once contact was made with the bait
(Fig. 2B). It then reached down, clasped and shuffled its
pereiopods for 3 s while drifting slightly down-current
away from the bait (Fig. 2C). During this time, the
distinctive orange body of the amphipod clearly con-
trasted against the red coloured underside of the decapod.
At the same time, the location on the bait previously
occupied by the large amphipod became visible and
vacant (Fig. 2D). The decapod remained stationary for a
Table 1
Deployment locations and environmental characteristics with decapod lengths, speeds, occurrences, arrival and staying times at all stations.
Tonga 9726
Latitude 18149.2
Longitude 149150.6
Depth (m) 5469 6007 6890 6945 7703 7966 8798 9726
Primary production rate
(g C m
82 87 87 193 193 87 87 87
Temperature (1C) 1.5 1.2 1.3 1.8 1.9 1.5 1.6 1.8
Estimated current velocity (cm s
)5–9 8–9 10–14 3–7 2–4
Month year Nov ‘07 July ‘07 July ‘07 Oct ‘07 Sept ‘08 July ‘07 July ‘07 July ‘07
Bottom time (hh:mm) 08:55 04:27 06:02 09:26 07:00 10:07 09:05 08:44
Benthesicymus crenatus
Mean body length (cm7S.D.) 23.5 22.073.9 22.472.6 15.372.9
Over ground swimming speed
(cm s
7.7 7. 471.8 6.971.6 6.972.0
Burst swimming speed (cm s
) 147.1 82.7
Total number of sightings 2 19 4 29 1
Number of individuals 1 10 2 20 1
Mean sightings per hour 0.2 4.7 0.7 3.1 0.14
First arrival time 01:02 00:41 02:42 00:10 04:01
Mean bait interaction time (s) 7 22.8 720.2 9 6.8 73.8 0
Acanthephyra sp.
Body length (cm) 13.2 14.0
Swimming speed (cm s
) 5.7 6.6 – – –
Total number of sightings 1 1
Number of individuals 1 1
Mean sightings per hour 0.2 0.2
First arrival time 03:40 05:50
Indicates that current speed was too low to estimate with confidence, therefore close to 0cm s
Indicates that the length and speed of the decapod was immeasurable because of its swimming altitude.
A.J. Jamieson et al. / Deep-Sea Research I 56 (2009) 641–647644
further 5 s with its forward appendages held tightly
against its ventral surface, before swimming away cross-
current. As the lander had sunk slightly into the sediment,
the area around where the amphipod had been was close
to the sediment-water interface and so ruled out the
possibility that the amphipod had been knocked off or
4. Discussion
The observations described here confirm that indeed
decapods do inhabit the hadal zone to at least 7703 m, but
the mechanisms dictating their occurrence and distribu-
tion at this time are unresolved. The behaviour of the
natantian decapods is similar to other baited camera
observations on the shallower abyssal plains. One study,
where the numbers of decapods (P. armatus) were high
was in the Arabian Sea at 40 00–4500 m (Janßen et al.,
2000). Although they were the first to arrive at bait
(within 1 h), they did not appear in the same place in
consecutive images and no loss of bait was visible when
only decapods were present. Similarly, only 40% of
individuals were seen in contact with the bait. This also
suggests that the decapods may have been exploiting the
temporarily high density of amphipods rather than
feeding at the bait itself. In the Atlantic (4000–5000m)
small clusters of P. armatus have been viewed directly on
the bait; however, in both instances still photography
could not confirm predatory behaviour (Thurston et al.,
1995). The lack of bait consumption by decapods in this
study and others (Janßen et al., 2000) suggests exclusive
dependency on carrion falls is unlikely. Stomach contents
from abyssal specimens have comprised phytodetritus,
small bivalves and ground-up crustacean parts (Domanski,
1986;Thurston et al., 1995), further evidence of facultative
necrophagy and possibly active epibenthic predation,
also suggested by these observations and others (Gore,
1985a, b). However, the possibility of some of the stomach
contents being derived from undigested food within the
gut of a swallowed amphipod is not discussed but may be
Thurston et al. (1995) also reported peaks in decapod
numbers during periods of low current speeds, a relation-
ship reinforced by Domanski (1986), who suggested that
natantian decapods utilise weak currents as a low-energy
mechanism to search for food. In this study, the decapods
in the eutrophic Japan Trench tended to continue foraging
up-current rather than perhaps preserving valuable
energy by drifting cross-current like those in the oligo-
trophic Kermadec Trench, where current speeds are
higher. This continual up-current foraging may only be
possible in the Japan Trench because of its location under
high surface productivity where other food sources
are readily available, as eutrophic trenches are known to
support a higher benthic biomass (Jumars and Hessler,
1976). This may explain why this population exhibits a
significantly higher body length per second swimming
speed (Fig. 4b) as the conservation of energy is less
important. In the oligotrophic Kermadec Trench, where
food is sparser and current speeds are higher, the
tendency to conserve energy by swimming slower and
Fig. 2. Predation of amphipods by B. crenatus at 6007 m in the Kermadec Trench. (A) Decapod approaching bait with pereiopods out and amphipod
feeding at bait (arrowed). (B) Decapod stopped and grappling with amphipod, just visible under decapod’s body (arrowed). (C) Confirmation that the
amphipod has been removed as the decapod backs off (arrowed). (D) The decapod leaves with pereiopods clasped underneath and amphipod is no longer
at the bait (scale bar ¼20 cm).
A.J. Jamieson et al. / Deep-Sea Research I 56 (2009) 641–647 645
drifting cross-current are perhaps more important.
The larger body size (Fig. 3) may also be an adaptation
to this low-food environment (compared to the eutrophic
Japan Trench), a foraging strategy supported further in the
bait interaction times. Those in the Kermadec Trench
spent approximately three times longer in close proximity
to the bait (and associated amphipods) than those in
the Japan Trench, again suggesting a varying degree
of importance of individual food-falls between the two
trenches. The early arrival times, particularly in the Japan
Trench (10 min) may reflect a high decapod population
density as opposed to highly efficient food-fall intercep-
tion (Sainte-Marie and Hargrave, 1987;Priede at al 1990),
a view also supported by Christiansen and Martin (2000).
B. crenatus have been described from French Polynesia
at 430 0 m around the Tuamoto Archipelago (Poupin, 1998)
and the North West Pacific close to Japan as deep as
5700 m (Kikuchi and Nemoto, 1991). These new findings
place the geographical distribution of B. crenatus further
west into Polynesia in the Kermadec Trench, confirm their
distribution in the North West Pacific and bridge the gap
between the two with sightings in the Micronesian
Marianas Region near Guam. It can be confirmed that
the geographical distribution of B. crenatus currently
known is the west Pacific Ocean between 401N and 261S
with a bathymetric range of 3530 m (Kikuchi and Nemoto,
1991) to 7703, 200 0 m deeper than previously thought.
5. Conclusion
Decapod crustaceans are active at hadal depths,
inhabiting the upper slopes of the Pacific Ocean Trenches
in both the Northern and Southern hemisphere. They are
capable of preying upon the abundant scavenging amphi-
pod community that thrives at these depths and form a
major component of the hadal food web (Blankenship et
al., 2006;Blankenship and Levin, 2007), thus adding a
new element to the hadal food web as a top predator in
the upper trenches. Although the upper limit of the hadal
zone was originally, and to all intents and purposes still is,
defined as 60 00 m, Wolff (1960) recommended 6800–
7000 m as a better reflection of the change in faunal
composition. As the decapods described in this study,
known from as shallow as 3530m are found beyond the
limits of Wolff’s recommendation, these individuals are
Japan Kermadec Marianas
Body length (cm)
Fig. 3. Box plots of the body size (cm) of Benthesicymus crenatus in three
regions. (The centre of the box is the median. The notch in the box
represents an approximate 95% confidence interval for the median. The
top and bottom of the box represent the 3rd and the 1st quartiles,
respectively. The capped whiskers extend to the maximum and
minimum values.)
Japan Kermadec Marianas
Region Region
Japan Kermadec Marianas
Swimming speed (BL s-1)
Swimming speed (BL s-1)
Fig. 4. Box plots of (a) the over ground swimming speed (cm s
) and (b) the speed expressed in body length per second (BL s
), of Benthesicymus
crenatus in three regions. In (b), the mean value for Japan Trench (n¼20) was significantly larger than that for Kermadec Trench (n¼16) (one-way
(1, 34)
¼10.4, po0.01).
A.J. Jamieson et al. / Deep-Sea Research I 56 (2009) 641–647646
non-endemic but at the deeper limits of their habitat that
happens to cross the abyssal–hadal transition zone.
The absence of decapods at 7966 m in the Kermadec
Trench (and the deeper sites in the Tonga Trench) and the
single sighting at 7703 m in the Japan Trench compared to
the larger numbers at the shallower sites suggest that
7700 m may be close to their maximum depth. The
limiting factor to their bathymetric range remains unclear.
The lack of physical specimens prohibits any conclusion
based on hydrostatic pressure as a limiting factor as
suggested by Wolff (1970). The reason decapods have not
been found at hadal depths previously is that they appear
to be extremely difficult to physically catch. The baited
camera method was successful in finding them at these
depths but does not provide the necessary physical
specimen to conclude any adaptations that could explain
why they survive at such high pressure nor any biological
tolerances that still limit them to around 80 00 m. Never-
theless, because of the limited number of hadal sampling
efforts it is unlikely that these observations of decapods
are in fact the deepest, but they do however, highlight
an oversight in our knowledge of deep-sea zonation.
For an entire and relatively conspicuous order of Crustacea
to remain undiscovered from such a large depth zone
emphasises the need for further exploration of these hadal
trenches with appropriate techniques in order to reveal
the true structure of the hadal community.
We are thankful to Prof. H.-J. Wagner (University of
Tubingen, Germany) and Prof. H. Tokuyama (University of
Tokyo, Japan) for supporting this work. We thank the crew
and company of the FS Sonne (SO194),RV Hakuho-Maru
(KH07-3) and the RV Kairei (KR07-16). This research was
funded jointly by the Natural Environmental Research
Council (UK) and the Nippon Foundation (Japan) with
additional support from the Sasakawa foundation (Japan)
and the University of Aberdeen (UK).
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A.J. Jamieson et al. / Deep-Sea Research I 56 (2009) 641–647 647
... It was named after Hades, the realm of the underworld in Greek mythology, and arguably remains the least explored and most mysterious environment on Earth. One of the major features of the hadal zone is the trenches, and there are a total of 27 subduction trenches, 13 troughs, and seven trench faults below 6000 m (Jamieson et al. 2009;Stewart and Jamieson 2018). The deepest point of the hadal zone is the Challenger Deep, part of the Mariana Trench, which is 10,902 to 10,929 m deep (Fryer et al. 2003). ...
... A high sediment organic matter content and biological activity are apparently sustained by the lateral transport of material from their surroundings and subsequent downslope focusing of labile organic material (Gooday et al. 2010;Ichino et al. 2015;Luo et al. 2017;Turnewitsch et al. 2014). Higher benthic oxygen consumption rates at a depth of 11,000 m water (Challenger Deep, Mariana Trench) compared with the nearby abyssal zone were discovered by in situ measurements, reflecting intensified diagenetic activity in the trench axis sediments (Glud et al. 2013 Despite the challenging physical and chemical conditions, animals are found in the hadal zone, including deep-sea fish and amphipods (Jamieson et al. 2009;Linley et al. 2017). Prokaryotes, such as Proteobacteria and Bacteroidetes, have also been studied (Nunoura et al. 2018). ...
... Later, baited traps and other associated equipment attached to the landers were used to capture fish and shrimps. For example, Jamieson et al. (2009) used an imaging lander containing a video system to observe the time course of bait interception and consumption. Landers can also be equipped with sensors for conductivity, temperature, and depth. ...
Full-text available
The hadal zone is the deepest point in the ocean with a depth that exceeds 6000 m. Exploration of the biological communities in hadal zone began in the 1950s (the first wave of hadal exploration) and substantial advances have been made since the turn of the twenty-first century (the second wave of hadal exploration), resulting in a focus on the hadal sphere as a research hotspot because of its unique physical and chemical conditions. A variety of prokaryotes are found in the hadal zone. The mechanisms used by these prokaryotes to manage the high hydrostatic pressures and acquire energy from the environment are of substantial interest. Moreover, the symbioses between microbes and hadal animals have barely been studied. In addition, equipment has been developed that can now mimic hadal environments in the laboratory and allow cultivation of microbes under simulated in situ pressure. This review provides a brief summary of recent progress in the mechanisms by which microbes adapt to high hydrostatic pressures, manage limited energy resources and coexist with animals in the hadal zone, as well as technical developments in the exploration of hadal microbial life.
... Based on the first major trawling efforts at hadal depths in the 1950s (Wolff, 1960(Wolff, , 1970, members of Decapoda were long thought to have no representatives greater than 5,700 m (Herring, 2002;Blankenship & Levin, 2007), despite some anecdotal evidence to the contrary (Pérès, 1965;Hessler et al., 1978). Jamieson et al. (2009a) demonstrated that shrimps belonging to superfamilies Penaeoidea (suborder Dendrobranchiata) and Oplophoroidea (infraorder Caridea) were present in the trenches of the Western Pacific (mainly the Japan and Kermadec trenches) to at least 7,703 m and 6,890 m, respectively. This conclusion was, however, based on just eight deployments of a baited camera spanning three localities in which decapods were observed in the shallowest five deployments. ...
... The study of Jamieson et al. (2009a) was followed by several other studies that showed that the dominant Penaeoidea was Benthesicymus crenatus Spence Bate, 1881 and a species of Oplophoroidea thought to belong to genus Acanthephyra A. Milne-Edwards, 1881. The former was clearly attracted to the baited camera by the elevated abundance of lysianassoid amphipods which they were observed to prey upon, while the latter appeared to be incidental observations as they showed no obvious interest in the bait or associated fauna (Jamieson et al., 2011Linley et al., 2017). ...
... The maximum depth of B. cf. crenatus in this study was 7,716 m in the Mariana Trench, which is just 13 m deeper than the previous depth record of 7,703 m in the Japan Trench (Jamieson et al., 2009a). Benthesicymus cf. ...
Decapod crustaceans are conspicuous members of marine benthic communities to at least 7,700 m deep. To assess the bathymetric extent of this taxonomic group, baited landers were deployed to across the abyssal-hadal transition zone of 11 subduction trenches spanning the Pacific, Atlantic, Southern, and Indian oceans and additional sites. Decapods were dominated by penaeid shrimps (superfamily Penaeoidea), in particular Benthesicymus Spence Bate, 1881 and Cerataspis Gray, 1828, with the former being found deeper. Benthesicymus cf. crenatus Spence Bate, 1881 was observed in the Kermadec, Mariana, New Hebrides, Puerto Rico, Peru-Chile, Tonga, San Cristobal, and Santa Cruz trenches, plus the South Fiji Basin and the Wallaby-Zenith Fracture Zone. They were not recorded in the Abaco Canyon, Agulhas Fracture Zone, Java Trench, or any of the polar locations. Cerataspis cf. monstrosus Gray, 1828 was present in the Kermadec, Mariana, New Hebrides, Puerto Rico, and Java trenches, the Abaco Canyon, Agulhas Fracture Zone, Wallaby-Zenith Fracture Zone and the South Fiji Basin, but absent from the Tonga, San Cristobal and Santa Cruz trenches. Hymenopenaeus nereus (Faxon, 1893) was only recorded in the Peru-Chile Trench. Unidentified species belonging to superfamily Oplophoroidea were observed to a maximum depth of 6,931 m. Decapods are thus are primarily represented at hadal depths by penaeoid shrimps, consistently present at tropical and temperate latitudes to ~7,700 m, while absent from equivalent depths in polar regions. Their maximum depth may be limited due to hydrostatic pressure, while potentially affected by temperature and oxygen in some instances. Muscle samples of three specimens from 6,000 m (Mariana and Kermadec trenches) were found to have high levels of trimethylamine N-oxide (TMAO; 260 mmol kg–1), the major piezolyte, a protectant against hydrostatic pressure, in other deep-sea organisms. We speculate that physiological limits to TMAO concentration may prevent them from inhabiting the greatest hadal depths.
... The voucher specimens collected by the HOV from the Yap Trench during the same cruises, deposited at the Repository of Second Institute of Oceanography, were used as an important key for those closely related groups. Previous published video analysis from the hadal trenches (Heezen and Hollister, 1971;Lemche et al., 1976;Hessler et al., 1978;Belyaev, 1989;Jamieson et al., 2009cJamieson et al., , 2011Fujii et al., 2010;Gallo et al., 2015;Jamieson, 2015;Linley et al., 2016Linley et al., , 2017 were also used as references for identification of the megafauna records from video data. There are limitations to identification of organisms from video so we applied the most conservative standard for taxonomic identification, assisted by consultation with many deep-sea taxonomy experts. ...
... Snailfishes are the top predator in hadal trenches. Before this study, they were mainly observed by baited landers (Jamieson et al., 2009c;Fujii et al., 2010;Linley et al., 2016), except in the Puerto-Rico Trench by the bathyscaphe Archimède (Pérès, 1965). According to the video data from baited landers, snailfish is likely targeting swarms of amphipods that are feeding on squid or fish remains (Gerringer et al., 2017b;Linley et al., 2017), swimming in an irregular spiral pattern, as well as temporarily resting in an unbalanced arched position (Pérès, 1965;Fujii et al., 2010). ...
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Hadal trenches remain one of the unexplored ocean ecosystems due to the challenges of sampling at great depths. It is still unclear how a faunal community changes from the abyssal to the hadal zone, and which environmental variables are the key impacting factors. In this study, nine dives of the Human Occupied Vehicle (HOV) "JIAOLONG" were conducted from abyssal to hadal depths (4,435-6,796 m) in the Yap Trench on the southeastern boundary of the Philippine Sea Plate in the western Pacific, divided into 48,200 m video transects, to describe the megafaunal communities and reveal their relationship with environmental factors. A total of 1,171 megafauna organisms was recorded, 80 morphospecies (msps) from 8 phyla were identified based on the video data, most of which were reported for the first time in the Yap Trench. Arthropoda was the most abundant phylum and Echinodermata was the most diverse phylum of the megafaunal community. The faunal abundance increased with depth, whereas the Shannon diversity index decreased with depth. Cluster analysis suggested seven assemblages, with five abyssal groups, one mixed group, and one hadal dominant group. Although megafaunal communities changed gradually from abyssal zone to hadal zone, both PERMANOVA and PERMDISP analyses revealed that the communities are significantly different between abyssal zone and hadal zone, indicating 6,000 m as the boundary between the two depth zones. Depth, substrate, slope, and latitude were identified as four important environmental factors with significant influence on megafaunal community structure. This study proposed a transition pattern from the abyssal to hadal zone in the Yap Trench, highlighted the importance of habitat heterogeneity in structuring megafaunal community in a hadal trench.
... Meanwhile, the high hydrostatic pressure of the hadal zone is considered to be one of the major obstacles for species to adapt to the hadal environment [46,47]. Different hadal amphipods live at specific depths, and they dominate scavenging communities and are regarded as the primary prey of hadal predators [48]. Accordingly, the study of amphipods is of great importance to the understanding of hadal environment adaptations and amphipods are often used as biological indicators of the hadal environment [49]. ...
Full-text available
Hadal trenches are a unique habitat with high hydrostatic pressure, low temperature and scarce food supplies. Amphipods are the dominant scavenging metazoan species in this ecosystem. Trimethylamine (TMA) and trimethylamine oxide (TMAO) have been shown to play important roles in regulating osmotic pressure in mammals, hadal dwellers and even microbes. However, the distributions of TMAO and TMA concentrations of hadal animals among different tissues have not been reported so far. Here, the TMAO and TMA contents of eight tissues of two hadal amphipods, Hirondellea gigas and Alicella gigantea from the Mariana Trench and the New Britain Trench, were detected by using the ultrahigh performance liquid chromatography–mass spectrometry (UPLC-MS/MS) method. Compared with the shallow water Decapoda, Penaeus vannamei, the hadal amphipods possessed significantly higher TMAO concentrations and a similar level of TMA in all the detected tissues. A higher level of TMAO was detected in the external organs (such as the eye and exoskeleton) for both of the two hadal amphipods, which indicated that the TMAO concentration was not evenly distributed, although the same hydrostatic pressure existed in the outer and internal organs. Moreover, a strong positive correlation was found between the concentrations of TMAO and TMA in the two hadal amphipods. In addition, evolutionary analysis regarding FMO3, the enzyme to convert TMA into TMAO, was also conducted. Three positive selected sites in the conserved region and two specific mutation sites in two conserved motifs were found in the A. gigantea FMO3 gene. Combined together, this study supports the important role of TMAO for the environmental adaptability of hadal amphipods and speculates on the molecular evolution and protein structure of FMO3 in hadal species.
... The hadal zone is the deepest area extending from 6,000 to 11,000 m depth from the ocean surface. It breaks the continuity of the abyssal plains and forms long but narrow topographic V-shaped ultra-deep habitats that occupy more than 45% of the total vertical depth of the marine environment (Lauro and Bartlett, 2008;Jamieson et al., 2009;Jamieson, 2015). In general, the hadal zone is an extreme environment characterized by low temperature, poor food resources, and high hydrostatic pressure (Bartlett, 1992). ...
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Hadal trenches are the deepest known areas of the ocean. Amphipods are considered to be the dominant scavengers in the hadal food webs. The studies on the structure and function of the hadal intestinal microbiotas are largely lacking. Here, the intestinal microbiotas of three hadal amphipods, Hirondellea gigas, Scopelocheirus schellenbergi, and Alicella gigantea, from Mariana Trench, Marceau Trench, and New Britain Trench, respectively, were investigated. The taxonomic analysis identified 358 microbial genera commonly shared within the three amphipods. Different amphipod species possessed their own characteristic dominant microbial component, Psychromonas in H. gigas and Candidatus Hepatoplasma in A. gigantea and S. schellenbergi. Functional composition analysis showed that “Carbohydrate Metabolism,” “Lipid Metabolism,” “Cell Motility,” “Replication and Repair,” and “Membrane Transport” were among the most represented Gene Ontology (GO) Categories in the gut microbiotas. To test the possible functions of “Bacterial Chemotaxis” within the “Cell Motility” category, the methyl-accepting chemotaxis protein (MCP) gene involved in the “Bacterial Chemotaxis” pathway was obtained and used for swarming motility assays. Results showed that bacteria transformed with the gut bacterial MCP gene showed significantly faster growths compared with the control group, suggesting MCP promoted the bacterial swimming capability and nutrient utilization ability. This result suggested that hadal gut microbes could promote their survival in poor nutrient conditions by enhancing chemotaxis and motility. In addition, large quantities of probiotic genera were detected in the hadal amphipod gut microbiotas, which indicated that those probiotics would be possible contributors for promoting the host’s growth and development, which could facilitate adaptation of hadal amphipods to the extreme environment.
... Prawns (Dendrobranchiata) and several families of caridean shrimps (Fig. 7.2C) (e.g., Alvinocarididae, Crangonidae, Glyphocrangonidae, Nematocarcinidae, Pandalidae, Bresiliidae (vents), and Hippolytidae) have penetrated the deep oceans. Moreover, some species range into the hadal zone, such as the benthesicymid prawn Benthesicymus crenatus and species of Acanthephyra (Caridea: Acanthephyridae) ( Jamieson et al. 2009). ...
The deep sea is the largest habitat on Earth, but it is the least accessible and comprehensible. This apparently harsh environment is inhabited by Crustacea of diverse evolutionary lineages that have, to various degrees, evolved uniquely specialized morphologies and lifestyles. Following a century of debate about the antiquity of the deep-sea fauna, studies of Crustacea reveal that the faunas of the deep and shallow oceans have been continuously and repeatedly exchanged, probably since the Mid-Paleozoic. Deep-sea colonization and subsequent diversification has occurred across many crustacean lineages, during several periods, and may still be underway. Despite a commonly held view that shallow–deep phylogenetic relationships are unidirectional, there is also evidence for evolutionary emergence from the abyss into shallower zones. As a result, the present-day fauna represents an amalgamation of clades of various ages. Environmental factors such as pressure, temperature, and energy supply differ substantially between shallow- and deep-water layers, creating gradients that pose important ramifications for crustacean physiology. Consequently, depth-range expansions require adaptations, which may lead to peculiar phenomena such as gigantism and dwarfism, as well as diverse crustacean radiations.
... A number of other anomurans occur down to abyssal depths, including king crabs (Lithodidae) and parapagurid hermit crabs (Wilson and Ahyong 2015). Decapods were long considered to be absent from the hadal zone, but a few species have been reported, the first being a spider crab Teratomaia collected from the Kermadec Trench by the Galathea expedition in the 1950s (Wilson and Ahyong 2015), and more recently, prawns of the dendrobranchiate genera Benthesicymus and Plesiopenaeus (as Cerataspis) have been observed down to 7,703 m ( Jamieson et al. 2009). These hadal species are more commonly observed on the abyssal plains and bathyal slopes, thus they are not endemic to the hadal zone but at the deeper limit of their habitat. ...
Crustaceans occur from the shelf to hadal depths, but the immense environmental change that occurs along this depth gradient results in significant faunal change. One well-established pattern is the dramatic decline in biomass with depth, a result of an exponential decline in food availability. Average body size becomes smaller, despite observations of deep-sea gigantism in some crustaceans. Crustacean species tend to occupy a limited depth range, resulting in high faunal turnover. The depths of the greatest faunal turnover vary widely throughout the oceans, and there do not appear to be distinct bathymetric “zones” at ocean-wide scales. Molecular research at the species level confirms that small bathymetric changes are often more significant at promoting population differentiation than geographic distance. Observation of crustaceans in the laboratory demonstrates that the interaction between pressure and temperature is likely to act together in limiting the bathymetric range of many species. Debate continues around species richness and diversity gradients, and it remains unclear whether there are more crustacean species on the shelf compared to bathyal depths. Diversity patterns vary between taxa. Decapods are species rich on the shelf and upper slope and less so in the abyss. Isopods show high bathyal diversity, although this pattern varies between regions. For other crustaceans, it is difficult to make generalizations on diversity gradients as there are fewer studies, and results vary depending on geographic region and the method used to estimate diversity and richness. In cumaceans, amphipods. and harpacticoids, species richness is often highest on the shelf, while maximum species diversity occurs in deeper water. Food availability and temperature are good correlates for depth-diversity gradients.
... They are in fact small, translucent pink, quirky little fish that swim like tad-poles and would not look out of place in a sunlit lagoon. Similarly, if we look at the deepest of the big crustaceans, the penaeid prawns (Benthesicymus crenatus), there is nothing too unfamiliar about them either (Jamieson et al., 2009). They can be up to 25 cm long, strikingly red in colour and swim and behave in exactly the way one would expect a prawn to swim and behave in our coastal regions. ...
A recurring question within deep-sea science and conservation is why do not people care about the deep sea? How does the deep-sea science community convince non-scientific audiences to support, engage, and care more for the largest habitat on Earth? Here, we examine various aspects of an apparent dichotomy of perspectives between the scientific and non-scientific communities by discussing the problematic roots from within human neuropsychology, and how knowledge of the deep sea is delivered to, perceived by, and ultimately valued by non-scientific audiences. The answers are complex, covering issues such as conscious and subconscious thalassophobia, perspectivism, aesthetics, phenomenology, abstract interpretation, epistemology and media-driven enigmatization, self-deprecation by the science community, and perceived value-driven ethics. This discussion focusses on the nexus of scientific and non-scientific perceptions to catalyze meaningful societal engagement with the deep sea and to try and understand “Why do not people care about the deep sea?”
... Members of this subphylum can be found from deep seas (e.g. benthesicymid prawns (Benthesicymus crenatus) (Jamieson et al., 2009)) to alpine peaks (e.g. freshwater copepods (Manca et al., 1994)) illustrating remarkable adaptability. ...
An understanding of the mechanisms and functions of animal migratory behaviour may provide insights into its evolution. Furthermore, knowledge about migration may be important for conservation of rare species and may help to manage species in a rapidly changing world. Upstream migration is common in riverine animals, but little is known about proximate cues and functions of the upstream migration in aquatic macroinvertebrates. In Ubon Ratchathani, Thailand, locals have observed a synchronous mass migration of freshwater shrimps on land. This so‐called ‘parading behaviour' occurs annually during the rainy season and has become a large ecotourism event. Yet, we know little about the natural history, proximate causation and function of this extraordinary behaviour. Here we describe the natural history of parading behaviour and report the results from a series of experiments and observations to address its mechanisms and functions. Parading behaviour is not associated with breeding and spawning; rather, shrimps leave the water to escape strong currents. Conditions promoting shrimps to leave the water include low light, high water velocity and low air temperature. In addition, there is variation explained the specific location. River topology that creates hydrological variability and turbulence plays a role in triggering the shrimps to move out of water. Furthermore, turbidity and water chemistry were associated with shrimp activity. Finally, our results support that parading behaviour in freshwater shrimps is a mass movement upstream due to hydrological displacement. This study highlights the mechanisms that stimulate parading behaviour; a common activity in Macrobrachium and other decapod crustaceans.
The diversity of bait-attending fishes at lower abyssal and upper hadal depths was assessed using baited cameras in 14 subduction trenches, three fracture zones and two holes, spanning all five oceans. A total of 184 lander deployments from depths >5000 m (plus some additional observation from a submersible) were analysed to resolve the bathymetric extent of fishes and variations between locations. The most common families were the Macrouridae (grenadiers), Ophidiidae (cusk eels) and the Liparidae (snailfishes). Other less common families such as the Zoarcidae (eel pouts), Synphobranchidae (cut-throat eels) are reported, and the Stephanoberycidae (pricklefishes), and Ateleopodidae (jellynoses) were observed for the first time at hadal depths. While acknowledging many cryptic species and difficulty in identifying some groups from video, this study more than doubles the number of species and records of fishes at hadal depths and serves as an updated and illustrated collation of deepest fish records. We also discuss putative influences of temperature and oxygen on the depth range within the liparidae family, of which we found nine new species at hadal depths.
Full-text available
We deployed 2 porpoise (Phocoena phocoena) carcasses at bathyal depth (2555 to 27 10 m) in the Porcupine Seabight, NE Atlantic for periods of 1 wk and 6 mo respectively. Consumption rates of 0.085 and 0.078 kg h(-1) were similar to those observed at abyssal depths in the Atlantic, and 1 order of magnitude slower than at bathyal depth in the Pacific. A distinct succession of scavenging species was observed at both carcasses: the abyssal grenadier Coryphaenoides armatus and the cusk eel Spectrunculus grandis numerically dominated the initial phase of carcass consumption and, once the bulk of the soft tissue had been removed (by Day 15), were succeeded by the squat lobster Munidopsis crassa. The blue hake Antimora rostrata and amphipod numbers were unexpectedly low, and consumption was attributed largely to direct feeding by C. armatus. The interaction of a crustacean prey species (M crassa) and cephalopod predator (Benthoctopus sp.) was observed for the first time, revealing that large food falls also attract secondary predators that do not utilise the food fall directly. The staying time of a single parasitised C, armatus (18 h) greatly exceeded previous estimates (<= 8 h). This study describes the first large food fall to be monitored at high frequency over a 6 mo period, and the first observations of a large food fall at bathyal depth in the NE Atlantic. It enables direct comparison with similarly sized food falls at abyssal depth, much larger megacarrion falls, and similar studies differing in geographic location, in particular those carried out under Pacific whale migration corridors.
Deep-sea shrimps belonging to the genus Benthesicymus were collected on 6 cruises from deep water in the western North Pacific, from 141°35.0′E to 158°06.5′E and from 20°48.1′N to 39°51.0′N. Fifty-two specimens representing 8 species, including 5 new records from the area and 1 new species were identified. Benthesicymus crenatus, B. urinator, B. strabus, B. longipes, B. carinatus, B. altus, B. investigatoris, and one new species, Benthsicymus brevirostris, are described. Keys are presented for the identification of these species. Vertical distributions of these rare species are also noted.
We explore hypotheses that alternate foraging strategies, diet, or nutrient partitioning could help explain the success of scavenging Lysianassoids (Amphipoda) in hadal oligotrophic trenches (depths of 6-11 km) by examining the nutritional strategies of four lysianassoid species (Eurythenes gryllus, Scopelocheirus schellenbergi, Hirondellea dubia, and Uristes sp. nov.) collected with baited traps (6.3-10.8 km) from the oligotrophic Tonga and Kermadec Trenches (southwest Pacific Ocean). Diets and foraging strategies were examined by use of (1) the nascent DNA-based analysis of hindgut contents, which provides a 'snapshot' of recently ingested organisms, and (2) natural abundance isotopic signatures, which reflect the source of nutrition and relative trophic position. The scavenging guild exhibits remarkable trophic plasticity, and each amphipod species employs alternate foraging modes, including detrivory or predation, to supplement necrophagy. The nutritional strategies of some species appear to shift with age, depth, and even between trenches. Thus, there is no single ubiquitous hadal food web; rather it is influenced by depth and overlying surface productivity. Isotopic data suggest that coexisting species partition the dietary items, providing evidence of competition among members of the scavenging guild. The extreme foraging flexibility of scavenging amphipods may ultimately contribute to their success in severely food-limited hadal ecosystems.
At depths exceeding 6000 m a gradual change in the composition of animal life takes place, resulting in a distinct hadal or ultra-abyssal fauna at the greatest ocean depths. This change is primarily caused by increased hydrostatic pressure, but probably also by favourable feeding conditions in the deep-sea trenches. Menzies and George (1967) questioned the existence of a specific hadal fauna, but based their main argument on results obtained at a maximum depth of 6200 m, which is not a typical hadal environment.
A conversion formula between pressure and depth is obtained employing the recently adopted equation of state for seawater (Millero et al., 1980). Assuming the ocean of uniform salinity 35 NSU and temperature 0°C the following equation is proposed, namely, z = (1-c1)p − c2p2. If p is in decibars and z in meters c1 = (5.92 + 5.25 sin2ϕ) × 10−3, where ϕ is latitude and c2 = 2.21 × 10−6. To take account of the physical conditions in the water column a dynamic height correction is to be added but for many purposes this may be ignored.
Benthopelagic nekton were sampled by trawl and baited trap arrays at two abyssal stations (WAST and CAST) in the northern Arabian Sea. The natantian decapod Plesiopenaeus armatus and fishes comprised most of the nekton caught by the trawls, whereas the amphipod Eurythenes gryllus dominated in the trap samples. At station WAST, Plesiopenaeus armatus made up 80% of the benthopelagic nekton in terms of biomass, fishes contributing 20%. This relationship was reversed at station CAST. The fishes caught belonged to 13 species in five families. Ophidiidae dominated in terms of abundance, followed by Synodontidae and Ipnopidae. Zoarcidae and Alepocephalidae were scarce, and no Macrouridae were caught. Synodontidae dominated in terms of biomass. Most fish were rather small, rarely exceeding a length of 40cm. The amphipod Eurythenes gryllus was largely restricted to the traps lying directly at the bottom. A total of only five specimens were captured in pelagic traps from 8 to 500m above bottom. The predominance of ophidiids and ipnopids, the small mean fish size, and the high standing stocks of natantian decapods suggest that the structure of the Arabian Sea benthopelagic nekton resembles that at abyssal depths in the tropical Atlantic and may be typical for the deep-sea at low latitudes.