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Salp-falls in the Tasman Sea: A major food input to deep-sea benthos

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Large, fast-sinking carcasses (food-falls) are an important source of nutrition to deep-sea benthic communities. In 2007 and 2009, mass depositions of the salp Thetys vagina were observed on the Tasman Sea floor between 200 and 2500 m depth, where benthic crustaceans were observed feeding on them. Analysis of a long-term (1981 to 2011) trawl survey database determined that salp biomass (wet weight, WW) in the eastern Tasman Sea regularly exceeds 100 t km(-3) yr(-1), with biomasses as high as 734 t km(-3) recorded in a single trawl. With fast sinking rates, salp fluxes to the seafloor occur year-round. Salps, like jellyfish, have been considered to be of low nutritional value; however, biochemical analyses revealed that T. vagina has a carbon (31% dry weight, DW) and energy (11.00 kJ g(-1) DW) content more similar to that of phytoplankton blooms, copepods and fish than to that of jellyfish, with which they are often grouped. The deposition of the mean yearly biomass (4.81 t km(-2) WW) of salps recorded from the trawl database in the Tasman Sea represents a 330% increase to the carbon input normally estimated for this region. Given their abundance, rapid export to the seabed and high nutritional value, salp carcasses are likely to be a significant input of carbon to benthic food webs, which, until now, has been largely overlooked.
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MARINE ECOLOGY PROGRESS SERIES
Mar Ecol Prog Ser
Vol. 49 1: 165 –175, 2013
doi: 10.3354/meps10450 Published October 2
INTRODUCTION
Food-limited deep-sea benthic ecosystems rely on
depositions of organic matter from the euphotic zone
(Gooday 2002). Concentrated pulses of particulate
organic matter (POM) derived from differing sources
including phytoplankton blooms, other plant or algal
matter, zooplankton faecal pellets and carcasses of
larger fauna are major contributors of organic matter
to the sea floor (Rowe & Staresinic 1979, Smith et al.
2008). Despite the majority of particles being small
(<5 mm) (Alldredge & Silver 1988), these pulses are
© Inter-Research 2013 · www.int-res.com*Email: n.henschke@unsw.edu.au
Salp-falls in the Tasman Sea: a major food input to
deep-sea benthos
Natasha Henschke1,2,*, David A. Bowden3, Jason D. Everett1,2, 4, Sebastian P. Holmes5,6,
Rudy J. Kloser7, Raymond W. Lee8, Iain M. Suthers1,2
1Evolution and Ecology Research Centre, University of New South Wales, Sydney, New South Wales 2052, Australia
2Sydney Institute of Marine Science, Building 22, Chowder Bay Road, Mosman, New South Wales 2088, Australia
3National Institute of Water and Atmospheric Research Ltd. (NIWA), 301 Evans Bay Parade, Greta Point, Wellington 6021,
New Zealand
4Plant Functional Biology and Climate Change Cluster, Faculty of Science, University of Technology Sydney, PO Box 123
Broadway, New South Wales 2007, Australia
5School of Biological Sciences, University of Sydney, Sydney, New South Wales 2006, Australia
6Water & Wildlife Ecology Gr oup (WWEG), School of Science & Health, University of Western Sydney (UWS), Penrith,
New South Wales 1797, Australia
7Commonwealth Scientific and Industrial Research Organisation (CSIRO) Marine Laboratories, PO Box 1538, Hobart,
Tasmania 7001, Australia
8School of Biological Sciences, Washington State University, PO Box 644236, Pullman, Washington 99164-4236, USA
ABSTRACT: Large, fast-sinking carcasses (food-falls) are an important source of nutrition to deep-
sea benthic communities. In 2007 and 2009, mass depositions of the salp Thetys vagina were
observed on the Tasman Sea floor between 200 and 2500 m depth, where benthic crustaceans
were observed feeding on them. Analysis of a long-term (1981 to 2011) trawl survey database
determined that salp biomass (wet weight, WW) in the eastern Tasman Sea regularly exceeds
100 t km3yr1, with biomasses as high as 734 t km3recorded in a single trawl. With fast sinking
rates, salp fluxes to the seafloor occur year-round. Salps, like jellyfish, have been considered to be
of low nutritional value; however, biochemical analyses revealed that T. vagina has a carbon (31%
dry weight, DW) and energy (11.00 kJ g1DW) content more similar to that of phytoplankton
blooms, copepods and fish than to that of jellyfish, with which they are often grouped. The depo-
sition of the mean yearly biomass (4.81 t km2WW) of salps recorded from the trawl database in
the Tasman Sea represents a 330% increase to the carbon input normally estimated for this
region. Given their abundance, rapid export to the seabed and high nutritional value, salp car-
casses are likely to be a significant input of carbon to benthic food webs, which, until now, has
been largely overlooked.
KEY WORDS: Benthic communities · Gelatinous zooplankton · Carbon cycling · Fluxes · Salp-fall ·
Jelly-fall
Resale or republication not permitted without written consent of the publisher
Mar Ecol Prog Ser 491: 165–175, 2013
an important source of nutrition for deep-sea benthic
communities, promoting both species richness and
abundance (Butman et al. 1995). Benthic ecosystem
functions are also positively related to increasing
POM supply, including sediment community respira-
tion rates and organic matter remineralisation (Witte
& Pfannkuche 2000, Smith et al. 2008, Sweetman &
Witte 2008).
Large, fast-sinking particles, such as carcasses,
provide food-fall events that augment the nutritional
ecology of deep-sea benthic communities (Rowe &
Staresinic 1979, Stockton & DeLaca 1982, Smith &
Baco 2003). The ‘gelatinous pathway’ (Billett et al.
2006, Lebrato et al. 2012) was first discovered by
Moseley (1880) and illustrates the potential for sink-
ing carcasses of gelatinous organisms to contribute a
large flux of organic matter to the benthic environ-
ment. Because of their swarming nature, depositions
of gelatinous carcasses generally accumulate in high
densities to the benthic environment in areas under-
lying large and persistent gelatinous populations
(Billett et al. 2006, Lebrato & Jones 2009). For ex -
ample, following swarms in surface waters (Wiebe et
al. 1979, Grassle & Morse-Porteous 1987), dense con-
centrations of salp carcasses were observed nearby
on the seafloor in the outer Hudson Canyon (3240 m)
in 1975 and 1986 (Cacchione et al. 1978). Similarly,
pelagic cnidarian deposits (jelly-falls) have been re -
corded on the sea floor off Oman (Billett et al. 2006),
in the Sea of Japan (Yamamoto et al. 2008) and in a
Norwegian fjord (Sweetman & Chapman 2011), while
pyrosome carcasses have been observed on the
Madeira Abyssal Plain (Roe et al. 1990) and on the
seafloor off the Ivory Coast (Lebrato & Jones 2009).
During 2 benthic sampling research voyages, we
observed mass depositions of the large salp Thetys
vagina on the Tasman Sea floor, prompting an exam-
ination into their subsequent fate and the nutritional
value provided by the carcasses to the deep-sea ben-
thic communities. T. vagin a reaches up to 306 mm in
size (Nakamura & Yount 1958) and has a distribution
spanning the top 200 m (Thompson 1948, Iguchi &
Kidokoro 2006) of sub-tropical and temperate waters
of the Mediterranean Sea and the Atlantic, Indian
and Pacific oceans (Berrill 1950). Salp carcasses can
potentially sink at rates of up to 1700 m d1(Lebrato
et al. 2013), suggesting that little, if any, decomposi-
tion occurs during descent, and mass depositions of
salp carcasses may represent an important and sub-
stantial food-fall event for the benthic ecosystem.
Although several reports indicate that gelatinous
organisms such as salps are important to the diet of
some marine organisms (e.g. Duggins 1981, Clark et
al. 1989, Lyle & Smith 1997, Gili et al. 2006), they are
still generally thought to be of low nutritional value
(Moline et al. 2004). Therefore, to determine whether
salp carcasses can positively contribute to the ben-
thic ecosystem, it is necessary to identify the quality
of food they provide.
In particular, we sought to (1) assess the frequency
and abundance of salp swarms in the Tasman Sea
and eastern New Zealand over 30 yr, (2) quantify the
biomass and relative abundance of Thetys vagina
carcasses on the sea floor, and (3) compare the ener-
getic input and the biochemical composition of T.
vagina carcasses with other gelatinous zooplankton.
MATERIALS AND METHODS
Study region
Long-term trawl surveys and 2 benthic sampling
cruises were conducted in the southern Tasman Sea
and Pacific Ocean east of New Zealand (Fig. 1A). For
the first benthic study on board the RV ‘Tangaroa’ in
June 2007 (TAN0707), sampling was carried out on
the Challenger Plateau, a large submarine plateau
extending from the west coast of central New Zea -
land and considered to be a region of low pelagic
productivity (Wood 1991). In October 2009, on the
second benthic study on board the RV ‘Southern Sur-
veyor’ (SS03/2009), sampling occurred off southeast-
ern Australia in Bass Canyon, one of the largest sub-
marine canyons in the world (Mitchell et al. 2007).
Trawl data analysis
Trawl data were available from 2 sources: a long-
term data series (30 yr) from the New Zealand fish-
eries research trawl database and pelagic trawls in
the Tasman Sea over 3 yr. Salp and pyrosome bio-
mass was obtained from analysis of the New Zealand
fisheries database (stock assessment, research and
observer-monitored commercial trawls) from 1981 to
2011 (n = 2044; see Fig 1A for sampling locations). As
the majority of data was opportunistically sampled,
sampling periods within a year are variable but on
average include every month per year. Trawls (mid-
water or benthic) were towed at a mean depth of
563.17 ± 342.40 m, ranging from 33 to 2532 m. Where
possible, recorded trawl dimensions and tow lengths
were used. If details of trawl size or tow distance
were not available, a standard averaged value calcu-
lated from all trawls was used (headline height = 8 m,
166
Henschke et al.: Salp carcasses as food-fall
wing distance = 30 m, tow distance = 4.4 km, tow
speed = 6.5 km h1). Individuals were not classified
into species. Thetys vagina biomass was obtained
from 3 trans-Tasman cruises in 2008, 2009 and 2011
(n = 12). Depth-stratified midwater tows with a
pelagic trawl were made at 200 m intervals to a max-
imum depth of 1000 m from the surface, with equal
20 min tows at 6.5 km h1. The biomass estimates of
T. vagina from the trans-Tasman pelagic trawls were
calculated from the net area with the smallest mesh
size capable of capturing them (minimum 40 mm
mesh). Graded mesh area information was not avail-
able for the nets used in the New Zealand fisheries
database, and as a result, biomass estimates are more
conservative than data obtained from the trans-
Tasman pelagic trawls. All biomass estimates are
represented in wet weight (WW).
Benthic sample collection and analysis
At both benthic sampling locations, video surveys
were conducted using towed camera platforms with
video and still image cameras. All individual salps
observed on the seabed were counted along the full
length of each video transect. If necessary, still cam-
era images taken every 2 min along the transects
were used to aid in identification of individuals.
167
140°E 145° 150° 155° 160° 165° 170° 175° 180°
50°
45°
40°
35°
30°
S
Tasman Sea
Sydney
Hobart
Wellington
Auckland
Australia
New
Zealand
A
19812011 Salp and pyrosome trawls
20082011 T. vagina trawls
2007 Challenger Plateau T. vagina deposition
2009 Bass Canyon T. vagina deposition
166°E 168° 170° 172°
42°
40°
38°
36°
S
New
Zealand
Salps per 1000m
2
No count
1
10
100
200
1000
1000
1000
600
600
600
00
2000
2000
C
147°E 148° 149° 150°
39°
38.5°
38°
S
Australia
Salps per 1000m
2
50
250
500
200
1000
2000
B
Fig. 1. (A) Survey area in the southern Tasman Sea and southwestern Pacific Ocean east of New Zealand showing trawl sta-
tions and benthic sampling stations. (B,C) Density distribution based on video footage/camera stills of Thetys vagina (ind. 1000
m2) at different stations (B) in Bass Canyon and (C) on the Challenger Plateau. Depth contours are displayed in metres
Mar Ecol Prog Ser 491: 165–175, 2013
Deployments lasted from 30 to 60 min, at speeds of
0.25 to 0.50 ms1. On the Challenger Plateau, 46
deployments of the Deep Towed Imaging System
(Hill 2009) were conducted at depths ranging from
237 to 1831 m. Both video and still cameras were
oriented directly downwards, to facilitate scaling,
and video frame width was calculated in ImageJ
(http://rsbweb.nih.gov/ij/) by measuring widths of
approximately 100 frame grabs using the camera’s
paired lasers (20 cm apart) as a reference. In Bass
Canyon, the Benthic Optical and Acoustic Grab Sys-
tem (Sherlock et al. 2010) was deployed at 3 depths:
450, 650 and 1500 m. As the camera system did not
have paired lasers, video frame width was measured
by using the average (± SD) length of Thetys vagina
species caught from the subsequent Bass Canyon
trawls (55.66 ± 5.90 mm, n = 30) to approximate frame
size from 17 randomly chosen screenshots containing
T. vagi na. Abundance of individuals per 1000 m2
(ind. 1000 m2) was calculated by determining salps
per corrected area of deployments (corrected area =
transect seabed area × percentage of usable video
footage). Video analyses were run in Ocean Floor Ob -
servation Protocol (http://ofop.texel.com); see methods
in Bowden et al. (2011). Still image analyses used
ImageJ software.
After each towed camera transect, benthic fauna
were sampled at the same site using either a beam
trawl (4 m mouth width, 10 mm mesh) or an epiben-
thic sled (1 m mouth width, 25 mm mesh). Trawls
were towed for approximately 15 min at 0.75 m s1.
Once back on deck, all fauna were sorted into species,
weighed for biomass estimates and frozen (20°C).
Salps were thawed, and total length and wet weight
were measured for each individual. Guts were
removed prior to biochemical analysis to ensure that
only body tissue was analysed. Randomly selected
individuals from each site were then freeze-dried
and their dry weights (DW) recorded. To determine
ash-free dry weight (AFDW) of the specimens, tissue
samples were taken and combusted at 550°C for 24 h.
All remaining tissue was ground in a ball mill to give
a homogenous powder for biochemical analyses.
Biochemical analyses
Protein content of the salps was measured using
the Bradford protein assay (Bradford 1976) with
bovine serum albumin as the standard. Lipid content
of the salps was estimated using a chloroform:
methanol procedure after Folch et al. (1957) and car-
bohydrate content was estimated following Dubois et
al. (1956) with D-glucose as the standard. Energetic
values of the salps were determined with a Parr
6200 isoperibol calorimeter using a benzoic acid stan -
dard and as per the manufacturer’s instructions (Parr
Instrument Company 2008).
Carbon and nitrogen contents were measured by
combusting the material and using gas chromatogra-
phy to separate the resulting N2and CO2gases. The
gases were then analysed with an Isoprime isotope
ratio mass spectrometer to give total carbon and
nitrogen content. An average of the carbon content
(n = 68, 31.35% DW) per salp for both locations was
used to calculate carbon standing stock (mg C m2)
from the carcasses observed. All salps viewed in the
video transects were assumed to have a DW of 0.38 g
(the mean of n = 27 weighed individuals), allowing
carbon standing stock to be calculated per square
metre. While this is an approximation, we are confi-
dent that all carcasses seen in the video and captured
in benthic gear were of similar size.
RESULTS
Observations of Thetys vagina on the sea floor
Carcasses of Thetys vagina were observed in all 3
video transects in Bass Canyon and in 38 out of 46
transects on the Challenger Plateau (Fig. 2A). In
total, 368 carcasses were recorded in Bass Canyon
comprising 47.8% of the total observed fauna over an
area of 2118 m2. The mean (± SD) density of T. vagina
was 219 ± 168 ind. 1000 m2, with a minimum density
of 85 and a maximum of 408 ind. 1000 m2(Fig. 1B).
On the Challenger Plateau, 1400 individuals were
observed, making up 9.8 % of total observed fauna
over an area of 72995 m2. In 11 transects where
abundances of T. vagi na were high (>20 ind. 1000 m2,
Fig. 1B), T. vagina carcasses ranged from 19.6 to
48.7% of the total fauna observed, similar to that
found in Bass Canyon. The mean (± SD) density of T.
vagina on the Challenger Plateau was 26 ± 39 ind.
1000 m2, significantly lower than densities found in
Bass Canyon (p < 0.001, F1,48 = 40.1, ANOVA), with a
minimum density of 0 and a maximum of 202 ind.
1000 m2(Fig. 1C). T. vagi na comprised 19.0% of
total haul biomass on the Challenger Plateau and
42.6% of total haul biomass in Bass Canyon and was
the dominant organism in both locations (see Appen-
dix 1). During one transect on the Challenger Pla -
teau, the deep-water spider crab Platymaia maoria
was twice observed directly feeding on T. vag ina car-
casses (Fig. 2B; Table 1). On 17 occasions across 9
168
Henschke et al.: Salp carcasses as food-fall
transects, demersal fish and sea stars were recorded
near the carcasses (Table 1). The most common dem-
ersal fish were rattails Coelorinchus spp. and were
found close to the carcasses on 10 occasions. At both
locations, all T. vagina individuals observed on the
sea floor were dead, whole and with no visible bacte-
rial mats or biofilms.
Abundance of Thetys vagina and other large salps
and pyrosomes in the Tasman Sea
Analysis of the New Zealand fisheries database from
1981 to 2011 determined that salp and pyrosome bio-
mass exceeded 100 t km3WW (56 t km2) in approx-
imately half of the years sampled (Fig. 3A). Biomass
ranged from 0.006 t km3WW (0.003 t km2) to 1464 t
km3WW (824 t km2), with a 30 yr average (± SD) of
8.54 ± 51.79 t km3WW (4.81 t km2). Salps and pyro-
somes were present year-round but appear to form
dense swarms an order of magnitude greater than
their normal occurrence between December and
June (Fig. 3B).
High densities of Thetys vagina were captured in 3
trans-Tasman cruises in 2008, 2009 and 2011 (Fig.
3A), with a maximum of 734 t km3WW (147 t km2)
caught in 2009 (minimum = 0.003 t km3WW, mean
SD) = 44.82 ± 158.20 t km3WW). Depth-stratified
sampling showed that 98% of T. va gina biomass
occurred in the top 200 m of the water column.
Biochemical composition of Thetys vagina
Lipids accounted for the highest proportion of
macronutrients, making up a mean SD) of 10.5 ±
2.8% DW (Table 2). Protein constituted 3.4 ± 1.5 %
DW, and carbohydrates constituted 4.4 ± 1.9%. The
mean (± SD) energetic content of Thetys vagina was
11.0 ± 1.4 kJ g1DW. AFDW was high, ranging from
33 to 88% DW, and total organic content of T. vagina
represented only 31% of AFDW.
Mean (± SD) carbon content for Thetys vagina
(31.4 ± 5.4% DW) was much higher than nitrogen
content (2.8 ± 1.1% DW; Table 2). Carbon standing
stock of the T. v agina deposition in Bass Canyon was
26.1 mg C m2. On the Challenger Plateau, carbon
standing stock was lower, with a mean of 3.1 mg C m2
169
Fig. 2. Sea floor photographs from the Tasman Sea. Scale
bars = 10 cm. (A) Thetys vagina carcasses at 1565 m depth
taken in Bass Canyon. (B) Platymaia maora feeding on
T. vagi na carcass at 482 m on the Challenger Plateau
No. of events
Crustacea
Platymaia maoria 2a
Fish
Coelorinchus sp.b10
Paraulopus sp. 1
Trip terophy cis g ilchr isti 1
Helicolenus sp.c1
Hoplichthys haswelli 1
Hydrolagus novaezelandiaed1
Echinodermata
Ophiuroidea 2
Asteroideae1
aDirect feeding observed; bClark (1985); cBax & Williams
(2000); dDunn et al. (2010); eDomanski (1984)
Table 1. Megafaunal taxa observed directly feeding on or
close to (potential feeders) Thetys vagina carcasses on the
Challenger Plateau. Footnotes b to e denote previous records
of taxa feeding on salps
Mar Ecol Prog Ser 491: 165–175, 2013
but reaching 24.1 mg C m2at some stations. Using
C:N ratio and energetic content as an indicator of nu-
tritional quality, T. vagi na is nutritionally similar
to phytoplankton (Fig. 4). Values for T. vagina are
much greater than reported values for cnidarians and
ctenophores.
DISCUSSION
Observations of Thetys vagina on the sea floor
Densities of Thetys vagina carcasses observed on
the sea floor in this study are among the highest
recorded for any gelatinous zooplankton deposition.
These mean densities of T. va gina (26 and
219 ind. 1000 m2for the Challenger Plateau
and Bass Canyon, respectively) are much
greater than those found for depositions of
the giant jellyfish Nemo pi lema nomurai in
the sea of Japan (1.1 ind. 1000 m2)
(Yamamoto et al. 2008) and the deep-sea
scyphozoan Periphylla periphylla in a Nor-
wegian fjord (10 ind. 1000 m2) (Sweetman &
Chapman 2011). Densities were similar to
those of Pyrosoma atlanticum carcas ses off
the Ivory Coast (70.6 ind. 1000 m2) described by
Lebrato & Jones (2009). The mass depositions of fresh
carcasses observed in this study indicate the recent
demise of swarms at both locations. On the Chal-
lenger Plateau, high densities of T. v agina were
observed at the surface during sampling, suggesting
that the swarm may still have been developing for
several weeks after sampling. Sampling during an
ongoing swarm may limit the accuracy of the deposi-
tion densities, as some salp and pyrosome species are
known to migrate to sea floor depths (Roe et al. 1990,
Gili et al. 2006). As T. vagina mainly occurs in the top
200 m of the water column and all carcasses viewed
on the video were dead or moribund, it is unlikely
that deposition abundances were overstated.
170
Salps and pyrosomes Thetys vagina
1000
211
100
221
Biomass (t km
-3
WW) Biomass (t km
-3
WW)
A
10000
54 152 54 12
100
10
1
0.1
1981 1983 1985 1987 1989 1991 1993 1995 1997 1999 2001 2003 2005 2007 2009 2011
B
1000
184 110
98
130 113 11 2 285
10
133 196 251
1
0.1
22 26 98 63 60 69 208 109
52 64
18
9
73182
9 10 57 347
6
1
2
61
50 30
4
6
1
Jan
Feb
Mar
Apr
May
Jun
Jul
Aug
Sep
Oct
Nov
Dec
Fig. 3. (A) Maximum yearly biomass for salps and pyrosomes (dark grey bars; New Zealand fisheries database) from 1981 to
2011 and Thetys vagina (white bars; trans-Tasman pelagic trawls) in 2008, 2009 and 2011. Yearly mean (+ SD) is represented
by the solid line. Number of trawls per year is indicated above each bar. Station locations are presented in Fig. 1. (B) Mean
(+SD) monthly biomass of salps and pyrosomes from 1981 to 2011. Number of trawls per month is indicated above each bar.
WW = wet weight
n Mean ± SD Range
Protein content (% DW) 68 3.42 ± 1.46 1.107.34
Lipid content (% DW) 31 10.50 ± 2.77 6.1916.48
Carbohydrate content (% DW) 18 4.36 ± 1.92 1.347.77
Energetic content (kJ g1DW) 9 11.00 ± 1.38 8.9113.33
Carbon content (% DW) 68 31.35 ± 5.34 18.7742.68
Nitrogen content (% DW) 68 2.82 ± 1.13 1.528.09
C:N 68 12.03 ± 3.03 4.7319.05
Table 2. Thetys vagina. Biochemical and elemental composition. n =
number of individuals measured
Henschke et al.: Salp carcasses as food-fall
Abundance of Thetys vagina and other large salps
in the Tasman Sea
Other large salps such as Salpa thompsoni (Nishi -
kawa et al. 1995, Perissinotto & Pakhomov 1998) and
S. aspera (Wiebe et al. 1979, Madin et al. 2006) fre-
quently form large swarms, but records of Thetys
vagina are sparse. The largest swarm recorded of T.
vagina occurred in 2004 in the Sea of Japan, with
biomasses as high as 900 t km3WW (Iguchi &
Kidokoro 2006), comparable to the maximum of 734 t
km3WW recorded in this study. As New Zealand
fisheries surveys were designed for the capture of
large pelagic and demersal fish, they are likely to
under-represent the true abundances of salps. Trawls
would only spend approximately 35% of their time in
the 0 to 200 m depth range that is preferred by the
majority of large salps in the Tasman Sea (Thompson
1948). Regardless, abundances of salps across the
30 yr dataset indicate that salp biomass in the Tas-
man Sea often exceeded 100 t km3WW, which is
considerably higher than previously thought.
Tranter (1962) recorded an average zooplankton
biomass (excluding salps) of 36 t km3WW from 1959
to 1961 in the Tasman Sea, with salps accounting for
an additional 53 t km3WW. Maximum swarm values
from the present study show that large salp and pyro-
some swarms in the Tasman Sea can frequently
exceed zooplankton biomass by 300%. Similarly,
Young et al. (1996) sampled zooplankton in the Tas-
man Sea from 1992 to 1994 and found salps on aver-
age made up 30% of zooplankton biomass across the
3 yr and at some times up to 90%. To put salp bio-
mass into perspective, hoki Macru ronus nova -
ezealandiae constitutes New Zealand’s largest fish-
ery (O’Driscoll 2004), with biomass estimated to be
1.2 t km2WW (based on an 8 yr average) and repre-
senting 97% of all fish biomass in the midwater
depth range (Bull et al. 2001). The mean 30 yr
average of large salp biomass (4.81 t km2WW) for
the Tasman Sea and New Zealand region not only
exceeds this value but also indicates the prevalence
of salp swarms in the Tasman Sea.
Biochemical composition of large salps
This study provides the first data on the biochemi-
cal composition of Thetys vagina. Results obtained
are within expected ranges observed for other large
salps (Madin et al. 1981, Clarke et al. 1992, Dubis-
char et al. 2006). Similar to our salps, higher propor-
tions of lipids to protein are found in the Antarctic
species Salpa thompsoni (5.7 to 6.8% DW) (Dubis-
char et al. 2006), while the opposite trend is observed
for North Atlantic salp species: 0.96, 0.25 and 0.97%
DW for Pegea confoderata, S. cylindrica and S. max-
ima, respectively (Madin et al. 1981). Differences in
the biochemical composition of salp species are likely
to arise from either differing lipid concentrations
within food sources (Larson & Harbison 1989) or en -
vironmental conditions inciting higher storage of
lipids in cooler waters (Dubischar et al. 2006). Previ-
ous studies show that carbohydrate contents for salps
are generally low (0.8 to 1.3% DW) (Madin et al.
1981, Clarke et al. 1992, Dubischar et al. 2006); how-
ever, this study recorded levels similar to those of
protein. These higher values are consistent with ex -
pected results, as the salp tunic is mainly comprised of
proteins and polysaccharides (Godeaux 1965).
Although the total organic content (lipids, proteins
and carbohydrates) of an organism should equal its
AFDW (Madin et al. 1981), high values of AFDW are
characteristic for gelatinous zooplankton because of
difficulties in removing ‘water of hydration’ (Madin
et al. 1981) when freeze-drying. Similar AFDW val-
ues have been found for other salps: 27 to 62.7% DW
for Salpa thompsoni (Huntley et al. 1989, Donnelly et
al. 1994) and 66.4% DW for S. fusiformis (Clarke et
al. 1992), with total organic contents ranging from 19
to 51% of AFDW (Madin et al. 1981, Dubischar et al.
171
Fig. 4. Relationship between mean (± SD) energetic content
and mean (±SD) C:N ratio as an indicator of quality of differ-
ent marine organisms as a food item. Values for Thetys
vagina obtained from this study. Other values obtained from
previous studies: phytoplankton (Platt & Irwin 1973), cope-
pods (Donnelly et al. 1994, Ikeda et al. 2006), cnidarians
and ctenophores (Clarke et al. 1992) and fish (Childress &
Nygaard 1973). DW = dry weight
Mar Ecol Prog Ser 491: 165–175, 2013
2006). Apart from residual water, the most likely
causes for the ‘missing’ compounds are those missed
by the methodology. For example, as the nitrogen
content of protein can be assumed to be 16% (protein
= N × 6.25) (Madin et al. 1981), from the nitrogen
values recorded here, protein content should have
been as high as 17.6% DW, 4 times higher than our
detected values. Similar problems detecting proteins
in gelatinous zooplankton have been seen in previ-
ous studies (Clarke et al. 1992, Dubischar et al. 2006)
and are thought to arise from problems with detect-
ing cross-linked proteins.
Contribution to the benthic food web
Energetic content of Thetys vagina was higher than
that of cnidarians and ctenophores (4.35 to 10.17 kJ
g1DW) (Percy & Fife 1981) and other pelagic tuni-
cates such as Pyrosoma atlanticum (4.94 ± 1.55 kJ g1
DW) (Davenport & Balazs 1991) and almost as high
as some crustacean species (14.77 ± 1.67 kJ g1DW)
(Wacasey & Atkinson 1987). Of all gelatinous zoo-
plankton studied to date, carbon content for T. va -
gina was second only to P. at lan tic um (Davenport &
Balazs 1991, Lebrato & Jones 2009). The energetic
content and C:N ratios suggest that T. vagin a car-
casses have higher food value than other gelatinous
zooplankton (cnidarians and ctenophores) (Fig. 4)
and nutritionally are more similar to the phytoplank-
ton blooms that normally sustain benthic communi-
ties (Rowe & Staresinic 1979, Smith et al. 2008) as
well as fish and copepods. As only the tunic of T.
vagina was analysed, nutritional quality has not been
elevated by gut contents. Compared to smaller salps,
the tunic of T. vagin a is relatively thick and com-
posed of densely packed fibrous material (Hirose et
al. 1999), possibly resulting in elevated nutritional
values. Based on maximum salp biomass values of
100 t km3WW, these deposition events can poten-
tially export up to 616 GJ km2of energy, or 16 t km2
of carbon, to the Tasman Sea benthos every year.
Several fish species feed exclusively on salps or
have salps as a major component of their diets. These
species tend to be opportunistic bentho-pelagic feed-
ers, such as the black oreo Allocyttus niger, smooth
oreo Pseudocyttus maculatus, spiky oreo Neocyttus
rhomboidalis, carinate rattail Macrourus carinatus
and small-scaled brown slickhead Alepocephalus
australis (Clark et al. 1989, Lyle & Smith 1997). Our
results suggest that the salp carasses often found in
these fish guts may result from scavenging at the
seafloor. Apart from fish, other benthic feeders
including sea stars (Domanski 1984), sea urchins
(Duggins 1981), octocorallians (Gili et al. 2006),
mushroom corals (Hoeksema & Waheed 2012) and,
from this study, the deep-water spider crab Platymaia
maora have been observed feeding on salps. Simi-
larly, pyrosome carcasses have provided food for a
range of megafauna including crustaceans, arthro-
pods, anemones and echinoderms (Roe et al. 1990,
Lebrato & Jones 2009), while anemones, shrimp,
crabs and molluscs have been observed near and
feeding on cnidarian carcasses (Yamamoto et al. 2008,
Sweetman & Chapman 2011). As salp carcasses can
sink at rates up to 1700 m d1(Lebrato et al. 2013),
they will be able to reach the seafloor in less than 2 to
3 d, before significant bacterial degradation can take
place. Preliminary experimental data suggest that at
seafloor temperatures (4°C), Thetys vagina indivi -
duals will retain 68% of their mass after 28 d (N.
Henschke unpubl. data). These results are slower
than a model-calculated decomposition time of
approximately 20 d for a gelatinous organism, which
in cludes more labile cnidarians (Lebrato et al. 2011).
As no bacterial mats or biofilms were observed on
any of the T. vagi na individuals viewed or collected
in this study, slow decomposition rates of T. vagina
would allow carcasses to remain on the sea floor until
scavenged or eventually remineralised via the micro-
bial loop.
Potential carbon standing stock
Studies in the world’s oceans (Smith & Kaufmann
1999), including the Pacific Ocean near New Zealand
(Nodder et al. 2003), have identified that food de -
mand in the benthic community (sediment commu-
nity oxygen consumption) often exceeds food supply
(POM). Salp carcasses are not detected by traditional
methods of sampling water column nutrient fluxes,
such as sediment traps (Lebrato & Jones 2009), and
consequently are not included in current carbon
budget calculations, resulting in a considerable
under estimation of the total flux. Hence, salp car-
casses may be supplementing the smaller POM that
can be collected by sediment traps, providing an
extra source of nutrition for the benthic community.
Since particles that generally make up the majority of
measured carbon flux in the Tasman Sea are <1 mm
(Kawahata & Ohta 2000), these salp deposition
events provide a substantial contribution of much
larger carbon parcels to the benthos. As swarms of
Thetys vagina were still in surface waters during
sampling on the Challenger Plateau, by the time the
172
Henschke et al.: Salp carcasses as food-fall 173
entire population had collapsed, the input from both
faecal pellets and carcasses would have been consid-
erably higher than values estimated here.
Depositions of Thetys vagina on the Challenger
Plateau in this study only represented 0.19% of the
regional annual carbon flux, whereas carbon pro-
vided from the Bass Canyon deposition was 10-fold
greater, representing 1.5% of the annual flux (Kawa-
hata & Ohta 2000). Although gelatinous zooplankton
depositions can occur across all bottom topographies,
studies have identified much greater biomasses and
carbon inputs when organisms are in environments
that promote concentration, such as canyons or struc-
tures like pipelines (Cacchione et al. 1978, Lebrato &
Jones 2009). Carbon standing stocks for cnidarian
carcasses in the Arabian Sea have been reported as
high as 78 g C m2in some areas, an order of magni-
tude higher than mean annual flux (Billett et al.
2006), and 22 g C m2has been reported for Pyro-
soma atlanticum carcasses off the Ivory Coast, 13
times greater than the annual flux (Lebrato & Jones
2009). Future studies may benefit from incorporating
bottom topographies when calculating the potential
for gelatinous organisms to accumulate on the sea
floor and their eventual contribution to carbon fluxes
in the area.
Concluding remarks
Mass depositions of salp carcasses represent a sig-
nificant pathway for the export of organic production
from surface waters to the deep sea. Salp biomass in
the Tasman Sea regularly exceeds 100 t km3WW,
with deposition events likely to export at least 16 t
km2of carbon, or 616 GJ km2of energy, to the ben-
thos every year. With higher organic content than
depositions of other gelatinous organisms, the input
of large salp carcasses (salp-fall) is likely to be im -
portant to the nutritional ecology of the deep-sea
benthos.
Acknowledgements. This research could not have been
completed without the kind and gracious assistance of S.
Mills and Dr. K. Schnabel from the Marine Invertebrate Col-
lection at NIWA; M. Lewis from CSIRO; and Dr. M. Cryer
and C. Loveridge from the Ministry of Fisheries, New
Zealand. We also thank M. Gall (UWS) for her assistance
with the biochemical analysis of the specimens and A. Hart
(NIWA) for fish identification. We are grateful to the anony-
mous reviewers for their helpful comments that improved on
the original version of this manuscript. The New Zealand
samples were collected under the Ocean Survey 20/20
Chatham/Challenger Biodiversity and Seabed Habitat pro-
ject, funded jointly by the New Zealand Ministry of Fish-
eries, Land Information New Zealand, NIWA and the New
Zealand Department of Conservation. The Australian sam-
ples were collected during a Next Wave transit voyage
(SS03-2009) funded by the Marine National Facility. This
is contribution 110 from the Sydney Institute of Marine
Science.
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Appendix 1. Percentage (wet weight, WW) of organisms and total haul weight (kg WW) across different depths from hauls performed on the Challenger Plateau, 2007,
and in Bass Canyon, 2009. Values outside parentheses denote % contribution (WW) to haul including fish; values inside parentheses denote % contribution (WW) to
haul excluding fish. Bold values indicate contribution of salps to the haul. n = number of hauls
Challenger Plateau Bass Canyon
n117104121111
Water depth (m) 200500 501600 601800 8011000 10011800 421441 800 16001631 2685
Fish 14.09 17.5 7.61 5.72 6.28 57 17 0 2.1
Tunicates – salps 12.49 (14.54) 22.23 (26.95) 23.74 (25.70) 17.43 (18.49) 18.87 (20.13) 20.6 (51.89) 30.3 (36.51) 63.1 (63.10) 55 (56.24)
Tunicates – other 0 (0) 0 (0) 0 (0) 0.02 (0.02) 0.15 (0.16) 1.1 (2 .77) 0.5 (0.60) 0.6 (0.6) 1 1.4 (11. 66)a
Sponges 0.01 (0.01) 11.73 (14.22) 15.14 (16.39) 0.16 (0.17) 4.48 (4.78) 10.2 (25.69) 1 (1.20) 0 (0) 0 (0)
Cnidarians 7.71 (8.98) 1.88 (2.28) 8.46 (9.16) 15.2 (16.12) 13.57 (14.48) 0.1 (0.25) 20.6 (24.82) 0.9 (0.90) 14.6 (14.93)
Echinoderms 22.71 (26.44) 12.89 (15.62) 12.52 (13.55) 14.94 (15.85) 21.67 (23.12) 2.6 (6.55) 23.8 (28.67) 29.9 (29.90) 15.7 (16.05)
Polychaetes 16.29 (18.96) 1.34 (1.62) 11.85 (12.83) 28.42 (30.15) 4.06 (4.33) 0.5 (1.26) 2.8 (3.37) 0.5 (0.50) 0.4 (0.41)
Sipunculids 0 (0) 0 (0) 0 (0) 0 (0) 0 (0) 0 (0) 0 (0) 0.7 (0.70) 0 (0)
Molluscs 6.53 (7.60) 8.87 (10.75) 4.81 (5.21) 7.47 (7.92) 14.24 (15.19) 1.1 (2.77) 1.2 (1.45) 3.2 (3.20) 0.6 (0.61)
Crustaceans 12.01 (13.98) 6.58 (7.98) 10.77 (11.66) 9.98 (10.59) 7.75 (8.27) 3.5 (8.82) 2.8 (3.37) 0.9 (0.90) 0.1 (0.10)
Other 8.15 (9.49) 16.98 (20.58) 5.09 (5.51) 0.65 (0.69) 8.93 (9.53) 0 (0) 0 (0) 0 (0) 0 (0)
Total haul (kg) 3.38 92.35 9.54 12.00 25.03 13.22 2.64 1.90 5.27
aSample includes Pyrosoma atlanticum
Editorial responsibility: Marsh Youngbluth,
Fort Pierce, Florida, USA
Submitted: November 13, 2012; Accepted: June 17, 2013
Proofs received from author(s): September 13, 2013
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... Traditional and new, state of the art approaches, e.g. stable isotope analysis (Cardona et al. 2012, Chi et al. 2021, animal-borne camera recordings (Thiebot et al. 2017), remotely operated vehicle observations (Robison 2004, Choy et al. 2017, and DNA metabarcoding of stomach contents and faecal pellets (Jarman et al. 2013, McInnes et al. 2016, have revealed that GZ are frequently consumed by a diverse set of marine vertebrate and invertebrate predators, including other GZ (Harrison 1984, Henschke et al. 2013, Choy et al. 2017, Thiebot et al. 2017, Brodeur et al. 2021. ...
... The biochemical composition of GZ -major elements such as carbon (C) and nitrogen (N) -are important data for studying biochemical cycles and can be directly linked to energy content. Henschke et al. (2013) showed that the C:N ratio (in multicellular animals, an indicator of food quality due to high lipid content) of the salp Thetys vagina is comparable with the ratio in phytoplankton (in plants, a high C:N ratio typically indicates a low nutritional value, e.g. Mei et al. 2005). ...
Article
Gelatinous and soft-bodied zooplankton (GZ) have long been considered to have low energetic value (‘trophic dead end hypothesis’) and are insufficient to sustain higher trophic levels. However, the nutritional composition and energy content of GZ are often poorly known for entire groups, ignoring species-, size- and stage-specific differences. In this study, organic matter and elemental composition (carbon and nitrogen) were measured for more than 1000 specimens from 34 GZ species collected from neritic and oceanic waters of the Northeast Pacific between 2014 and 2020. Species included three gastropods, sixteen hydrozoans, two nude ctenophores, six scyphozoans, three tentaculate ctenophores, and four thaliaceans. Organic content and elemental composition were used to estimate energy content using published conversion factors and differed between and within-taxonomic classes. Size-dependent variability was shown for several species. Differences in organic content and elemental composition by development stage were observed in a salp and scyphomedusa species, highlighting the need to consider life cycle stages separately. The relative energy values of GZ were generally low and highly variable, although some taxa were comparable to those of crustaceans. The findings of the present study emphasised the need for a more detailed consideration of GZ in marine food web models and time series analyses, to take into account their inter- and intraspecific variability.
... Appendicularians are small, freeswimming organisms that produce gelatinous houses for filter-feeding, which are discarded when clogged and re-created multiple times per day. Thaliaceans are also filter-feeders, but unlike appendicularians, are colonial (though salps and doliolids have solitary life stages), form rapidly sinking fecal pellets (Perissinotto and Pakhomov, 1998), and exhibit mass die-offs (jelly-falls; Henschke et al., 2013). ...
... Pelagic tunicates have long been identified as a potentially important source of carbon export, due to fecal pellets from salps (Iversen et al., 2017;Madin et al., 2006;Ramaswamy et al., 2005;Smith Jr et al., 2014;Urrère and Knauer, 1981) and appendicularians (Wilson et al., 2013), discarded appendicularian houses (Berline et al., 2011;Lombard and Kiørboe, 2010;Robison, 2005), and salp and pyrosome carcasses from jelly-falls (Henschke et al., 2013;Lebrato et al., 2013;Lebrato and Jones, 2009). Given the boom-and-bust population dynamic of pelagic tunicates, they can often be found to dominate POC export when present (Madin et al., 2006;Smith Jr et al., 2014). ...
Article
The pelagic tunicates, gelatinous zooplankton that include salps, doliolids, and appendicularians, are filter feeding grazers thought to produce a significant amount of particulate organic carbon (POC) detritus. However, traditional sampling methods (i.e., nets), have historically underestimated their abundance, yielding an overall underappreciation of their global biomass and contribution to ocean biogeochemical cycles relative to crustacean zooplankton. As climate change is projected to decrease the average plankton size and POC export from traditional plankton food webs, the ecological and biogeochemical role of pelagic tunicates may increase; yet, pelagic tunicates were not resolved in the previous generation of global earth system climate projections. Here we present a global ocean study using a coupled physical-biogeochemical model to assess the impact of pelagic tunicates in the pelagic food web and biogeochemical cycling. We added two tunicate groups, a large salp/doliolid and a small appendicularian to the NOAA-GFDL Carbon, Ocean Biogeochemistry, and Lower Trophics version 2 (COBALTv2) model, which was originally formulated to represent carbon flows to crustacean zooplankton. The new GZ-COBALT simulation was able to simultaneously satisfy new pelagic tunicate biomass constraints and existing ecosystem constraints, including crustacean zooplankton observations. The model simulated a global tunicate biomass of 0.10 Pg C, annual tunicate production of 0.49 Pg C y⁻¹ in the top 100 m, and annual tunicate detritus production of 0.98 Pg C y⁻¹ in the top 100 m. Tunicate-mediated export flux was 0.71 Pg C y⁻¹, representing 11% of the total export flux past 100 m. Overall export from the euphotic zone remained largely constant, with the GZ-COBALT pe-ratio only increasing 5.3% (from 0.112 to 0.118) compared to the COBALTv2 control. While the bulk of the tunicate-mediated export production resulted from the rerouting of phytoplankton- and mesozooplankton-mediated export, tunicates also shifted the overall balance of the upper oceans away from recycling and towards export. Our results suggest that pelagic tunicates play important trophic roles in both directly competing with microzooplankton and indirectly shunting carbon export away from the microbial loop.
... Gelatinous macro-and megazooplankton show high diversity and abundance in the epi-and mesopelagic zones (Robison 2004) and are important players in the oceanic food web (Madin & Harbison 2001, Hays et al. 2018. Deposition events of carcasses of jellyfish and other gelatinous macrozooplankton may contribute substantially to the local carbon pump and fueling deep-sea benthic food webs (Billett et al. 2006, Lebrato & Jones 2009, Sweetman & Chapman 2011, Henschke et al. 2013, Sweetman et al. 2014, 2016. In Norwegian fjords, the carbon flux associated with jellyfish food falls may be regionally approximately equal to the phytodetrital flux (Sweetman & Chapman 2015). ...
... Pelagic tunicates have long been identified as a potentially important source of carbon 842 export, due to fecal pellets from salps (Iversen et al., 2017;Madin et al., 2006;Ramaswamy et 843 al., 2005;Smith Jr et al., 2014;Urrère and Knauer, 1981) and appendicularians (Wilson et al.,844 2013), discarded appendicularian houses (Berline et al., 2011;Lombard and Kiørboe, 2010;845 Robison, 2005), and salp and pyrosome carcasses from jelly-falls (Henschke et al., 2013;Lebrato 846 et al., 2013;Lebrato and Jones, 2009). Given the boom-and-bust population dynamic of pelagic 847 tunicates, they can often be found to dominate POC export when present (Madin et al., 2006;848 Smith Jr et al., 2014). ...
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The pelagic tunicates, gelatinous zooplankton that include salps, doliolids, and appendicularians, are filter feeding grazers thought to produce a significant amount of particulate organic carbon (POC) detritus. However, traditional sampling methods (i.e., nets), have historically underestimated their abundance, yielding an overall underappreciation of their global biomass and contribution to ocean biogeochemical cycles relative to crustacean zooplankton. As climate change is projected to decrease the average plankton size and POC export from traditional plankton food webs, the ecological and biogeochemical role of pelagic tunicates may increase; yet, pelagic tunicates were not resolved in the previous generation of global earth system climate projections. Here we present a global ocean study using a coupled physical-biogeochemical model to assess the impact of pelagic tunicates in the pelagic food web and biogeochemical cycling. We added two tunicate groups, a large salp/doliolid and a small appendicularian to the NOAA-GFDL Carbon, Ocean Biogeochemistry, and Lower Trophics version 2 (COBALTv2) model, which was originally formulated to represent carbon flows to crustacean zooplankton. The new GZ-COBALT simulation was able to simultaneously satisfy new pelagic tunicate biomass constraints and existing ecosystem constraints, including crustacean zooplankton observations. The model simulated a global tunicate biomass of 0.10 Pg C, annual production of 0.49 Pg C y-1 in the top 100 m, and export flux of 0.7 Pg C y-1, representing 11% of the total export flux past 100 m. Overall export from the euphotic zone remained largely constant, with the GZ-COBALT pe-ratio only increasing 5.3% (from 0.112 to 0.118) compared to the COBALTv2 control. While the bulk of the tunicate-mediated export production resulted from the rerouting of phytoplankton- and mesozooplankton-mediated export, tunicates also shifted the overall balance of the upper oceans away from recycling and towards export. Our results suggest that pelagic tunicates play important trophic roles in both directly competing with microzooplankton and indirectly shunting carbon export away from the microbial loop.
... Other carbon sources, such as the active transport of carbon by zooplankton migrators, and dissolved organic carbon excretion by migratory or resident zooplankton, were suggested as alternative carbon sources to explain the deficit between supply and demand of carbon (Sampei et al., 2009;Steinberg et al., 2008). Zooplankton carcasses with higher sinking speeds and lower degradation rates have also been increasingly considered as an important export flux and additional food sources for the omnivorous and carnivorous species dwelling in the mesopelagic layer, especially outside the phytoplankton growth periods when other food sources are scarce (Henschke et al., 2013;Lebrato et al., 2011;Sampei et al., 2020). Higher protein content and N:C ratio of fresh zooplankton carcasses compared with phytoplankton make them highly nutritional food sources (Giesecke et al., 2017;Tang and Elliott, 2014). ...
Article
Zooplankton carcasses and their contribution to carbon export are increasingly garnering attention in food web studies of polar oceans. We investigated the occurrence of carcasses of dominant copepod species in four depth layers (100–200 m, 200–500 m, 500–1000 m, 1000–1500 m) and their potential contribution to particulate organic carbon (POC) concentration in the Cosmonaut Sea, Antarctica, during summer of 2019/2020. The abundance of small copepods (<2 mm), either live or dead individuals, was 1–3 orders of magnitude higher than the four dominant large copepod species Calanoides acutus, Calanus propinquus, Metridia gerlachei and Rhincalanus gigas in each depth layer. Most carcasses were observed in surface (100–200 m), while the proportions of dead individuals increased with depth, from 22% of the surface 100–200 m layer to 70% of the 500–1500 m layer. The total number of passive sinkers (carcasses and moults) was dominated by carcasses of small copepods in each depth layer, while the carbon biomass of passive sinkers was dominated by carcasses of large copepods. Both abundance and carbon biomass of passive sinkers decreased with depth. The average contribution of passive sinkers to the POC concentration decreased from 0.16% in the 100–200 m depth stratum to 0.03% in the 1000–1500 m layer. This study provides the first report of occurrence and contribution of carcasses to the copepod population from the surface to the mesopelagic layer of the Southern Ocean. This information can improve understanding of the role zooplankton play in downward carbon flux within the ocean's twilight zone.
... Salps may be accessible to benthic predators after they reach the bottom through currents and vertical migration [4,5]. When they die and sink to the ocean floor, their dead bodies may also be eaten by benthos [6]. It is only recently that detailed information has started to become available on corals (Phylum Cnidaria, Class Anthozoa) as salp predators [5,7,8]. ...
Article
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A salp swarm was observed in Director’s Bay, Curaçao in July 2021, where salps were caught and consumed by three scleractinian colonial reef corals: Madracis auretenra, Locke, Weil & Coates, 2017; Meandrina meandrites (Linnaeus, 1758), and Montastraea cavernosa (Linnaeus, 1767). The first two scleractinians are newly recorded salpivores. Since the coral polyps were collaborating, predation was not restricted by polyp size. This is the first detailed report on salpivorous corals in the Caribbean.
... The blastozooid salps are able to produce massive aggregations that can affect the ocean's biological pump (Cabanes et al. 2017). For example, they transport carbon rich particles from the euphotic zone to the bottom of the ocean through fast sinking non-digested fecal pellets and detritus (Phillips et al. 2009;Henschke et al. 2013). Also, they are important food source for about 202 marine species, including fish, turtles and crustaceans (Henschke et al. 2016). ...
Article
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The occurrence of a pelagic salp Iasis cylindrica (Cuvier, 1804) is noted, for the first time, from Bangladesh marine waters since its first record from the Bay of Bengal region nearly four decades ago. A total of eight solitary zooids of I. cylindrica were collected from a rocky intertidal habitat characterized by water temperature, salinity and pH of 30°C, 31‰ and 8.2, respectively. The species was identified by examining morphological characteristics, for which detailed descriptions and photographs (both live and stained) are provided. Such information about the Bay of Bengal specimens of I. cylindrica is lacking in the literature. In addition, comparison between I. cylindrica and its closely related species of the genus Salpa are pointed out as they often co-occur.
... Salps, in contrast, produce rapidly sinking fecal pellets that can substantially increase particle flux out of the upper ocean (Madin 1982;Stone and Steinberg 2016). Their carcasses can also contribute substantially to export flux (Henschke et al. 2013;Smith et al. 2014). It thus seems likely that, while salp blooms may increase trophic efficiency and enhance transfer to top predators, they may also decrease the duration of phytoplankton blooms by reducing remineralization rates. ...
Article
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We investigated competition between Salpa thompsoni and protistan grazers during Lagrangian experiments near the Subtropical Front in the southwest Pacific sector of the Southern Ocean. Over a month, the salp community shifted from dominance by large (> 100 mm) oozooids and small (< 20 mm) blastozooids to large (~ 60 mm) blastozooids. Phytoplankton biomass was consistently dominated by nano‐ and microphytoplankton (> 2 μm cells). Using bead‐calibrated flow‐cytometry light scatter to estimate phytoplankton size, we quantified size‐specific salp and protistan zooplankton grazing pressure. Salps were able to feed at a > 10,000 : 1 predator : prey size (linear‐dimension) ratio. Small blastozooids efficiently retained cells > 1.4 μm (high end of picoplankton size, 0.6–2 μm cells) and also obtained substantial nutrition from smaller bacteria‐sized cells. Larger salps could only feed efficiently on > 5.9 μm cells and were largely incapable of feeding on picoplankton. Due to the high biomass of nano‐ and microphytoplankton, however, all salps derived most of their (phytoplankton‐based) nutrition from these larger autotrophs. Phagotrophic protists were the dominant competitors for these prey items and consumed approximately 50% of the biomass of all phytoplankton size classes each day. Using a Bayesian statistical framework, we developed an allometric‐scaling equation for salp clearance rates as a function of salp and prey size: where ESD is prey equivalent spherical diameter (µm), TL is S. thompsoni total length, φ = 5.6 × 10−3 ± 3.6 × 10−4, ψ = 2.1 ± 0.13, θ = 0.58 ± 0.08, and γ = 0.46 ± 0.03 and clearance rate is L d‐1 salp‐1. We discuss the biogeochemical and food‐web implications of competitive interactions among salps, krill, and protozoans.
... Despite their low protein content, gelatinous zooplankton are common prey of many marine taxa including fishes, crustaceans, turtles and even some cephalopods (Heeger et al. 1992;Cardona et al. 2012;Hoving and Haddock 2017). The complex trophic interconnections of gelatinous zooplankton in the pelagic foodweb mark their central role within the pelagic ecosystem and their potential importance in the biological carbon pump (Alldredge 2004;Lebrato et al. 2012;Henschke et al. 2013;Sweetman and Chapman 2015). Gelatinous organisms have several traits that may give them an advantage in warmer, deoxygenated waters (Thuesen et al. 2005;Ekau et al. 2010). ...
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Observations of the diversity, distribution and abundance of pelagic fauna are absent for many ocean regions in the Atlantic, but baseline data are required to detect changes in communities as a result of climate change. Gelatinous fauna are increasingly recognized as vital players in oceanic food webs, but sampling these delicate organisms in nets is challenging. Underwater (in situ) observations have provided unprecedented insights into mesopelagic communities in particular for abundance and distribution of gelatinous fauna. In September 2018, we performed horizontal video transects (50–1200 m) using the pelagic in situ observation system during a research cruise in the southern Norwegian Sea. Annotation of the video recordings resulted in 12 abundant and 7 rare taxa. Chaetognaths, the trachymedusa Aglantha digitale and appendicularians were the three most abundant taxa. The high numbers of fishes and crustaceans in the upper 100 m was likely the result of vertical migration. Gelatinous zooplankton included ctenophores (lobate ctenophores, Beroe spp., Euplokamis sp., and an undescribed cydippid) as well as calycophoran and physonect siphonophores. We discuss the distributions of these fauna, some of which represent the first record for the Norwegian Sea.
... However, data on drivers and rates of mortality and carcass flux from the Southern Ocean are currently not available. The lack of data could lead to an underestimation of carbon flux, especially in the HNLC waters, where fast-sinking salp blooms could significantly increase the downward carbon flux as "jelly falls, " e.g., by 330% in the Tasman Sea further north (Henschke et al., 2013). Similarly, active transport of carbon by zooplankton, both by diel and seasonal vertical migrators, is not well understood. ...
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Marine ecosystems regulate atmospheric carbon dioxide levels by transporting and storing photosynthetically fixed carbon in the ocean’s interior. In particular, the subantarctic and polar frontal zone of the Southern Ocean is a significant region for physically-driven carbon uptake due to mode water formation, although it is under-studied concerning biologically-mediated uptake. Regional differences in iron concentrations lead to variable carbon export from the base of the euphotic zone. Contrary to our understanding of export globally, where high productivity results in high export, naturally iron-fertilized regions exhibit low carbon export relative to their surface productivity, while HNLC (High Nutrient, Low Chlorophyll) waters emerge as a significant area for carbon export. Zooplankton, an integral part of the oceanic food web, play an important role in establishing these main carbon export regimes. In this mini review, we explore this role further by focusing on the impact of grazing and the production of fecal pellets on the carbon flux. The data coverage in the subantarctic region will be assessed by comparing two case studies - the iron-replete Kerguelen Plateau and the HNLC region south of Australia. We then discuss challenges in evaluating the contributions of zooplankton to carbon flux, namely gaps in seasonal coverage of sampling campaigns, the use of non-standardized and biased methods and under-sampling of the mesopelagic zone, an important area of carbon remineralization. More integrated approaches are necessary to improve present estimates of zooplankton-mediated carbon export in the Southern Ocean.
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Particulate organic matter (POM) in the deep sea is derived from five major sources: planktonic material, carcasses of large nekton, marine macrophyte detritus, terrigenous matter and chemoautotrophic production. The direct contribution of terrigenous matter to deep marine sediments is small. Sediment trap measurements show that small planktonic POM adds about 4 g C m⁻²yr⁻¹ to the deep-sea carbon pool. The maximum expected input of pelagic Sargassum to the deep Atlantic is one-tenth of this, 0.4 g C m⁻²yr⁻¹. Calculations suggest the remains of large nekton contribute approximately 50 mg C m⁻²yr⁻¹ while the rate of primary carbon synthesis by chemoautotrophs is estimated to be 0.01 to 0.1 mg C m⁻²yr⁻¹.
Article
The researchers at the National Institute of Water & Atmospheric Research (NIWA), Wellington have developed the Deep Towed Imaging System (DTIS) using telecom modems and existing single conductor winch and cable in order to replace their old film drop camera with a modern towed system with both still and video digital cameras. The video camera is a Sony HDR-HC1 high-definition camcorder that records onto MiniDV tapes, offering images with significant clarity and detail. Power is provided by two DeepSea Power & Light 12-volt, 80 ampere-hour pressure-compensated oil-filled batteries that can power the vehicle for 2.3 hours. The live video image is also cabled to a display for the winch driver. The operator flies the vehicle close to the seafloor by winching tow cable in and out, using the live video and the overwritten vehicle altitude and depth data. The DTIS has been used on 11 research voyages since 2006.
Article
The morphology and cellulosic composition of the tunic was studied in pelagic tunicates (3 pyrosomas, 2 doliolids, and 13 salps). The tunic is transparent and gelatinous, consisting of an electron-dense cuticular layer with a fibrous tunic matrix. The thickness and density of the cuticular layer and of the tunic matrix differ from species to species. In some salps, the cuticular layer has numerous minute protrusions that are structurally identical to those found in several ascidians. Free mesenchymal cells (tunic cells) are distributed in the tunic. Whereas the number of tunic cells in the pyrosomas is similar to that in ascidians, there are many fewer tunic cells in doliolids and salps. These differences may be caused by the different functions of the tunic in each group. The existence of cellulose in the tunic was confirmed using electron diffraction in all of the species studied thus far. Their diffractograms indicate that the cellulose microfibrils consist of nearly pure I{beta} of the allomorph. These results show that tunic morphology and cellulosic composition are similar in ascidians and thaliaceans (pyrosomas, doliolids, and salps). The tunic is considered to be a homologous tissue in these animals, and their most recent common ancestor would have possessed this tissue. Copyright © 1999 by Marine Biological Laboratory.