Download LIMNOLOGY Novel method to concurrently sample the planktobenthos and benthos

LIMNOLOGY
and
OCEANOGRAPHY: METHODS
Limnol. Oceanogr.: Methods 7, 2009, 823–832
© 2009, by the American Society of Limnology and Oceanography, Inc.
Novel method to concurrently sample the planktobenthos and
benthos
R. Przeslawski and M. A. McArthur
Marine and Coastal Environment Group, Geoscience Australia, GPO Box 378, Canberra, Australian Capital Territory, 2617
Australia
Abstract
The planktobenthos is an important area with unique environmental conditions that represents the immediate link between the benthos and the water column, yet it has never been deliberately sampled concurrently
with the benthos. We have developed a new sampling method to allow concurrent collection of benthic and
planktobenthic specimens. The Mounted Assembly for Planktobenthic Sampling (MAPS) uses a novel trilayered
net with a seafloor-triggered opening and closing mechanism attached to an epibenthic sled. The MAPS was
deployed on the Carnarvon Shelf off Western Australia and was successful at separately sampling both benthic
and planktobenthic fauna. A wide variety of epibenthic and infaunal animals were collected from the sled, and
planktobenthic animals such as mysids were identified from all three nets. The trilayered net was particularly
effective at collecting a broad range of planktobenthic organisms, including smaller fragile larvae and adults
that may have otherwise been destroyed during collection in a single net or grab. The number of species in
planktobenthic and benthic samples was correlated, although the strength and significance of this relationship
varied among taxonomic groups, suggesting that rich benthic assemblages are linked to rich planktobenthic
assemblages. Importantly, the MAPS is a value-adding method, collecting two sample sets for the cost of one,
and can be modified for use on a wide variety of benthic sleds to target a range of organisms. The concurrent
collection of planktobenthic and benthic biota will contribute to a range of research areas, including larval ecology, nutrient cycling, and surrogacy research for habitat mapping.
Introduction
2005). Vertical tows are perhaps the simplest method to
actively collect zooplankton, but they prohibit differentiation
of animals according to depth, an important factor in determining marine species distribution (Nellen and Ruseler 2004).
Horizontal tows sample at discrete depths, but all subsurface
tows must include an opening and closing mechanism to prevent contamination from nontargeted depths during descent
and retrieval (Wiebe et al. 1976). Because of the complexity
associated with such mechanisms and logistical constraints on
many studies, the majority of plankton sampling has occurred
at the surface.
In comparison, planktobenthic sampling, or sampling
immediately above the seafloor, is not often undertaken (but
see Wiebe and Benfield [2003] and Brenke [2005] for excellent
reviews of zooplankton sampling methods, including of the
planktobenthos). This is likely due to the combination of the
requirement for a robust opening and closing mechanism and
the difficulties associated with sampling so close to the
seafloor, such as contamination from benthic detritus (Dauvin
and Vallet 2006).
The planktobenthos is often considered synonymous with
various other terms, including hyperbenthos and supraben-
The study of zooplankton has a rich history of sampling
gear and methods, each of which targets a particular size range
of animals in a given area (Wiebe and Benfield 2003; Brenke
*Corresponding author: E-mail: [email protected]
Acknowledgments
We are extremely grateful to Andrew Hislop (“Rowdy”) and Gareth
Crook for constructing and modifying the MAPS. The crew of the R/V
Solander assisted in deployment. Peter Wiebe and Sadie Mills offered
helpful suggestions during the early phases of this project. Tara
Anderson, Scott Nichol, Nic Bax, and two anonymous reviewers provided valuable comments on this manuscript. This work is part of the
Surrogates Program in the Marine Biodiversity Hub, which is funded
through the Commonwealth Environment Research Facilities (CERF) programme, an Australian Government initiative supporting world-class,
public-good research. The CERF Marine Biodiversity Hub is a collaborative partnership between the University of Tasmania, CSIRO Wealth from
Oceans Flagship, Geoscience Australia, Australian Institute of Marine
Science, and Museum Victoria. This paper is published with the permission of the chief executive officer of Geoscience Australia.
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that future concurrent collection of planktobenthic and benthic biota will contribute to a range of research areas including larval ecology, nutrient cycling, trophodynamics, biogeography, and surrogacy research for habitat mapping.
thos (Dauvin and Vallet 2006). In theory, this zone includes a
distinct environment in which boundary-layer hydrodynamics are clearly different from the water column above (Dauvin
and Vallet 2006). In practice, hydrodynamics are often
unknown and can vary across very small scales, so this zone is
often specified a priori as a subjective measurement above the
seafloor (e.g., Choe and Deibel 2000).
The planktobenthos is an important area, as it represents a
narrow band of habitat with unique environmental conditions and communities (Cartes et al. 1994; Dauvin and Vallet
2006) with fewer proportions of species vertically migrating
than in the water column (Carleton and Hamner 2007). Sampling in this zone therefore provides scope for the discovery of
new species. The planktobenthos is important as a potential
habitat for certain life stages of pelagic, benthic, or infaunal
species such as negatively or neutrally buoyant eggs, embryos,
and larvae (Metaxas et al. 2008) and may therefore be important to recruitment and dispersal strategies of marine organisms. These life stages could otherwise remain unsampled
away from the seafloor, leading to underestimates in abundance or dispersal potential. The planktobenthos also represents the immediate link between the benthos and the water
column, thereby playing important roles in nutrient cycling
(Austen et al. 2002; Le Loc’h et al. 2008), sediment stability
and resuspension (Roast et al. 2004), and even parasite transmission (Jackson et al. 1997).
Despite its close links with the seafloor, the planktobenthos
has never been deliberately and concurrently sampled with the
benthos (Brenke 2005; Cartes et al. 1994; Dauvin and Vallet
2006). Brenke (2005) and Brandt and Barthel (1995) describe
the development of their respective suprabenthic and epibenthic sledges, but they sampled higher than 25 and 27 cm above
the seafloor, respectively, ignoring the benthos itself. Knowledge of both planktobenthic and benthic animals would
advance our understanding of the links between benthic and
pelagic systems by identifying species, life stages, or communities that overlap both habitats or those that occur in only one
(Brandt and Barthel 1995; Vallet and Dauvin 2004). In addition, differential relationships between biological and environmental factors can be investigated, as benthic organisms could
be expected to be more closely associated with sediment characteristics (Post 2008) while planktobenthic organisms may be
more affected by water properties (Cartes et al. 2007).
We have developed a new method for planktobenthic sampling that allows concurrent collection of benthic and
suprabenthic specimens. The Mounted Assembly for Planktobenthic Sampling (MAPS) uses a novel trilayered net with a
seafloor-triggered opening and closing mechanism attached to
a Woods Hole model epibenthic sled and was deployed on
Carnarvon Shelf off Western Australia. This represents the first
time that spatially and temporally matched samples have
been collected from the benthos and planktobenthos. In this
article, we describe the MAPS design and deployment, as well
as results from the first successful deployment in anticipation
Materials and procedures
MAPS design—The MAPS consists of a trilayered net
attached to a hinged frame mounted on top of a modified
Woods Hole epibenthic sled, the latter of which has no
opening or closing mechanism (Hessler and Sanders 1967).
The frame is composed of hollow, square section steel tubes
connected to a lever on the underside of the sled (Fig. 1).
When depressed by contact with the seafloor, the lever
causes the net frame to swing up into the open position,
allowing plankton into the trilayered net (Figs. 1, 2a). When
the sled leaves the seafloor, springs collapse the net frame,
preventing planktonic sampling beyond the planktobenthos (Fig. 2b). Two buoys fixed to the top of the sled keep
the system upright on descent (Fig. 2), and a steel shield is
fixed to the top of the frame to protect the net in case the
sled does land upside down (Figs. 1, 2). The weight of the
shield and force applied by the closing springs make the net
inappropriate for sampling larger macrofauna, as such specimens could be squashed when the frame closes. Using the
MAPS on the Woods Hole sled, the planktobenthos is sampled at 250–500 mm above the seafloor, and the benthos at
0–200 mm above the seafloor.
The net is composed of three layers of Nitex nylon, incorporating decreasing mesh sizes. The largest mesh (1000 µm) is
the inner layer of the cod-end through which samples passed
first, the medium mesh (500 µm) is the middle layer, and the
Fig. 1. A schematic diagram of the MAPS structure showing an angled
(top) and sideways (bottom) view of the sled modifications, including the
lever and frame system. The MAPS is shown here with the lever depressed
and the planktobenthic frame extended as would occur on the seafloor.
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Benthic-planktobenthic sampling method
Fig. 3. Schematic diagram of the MAPS trilayered nets used to sample
the planktobenthos: (a) the three layers of decreasing mesh size with
detachable metal bars represented by thick black lines; (b) the attachment method for the nets onto the frame to facilitate easy separation of
the layers and release from the frame.
attached to the frame by stitched loops, Velcro, and a detachable flat steel bar for easy separation after specimens are collected (Fig. 3).
A preliminary trial of the MAPS at 35-m depth resulted in
poor operation of the opening-closing mechanism and sediment plume contamination of the plankton nets. Accordingly,
the adjustable spring was added to prevent the frame from
swinging open during deployment, and an aluminum visor
was bolted to the top of the sled to deflect sediment plumes
generated by the sled’s movement along the bottom (Fig. 2)
Deployment—The MAPS was deployed from R/V Solander
during August and September 2008 at five stations on the
Carnarvon Shelf, Western Australia, spanning 62–82 m depth
(Fig. 4). Stations were selected for soft sediments and lack of
large macrofauna, as the sled we used had a very low opening
unsuitable for sponges and consolidated material observed at
other locations in the area. Stations were numerically named
based on Brooke et al. (2009). For each station, the sled was
towed along the bottom for 100 m.
The nets were immediately removed and placed in individual buckets of seawater with the mouth of the net facing
upward such that no contamination of samples occurred.
Each net was rinsed into a container with 100-µm-filtered seawater, and samples were elutriated for 5 min onto a 100-µm
sieve. Although the amount of sediments retained in the nets
was small (no more than 2 tablespoons), elutriation further
reduced the amount of sediment in the retained sample so
that the specimens would be easier to sort and identify. Benthic samples retained in the sled consisted primarily of large
quantities of coarse sediments, and they were therefore sub-
Fig. 2. The MAPS with the frame extended and nets open (a) and the
frame collapsed and nets closed (b). The inset photo shows the adjustable
spring attached to the frame on each side of the sled. Br, bridle; V, sediment visor; SM, sled mouth; NM, net mouth; L, bottom-sensing lever; F,
frame; S, shield; B, buoys; Sp, adjustable spring. Scale bar, 500 mm at
front of sled.
small mesh (100 µm) is the external layer (Fig. 3). This trilayered design reduces the risk of clogging and damage to the
nets and protects samples from associated increases in water
pressure. This is particularly important for the 100-µm layer,
which otherwise would have been clogged with detritus and
larger organisms, increasing the likelihood of damage to small
fragile animals. In addition, layering allows the presorted collection of a broad range of species, thereby reducing the time
required to sort samples based on size. Importantly, the planktobenthic samples from the 1000-µm layer are directly comparable to benthic samples collected from the 1000-µm sled
mesh. A trilayered net also adds a redundancy element to sampling, such that if a tear occurs in the inner or middle net, the
sample is still retained in the outer net. The net mouth is 300
× 500 mm, and the cod-end is 800 mm long. The layers are
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Przeslawski and McArthur
Benthic-planktobenthic sampling method
(Young et al. 2006). We also recorded presence of major groups
from the benthic sled and planktobenthic nets, as well as abundances for each planktobenthic net. Because all benthic sled
samples were subsampled, abundance data are not comparable
between planktobenthos and benthos and are not presented for
the benthos. Benthic samples were lodged at the Museum of
Victoria for future fine-scale taxonomic identification.
Assessment
Data results—Crustaceans were the most species-rich and
abundant taxa collected in the planktobenthic nets (Tables 1a,
2a), with copepods encompassing the majority of crustaceans
(Table 2a). Polychaetes and chaeotognaths were also prominent taxa (Tables 1a and 2a). Only a very few benthic animals
were collected in the nets, including small pieces of sponge and
a bryozoan fragment (Table 2a); these were likely released into
the water column as the sled moved over the seafloor. In addition to numerous adults, early life stages were identified from
the planktobenthic nets, including gastropod veligers, brooding ostracods, crustacean zoea, and chordate eggs and larvae
(Table 2b) (see Brooke et al. 2009 for photographs).
The nets successfully separated organisms based on their
size and in some cases allowed the broad separation of taxonomic groups. The majority of most taxonomic groups were
collected in the 100-µm net, with up to 70 times more copepods and 28 times more chaetognaths found in this net than
the 500-µm net (Table 2a). Similarly, more eggs and larvae
were collected in the smaller 100- and 500-µm nets than the
1000-µm net (Table 2b).
In the benthic sled, crustaceans were the most species-rich
taxa, with decapods encompassing the majority of species
(Table 1b). Polychaetes, molluscs, echinoderms, and chordates
were also prevalent (Table 1b). The vast majority of animals
collected in the sled were either infaunal (e.g., capitellid), epifaunal (e.g., bryozoan), or demersal (e.g., fish), with pelagic
specimens represented by only a small proportion of taxa (e.g.,
copepod). As the sled mouth had no opening/closing mechanism, these planktonic taxa may have been collected during
descent or ascent. No eggs or larvae were identified from the
sled collections, comparable to results obtained from the
equivalent mesh size in the planktobenthic nets (1000 µm).
Species richness of sled specimens and net specimens was
positively correlated (Fig. 5a), but this relationship was not
significant (r = 0.6983, P = 0.1897), possibly owing to low sample numbers increasing the probability of failing to detect a
significant relationship (type II error). We examined two taxonomic groups that dominated both sled and net specimens
and found that crustacean species richness was significantly
correlated between sled and net samples (Fig. 5b) (r = 0.9030,
P = 0.0357), whereas polychaete species richness was clearly
not correlated (Fig. 5c) (r = 0.1316, P = 0.8329).
Assessment of method—The MAPS was successful at separately
sampling both benthic and planktobenthic fauna. A wide variety of epibenthic and infaunal animals were collected from the
Fig. 4. Location of sampling stations along Carnarvon Shelf, Western
Australia.
sampled in a 30-L bin (approximately 10% of total sample)
and elutriated on collection onto a 500-µm sieve.
Preservation and identification of zooplankton and benthic animals—Zooplankton were preserved onboard in 4% formalin
(Koppelmann and Weikert 2007), and benthic animals were
preserved in 90% isopropyl alcohol for sorting and identification at the lab. Zooplankton and benthic animals were separated into morphospecies and identified to lowest taxonomic
resolution using identification guides (Dakin and Colefax 1940;
Poore 2004; Poore and Taylor 1997; Wilson et al. 2003; Young
et al. 2006). For each station, species richness was recorded separately for planktobenthos and benthos. Because of the inability to separate chaetognaths into species, this group was treated
as one species. Copepods from the 100-µm net were also
excluded from species richness calculations because of their
extremely high abundance and the inability to accurately differentiate species. Eggs and larvae were not included in species
richness calculations, as larval development of many invertebrates include disparate morphologies among a single species
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Benthic-planktobenthic sampling method
Table 1. Species richness (number of species) based on gross morphological differences from all planktobenthic nets (a) and benthic
sled (b).
a. All planktobenthic nets
Porifera
Chaetognatha
Polychaeta
Nonpolychaete worms
Mollusca: Gastropoda
Arthropoda: Crustacea
Ostracoda
Copepodaa
Cirripedia
Mysida
Cumacea
Amphipoda
Isopoda
Decapoda
Bryozoa
Echinodermata
Chordata
Urochordata
Cephalochordata
Total
b. Benthic sled
Chaetognatha
Nemertea
Polychaeta
Scolecida
Eunicida
Phyllodocida
Terebellida
Mollusca
Aplacophora
Gastropoda
Bivalvia
Scaphopoda
Arthropoda: Crustacea
Ostracoda
Copepoda
Leptostraca
Stomatopoda
Cumacea
Tanaidacea
Isopoda
Amphipoda
Decapoda
Arthropoda: Pycnogonida
Bryozoa
Echinodermata
Crinoidea
Asteroidea
Ophiuroidea
Echinoidea
Chordata
Urochordata
Vertebrata
Total
Station 3
Station 12
Station 132
Station 133
Station 134
1
1
14
3
0
33
4
9
1
3
2
11
2
1
1
0
1
0
1
54
0
1
10
1
2
34
5
12
0
3
3
8
3
0
0
1
2
2
0
51
0
1
2
1
3
10
1
5
0
2
0
1
1
0
0
0
1
1
0
18
0
1
2
0
0
11
2
5
0
2
0
2
0
0
0
0
0
0
0
14
0
1
1
0
0
14
3
8
0
1
0
1
1
0
0
0
0
0
0
16
1
1
6
1
1
3
1
4
1
0
3
0
20
2
0
1
0
2
0
3
5
7
0
0
2
1
0
0
1
2
0
2
36
0
0
1
0
0
1
0
0
0
0
0
0
21
1
1
0
0
3
1
3
6
6
1
0
2
0
0
1
1
1
0
1
27
0
0
7
1
2
3
1
3
0
1
1
1
12
0
1
0
0
1
1
0
1
8
0
0
5
0
1
3
1
4
1
3
30
0
0
1
0
0
1
0
3
0
0
3
0
9
0
1
0
1
0
1
1
1
4
0
1
4
0
0
3
1
0
0
0
18
0
0
3
1
1
1
0
1
0
0
1
0
6
0
1
0
0
0
1
0
2
2
0
0
0
0
0
0
0
1
0
1
11
Eggs and larvae are excluded.
a
Species richness does not include copepods from 100-µm net because of extremely high abundances and associated inability to differentiate species.
827
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Benthic-planktobenthic sampling method
Table 2. Abundance of adults and juveniles (a) and eggs and larvae (b) from each planktobenthic net.
a. Adults and juveniles
Chaetognatha
Polychaeta
Nonpolychaete worms
Mollusca: Gastropoda
Arthropoda: Crustacea
Ostracoda
Copepoda
Cirripedia
Mysida
Cumacea
Amphipoda
Isopoda
Caridea
Bryozoa
Echinodermata
Chordata
Urochordata
Cephalochordata
b. Eggs and larvae
Eggs
Chordate
Unknown
Porifera
Polychaetab
Nonpolychaete worms
Mollusca
Gastropoda
Bivalvia
Arthropoda: Crustacea
Decapoda: Brachyura
Other
Chordata
Cephalochordata
Vertebrata
Station 3
100 500 1000
Station 12
100 500 1000
Station 132
100 500 1000
Station 133
100 500 1000
Station 134
100 500a
82
14
4
0
1458
8
1435
0
4
0
8
3
0
0
0
0
0
0
17
3
0
0
76
4
51
0
10
2
7
0
2
3
0
2
0
2
2
0
0
0
15
0
6
7
0
0
2
0
0
0
0
0
0
0
33
9
1
1
2673
25
2588
0
47
1
6
6
0
0
1
0
0
0
8
0
0
1
50
3
37
0
6
1
4
0
0
0
0
1
1
0
2
3
0
0
8
0
6
0
1
1
0
0
0
0
0
2
2
0
74
3
1
1
545
1
538
0
3
0
1
2
0
0
0
0
0
0
2
0
0
0
12
0
12
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
1
1
0
30
2
0
0
339
3
333
0
1
0
2
0
0
0
0
0
0
0
0
0
0
0
4
0
4
0
0
0
0
0
0
0
0
0
0
0
1
0
0
0
2
0
1
0
1
0
0
0
0
0
0
0
0
0
76
2
0
0
687
6
678
0
1
0
0
2
0
0
0
0
0
0
3
0
0
0
16
0
15
0
0
0
1
0
0
0
0
0
0
0
20
3
17
1
—
3
3
3
0
2
1
1
1
0
1
3
1
2
0
—
0
1
1
0
9
3
6
1
0
1
0
0
0
0
—
0
0
0
0
0
0
0
0
0
0
3
0
3
0
—
1
2
0
2
4
2
2
1
1
0
0
0
0
0
—
0
1
1
0
1
0
1
0
0
0
1
1
0
0
—
0
0
0
0
2
0
3
0
0
0
0
0
0
0
—
0
0
0
0
0
0
0
4
0
4
8
5
3
0
—
0
0
0
0
2
1
1
0
0
0
0
0
0
0
—
0
0
0
0
0
0
0
0
0
0
1
1
0
0
—
0
0
0
0
0
0
0
1
0
1
2
0
2
0
—
0
1
1
0
0
0
0
0
0
0
0
0
0
0
—
0
0
0
0
0
0
0
0
0
0
6
0
6
0
—
0
0
0
0
0
0
0
0
0
0
10
7
3
0
—
0
0
0
0
2
0
2
0
0
0
Because of subsampling undertaken with benthic samples, abundance data are not presented for sled specimens.
a
The 1000-µm net tore during the transect at this station, and all samples from this net and the intact 1000-µm net were therefore combined.
b
All polychaetes are treated as adults and juveniles in Table 2a, although these likely include some larvae. We could not accurately differentiate between
polychaete larvae and settled juveniles and adults owing to the propensity for adults to break into smaller pieces during collection, the lack of morphological difference between late larval and juvenile stages (Young et al. 2006), and the possibility that smaller benthic polychaetes were being collected
by the planktobenthic nets during sediment disturbance.
MAPS nets are similar to those collected by planktobenthic
sledges from previous studies featuring high abundance and
diversity of crustaceans (Carleton and Hamner 2007; Cartes
1998; Lorz and Brandt 2003; Sanvicente et al. 1997), high
abundance of chaetognaths (Cartes 1998), and extremely high
abundance of copepods (Vallet and Dauvin 2004). Similarly,
benthic and infaunal communities collected by the sled are similar to those from previous studies, particularly dominance of
sled, and planktobenthic animals such as mysids were identified from all three nets. These crustaceans are known to occur
primarily in the area immediately above the seafloor (Cartes
and Sorbe 1995). The nets remained closed during deployment
and retrieval and, to our knowledge, no organisms were collected that exclusively inhabit nonplanktobenthic waters, suggesting that the MAPS successfully excludes organisms from
these habitats. Planktobenthic communities collected from the
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Benthic-planktobenthic sampling method
animals that may have otherwise been destroyed during collection in a single net. Mesh size had a strong effect on abundance estimates in this study, supporting previous research in
which a 100-µm sieve collected an order of magnitude more
animals than a 333-µm sieve (Hwang et al. 2007). In addition,
the trilayered net preserved the integrity of our sample at one
station where the 1000-µm net tore, leaving a hole through
which animals passed but were retained on the 500-µm net.
Without the nested nets, specimens would have been lost.
Discussion
The MAPS allows spatially and temporally matched sampling and characterization of planktobenthic and benthic
assemblages, results of which are relevant to a range of broader
research questions:
There has recently been much focus on physical surrogacy
research, in which biologically relevant abiotic factors are
investigated as potential predictors for biodiversity (Cartes et
al. 2007; Post 2008; Sarkar et al. 2005). The rationale is that
environmental data are often much easier and faster to collect
and process than biological data (Post 2008). Surrogacy
research has primarily focused on infaunal or epibenthic communities (Brooke et al. 2009; Post 2008; Sarkar et al. 2005),
although there has been some research on suprabenthic communities (Cartes et al. 2007). The ability to concurrently sample in, on, and immediately above the seafloor will incorporate multiple habitats into surrogacy research in which
biological communities can be quantified based on environmental factors. This will allow researchers to investigate
potential differences in the utility of surrogates among habitats. For example, sediment properties may be more useful surrogates for infaunal organisms than planktobenthic organisms
(Kelaher and Levinton 2003), and water properties may be
more suitable surrogates for planktobenthic organisms than
benthic organisms (Cartes et al. 2007). In addition, our study
has shown that the MAPS nets retain larvae in the planktobenthos, and these larvae may reveal potential surrogacy relationships more clearly than adults, as they are a more vulnerable life stage and more sensitive to environmental conditions
(Bielmyer et al. 2005).
Marine nutrient cycling occurs when organic matter in the
water column falls to the seafloor and is degraded by
microbes, infauna, and epifauna such that nutrients are
released back into the water column via bioturbation and predation (Norling et al. 2007). The rate of nutrient cycling
depends not only on depth, ocean currents, and seafloor properties but also on the associated biological communities (Biles
et al. 2002). The MAPS seems an appropriate method with
which to study benthic–pelagic coupling, as it facilitates the
segregated collection of animals from the seafloor and immediately above. This represents both sides of the interface where
organic matter is converted to and from usable nutrients.
Researchers can then collect additional geochemical data from
the sediments and near-bottom water to quantify available
Fig. 5. Relationship between planktobenthos and benthos, including
total species richness (a), crustacean species richness (b), and polychaete
species richness (c). Each point is labeled with the station number. Lines
represent best fit.
polychaetes (Hutchings and Jacoby 1994) and crustaceans
including decapods (Poore et al. 2008). Analysis of samples
from the two habitats showed that benthic and planktobenthic species richness are related, but these relationships vary
among taxonomic groups. Future studies may further
explore these trends using the MAPS design and finer taxonomic identification.
The trilayered net was very successful at collecting a broad
range of planktobenthic organisms, including smaller fragile
829
Przeslawski and McArthur
Benthic-planktobenthic sampling method
The design of the MAPS was dictated by the need to minimize cost, building effort, and complications to the existing
sampling program (see Brooke et al. 2009 for description of
main survey objectives). However, if a dual benthos and
plankton sampling system were to be built from scratch with
no need to fit onto an existing benthic sled, the following
attributes would offer improved performance over our unit:
(1) A towing bridle cantilevered up and out of the way of the
sampling apertures would reduce net avoidance in planktonic
organisms able to swim against currents (e.g., larger mysids).
(2) Projecting the mouth of the plankton net forward of the
mouth of the benthic sled would further reduce net avoidance
and negate the need for a plume deflector. (3) Adding a sled
mouth shutter, triggered by the same opening and closing
mechanism as used on the plankton net, would give assurance
of discrete benthic sampling spatially matched with the plankton component. In the current study, we used an existing sled
without an opening/closing mechanism, as this is standard for
many benthic sleds (Brooke et al. 2009; Heap et al. 2009 Q1).
Our purpose here was to test the utility of the MAPS in collecting both benthic and planktobenthic animals; thus, the
lack of a closing mechanism on the sled mouth was not an
issue. Nevertheless, if quantitative benthic–planktobenthic
comparisons are to be made and if researchers are unable to
easily differentiate benthic and planktobenthic animals, we
recommend the inclusion of an opening/closing mechanism
for the sled mouth. Such a modification would exclude all
pelagic organisms from the sled and could be accomplished
using previous designs of opening and closing mechanisms for
sled mouths (Brenke 2005; Wiebe and Benfield 2003).
One of the strengths of the MAPS is that its design can be
modified to fit other epibenthic sleds, and this method is therefore applicable for any researcher with access to a sled. The MAPS
design is also easily modified to accommodate a range of substrates and organism sizes and habitats. First of all, the habitat
targeted can be modified by adjusting the height of the sled and
the nets. For example, if the hydrodynamics of a system revealed
an obvious difference in current speed 0.5 m above the seafloor,
benthic and planktobenthic specimens could be segregated
based on this gradient by ensuring the sled height was at least
0.5 m. The organisms targeted can be varied by adjusting the
mesh sizes (Nichols and Thompson 1991) or number of layers
used in the planktobenthic nets. For example, if interested only
in small planktotrophic larvae, a researcher could use a trilayered
net consisting of 1000 and 100 µm solely to filter out large particles, surrounded by a 50-µm net to retain small larvae. Finally,
the MAPS can be used in a variety of substrates by ensuring that
an appropriate sled is selected for the sampling habitat (e.g.,
Lewis 1999) and mounting the planktobenthic frame and nets
on such a sled. In addition to sled and net modifications, video
cameras and environmental sensors such as those used in other
zooplankton samplers (e.g., Wiebe et al. 1985) can be added,
thereby allowing the simultaneous collection of data about the
environment in which the sampled animals live.
nutrients and correlate this with environmental factors and
infauna, benthos, and planktobenthos, thereby identifying
the driving forces behind biodiversity among several habitats.
The MAPS could also be used to investigate aspects of larval
ecology and reproductive biology. Although eggs and early larval stages of many species are buoyant, some species or later
larval stages are neutrally or negatively buoyant and can be
detected only by benthic or planktobenthic sampling (Kelman
and Emlet 1999). Benthic sampling is impractical for egg and
larval collection, as the large amounts of sediment collected in
the small mesh size needed to retain most larvae would make
the sorting of any larvae collected extremely time-consuming
and difficult. The MAPS allows the collection of neutrally or
negatively buoyant eggs and larvae with minimal sediment
contamination and the opportunity to match or contrast
these life stages with the adult benthic fauna among which
they may settle. The ability to sample larvae from certain habitats is important to accurately estimate larval supply, settlement, and associated population dynamics (Moksnes and
Wennhage 2001) and to appropriately characterize some communities (Carleton and Hamner 2007). In addition, larval
sampling near the seafloor could enable researchers to empirically investigate intriguing ecological and evolutionary
issues, such as the evolution of shorter larval stages in highdisturbance environments (Buhl-Mortensen and Hoeg 2006),
evidence of larval detrital feeding outside the photic zone
(Young and Eckelbarger 1994), and retention of larvae and
other zooplankton in valleys and similar features (Mullineaux
et al. 2005).
Comments and recommendations
We have shown that the MAPS is an appropriate sampling
method over soft sediments in waters up to 82 m. The utility
of the MAPS in the deep sea and over rough terrain has yet to
be tested (e.g., Lewis 1999), with the most important considerations being frame strength, function of the opening/closing mechanism, and selection of suitable incompressible buoys. Frame strength can be increased by using solid
steel, instead of hollow tubes as used here; but attention must
be paid to the function of the lever and tension of the springs
to ensure that the lever will open the frame on contact with
the seafloor. Shallow-water tests are recommended before
committing a new unit to deep-water work. As depth
increases, the opportunity for the sled to swing around in the
water column increases, thereby increasing the risk that the
net frame will swing open in the water column or the sled will
land upside down. The only way to be certain that the frame
remains closed during long periods of ascent and descent is to
mount a video camera on the sled such that the frame is visible during the entire deployment. When sampling in deep
waters, buoys must be rated for the appropriate pressure to
ensure that the sled lands upright. In addition, the towing bridle should be positioned such that it would be unlikely for the
sled to land upside down (Lewis 1999).
830
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Benthic-planktobenthic sampling method
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832