ESSDEarth System Science DataESSDEarth Syst. Sci. Data1866-3516Copernicus PublicationsGöttingen, Germany10.5194/essd-10-1457-2018Copepod species abundance from the Southern Ocean and other regions (1980–2005) – a legacyCopepod species abundance from the Southern Ocean CornilsAstridastrid.cornils@awi.dehttps://orcid.org/0000-0003-4536-9015SiegerRainerMizdalskiElkeSchumacherStefaniehttps://orcid.org/0000-0002-8310-9743GrobeHanneshttps://orcid.org/0000-0002-4133-2218Schnack-SchielSigrid B.Alfred-Wegener-Institut Helmholtz-Zentrum für Polar- und
Meeresforschung, Bremerhaven, Germany
deceasedAstrid Cornils (astrid.cornils@awi.de)16August20181031457147116March201829March201826May20188July2018This work is licensed under the Creative Commons Attribution 4.0 International License. To view a copy of this licence, visit https://creativecommons.org/licenses/by/4.0/This article is available from https://essd.copernicus.org/articles/10/1457/2018/essd-10-1457-2018.htmlThe full text article is available as a PDF file from https://essd.copernicus.org/articles/10/1457/2018/essd-10-1457-2018.pdf
This data collection originates from the efforts of Sigrid
Schnack-Schiel (1946–2016), a zooplankton ecologist with great expertise
in life cycle strategies of Antarctic calanoid copepods, who also
investigated zooplankton communities in tropical and subtropical marine
environments. Here, we present 33 data sets with abundances of planktonic
copepods from 20 expeditions to the Southern Ocean (Weddell Sea, Scotia Sea,
Amundsen Sea, Bellingshausen Sea, Antarctic Peninsula), one expedition to
the Magellan region, one latitudinal transect in the eastern Atlantic Ocean,
one expedition to the Great Meteor Bank, and one expedition to the northern
Red Sea and Gulf of Aqaba as part of her scientific legacy. A total of 349
stations from 1980 to 2005 were archived. During most expeditions
depth-stratified samples were taken with a Hydrobios multinet with five or
nine nets, thus allowing inter-comparability between the different expeditions.
A Nansen or a Bongo net was deployed only during four cruises. Maximum
sampling depth varied greatly among stations due to different bottom depths.
However, during 11 cruises to the Southern Ocean the maximum sampling
depth was restricted to 1000 m, even at locations with greater bottom
depths. In the eastern Atlantic Ocean (PS63) sampling depth was restricted
to the upper 300 m. All data are now freely available at PANGAEA via the
persistent identifier 10.1594/PANGAEA.884619.
Abundance and distribution data for 284 calanoid copepod species and 28 taxa
of other copepod orders are provided. For selected species the abundance
distribution at all stations was explored, revealing for example that species
within a genus may have contrasting distribution patterns (Ctenocalanus, Stephos). In
combination with the corresponding metadata (sampling data and time,
latitude, longitude, bottom depth, sampling depth interval) the analysis of
the data sets may add to a better understanding how the environment
(currents, temperature, depths, season) interacts with copepod abundance,
distribution and diversity. For each calanoid copepod species, females, males
and copepodites were counted separately, providing a unique resource for
biodiversity and modelling studies. For selected species the five
copepodite stages were also counted separately, thus also allowing the
data to be used to study life cycle strategies of abundant or key species.
Introduction
Copepoda (Crustacea) are probably the most successful metazoan group known,
being more abundant than insects, although far less diverse (Humes, 1994;
Schminke, 2007). They occur in all aquatic ecosystems, from freshwater to
marine and hypersaline environments, and from polar waters to hot springs
(Huys and Boxshall, 1991). Although copepods are evolutionary of benthic
origin (Bradford-Grieve, 2002), they have also successfully colonised the
pelagic marine environment, where they can account for 80 %–90 % of the
total zooplankton abundance (Longhurst, 1985). In the Southern Ocean,
copepods are the most important zooplankton
organisms next to Antarctic krill and salps, both in abundance and biomass (e.g. Pakhomov et al., 2000; Shreeve
et al., 2005; Smetacek and Nicol, 2005; Ward et al., 2014; Tarling et al.,
2017). In the Southern Ocean, copepods are also the most diverse zooplankton
taxon, accounting for more than 300 species (Kouwenberg et al., 2014).
However, only a few species dominate the Antarctic epipelagic assemblage: the
large calanoids Calanoides acutus, Calanus propinquus,
Metridia gerlachei, and Paraeuchaeta antarctica; the small
calanoids Microcalanus pygmaeus and Ctenocalanus citer; and the
cyclopoids Oithona spp. and species of the family Oncaeidae (e.g.
Hopkins, 1985; Atkinson, 1998; Schnack-Schiel, 2001; Tarling et al., 2017).
Together these taxa can comprise up to 95 % of the total abundance and up
to 80 % of the total biomass of copepods (Schnack-Schiel et al., 1998).
However, the smaller calanoid species alone can account for up to 80 % of
the abundance of calanoid copepods (Schnack-Schiel, 2001). Stage-resolve
counts for selected species will also allow future users to study life cycle
strategies of abundant or key species.
Numerous studies on zooplankton have been conducted in the past in the
Atlantic sector of the Southern Ocean (e.g. Boysen-Ennen and Piatkowski,
1988; Hopkins and Torres, 1988; Boysen-Ennen et al., 1991; Pakhomov et al.,
2000; Dubischar et al., 2002; Ward et al., 2014; Tarling et al., 2017). A
major zooplankton monitoring programme in the Southern Ocean is the
Continuous Plankton Recorder survey (SO-CPR), providing a large-scale
coverage of surface Antarctic zooplankton species distribution abundances
over the last 25 years (Hosie et al., 2003; McLeod et al., 2010). A recent
review summarizes the present knowledge on abundance and distribution of
Southern Ocean zooplankton (Atkinson et al., 2012). Especially in the Weddell
Sea occurrence data of copepods and other zooplankton species are scarce. One
of our aims is to fill this gap with the here-presented data sets from the
Southern Ocean, collected by Sigrid Schnack-Schiel (1946–2016) over the
period of 1982 to 2005.
In recent years there has been ample evidence that marine ecosystems are greatly
affected by climate change and ocean acidification (e.g. Beaugrand et al.,
2002; Edwards and Richardson, 2004; Rivero-Calle et al., 2015; Smith et al.,
2016). In the Southern Ocean, the pelagic ecosystem is likely to be severely
affected by increasing water temperatures and the resulting reduction of sea
ice coverage in the Southern Ocean (Zwally, 1994; Smetacek and Nicol, 2005).
It has already been observed over decades that the biomass of Antarctic
krill decreases (Atkinson et al., 2004), but little is known about the
environmental effects on copepods. Within the pelagic ecosystem zooplankton
communities and thus copepods are good indicators for ecosystem health and
status due to their short life cycles und their rapid response to changing
environments (Reid and Edwards, 2001; Chust et al., 2017). Furthermore, they
are generally not commercially exploited and thus are likely to reflect
impacts of environmental changes more objectively. To better understand the
effects of environmental change on planktonic copepods, e.g. via biodiversity
analyses and ecological niche modelling, data on species occurrence,
abundance and distribution are essential. However, modelling studies
are often limited by the scarcity of available plankton data (Chust et al., 2017).
Thus, freely available data sets on abundance and presence or absence of
copepod species are of great importance for future studies on environmental
changes in the pelagic realm. The data sets presented here on copepod
species and life stages (female, male, copepodites) occurrences and
abundance from the Southern Ocean, the eastern Atlantic Ocean, the Magellan
region and the Red Sea provide a unique resource for biodiversity and
modelling studies. They may also help to enhance our understanding of how the
environment (currents, temperature, depths, season) interacts with copepod
abundance, distribution and diversity.
MethodsSampling locations
The presented data sets were collected during 24 research cruises with
several research vessels from 1980 to 2005 (Table 1; Cornils and Schnack-Schiel, 2018). Most of the data sets
(28 data sets from 20 cruises) are based on samples from the Southern Ocean
(Fig. 1), collected on-board R/V Polarstern (25 data sets from 16
cruises), R/V Meteor (1 data set), R/V John Biscoe (1 data
set) and R/V Polarsirkel (1 data set). Southern Ocean sampling
locations were restricted to the Weddell Sea, the Scotia Sea, the Antarctic
Peninsula, the Bellingshausen Sea and the Amundsen Sea (Fig. 1).
Overview of all stations and sampling regions, including the maximum
sampling depths (colour scale bar) of the data set.
Overview of the sampling periods and research cruises. Abbreviations
of regions: Antarctic Peninsula (AP), Weddell Sea (WS), eastern Weddell Sea
(EWS), Scotia Sea (SCO), Bellingshausen Sea (BS), Amundsen Sea (AS), western
Weddell Sea (WWS), eastern Atlantic Ocean (EAO), Magellan region (MR), Great
Meteor Bank (GMB), Red Sea (RS); MN: Multinet. * Data sets with abundance
only for non-calanoid copepod species.
Additionally, four data sets were collected in other regions (Table 1). In
1994 net samples were collected on-board R/V Victor Hensen in the
Magellan region. Two data sets are based on research cruises with R/V
Meteor, to the Great Meteor Bank in the North Atlantic (1998) and to
the northern Red Sea and the Gulf of Aqaba (1999). In 2002, plankton net
samples were taken during a research cruise with R/V Polarstern
along a transect in the eastern tropical Atlantic Ocean (Table 1).
Maximum sampling depth varied greatly among stations due to different bottom
depths (Table 1). However, during 11 cruises to the Southern Ocean the
maximum depth was restricted to 1000 m, even at locations with greater
bottom depths. In the eastern Atlantic Ocean (PS63) sampling depth was
restricted to the upper 300 m.
Sampling gear
Three types of plankton nets were deployed: Bongo nets, single
opening–closing Nansen nets and multiple opening–closing nets. During all
expeditions vertical hauls were taken, thus allowing no movement of the
vessel.
Nansen net
During the expeditions PS04, DAE1979/80 and JB03 net sampling was carried
out with a Nansen net (Table 1). The Nansen net is an opening–closing
plankton net for vertical tows (Nansen, 1915; Currie and Foxton, 1956). Thus,
it is possible to sample discrete depth intervals to study the vertical
distribution of zooplankton. The Nansen net has an opening of 70 cm diameter
and is usually 3 m long. Two different mesh sizes were used:
200 µm for the cruises PS04 and JB03, and 250 µm for
DAE1979/80. To conduct discrete depth intervals the net is lowered to maximum
depth and then hauled to a certain depth and closed via a drop weight. Then
the net is hauled to the surface and the sample is removed. This process of
sampling depth intervals can be repeated until the surface layer is reached.
The volume of filtered water was calculated using the mouth area and depth
interval due to the lack of a flowmeter.
Multinet systems
Most presented data sets are based on plankton samples taken with a multinet
system (MN) from Hydrobios (Table 1) a revised version (Weikert and John,
1981) of the net described by Bé et al. (1959). The multinet is equipped with
five (midi) or nine (maxi) plankton nets, with a mouth area of 0.25 and
0.5 m2, respectively. These nets can be opened and closed at depth on
demand from the ship via a conductor cable. Thus, they allow sampling of
discrete water layers. The net system was hauled at a general speed of
0.5 m s-1. Mesh sizes varied between
the data sets from 55 to 300 µm (Table 1). In the Southern Ocean
the mesh sizes were consistent within regions: in the Weddell Sea
100 µm mesh size was used with a few exceptions during PS06. In the
Scotia Sea and near the Antarctic Peninsula a mesh size of 200 µm
was employed. In the Bellingshausen Sea and the Amundsen Sea multinet hauls
with 55 µm mesh sizes were carried out. In other regions mesh sizes
of 100 µm (PS63, M42/3), 150 µm (M44/2) and
300 µm (VH1094) were used. The MN maxi was only deployed during the
research cruise M44/2 in the northern Red Sea.
Generally, the volume of filtered water was calculated from the surface area
of the net opening (midi: 0.25 m2, maxi: 0.5 m2) and the sampling
depth interval. For the data sets from PS63, PS65, PS67 and M44/2 a
mechanical digital flowmeter was used to record the filtering efficiency and
to calculate the abundances (see Skjoldal et al., 2013, p. 4). The flowmeter
is situated in the mouth area of the net and measures the water flow,
providing more accurate volume values of the filtering efficiency.
Bongo net
During one research cruise (PS06) 61 additional samples were taken with the
Bongo net (McGowan and Brown, 1966) to study selected calanoid copepod
species. The Bongo net contains two nets that are lowered simultaneously for
vertical plankton tows. The opening diameter is 60 cm, and the length of the
nets is 2.5 m with a mesh size of 300 µm. The volume of filtering
water was recorded with a flowmeter and used for the calculation of
abundance.
Effects of variable net types and mesh sizes
Quantitative sampling of copepods and zooplankton is challenging. Major
sources of error are patchiness, avoidance of nets and escape through the
mesh (Wiebe, 1971; Skjoldal et al., 2013). These errors are defined by mesh
sizes and net types, in particular the mouth area. The effect of patchiness
cannot be investigated here due to the lack of replicates.
To our knowledge the sampling efficiency of the Nansen net and the MN midi
have not been compared directly (Wiebe and Benfield, 2003; Skjoldal et al.,
2013). However, it has been stated that the catches with Nansen net are
considerably lower than with the WP-2 net (Hernroth, 1987), although the WP-2
net is considered as a modified Nansen net with a cylindrical front section
of 95 cm and a smaller mouth area (57 cm2, Skjoldal et al., 2013). The
WP-2 net with 200 µm mesh size however, is in its sampling
efficiency, measured as total zooplankton biomass, comparable to the MN midi
with 200 µm mesh size (Skjoldal et al., 2013). Thus, it has to be
taken into account during future analysis that the abundance values from the
Nansen net are not directly comparable to those from the MN midi.
The mesh size has a different effect on the zooplankton catch. It is well
known that small-sized copepod species (<1 mm), and thus in particular
non-calanoid species (e.g. Oithonidae, Oncaeidae) and also juvenile stages
from calanoid copepods (e.g. Microcalanus, Calocalanus,
Disco), pass through coarse mesh sizes (≥200µm),
while they are retained in finer mesh sizes (Hopcroft et al., 2001;
Paffenhöfer and Mazzocchi, 2003). Thus, abundances of smaller specimens
as well as the species and life stage composition may vary considerably, when
comparing samples from the Bellingshausen and Amundsen Seas (55 µm
mesh size), around the Antarctic Peninsula (200 µm) and the Weddell
Sea (100 µm).
Sample processing and analysis
All samples were preserved immediately after sampling in a 4 %
formaldehyde–seawater solution. Samples were stored at room temperature
until they were sorted in the laboratory. The formaldehyde solution was
removed, the samples were rinsed and copepods were identified and counted
under a stereomicroscope, using a modified mini-Bogorov chamber with high
transparency as described in the ICES Zooplankton Methodology Manual (Postel
et al., 2000). Abundant species were sorted from one-quarter or less of the
sample while the entire sample was screened for rare species. Samples were
divided with a Motoda plankton splitter (Motoda, 1959; Van Guelpen et al.,
1982). Abundance was calculated using the surface area of the net opening
and the sampling depth interval or the recordings of the flowmeter. Samples
for re-analysis are only available for the cruises M42/3 and M44/2.
Except for five data sets (Cornils and Schnack-Schiel, 2017; Cornils et al.,
2017a, b, c, d) all data sets were sorted and identified by Elke Mizdalski.
Thus, the taxonomic concept has been used consistently throughout the data
sets. A wide variety of identification keys and species descriptions have
been used to identify the copepods, which cannot all be named here.
References for the species descriptions and drawings of all identified marine
planktonic species can be found in Razouls et al. (2005–2018). Calanoid
copepods were identified to the lowest taxa possible, in general genus or
species. Furthermore, for each identified taxon, females, males and copepodite
(juvenile) stages were separated. Cyclopoid copepods were identified to
species level in four data sets (Cornils et al., 2017a, b, c, d).
Previously published data sets were revised to ensure consistency of species
names throughout the data set collection (Michels et al., 2012;
Schnack-Schiel et al., 2007, 2010; Schnack-Schiel, 2010a). In the present compilation we have used the currently acknowledged
copepod taxonomy as published in WoRMS (World register of Marine Species,
WoRMS Editorial Board, 2018) and in Razouls et al. (2005–2018). Species
names have been linked to the WoRMS database, so future changes in taxonomy
will be tracked. In the parameter comments the “old” names are archived
that were used initially when the specimens were identified. All used species
names can be found in the “Copepod species list” under “Further details” at
10.1594/PANGAEA.884619 or at
http://hdl.handle.net/10013/epic.65463ec2-e309-4d57-8fe3-0cebdd7dce70 (last access: 10 February 2018). We also provided the unique identifier (Aphia ID)
from WoRMS (WoRMS Editorial Board, 2018) and notes on the distribution of each species.
When specimens could not be identified due to the lack of identification
material, uncertainties in the taxonomy or missing parts, they were summarized
under the genus name (e.g. Disco spp., Diaixis spp.,
Paracalanus spp., Microcalanus spp.) or family name (e.g.
Aetideidae, copepodites). In most data sets some individuals could not be
assigned to any family or genus. These are summarized as Calanoida
indeterminata, female; Calanoida indeterminata, male; and Calanoida
indeterminata, copepodites.
Data setsMetadata
Each data set has its own persistent identifier. The metadata are consistent
among all data sets, thus ensuring the comparability of the data sets and
document their quality.
The following metadata can be found in each data set:
“Related to” includes the corresponding cruise report, related data
sets, and scientific articles of Sigrid Schnack-Schiel and others that have
used part of the data previously.
“Other version” in a few cases we have revised a previously published
version of the data to ensure consistent species names throughout all data
sets (for more information see Sect. 2.3).
“Projects” shows internal projects or those with external funding. In the
present case all data sets are related to internal projects of the AWI
(Alfred Wegener Institut Helmholtz Centre for Polar and Marine Research)
research program.
“Coverage” gives the minimum and maximum values of the georeferences
(latitude–longitude) of all stations.
“Event(s)” comprises a list of station labels, a combination of cruise
abbreviation and station number. Latitude and longitude of the position (units
are in decimals with six decimal places), date and time of start and end of
station, and elevation giving the bottom depth. Latitude and longitude, date and time
and elevation were all recorded by the systems of the respective scientific
vessel. The campaign name contains the cruise label (including optional labels), the basis of which is
the name of the research vessel. The name of the device contains the net type that was
deployed, and the comment may show further details of the station operation.
“Parameter(s)” is a list of parameters used in the data set with columns
containing the full and short name, the unit, the PI (which in this data
compilation is always Sigrid Schnack-Schiel, except for one data set
(10.1594/PANGAEA.880239), and the method with a comment. The parameter
“Date/Time of event” is not always identical with “Date/Time” given in
the event. This is the case when the “Device” in the event is set to
“Multiple Investigations” and thus the starting time of all investigations
at this event is given. “Date/Time of event”, however, is the time when the
plankton net haul started. “Date/Time” recorded on R/V Polarstern
and during the cruises M42/3 and JB03 was UTC (Coordinated Universal Time)
and during cruise M44/2 local time was recorded (UTC+2). No information on
“Date/Time” was found for the cruises DAE1979/80, M11/4 and VH1094.
“Elevation” provides information on the bottom depth of the plankton
station, if available.
Three parameters describe the sampling depths interval. “Depth, water” is
the mean depth of the sampled depth interval. “Depth top” and “Depth
bot” describe the upper and lower limit of the sampling depth interval,
respectively.
“Volume” is the amount of water that was filtered during each net tow,
calculated either using the mouth area of the net and depth interval or with
a flowmeter (Sect. 2.2.2). “Comment” gives the detailed information on the
net type, the net number and mesh size.
In the following list of parameters
are the copepod taxa for which abundance data were recorded. Calanoid taxa
are separated into female, male and copepodites. Species names are consistent
throughout all data sets, which ensures the comparability of the data sets.
Clicking the link on the species names leads to their respective WoRMS ID (see
Sect. 2.3). The “short names” of each taxon consist of the first letter of
the generic name and the name of the species. In nine cases this results in
identical short names (Pleuromamma antarctica, Paraeuchaeta antarctica=P. antarctica; Temoropia minor,
Temorites minor=T. minor; Chiridius gracilis,
Centropages gracilis=C. gracilis; Clausocalanus minor, Calanopia minor =C. minor;
Heterostylites longicornis, Haloptilus longicornis=H. longicornis; Scolecithricella abyssalis,
Spinocalanus abyssalis=S. abyssalis;
Scaphocalanus magnus, Spinocalanus magnus=S. magnus). Thus, we advise to use the full scientific names of these species
in further analyses.
Temporal station distribution
While samples of the Magellan region (November 1994), the Gulf of Aqaba and
the northern Red Sea (February–March 1999), the Great Meteor Bank
(September 1998), and the eastern Atlantic Ocean (November 2002) were restricted
to 1 year and 1 season, the Southern Ocean was sampled multiple times
(Table 1). Samples in the Southern Ocean were taken from 1980 to 2005
(Table 1, Fig. 2a, b). The highest number of zooplankton samples was taken in
the 1980s (Fig. 2b). In the 1980s the sampling effort was concentrated to the
Antarctic Peninsula, the Scotia Sea and the Weddell Sea (Fig. 2a). Samples
were taken in multiple years. In the 1990s until 2005 most samples were taken
in the Bellingshausen and Amundsen Sea, with fewer samples in the western and
eastern Weddell Sea. Two transects were sampled across the Weddell Sea in the
1990s in austral summer and autumn (Fig. 2b). In general, most stations were
sampled during summer (December to February), followed by autumn (March to
May) and spring (September to November), while winter samples are only
available from 1986 in the eastern Weddell Sea (Fig. 2b, c). Summer and
autumn samples are widely distributed from the Amundsen Sea to the eastern
Weddell Sea (Fig. 2b), while spring and autumn samples are mostly present
from the Scotia Sea and eastern Weddell Sea. Most samples were taken in
January and February (Fig. 2d). Samples are scattered throughout the entire
day (Fig. 3).
Sampling effort in the Southern Ocean: (a) station
distribution in years, (b) station distribution in the annual cycle,
(c) number of stations per year and season, (d) number of
stations per month and year.
Sampling effort during day-time in the Southern Ocean. Day-time is
important to understand the behaviour of diel vertical migrators. The number
of stations is summarized for every hour of the day, e.g. the bar at 00:00
contains all stations taken between 00:00 and 00:59.
It should be taken into account that several copepod species in regions with
pronounced seasonality of primary production, e.g. in high latitudes or
upwelling regions (Conover, 1988; Schnack-Schiel, 2001), undergo seasonal
vertical migration (e.g. Rhincalanus, Calanoides). They reside in deep water layers during
periods
of food scarcity and rise to the surface layers when the phytoplankton
blooms start. Furthermore, other species undergo pronounced diel vertical
migrations (e.g. Pleuromamma) from mesopelagic layers during day-time to avoid
predators, moving to epipelagic waters at night to feed (Longhurst and Harrison, 1989). Thus,
to avoid biases in the comparison of the vertical distribution of copepod
species, season and day-time should be considered during further analysis of
the data sets.
Copepoda
In total, specimens from six copepod orders were recorded in the compiled
data sets.
However, in 29 data sets only calanoid copepods were identified on species
level. Specimens of other copepod orders were comprised in families or
orders.
Calanoida
List of calanoid copepod families and genera, cyclopoid families,
and other orders compiled in this data collection. The number of species for
each genus is written in parentheses. The presence of the calanoid and
cyclopoid families and other copepod orders in the five different regions is
marked (X). For a complete overview of all species see the “Copepod species
list” at https://doi.org/10.1594/PANGAEA.884619.
In total 284 calanoid species could be separated into 29 data sets (see
“Copepod species list” at 10.1594/PANGAEA.884619). These species are
representatives of 28 families and 91 genera (Table 2). Abundance and distribution data for 96 calanoid species in the Southern Ocean were archived. In the
eastern Atlantic Ocean 125 and around the Great Meteor Bank 135 calanoid
copepod species could be identified (Table 2). These numbers already indicate
the well-known fact that species richness in the tropical and subtropical
open oceans is much higher than in the polar Southern Ocean (e.g. Rutherford
et al., 1999; Tittensor et al., 2010). Compared to these the number of
calanoid species (60) in the subtropical northern Red Sea is low, which is
expected due to the shallow sills at the entrance of the Red Sea and the high
salinity (see Cornils et al., 2005). The lowest number of calanoid species
(35) was found in the Magellan Region. Calanoid copepod families with the
highest number of species were Aetideidae (33), Augaptilidae (27) and
Scolecitrichidae (40; Table 2).
For selected species from the Southern Ocean and the northern Red Sea and
Gulf of Aqaba, the five copepodite stages were also counted individually
(Table 3), providing valuable information on the seasonal and vertical
distribution of the five copepodite stages. During four cruises,
Rhincalanus gigas nauplii were also counted (PS09, PS21, PS23, PS29). In
the 1990s Sigrid Schnack-Schiel used these data to publish a series of
papers on life cycle strategies of Antarctic calanoid copepods such as
Calanoidesacutus, Rhincalanusgigas,
Microcalanus cf. pygmaeus or Stephoslongipes (e.g. Schnack-Schiel and Mizdalski, 1994; Schnack-Schiel et
al., 1995; Ward et al., 1997; Schnack-Schiel, 2001). However, the
stage-resolved copepod data of most species in Table 3 have not been
analysed.
List of species and cruises to the Southern Ocean where copepodite
stages 1–5 were separated and counted. Species with asterisks were
separated from samples of cruise M44/2 to the northern Red Sea and the Gulf
of Aqaba.
Distribution and abundance as individuals per cubic metre (Ind m-3) of selected genera
(Microcalanus, Spinocalanus, Ctenocalanus,
Stephos). Depth (m) is the mean depth of each sampling depth
interval (“Depth water”).
It is notable that none of the calanoid species were found in all five
regions (see “Copepod species list” at 10.1594/PANGAEA.884619). In
contrast, many species were only recorded in one region: 60 species were
found only in the Southern Ocean, while 43 and 38 were found only in the data
sets from the Great Meteor Bank and the transect in the eastern Atlantic
Ocean, respectively. A total of 24 species were found only in the Red Sea and 6 were
identified only from samples in the Magellan region. Of the 28 calanoid
families, 11 were distributed in all five regions (Table 2).
As an example of the geographical and vertical distribution of the copepods,
three abundant genera were chosen (Fig. 4). While Microcalanus spp.
(not separated into species due to uncertainties in the taxonomy) and
Spinocalanus spp. (nine species; Table 2) are abundant down to 1000 m,
the two species of Ctenocalanus (two species, Fig. 4) and
Stephos occur mainly in the epipelagic layer of the ocean. This is
in accordance with their known vertical distribution (Schnack-Schiel and
Mizdalski, 1994; Bode et al., 2018). Comparing the abundance of
Spinocalanus and Microcalanus from all regions suggests
that the abundance of these taxa is far greater in the Southern Ocean than in
the warmer regions of the ocean. This picture, however, has to be treated with
caution, since the tropical Atlantic was only sampled in the upper 300 m of
the water column and was thus too shallow for the meso- and bathypelagic
genera (Bode et al., 2018).
In the case of Ctenocalanus and Stephos our data sets
reveal that closely related species within a genus may have contrasting
distribution patterns. Stephos longipes and Ctenocalanus citer are restricted to colder and polar waters of the Southern Hemisphere,
while Ctenocalanus vanus occurs in both the Red Sea and the warm
Atlantic Ocean. Stephos maculosus occurs only in the Red Sea (see
arrow in Fig. 4). Furthermore, the distribution patterns reveal that of the
four genera only C. citer has a higher abundance in the samples from
the Bellingshausen and Amundsen Seas, and around the Antarctic Peninsula,
while S. longipes, Microcalanus spp. and
Spinocalanus spp. all have higher abundances in the eastern Weddell
Sea. This may be due to the lower water depth at the Peninsula since
Microcalanus and Spinocalanus are considered as mesopelagic
to bathypelagic. Thus, they are often not found at shallow stations (<300 m depth). In case of the sea-ice-associated S. longipes, low
sea-ice conditions and offshore stations may have caused the restricted
distribution. S. longipes occurred mainly in the upper water layers,
but it was also recorded with low abundances in deeper layers (Fig. 4). This
pattern may be due to its life cycle, shifting seasonally from a sea-ice-associated to a bentho-pelagic life cycle (Schnack-Schiel et al., 1995).
Other Copepoda
In total, 28 non-calanoid taxa were recorded. Four data sets provide only
abundance and distribution data for non-calanoid copepod orders (PS06, PS10,
PS29, PS35; Table 1), in particular on species of the order Cyclopoida from
the families Oithonidae (two species) and Oncaeidae (six species; Table 2). They
were separated into female, male, and copepodite stages 1, 2, 3, 4 and 5. During
VH1094 Oithona species were also identified (Table 2). In all other
data sets species of these two families were not separated. In all regions
representatives of the family Lubbockiidae were recorded. In the subtropical
and tropical samples of PS63, M44/2 and M42/3 abundances of species of
the families Corycaeidae and Sapphirinidae, and of the genus Pachos
were also recorded. Except for PS65, species of the order Harpacticoida were not
separated. In the latter five species were identified, mainly sea-ice-associated harpacticoids (Table 2; Schnack-Schiel et al., 1998). Also,
specimens of the orders Monstrilloida, Mormonillida and Siphonostomatoida
were counted.
In most data sets, copepod nauplii are also recorded as one parameter.
However, due to the small size of nauplii they were not sampled
quantitatively and should be discarded in further analysis.
Further remarks on the usage of the data compilation
Generally, the cruise reports have been linked to each data set. The cruise
reports provide valuable information on the itinerary, zooplankton sampling
procedures and on other scientific activities on-board that could be useful
for the data analysis (e.g. CTD data). Abundance data of selected species
and data sets have been published previously in scientific articles. These
articles are linked to the respective data sets (under “Related to”).
To use the data, they can be downloaded individually as tab-delimited text
files or altogether as a .zip file to allow an import to other software, e.g.
R (R core team, 2018) or Ocean Data View (Schlitzer, 2015) for further
analysis. Due to the consistent taxonomic nomenclature the individual files
can be concatenated easily. It should be kept in mind, however, that not all
data sets are directly comparable due to differences in net type and mesh
sizes (see Sect. 2.2.4). As noted in Sect. 3.2, several species undergo
pronounced seasonal and diel vertical migrations. Therefore, nets from
surface waters may not always sample the full vertical extent of the
populations, particularly of the biomass dominants.
To evaluate the vertical and spatial distribution of marine plankton,
hydrographic information such as temperature and salinity profiles is
essential. The relevant publications are available at
10.1594/PANGAEA.884619; see “Further details”. Recently, a summary of
the physical oceanography of R/V Polarstern has been published
(Driemel et al., 2017) with CTD data archived in PANGAEA as well (Rohardt et
al., 2016), except for the cruises PS04 (ANT-II/2), PS14 (ANT-VII/2), PS21
(ANT-X/3), PS63 (ANT-XX/1) and PS65 (ANT-XXII/2) (see Table 1). For these
five cruises information on temperature and salinity profiles exist only for
PS63 (Schnack-Schiel et al., 2010) and for PS65 the CTD profiles can be
downloaded (10.1594/PANGAEA.742627; Absy et al., 2008). For M11/4 a CTD
data set is also available (10.1594/PANGAEA.742745; Stein, 2010). To
connect the CTD data with the corresponding plankton net haul the metadata
“Event“ and “Date/time“ can be used. Furthermore, cruise track and
station information are available in the cruise reports as well as on the
station tracks for each cruise
(https://pangaea.de/expeditions/, last access: 10 February 2018). For the other two R/V Meteor cruises hydrographic information is
available in scientific articles (M42/3: Beckmann and Mohn, 2002; Mohn and
Beckmann, 2002; M44/2: Cornils et al., 2005; Plähn et al., 2002).
Metadata information of the cruise JB03 can be downloaded from
https://www.bodc.ac.uk/resources/inventories/cruise_inventory/report/5916/ (last access: 10 February 2018). To date, no hydrographic information is publicly
available for the cruises DAE79/80 and VH1094.
Additionally, abundances of all other zooplankton organisms in the net
samples used for the copepod data sets are available for the four cruises
ANT-X/3, ANT-XVIII/5b, M42/3 and M44/2. These can be downloaded at
10.1594/PANGAEA.883833, 10.1594/PANGAEA.884581,
10.1594/PANGAEA.883771 and 10.1594/PANGAEA.883779.
All data presented here are archived in the database PANGAEA. There are,
however, other data archiving initiatives that also store data on copepod
abundance and distribution such as COPEPOD
(https://www.st.nmfs.noaa.gov/copepod/, last access: 10 February 2018), BODC (https://www.bodc.ac.uk, last access: 10 February 2018) or OBIS (http://www.iobis.org, last access: 10 February 2018). The here-presented data, however, have not been
published in any other cataloguing initiative before.
In total 33 data sets with 349 stations were archived in
the PANGAEA® (Data Publisher for Earth &
Environmental Science, www.pangaea.de) database (Cornils and Schnack-Schiel, 2018). The persistent
identifier 10.1594/PANGAEA.884619 links to the splash page of the data
compilation. We encourage the users of these data to cite both the DOI of the
data collection in PANGAEA as well as the present data publication as a
courtesy to Sigrid Schnack-Schiel and the people preparing the data for
open access. Metadata include DOIs to cruise reports and related physical
oceanography. Data are provided in consistent format as tab-delimited
ASCII files and are available through open access under a CC BY license (Creative Commons
Attribution 3.0 Unported).
Concluding remarks
Pelagic marine ecosystems are threatened by increasing water temperatures due
to climate change. These environmental changes are also expected to cause
shifts in the community structure of pelagic organisms. Within the pelagic
food web copepods have a central role as intermediator between the microbial
loop and higher trophic level. Due to their short life cycles and their high
diversity copepods offer a unique opportunity to study effects of
environmental variables on numerous taxa with different life cycle
strategies. It is also known that their species composition and abundance
often reflect environmental changes such as temperature, seasonal variability
or stratification (Beaugrand et al., 2002). To understand the complexity of
ecological niches and ecosystem functioning, but also to investigate the
effects of environmental changes, a detailed knowledge of species diversity,
distribution and abundance is essential. The present data compilation
provides further information on spatial, vertical and temporal distribution
of copepod species and may thus be used to obtain a better picture of species
biogeographies. Many individual data sets can also be linked to corresponding
CTD profiles (Table 1) and may thus be useful for modelling approaches such as
species distribution or environmental niche modelling.
Furthermore, for all calanoid copepods females, males and copepodites were
enumerated separately, and for selected species a distinction between copepodite
stages was made. This detailed resolution of abundance data will
also allow future investigations on life cycle strategies as well as show how the
different stages interact with the environment (e.g. temperature, currents,
depth).
AC and HG were initiators of the data collection and the paper.
Data collection and initial analysis was carried out by SiS. Copepod
identification (except cyclopoid copepods) and the curation of taxon names
was carried out by EM and AC. Data curation was carried out by RS and StS. AC
drafted the paper and EM, StS, and HG provided input.
The authors declare that they have no conflict of
interest.
Acknowledgements
We would like to thank numerous scientists, technicians and students who
helped with the sampling on-board, and the sample processing and analysis in
Bremerhaven, in particular Ruth Alheit. We are grateful to the crews of R/Vs
Polarstern, Meteor, Victor Hensen, John Biscoe and Polarsirkel, who helped in many ways during every
expedition. We would also like to thank Thomas Brey who strongly supported
the effort to archive this data collection. Finally, we thank Angus Atkinson
and two anonymous reviewers whose comments improved the
paper.Edited by: Falk Huettmann
Reviewed by: Angus Atkinson and two anonymous referees
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