HPLC accessory pigment dataset for the North Sea in 2010 and 2011 accompanying publication of Ford et al. 2017

The International Bottom Trawl Survey (IBTS) is a multinational
ecological research effort established by the International
Council for the Exploration of the Sea (ICES)
in the early 1970s. Surveys using fisheries research vessels
currently take place in the first and third quarter of
30 the year and cover the entire North Sea, using standardized
sampling gears and protocols. With cruise lengths of
typically 6–8 weeks, each vessel undertakes a gridded survey
of the North Sea, repeated each year, in which stations
are sampled for groundfish (the primary target of
35 the survey), but also secondary targets such as benthos,
seabed litter, and hydrographic parameters. Individual station
sampling is often accompanied by visual seabird and
cetacean estimates, underway acoustics, and online monitoring
of near-surface water quality using FerryBox-type in40
struments (Petersen et al., 2008). The IBTS thus fits the
needs of a multi-disciplinary survey capable of collecting
data on human pressures and ecosystem responses for
legislation such as the MSFD (http://www.jpi-oceans.eu/
multi-use-infrastructure-monitoring). The open data policy
45 of ICES has resulted in many significant publications in
fisheries research (Jennings et al., 2002; Daan et al., 2005)
and fisheries policy (Rombouts et al., 2013; Shephard et al.,
2015).
Prior to 2010, phytoplankton had not been systematically
50 sampled on the UK IBTS. Advances in the autonomous sampling
and detection of particles in the water column (e.g.online flow cytometry, Thyssen et al., 2015), and also the
need for high-quality in situ data for validation of satellite
remote-sensing data, indicated that the addition of phytoplankton
to the survey would be beneficial. Hence, sam- 55
pling of PFTs using high-pressure liquid chromatography
(HPLC – pigment fingerprinting), and analytical flow cytometry
(results reported elsewhere) were initiated on the third
quarter IBTS cruise of the RV Cefas Endeavour in August–
September 2010 and subsequent years. 60
Seawater samples from depths of 4m (“surface”) were collected
using 10 L Niskin bottles when weather conditions
permitted, or from the ship’s bow-intake flow-through clean
seawater supply during adverse weather conditions. A known
amount of water, typically 1000 mL, was passed through a 65
200 μm gauze to remove larger zooplankton and debris, then
filtered within 1 h on 47mm GFF filters, which were folded
in half, wrapped in aluminium foil and snap frozen in liquid
nitrogen dry shippers. On return to shore, samples were
transferred to a 􀀀80 C freezer for a storage period of 1– 70
2 months before shipping of samples on dry ice to an accredited
HPLC laboratory (DHIWater Quality Institute; Horsholm,
Denmark) for chlorophyll a (Chl a) quantification
and full accessory pigment analysis (Schlüter et al., 2011).
Pigment data from the surface stations were quality data 75
controlled in several steps: first, with an initial comparison
of HPLC Chl a against independent measures of chlorophyll
fluorescence from the fluorometers on the ship’s FerryBox
and CTD system. This step corrected a small number of
mislabelled samples. In a second step, anomalies within a 80
sample were detected using methods described by Aiken et
al. (2009), e.g. regression of total accessory pigments against
Chl a concentration and search for outliers.
Diagnostic pigment analysis was then used on the qualitycontrolled
data set to relate the composition of specific ac- 85
cessory pigments to the relative contribution of different
size classes to the total phytoplankton biomass. The designation
of specific accessory pigments to algal taxonomic
groups of different size, e.g. fucoxanthin and peridinin for
large-cell diatoms and dinoflagellates, has been widely es- 90
tablished in the biological oceanographic literature (Uitz et
al., 2006, 2008). The equations used to estimate the contribution
of pico-phytoplankton (0–2 μm), nano-phytoplankton
(2–20 μm) and micro- or net phytoplankton (>20 μm) were
later modified by Hirata et al. (2008, 2011) and Brewin 95
et al. (2010). The various methods differ in the degree to
which the marker pigments chlorophyll b (Chl b) and 19-hexfucoxanthin
(19-hex) are attributed to the three size classes.
Here, Chl b and 19-hex were assigned equally to the picophytoplankton
and nano-phytoplankton size classes. Pico- 100
phytoplankton are therefore represented by zeaxanthin, Chl
b, and 19-hex; nano-phytoplankton are represented by 19-
hex, 19-but, alloxanthin, and Chl b; and micro-phytoplankton
are represented by fucoxanthin and peridinin. Results are expressed
as a proportion of the total Chl a concentration for 105
each station.