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