Distributional records of Ross Sea (Antarctica) planktonic Copepoda from bibliographic data and samples curated at the Italian National Antarctic Museum (MNA)

Study Extent

The study of the copepods in the Ross Sea has been one of the earliest scientific efforts and main aims of the first oceanographic expeditions of the Italian National Antarctic Research Program (PNRA), which started in 1985. In fact, during the III (1987-88), the V (1989-90), and the X (1994-95) oceanographic expeditions, an extensive amount of biological and environmental data was acquired at the same sampling stations in a collaborative framework.

Sampling

Most samples composing this dataset were collected using a BIONESS, a zooplankton sampler consisting of multiple (usually ten) nets, stacked horizontally, that opened and closed, by an on-board operator, at desired depths while the instrument was towed by a vessel (ICES 2000). Due to the exceptional filtration to mouth area ratio (10:1), a 90% filtration efficiency can be reached for a clean net towed at 1.5 m s-1. Zooplankton samples are collected in dedicated cod-end numbered buckets for the subsequent handling and processing. During the PNRA expeditions environmental data were acquired by a multiparametric probe fixed on the BIONESS that recorded: temperature, salinity, depth, speed, in- and out-flow through the net, filtration efficiency and net number. Another sampling device employed during these PNRA activities was the WP2 (Working Party II) standardized net. This net had a 57 cm (0,25 m2) opening and length of 2,6 m which, combined with a 200/250 µm mesh width, offers high efficiency while performing vertical samplings of mesozooplankton (Fraser 1966, ICES 2000).

Quality Control

All data were gathered in a single dataset which was formatted in order to fulfill the Darwin Core standard protocol (Wieczorek et al. 2012) required by the OBIS scheme (http://www.iobis.org/manual/lifewatchqc/) and according to the SCAR-MarBIN Data Toolkit (http://www.scarmarbin.be/documents/SM-FATv1.zip). The dataset was uploaded and integrated with the ANTOBIS database (the geospatial component of SCAR-MarBIN). All taxonomy was checked and updated through WoRMS (Horton et al. 2019, World Register of Marine Species; http://www.marinespecies.org; last accessed 02 December 2019). Different control and data-cleaning steps have been undertaken, where possible, in order to increase data quality (fare riferimento al flow chart). The map was produced using the collection of dataset “Quantarctica” (Matsuoka et al. 2018) and QGIS (QGIS Development Team 2020). The Darwin Core elements included in the dataset are: occurrenceID, BasisOfRecord (HumanObservation for the bibliographic records and PreservedSpecimen for the museum specimen records), type (identifying the nature of the resource), scientificName (the name in the lowest taxonomic rank identified and updated according to WoRMS with authorship and date for the records identified at the species level), order, family, genus, specificEpithet, scientificNameAuthorship (corresponding to the updated taxonomy according to WoRMS, together with the previous four elements), originalNameUsage (the original identification as reported in the bibliographic resource), identificationQualifier (the qualifier for the uncertainty of identification), scientificNameID (the globally unique identifier for the taxonomic information related to the scientificName and stored in WoRMS), taxonRemarks (notes and considerations regarding the taxonomy of the record), organismQuantity, organismQuantityType (the type of quantification system used, such as the number of individuals or abundance per 100 or one cubic metre), sex, lifeStage (following the controlled vocabulary ‘BODC parameter semantic model biological entity development stage terms‘ at https://github.com/nvs-vocabs/S11), occurrenceRemarks (name of the PNRA research expedition), fieldNumber (name of the sampling station and net number, separated by an underscore), eventDate (date of the sampling event), decimalLatitude, decimalLongitude, minimumDepthInMeters, maximumDepthInMeters, sampleSizeValue (the number of cubic meters filtered by the net as reported in the bibliographic resource), sampleSizeUnit, samplingProtocol (following the controlled vocabulary at http://vocab.nerc.ac.uk/collection/B07/current/, Wiebe et al. 2014), eventRemarks (name of the sampling gear as reported in the bibliographic reference and mesh size of the net, separated by a pipe), associatedReferences (bibliographic reference associated to the resource), preparations (following ‘Documentation for code table SPECIMEN_PART_NAME’ at http://arctos.database.museum/info/ctDocumentation.cfm?table=CTSPECIMEN_PART_NAME), catalogNumber (museum voucher code for the specimen). Most of the sampling stations have two sets of coordinates: the starting and ending points. In such cases, the coordinates reported in the dataset refer to the starting point of the sampling event. Some museum records do not report the net number. For these records, the minimum depth has been omitted, while for the maximum depth has been reported the value registered for the corresponding sampling station.

Method steps

1. All the literature occurrences (defined by the term ‘HumanObservation’ under the column ‘BasisOfRecord’) were manually extracted from five different data reports published in 1990, 1992 and 2002 (Carli et al. 1990, 1992, 2002, Zunini Sertorio et al. 1990, 1992). The information regarding the sampling events for the III and V Italian Antarctic expeditions (e.g. sampling station coordinates, depth, volume filtered, etc.) was manually extracted from two other data reports (Guglielmo et al. 1990, 1992). The general characteristics of the sampling events are here reported (Supplementary material 1) with starting and ending coordinates along with information on the subsequent samples handling (e.g. aliquot examined). All the natural collection occurrences (defined by the term ‘PreservedSpecimen’ under the column ‘BasisOfRecord’) correspond to a portion of the entire batch of samples collected during the III and V expeditions, acquired by the MNA. The recent taxonomic revision was carried out by GB and MC mainly focusing on those samples for which no sorting at the species level was carried on, for example for those which originated from the first net (usually denoted with the number ‘0’) of the Bioness. This net is deployed open from the surface and closed once at the predetermined starting depth for the second net (denoted with the number ‘1’) (Wiebe et al. 2014). The collected samples were initially fixed in 4% formalin and later transferred in pure Ethanol. As the two different kind of distributional data (e.g. preserved specimens and human observation) originated from the same sampling events, but were generated by multiple groups of researchers in different years, an apparent conflict might derive from multiple records sharing the same taxonomic, event (e.g. sampling station, depth, etc.) and organism quantity information. However, most of the literature occurrences were reported with abundance measures, whereas all the preserved specimen records were reported with the number of individuals, originated by a merely qualitative approach and from different aliquots with respect to the ones used by the original authors. Some bibliographic records from the V expedition were originally reported with the number of individuals (Zunini Sertorio et al. 1992), instead of an abundance measure. Nevertheless, for the same reason mentioned earlier, being different the aliquots examined, the conflict still doesn’t arise. Moreover, the number of individuals reported for these particular bibliographic records can still be converted in abundance measures, as the authors of the original bibliographic reference provided the volumetric information on the aliquot examined, here reported as well

The study area covers a high portion of the northwestern Ross Sea, spanning from the Drygalski Ice Tongue in Terra Nova Bay to the continental slope surrounding the Central Basin. Some sampling stations exceed the Antarctic circle to reach the Balleny Islands and the northwestern stretch of sea.