DOI: 10.5061/dryad.w0vt4b90c
title: Data from: Distribution, population dynamics and potential impacts of the invasive snail, Tarebia granifera in aquatic ecosystems of north-eastern South Africa

description: Aquatic ecosystems globally have been invaded by molluscs. Tarebia
 granifera is a highly successful invader, often becoming the dominant
 aquatic invertebrate species in an invaded ecosystem. Resultingly, it has
 been suggested that T. granifera may have severe negative impacts on these
 invaded ecosystems. Limited information is available regarding the
 population structures and densities of T. granifera, particularly in
 invaded countries such as South Africa, and information on this could
 assist in developing management and control strategies for this invasive
 species. The aim of the present study was to assess the current
 distribution, densities, and population structures of T. granifera in
 invaded habitats on the Limpopo and Phongolo River systems, South Africa.
 This was accomplished by collecting aquatic benthic molluscs from sites
 across these systems. Water quality parameters were measured at each site
 and water samples collected for chemical nutrient analyses. The density of
 snails was determined for each site and the population size and structure
 as well as birth rate was calculated for T. granifera. Tarebia granifera
 was found to be the dominant molluscan species in habitats where it was
 present and all size classes from new-born to mature adults were found
 throughout at some of the highest densities globally. Worryingly, native
 molluscan species, were often absent or in much lower densities than
 reported in literature at sites where T. granifera was present, suggesting
 a negative effect on the native molluscan density and diversity. Contrary
 to most previous studies, there were no significant correlations between
 T. granifera and the selected water quality parameters. Higher densities
 and new-born recruitment of T. granifera were observed in the spring than
 autumn, likely in response to shifts in environmental conditions. This
 study provides crucial insights into the population structure and dynamics
 of T. granifera in invaded habitats, particularly for relatively newly
 invaded regions such as southern Africa.
description: Nineteen sites were selected for sampling in this study based on
 known distributions of aquatic snails (invasive and native) and
 accessibility to sites (Figure 1). Four sites were sampled on the lower
 Phongolo River in northern KwaZulu-Natal (August – September 2017), South
 Africa, and a total of 15 sites were sampled on the Limpopo River and its
 tributaries (Limpopo River system), in the Mpumalanga and Limpopo
 provinces of South Africa (April – May 2021). Two sites in the Limpopo
 River system on the Olifants River (OLIF-1, OLIF-2) were sampled in
 consecutive years (2020 and 2021).  Mollusc sampling
 and identification Each of the 19 selected sites was
 sampled for aquatic benthic molluscs (including snails and
 bivalves/clams), using a metal-frame square benthic sampler (30 x 30 cm, 2
 mm mesh size). The sampler was used to scoop up sediment and sieve through
 the benthic zone of the river. Random samples, each comprising three
 replicates consisting of ten scoops per replicate (30 sampler scoops)
 covering a total area of 2.7 m<sup>2</sup> were collected.
 Sampling occurred randomly within the site areas, avoiding deep waters due
 to the presence of crocodiles (<em>Crocodylus niloticus</em>).
 Samples were preserved with 70% ethanol in plastic jars and transported
 back to the laboratory and molluscs were identified to species level
 according to Appleton (2002) and Fry (2021). Only individuals that were
 considered “alive” (i.e., shell closed by operculum) at the time of
 sampling were counted and the density of each species per site (number of
 individuals sampled/m<sup>2</sup>) determined.
 To determine the population size structures for <em>T.
 granifera</em>, samples were processed through sieves and snails
 divided into size classes according to shell length (Table 2). For this
 study, size classes were used to describe age groups based on the size of
 sexual maturity in the populations obtained from published literature.
 Samples were separated into size classes using a King Test (VB 200 300)
 sieve shaker with Clear Edge Test sieves. <em>Tarebia
 granifera</em> were divided into mature adults (&gt; 10.39 mm)
 that are considered able to reproduce, adults (5.28 - 10.39 mm) becoming
 sexually mature and starting to reproduce, juveniles (1.92 - 5.27 mm) not
 able to reproduce, and new-born snails (&lt; 1.9 mm) that were
 recently born (Appleton <em>et al.</em>, 2009; Miranda
 <em>et al</em>., 2011b). Water quality
 analysis Physiochemical water quality variables: pH,
 temperature (˚C), electrical conductivity EC) (μS/cm), total dissolved
 solids (TDS) (mg/L), dissolved oxygen (mg/L) and percentage oxygen
 saturation (%) were measured <em>in situ</em> at each site
 using Extech EC500 pH/electrical conductivity and Extech DO600 dissolved
 oxygen water quality meters. Water samples (250 mL) from each site were
 collected in triplicate for chemical nutrient analyses. Samples were
 preserved by freezing (-4 ˚C) them on-site using a portable camping
 fridge/freezer until analysis. In the laboratory, water samples were left
 to defrost at room temperature and analysed for the following chemical
 nutrient variables: Turbidity (FAU),
 SO<sub>4</sub><sup>2- </sup>(14791),
 NH<sub>4</sub><sup>+</sup> (14752),
 NO<sub>3</sub><sup>- </sup>(14773),
 NO<sub>2</sub><sup>-</sup> (14776),
 PO<sub>4</sub><sup>3-</sup> (14848), and
 Cl<sup>-</sup> (14897) (mg/L) using the appropriate test kits
 (test kit catalogue numbers in parentheses) and standard protocols with a
 Merck Spectroquant Pharo 300 Spectrophotometer (Gerber <em>et
 al</em>., 2015b; de Necker <em>et al</em>.,
 2022a).
description: # Tarebia granifera and other benthic snails abundances and associated
 Water Quality at selected sites of easterly flowing rivers in South Africa
 ## Description of the data
 and file structure The data for this paper is all within a single Excel
 file. Each tab in the file is associated with a different metric across
 the 19 sites. These include Abundance, density and percentage contribution
 of size classes to a population and/or species to a community. Site names
 correspond to those used in the article. ###### Site-Specific Information
 - Relevant to all data sheets in the Excel file 1.) Numbers in parentheses
 refer to the year the site was sampled. 2.) Four letter site code refers
 to the specific river: PHON = Phongolo River, OLIF = Olifants River, LIMP
 = Limpopo River, MOGA = Mogalakwena River, LUVU = Luvuvhu River, G-LETA =
 Groot Letaba River, LETA = Letaba River, SHIN = Shingwedzi River. 3.)
 Number following the site code indicates upstream to downstream. i.e. 1 is
 the most upstream on the specific river and 4 is the most downstream on
 each river. ###### Data Sheet 1 - Tarebia abundance This data sheet
 contains the count data of the snail *Tarebia granifera* collected at each
 of the sites. These were done by scooping through benthic sediments a
 select number of times. For the Phongolo system this was 10 scoops in
 total whereas for the other sites count data consisted of three replicates
 of which each replicate was made up of 10 scoops. * Numbers in cells
 represent the counts in each scoop or replicate. * Thereafter the total
 number of *T. granifera* sampled overall was calculated and thereafter the
 mean number of *T. granifera* individuals and standard deviation (SD) per
 scoop/replicate was calculated. ###### Data Sheet 2 - Tarebia density/m2
 This data sheet contains the density data of the snail *Tarebia granifera*
 calculated at each of the sites. This was calculated using count data and
 the area of the benthic sampler and converted to a density per square
 meter. For the Phongolo system this was 10 scoops in total whereas for the
 other sites count data consisted of three replicates of which each
 replicate was made up of 10 scoops. * Numbers in cells represent the
 densities of *T. granifera* in each scoop or replicate at each of the
 sites. * Thereafter the mean densities of *T. granifera* individuals and
 standard deviation (SD) per scoop/replicate was calculated. ###### Data
 Sheet 3 - Tarebia size abundance This data sheet contains the count data
 of the snail *Tarebia granifera* calculated at each of the sites across
 four size classes ranging from mature to immature/juveniles. Snails from
 each site were divided into size classes and is not based on replicates
 but all individuals sampled at a site. * Numbers in cells represent the
 count data of *T. granifera* in each of the size classes at each of the
 sites. * Thereafter the total *T. granifera* individuals per site was
 calculated. ###### Data Sheet 4 - Tarebia size % This data sheet contains
 the percentage contribution of each size class of the snail *Tarebia
 granifera* calculated at each of the sites across four size classes
 ranging from mature to immature/juveniles, to the population found at the
 site. Snails from each site were divided into size classes and is not
 based on replicates but all individuals sampled at a site. * Numbers in
 cells represent the percentage contribution of that specific size class of
 *T. granifera* to the population at each of the sites. ###### Data Sheet 5
 - Mollusc abundance This data sheet contains the count data of all mollusc
 species collected at each of the sites. These were done by scooping
 through benthic sediments a select number of times. For the Phongolo
 system this was 10 scoops in total whereas for the other sites count data
 consisted of three replicates of which each replicate was made up of 10
 scoops. * Numbers in cells represent the counts of each species at each of
 the sites. ###### Data Sheet 6 - Mollusc abundance/m2 This data sheet
 contains the density data of all mollusc species collected at each of the
 sites. This was calculated using count data and the area of the benthic
 sampler and converted to a density per square meter. For the Phongolo
 system this was 10 scoops in total whereas for the other sites count data
 consisted of three replicates of which each replicate was made up of 10
 scoops. * Numbers in cells represent the densities of each species at each
 of the sites. ###### Data Sheet 7 - Mollusc % This data sheet contains the
 percentage contribution of mollusc species collected at each of the sites.
 * Numbers in cells represent the percentage contribution of that specific
 species to the mollusc community at each of the sites.