DOI: 10.5061/dryad.gtht76j0d
title: Mineralogy and organic content are major predictors of shell loss in bivalves under reduced salinity, ocean freshening conditions

description: Ocean freshening due to increased precipitation and ice melting in a
 warming world poses a significant threat to marine calcifiers. The reduced
 availability of calcification substrates and an undersaturated calcium
 carbonate state challenge shell construction and maintenance. The
 corrosive potential of ocean acidification on biomineralised skeletons is
 well understood, but few studies have investigated the corrosive potential
 of significant and irregular freshwater input into marine habitats. To
 examine the susceptibility of invertebrate biocomposites to low salinity,
 we exposed blocks containing shell material of six bivalve taxa,
 representing different mineralogies and microstructures, to a salinity
 gradient (0–45‰) for 180 days. By measuring the loss of shell thickness,
 we revealed a significant correlation between dissolution and decreasing
 salinity. Significantly different amounts of shell thickness loss were
 observed across microstructures, revealing mineralogy and organic content
 as important predictors for dissolution. Aragonite layers lost
 significantly more shell thickness than calcite, and higher organic
 content retarded dissolution in aragonitic microstructures. Overall, shell
 dissolution in low salinities is greater than under the acidification
 predicted for end-of-century ocean pH conditions. The compromised
 integrity of marine invertebrate biomineralised skeletons because of ocean
 freshening is of critical concern with future predicted increases in
 precipitation and sea ice melt.
description: # Mineralogy and organic content are major predictors of shell loss in
 bivalves under reduced salinity, ocean freshening conditions Dataset DOI:
 [10.5061/dryad.gtht76j0d](https://doi.org/10.5061/dryad.gtht76j0d) ##
 Description of the data and file structure Resin blocks with shell
 fragments flush on the surface were placed in salinity treatments for 180
 days before being removed. Shell thickness loss (dissolution) was measured
 using an ultra-high-definition digital microscope at magnifications of
 100x, 400x, or 700x to measure the greatest change in depth (μm) relative
 to the resin surface. Crystal width (to the nearest 0.1 µm) and
 variability (standard deviation) were measured from scanning electron
 micrographs of the exposed shell surfaces in the resin blocks using the
 ImageJ software. Organic content was measured by thermogravimetric
 analysis. ### Files and variables #### File: Data_file.xlsx
 **Description:** We have submitted an Excel file (Data_file.xlsx) with
 separate sheets that include the raw data for analyses of the resin blocks
 ("Resin_blocks_shell_loss") and separate sheets for calculating
 average Crystal size ("Crystal_size") and Organic content
 ("Organic content"). ##### Variables *Resin_blocks_shell_loss* *
 Salinity: Salinity of treatment. * Microstructure: Shell microstructure
 exposed in the resin, where two are the same, they are identified by a 1
 or 2, depending on the species. Polymorphs indicated by (A) aragonite or
 (C) calcite. * Microstructure_b: Shell microstructure (can be shared
 between species). * Species: The species from which the microstructure was
 obtained. * Mineralogy: Determines which calcium carbonate polymorph makes
 up the microstructure. * Block ID: Identification of individual resin
 blocks. * Measurement: Transect, i.e., measurement across the whole shell
 surface, or two-point, i.e., measurements taken from within the shell to
 the resin surface. * Shell_loss: change in depth from resin surface to
 shell surface, measured in μm. * Magnification: Magnification of the
 microscope at which measurements were made. * Organics: Weight proportion
 of organic content in each microstructure. * Mg_Ca: measured Mg/Ca ratio,
 only present in calcite, NA for aragonitic microstructures. * Crystal
 size: measured 15 individual prisms in μm for each taxon. Calculated the
 average value and standard deviation. * Tub: Treatment tub where the resin
 block was placed. *Crystal size* * Measurement: Measurement ID. * Column
 headings: Species measurements were collected from. * Observations:
 Average crystal width (to the nearest 0.1 µm) and variability (standard
 deviation) were calculated from 15 measurements of crystal width from
 scanning electron micrographs of the exposed shell surfaces in the resin
 blocks using the ImageJ software. *Organic content* * Taxon: Species ID. *
 Organics (wt%): Weight proportion of organics in each species
 microstructure. * SD: Standard deviation was calculated on samples of
 large enough size. * Where samples were n=1 and standard deviation could
 not be calculated, blank cells are used to show no available data. ##
 Code/software Data can be viewed using Excel. ## Access information Other
 publicly accessible locations of the data: *
 [https://github.com/bethanyfrancesking/Salinity_Dissolution](https://github.com/bethanyfrancesking/Salinity_Dissolution) Data was derived from the following sources: * Raw data were collected between January 2024 and August 2024. * Crystal widths of the crossed lamellar were measured using ImageJ from SEM images published in Figure 4 of Milano et al. [74] to take advantage of demarcated individual laths. * Mg:Ca ratios were taken from Chadwick et al. [47].