DOI: 10.5061/dryad.rj4cg1t
title: Data from: A decline in molluscan carbonate production driven by the loss of vegetated habitats encoded in the Holocene sedimentary record of the Gulf of Trieste

description: Carbonate sediments in non-vegetated habitats on the NE Adriatic shelf are
 dominated by shells of molluscs. However, the rate of carbonate molluscan
 production prior to the 20th century eutrophication and overfishing on
 this and other shelves remains unknown because (1) monitoring of
 ecosystems prior to the 20th century was scarce and (2) ecosystem history
 inferred from cores is masked by condensation and mixing. Here, based on
 geochronological dating of four bivalve species, carbonate production
 during the Holocene is assessed in the Gulf of Trieste, where algal and
 seagrass habitats underwent a major decline during the 20th century.
 Assemblages of sand-dwelling Gouldia minima and opportunistic Corbula
 gibba are time-averaged to &gt; 1,000 years and C. gibba shells are
 older by &gt;2,000 years than shells of co-occurring G. minima. This
 age difference is driven by temporally disjunct production of two species
 coupled with decimeter-scale mixing. Stratigraphic unmixing shows that
 Corbula gibba declined in abundance during the highstand phase and
 increased again in the 20th century. In contrast, one of the major
 contributors to carbonate sands, Gouldia minima, increased in abundance
 during the highstand phase, but declined to almost zero abundance over the
 past two centuries. G. minima and herbivorous gastropods associated with
 macroalgae or seagrasses are abundant in the top-core increments but are
 rare alive. Although G. minima is not limited to vegetated habitats, it is
 abundant in such habitats elsewhere in the Mediterranean Sea. This
 live-dead mismatch reflects the difference between highstand baseline
 communities (with soft-bottom vegetated zones and hard-bottom Arca beds)
 and present-day oligophotic communities with organic-loving species.
 Therefore, the decline in light penetration and the loss of vegetated
 habitats with high molluscan production traces back to the 19th century.
 More than 50% of the shells on the seafloor in the Gulf of Trieste reflect
 inactive production that was sourced by heterozoan carbonate factory in
 algal or seagrass habitats.
description: Supplement Table 1-core
 dataAbsolute abundances of
 molluscs in two cores at Piran 1 and Piran 2, including two surface living
 assemblages collected by Van Veen grabs at the same sites in 2014 (1 mm
 mesh size). Complete valves or fragments with umbo preserved were selected
 from the &gt;1 mm sieve fraction of each increment, identified to species
 level, and counted. For each species, the higher number of single valves
 (either right or left) was added to the number of double-valved specimens
 to get the final count in each increment.Supplement Table
 2-Gouldia age dataAmino acid racemization
 data and calibrated estimates of postmortem age of Gouldia minima
 collected from the shell bed at Piran 1 and Piran 2.Supplement Table
 3-Corbula age dataAmino acid racemization
 data and calibrated estimates of postmortem age of Corbula gibba and Piran
 2.Supplement Table 4-LA
 dataAbsolute abundances of
 molluscs in living assemblages collected by Van Veen grabs at 11 stations
 in 2011.Gouldia age unmixing
 finalR language source code
 for analyses of age data and age unmixing