DOI: 10.5061/dryad.84g36m4
title: Data from: Tracing the effects of eutrophication on molluscan communities in sediment cores: outbreaks of an opportunistic species coincide with reduced bioturbation and high frequency of hypoxia in the Adriatic Sea

description: Estimating the effects and timing of anthropogenic impacts on the
 composition of macrobenthic communities is challenging because early 20th
 century surveys are sparse and the corresponding intervals in sedimentary
 sequences are mixed by bioturbation. Here, to assess the effects of
 eutrophication on macrobenthic communities in the northern Adriatic Sea,
 we account for mixing with dating of the bivalve Corbula gibba at two
 stations with high sediment accumulation (Po prodelta) and one station
 with moderate accumulation (Isonzo prodelta). We find that, first,
 pervasively bioturbated muds typical of highstand conditions deposited in
 the early 20th century were replaced by muds with relicts of flood layers
 and high content of total organic carbon (TOC) deposited in the late 20th
 century at the Po prodelta. The 20th century shelly muds at the Isonzo
 prodelta are amalgamated but also show an upward increase in TOC. Second,
 dating of C. gibba shells shows that the shift from the early to the late
 20th century is characterized by a decrease in stratigraphic disorder and
 by an increase in temporal resolution of death assemblages from ~25-50
 years to ~10-20 years in both regions. This shift reflects a decline in
 the depth of the fully-mixed layer from more than 20 cm to few
 centimeters. Third, the increase in abundance of the opportunistic species
 C. gibba and the loss of formerly abundant, hypoxia-sensitive species
 coincided with the decline in bioturbation, higher preservation of organic
 matter, and higher frequency of seasonal hypoxia in both regions. This
 depositional and ecosystem regime shift occurred in ~1950 AD. Therefore,
 the effects of enhanced food supply on macrobenthic communities were
 overwhelmed by oxygen depletion even when hypoxic conditions are limited
 to few weeks per year in the northern Adriatic Sea. Preservation of trends
 in molluscan abundance and flood events in sedimentary sequences was
 enhanced by eutrophication that reduced bioturbational mixing.
description: Supplementary Table
 1Supplementary Table 1 –
 210Pb sediment data (with standard deviations) measures at three
 stations.Supplementary Table
 2Supplementary Table 2 –
 Amino acid racemization and calibrated age data of Corbula gibba from two
 Po stations (analyzed in this paper), from the Bay of Panzano (Tomasovych
 et al. 2017, Geology, and analyzed this paper), and from Piran (Mautner et
 al. 2018, Marine Pollution Bulletin).Supplementary Table
 3Supplementary Table 3 –
 Abundances of mollusks in two replicate cores at Po 3 (cores M13 and M14),
 at Po4 (cores M20 and M21), and in the Bay of Panzano (cores M28 and M29),
 and concentrations of elements, TOC, and total
 nitrogen.Supplementary
 codeR
 language source code for age unmixing procedure and for reproduction of
 some plots and analyses underlying the manuscript.The excel file
 "Supplementary Table 2" should be saved as tab-delimited txt
 file. This file is uploaded by the script.