Abstract
Abstract. A monitoring survey of the coastal area facing the industrial area of Portoscuso-Portovesme (south-western Sardinia, Italy) revealed intense bioerosional processes. Benthic foraminifera collected at the same depth (about 2 m) but at different distances from the pollution source show extensive microbial infestation, anomalous Mg/Ca molar ratios and high levels of heavy metals in the shell associated with a decrease in foraminifera richness, population density and biodiversity with the presence of morphologically abnormal specimens. We found that carbonate dissolution induced by euendoliths is selective, depending on the Mg content and morpho-structural types of foraminiferal taxa. This study provides evidences for a connection between heavy metal dispersion, decrease in pH of the sea-water and bioerosional processes on foraminifera.
Highlights
Boring microflora, constituted by cyanobacteria, algae and fungi may colonise carbonate substrates of both dead and living tissues of carbonate organisms (Tribollet, 2008)
The aim of our study is to investigate the effects of microbioerosion on benthic foraminifera and trace element dynamics in a known coastal industrial site polluted by heavy metals and industrial release of CO2 (Schintu and Degetto, 1999)
From Environmental scanning electron microscopy (ESEM) images of the traces on external surfaces of foraminiferal tests, our observations show that the taxa affected by higher bioerosion belong to the high-Mg porcelanaceous group (Suborder Miliolina) and, among these, to the genus Quinqueloculina which exhibits heavy microbial bioerosion
Summary
Boring microflora, constituted by cyanobacteria, algae and fungi may colonise carbonate substrates of both dead and living tissues of carbonate organisms (Tribollet, 2008). Boring is evident in carbonate organisms from the Mesoproterozoic (Zhang and Golubic, 1987) to the present day as a consequence of environmental conditions (Hallock, 2005). Microborings are major agents of bioerosion dissolving large quantities of calcium carbonate with a potential in buffering seawater pH, which leads to new questions on the effects of environmental factors such as eutrophication and atmospheric CO2 increase on ocean composition evolution (Tribollet, 2008). Present-day geochemical models predict that the saturation state of surface ocean water with respect to carbonate minerals should decline during the twenty-first century. Organisms utilizing the more soluble form of CaCO3 (aragonite or high-Mg calcite) would be more adversely affected by elevated pCO2 than those utilizing the less soluble low-Mg calcite (Morse, 1983; Morse et al, 2007)
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