Abstract
Marine macroinvertebrates are ideal sentinel organisms to monitor rapid environmental changes associated with climatic phenomena. These organisms build up protective exoskeletons incrementally by biologically-controlled mineralization, which is deeply rooted in long-term evolutionary processes. Recent studies relating potential rapid environmental fluctuations to climate change, such as ocean acidification, suggest modifications on carbonate biominerals of marine invertebrates. However, the influence of known, and recurrent, climatic events on these biological processes during active mineralization is still insufficiently understood. Analysis of Peruvian cockles from the 1982–83 large magnitude El Niño event shows significant alterations of the chemico-structure of carbonate biominerals. Here, we show that bivalves modify the main biomineralization mechanism during the event to continue shell secretion. As a result, magnesium content increases to stabilize amorphous calcium carbonate (ACC), inducing a rise in Mg/Ca unrelated to the associated increase in sea-surface temperature. Analysis of variations in Sr/Ca also suggests that this proxy should not be used in these bivalves to detect the temperature anomaly, while Ba/Ca peaks are recorded in shells in response to an increase in productivity, or dissolved barium in seawater, after the event. Presented data contribute to a better understanding of the effects of abrupt climate change on shell biomineralization, while also offering an alternative view of bivalve elemental proxy reconstructions. Furthermore, biomineralization changes in mollusk shells can be used as a novel potential proxy to provide a more nuanced historical record of El Niño and similar rapid environmental change events.
Highlights
Biological consequences of El Nino events are well documented [1], with a clear disruption of fisheries and mass mortality of bivalve mollusks in the coastal areas of Peru and Ecuador [1,2]
Prior to in situ quantitative measurements, qualitative variations in trace elements were determined by electron probe microanalysis (EPMA) mapping (Figure S2)
There is an enhancement in the signal of both elements, the strontium signal is only present at the scar while the magnesium concentration appears to increase prior to the scar as well (Figure S2)
Summary
Biological consequences of El Nino events are well documented [1], with a clear disruption of fisheries and mass mortality of bivalve mollusks in the coastal areas of Peru and Ecuador [1,2]. Some bivalve and gastropod species, survive and continue the production of shell components during these events. These surviving mollusk shells, represent ideal proxybearers for reconstructions of climatic and environmental changes associated with El Nino along the west coast of South America [3,4]. Trace element proxies (metal-to-calcium ratios [Me/Ca]) of bivalve shells have been scarcely explored for the characterization of El Nino events [4,8], despite their usefulness in climatic and environmental studies [9,10,11]. Preliminary studies suggest that surviving bivalves experience levels of environmental stress responsible for morphological changes in shells [2,3]
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