Climate variation during the Holocene influenced the skeletal properties of Chamelea gallina shells in the North Adriatic Sea (Italy)

Abstract

Understanding how marine taxa will respond to near-future climate changes is one of the main challenges for management of coastal ecosystem services. Ecological studies that investigate relationships between the environment and shell properties of commercially important marine species are commonly restricted to latitudinal gradients or small-scale laboratory experiments. This paper aimed to explore the variations in shell features and growth of the edible bivalve Chamelea gallina from the Holocene sedimentary succession to present-day thanatocoenosis of the Po Plain-Adriatic Sea system (Italy). Comparing the Holocene sub-fossil record to modern thanatocoenoses allowed obtaining an insight of shell variations dynamics on a millennial temporal scale. Five shoreface-related assemblages rich in C. gallina were considered: two from the Middle Holocene, when regional sea surface temperatures were higher than today, representing a possible analogue for the near-future global warming, one from the Late Holocene and two from the present-day. We investigated shell biometry and skeletal properties in relation to the valve length of C. gallina. Juveniles were found to be more porous than adults in all horizons. This suggested that C. gallina promoted an accelerated shell accretion with a higher porosity and lower density at the expense of mechanically fragile shells. A positive correlation between sea surface temperature and both micro-density and bulk density were found, with modern specimens being less dense, likely due to lower aragonite saturation state at lower temperature, which could ultimately increase the energetic costs of shell formation. Since no variation was observed in shell CaCO3 polymorphism (100% aragonite) or in compositional parameters among the analyzed horizons, the observed dynamics in skeletal parameters are likely not driven by a diagenetic recrystallization of the shell mineral phase. This study contributes to understand the response of C. gallina to climate-driven environmental shifts and offers insights for assessing anthropogenic impacts on this economic relevant species.

Oxygen and carbon isotope variations in Chamelea gallina shells: Environmental influences and vital effects

“…The biology of the clam C. gallina in the Adriatic Sea was already studied in terms of growth rate (Bargione et al, 2020;Keller et al, 2002;Mancuso et al, 2019), physiology (Matozzo et al, 2007;, and shell properties (Cheli et al, 2021;Gizzi et al, 2016; Mancuso time (Keller et al, 2002). However, this confined area is not representative of the wide shifts in C. gallina habitat from North to South of the Adriatic basin that influence shell growth (Mancuso et al, 2019).…”

“…The biology of the clam C. gallina in the Adriatic Sea was already studied in terms of growth rate (Bargione et al, 2020 ; Keller et al, 2002 ; Mancuso et al, 2019 ), physiology (Matozzo et al, 2007 ; Monari, Matozzo, et al, 2007 ; Monari, Serrazanetti, et al, 2007 ), and shell properties (Cheli et al, 2021 ; Gizzi et al, 2016 ; Mancuso et al, 2019 ). A previous study conducted in the Bay of Trieste in the North of the Adriatic Sea investigated the shell isotopic composition of C. gallina in relation to its growth rates and settlement time (Keller et al, 2002 ).…”

“…In the past, the North Western Adriatic coastal area was characterized by estuary systems, bounded seaward by a series of sandbars that isolated coastal lagoons and limited riverine plumes into the Adriatic (Amorosi et al, 2019 ). This past more stable shoreface depositional setting due to reduced influence of riverine plumes, warmer temperature and higher aragonite saturation state than today seemed to reduce the thermodynamic work required for organisms to deposit calcium carbonate (Hall‐Spencer & Harvey, 2019 ), making the calcification less expensive in terms of metabolic cost (Cheli et al, 2021 ; Clarke, 1993 ). Nowadays, the western Adriatic basin is characterized by the northern area with shallow continental shelf, representing the result of several southward progradations driven by sea level cycles, by the central Adriatic Sea, a small remnant basin reaching 260 m water depth and confined to the north by the Po River delta formed during the last sea level lowstand and by the Southern Adriatic Sea, originated as a consequence of the interaction between mass transport processes and deep water circulation (Ridente et al, 2007 , 2008 ).…”