Fossil evidence for accelerated growth and shorter lifespan in the harvested bivalve Arca noae in the Adriatic Sea

Changes in life history of marine species in response to harvesting and human-induced environmental changes are frequently observed in modern ecosystems, but the true magnitude of these shifts is difficult to evaluate without robust information on the pre-impact state of the affected populations. The edible bivalve Noah’s Ark shell ( Arca noae L.) was extensively harvested in the eastern Adriatic Sea in the late 19th and early 20th century until its fishery collapsed following mass mortality in the late 1940s. The lack of data on growth parameters of this species prior to that event biases our understanding of its life history and complicates establishing sustainable levels of harvesting. To provide a baseline for assessment of the current state of populations of A. noae in the Adriatic Sea, we compared growth rates and lifespan between live-collected individuals and fossil (Holocene) specimens sampled from sediment cores based on annual shell growth lines. The maximum age observed in our modern samples was 35 years whereas the ontogenetically oldest fossil specimens lived for at least 85 years, extending the longest recorded lifespan for the Arcidae family by over three decades. Our results indicate that individuals of A. noae collected in the 21 st century grow faster and have much shorter lifespan compared to their Holocene counterparts, suggesting that intensive harvesting in the past combined with increasing water temperatures and eutrophication of the northern Adriatic Sea had a significant impact on the population dynamics of this species. • Growth patterns of live-collected individuals and fossil specimens were compared • Maximum lifespan observed in the Middle-Late Holocene samples was 85 years • Modern individuals grow faster and have much shorter lifespan (up to 35 years) • Only a subset of potential life history variation is realized in modern populations