Changes in growth and longevity of the exploited bivalve Arca noae in the northern Adriatic Sea: a conservation paleobiology perspective

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.) is commercially exploited in the eastern Adriatic Sea, where its fishery rapidly expanded during the first half of the 20th century until a mass mortality in the late 1940s caused a population collapse. In spite of partial recovery, the lack of data on growth parameters of this species prior to that event complicates establishing sustainable levels of harvesting. To provide a baseline for assessment of the current state of populations of A. noae we compared modern and fossil (middle to late Holocene) specimens from the northern Adriatic Sea using samples from benthic surveys and sediment cores. Estimates of growth and longevity were based on annual shell growth lines visible in acetate peel replicas of the umbo and outer prismatic shell layer. The maximum lifespan observed in our modern samples was 35 years – a full decade longer than previously documented for this species. However, this estimate was still much shorter than the lifespan of multiple fossil specimens, among which the ontogenetically oldest one reached the age at least 85 years. Our results indicate that modern individuals of A. noae grow faster and have shorter lifespan compared to their Holocene counterparts, suggesting that harvesting pressure combined with increasing water temperatures and eutrophication of the northern Adriatic Sea had a significant impact on the population dynamics of this species.