Age and growth of bamboo coral Isidella elongata (Esper, 1788): a Mediterranean Vulnerable Marine Ecosystem indicator taxa

The General Fisheries Commission for the Mediterranean of the Food and Agriculture Organization of the United Nations (FAO) recognises bamboo coral forests as Vulnerable Marine Ecosystems due to their high ecological importance (e.g., habitat-forming, shelter-role, and hot-spot biodiversity). The major cause of bamboo coral vulnerability lies in their slow growth rate, which limits their ability to recover from fisheries-related damage. This is particularly true for the bamboo coral Isidella elongata in the Mediterranean Sea. Despite the need to take action to ensure the conservation of the I. elongata forests, crucial information regarding life-history traits such as age, growth rate, and life span is still limited. This study takes advantage of the incidental catch of 751 I. elongata colonies (basal diameter 0.36–7.3 mm) through experimental trawl fishing surveys (2012–2023) in South Adriatic Sea. We modelled the species’ growth through thin sections (basal diameter < 2 mm) and radiocarbon dating (basal diameter > 4 mm). The estimated ages, considering both methods, ranged between 1 and 59 years, while the species’ lifespan in the area was predicted to be from 57.5 to 59 years. Age data were fitted to seven different growth models, with the exponential model proving to be the most accurate in describing the species’ growth with significant difference between two groups of age data (< 12 and > 48.8 years). Our findings are the first providing direct ageing of I. elongata in the Mediterranean Sea, which is a critical aspect in determining the species’ long-term population dynamics and recovery capacity from an ecosystem-based fishery management perspective.