Are colony growth rates depth-dependent in the Mediterranean red coral?

The precious red coral Corallium rubrum (Linnaeus, 1758) is a charismatic species living in the Mediterranean Sea and its Atlantic surroundings, known for its slow growth and long lifespan. The development of a reliable method for assessing colony age has enabled the comparison of average annual growth rates, minimising age-related variability. This study aimed to investigate the potential effect of depth on colony growth by analysing a set of morphometric parameters - basal diameter, height, weight, total branch length (TBL), and number of apexes - normalised per year. The analysis was conducted on 59 specimens collected from shallow (<60 m) and mesophotic (>60 m) banks along the Italian coast, which are subject to diverse environmental conditions. The colonies’ estimated average age was approximately 30 years, regardless of depth. Notably, the annual growth rate in weight was significantly higher in colonies from the deeper depth range, while growth rates for the other morphometric parameters showed no variation with depth.