Modelling red coral (Corallium rubrum) growth in response to temperature and nutrition

Octocorals are marine modular organisms with high ecological and economic importance. Mediterranean Red Coral (Corallium rubrum), is endemic to the Mediterranean sea and neighboring Atlantic rocky shores and has been exploited for jewelry since ancient times. Despite the lack of photosynthetic symbionts (Symbiodinium spp.), red coral growth and survival do depend on sea water temperature, as well as on trophic conditions and other physico-chemical parameters. We developed and applied a mechanistic numerical model to describe the growth of a C. rubrum colony (polyps number, polyp and gametes biomass, skeletal inorganic and organic matter) as a function of food availability and seawater temperature. The model follows a bioenergetic approach and is calibrated vs available experimental observations. Model results highlight that larger colonies are more sensitive to high temperature and actual limits of the ecological niche also depend on food availability, hydrodynamic condition and coral morphology. Bioenergetic considerations also support the conclusion that, though a modular organism, red coral exhibits constrained growth, because of the competition for available food between polyps from the same colony.