Population Dynamics of Colonizing Fauna and Its Effect on Growth Rates of the Farmed Red Alga Alsidium triquetrum (S. G. Gmelin) Trevisan

Herbivores can drastically alter the morphology of macroalgae by directly consuming tissue and by inflicting structural wounds. Macroalgae host abundant and diverse epibiont communities, the dynamics of which tend to be mostly unknown in space and time. As the cultivation of macroalgae gains momentum worldwide, it is key to measure how epibionts could affect algal performance. We examined the epibiont community associated with farmed Alsidium triquetrum, a red macroalga with growing pharmacological interest. Measurements were conducted over two independent 60-day periods, one in summer and one in winter. Epibionts showed different patterns of succession in both seasons. Crustaceans, mainly amphipods, showed the highest overall density, with deleterious effects on daily growth rates of A. triquetrum in winter. Adverse effects as a function of epibionts were not detected in summer. A. triquetrum is a perennial alga. However, its performance as a crop in the nearshore can be significantly affected by the epibiont community structure that persists in winter. Amphipods and ascoglossan molluscs were risk factors in the mariculture of this agarophyte. In winter, they can destroy plants when they reach more than five individuals per gram of fresh biomass. Results highlight that commercial farming of A. triquetrum would be successful if grown throughout the summer.