An ex-situ approach for cultivating coralline algae in a restoration perspective

Mediterranean coralligenous reefs are hotspots of biodiversity, but they are declining due to multiple impacts, prompting a growing number of conservation and restoration efforts. Restoration through the outplanting of the habitat foundation species, crustose coralline algae (CCA, Rhodophyta, Corallinophycidae), is still largely unexplored, although they make a major contribution to building these valuable ecosystems. In this study, we tested the feasibility of ex-situ culture of Lithophyllum stictiforme, one of the most common CCA of the coralligenous reefs, with nutrient-enriched artificial seawater medium, contributing to the knowledge of early life stage development and calcification. Thalli fragments with conceptacles were collected at a depth of 28 m (Costa Paradiso, northern Sardinia). We tested two light intensities, (L− 40 µmol photons m−2s−1, L+160 µmol photons m−2s−1) and two temperatures, (T− 14 °C, T+ 20 °C), the lower settings were chosen to simulate conditions at the sampling site, while the higher values were explored as potential growth promoters. Spore settlement, density and growth were estimated for two-weeks. Calcification was analyzed at the end of the culture period using Scanning Electron Microscopy in combination with Energy Dispersive Spectroscopy (SEM-EDS). The L− treatments had a positive effect on germination success and density, whereby the growth of the germination disc was enhanced in the L−T+ treatment. SEM-EDS showed that the marginal area of the germination discs had a higher Ca content than the core area, and that the L− treatments promoted a higher cell wall Ca percentage.