Towards streamlined restoration of macroalgal forests: integrating suspended algaculture and ex situ outplanting

Ericaria amentacea, a key habitat-forming brown macroalga on Mediterranean rocky coasts, faces severe decline due to anthropogenic stressors and climate change. Natural recovery is hindered by its limited dispersal and connectivity potential, and active restoration is therefore critical to restocking lost populations. This study evaluates a two-phase restoration approach combining laboratory culture and suspended aquaculture to optimize E. amentacea restoration, enabling multiple culture cycles within a single fertility window. Three experimental conditions were tested: (A) 5 days in the laboratory followed by 12 days in suspended aquaculture, (B) 12 days in the laboratory followed by 5 days in suspended aquaculture, and (C) 17 days in the laboratory without suspended aquaculture. Culture performance was assessed in terms of coverage, length of individuals, and photosynthetic efficiency. Results outlined that condition C achieved the best performance at the final time point. Condition B showed intermediate outcomes, with length and photosynthetic efficiency comparable to condition C, but lower coverage, with significant recovery post-outplanting. Condition A exhibited poor resilience, with declining coverage and reduced photosynthetic efficiency. These findings suggest that a moderate reduction in laboratory culture (12 days) may represent an effective trade-off between resource efficiency and germling development. This approach is particularly relevant in the context of climate change, where shorter fertility periods and extreme events challenge restoration efforts. This study highlights the potential of integrated laboratory-aquaculture protocols to enhance the scalability and success of E. amentacea restoration, offering a promising strategy for marine habitat recovery.