Threatened canopy algae: an experimental investigation of factors affecting the successful transplantation on artificial marine infrastructures

We present the results of experimental work aimed at examining the feasibility of controlling the growth of desirable species on man-made coastal defense structures (CDS). We focused on important habitat forming macroalgae of the genus Cystoseira, threatened by loss in the Mediterranean sea. We analyzed the role of grazing in influencing the survival and growth of Cystoseira on CDS, as pilot tests suggested herbivory has a potentially limiting role. Grazers’ impact on growth and survival of juvenile thalli of C. barbata was assessed using cages of different mesh size. Consistency of grazing effects was tested among sites kilometers apart along the Adriatic coast. Grazing was an important factor affecting macroalgae transplanted on CDS: juveniles grew whenever protected by cages, otherwise they suffered massive mortality and height decrease. The trend was relatively consistent at different sites when using cages of small mesh size, while the effects of cages of larger mesh were more variable. We tried to mitigate grazing using different transplantation approaches: a larger juvenile size or a higher transplantation base increased the survival of transplants. Characterizing ecological factors in CDS environments improves our ability to use artificial marine infrastructures as a scaffold for the conservation of threatened species. Supporting info Coastal erosion is a problem of major concern all over the world for which hard engineering solutions are widely implemented. However, man-made coastal defense structures have several ecological impacts (e.g. the spread of opportunistic and invasive species). We promote the idea that habitats developed on marine infrastructures can be managed to obtain a different colonization pattern. In particular, marine infrastructures can be used as a scaffold for the conservation of species of higher ecological value, often threatened in their natural habitats. In this perspective, it is vital to understand ecological factors ruling interactions between species on artificial structures