Abstract

Posidonia oceanica meadows have suffered a global regression in the Mediterranean Sea during the last decades. In order to counter this decline, some restoration projects have relied on the use of seedlings as a strategy to accelerate the natural recovery of their meadows and increase genetic diversity. Furthermore, understanding the dynamics and interactions that affect each species and between different organisms are key to enhance restoration success. On this project, we set an experiment in Pollensa Bay (Mallorca, Spain) to study whether P. oceanica seedlings, which had been previously cultured in controlled conditions for three months, improve their survivorship rates at different planting densities (1, 4, 8, 12 and 16 seedlings/0.04 m2). We planted the seedlings in two locations of Pollensa Bay, which presented different substrates: dead matte with marine phanerogams, sand with marine phanerogams and bare sand. Six months after plantation, no density-dependent effect was observed in any of the clumps anywhere. However, an interspecific facilitation effect was noticed for the seedlings planted in sand with other marine phanerogams, as they displayed a 39.27% ± 34.56 average survivorship rate, compared to 0% survivorship on this same substrate without any other seagrass around. Moreover, dead matte remained as the best substrate for restoration purposes, with an average survivorship rate of 57.07% ± 29.92. Our results reinforce the relevance of understanding the ecological interactions between seagrass species in order to increase restoration success, as well as the main factors affecting the survivorship of P. oceanica seedlings in the early stages after establishment in the substrate.