RESEARCH ARTICLE Experimental Evaluation of the Restoration Capacity of a Fish-Farm Impacted Area with Posidonia oceanica (L.) Delile Seedlings Marta Domínguez, 1,2 David Celdr´ an, 3 Ana Mu˜ noz-Vera, 4 Eduardo Infantes, 1 Pedro Martinez-Ba˜ nos, 4 Arnaldo Marín, 3 and Jorge Terrados 1 Abstract Marine aquaculture is an activity that has induced severe local losses of seagrass meadows along the coastal areas. The purpose of this study was to evaluate the capacity of an area degraded by fish-farm activities to support Posidonia oceanica seedlings. In the study site, a bay in the southeast coast of Spain where part of a meadow disappeared by fish- farm activities, seedlings inside mesh-pots were planted in three areas. Two plots were established in each area, one in P. oceanica dead matte and another inside a P. oceanica meadow. To evaluate if sediment conditions were adequate for the life of the seedlings, half of them were planted in direct contact with the sediment and the other half were planted above the surface of the sediment in each plot. Monitoring during 1 year showed that there were large differences in seedling survival between the dead matte and the P. oceanica meadow. While seedlings planted in dead matte had a high survivorship after 1 year (75%), seedlings planted in P. oceanica progressively died (sur- vivorship of 20% after 1 year). The average leaf length of the seedlings surviving in the two substrata was not differ- ent, but the leaf area per seedling was lower in the seedlings growing inside the P. oceanica meadow during most part of the year. Seedling survivorship and vegetative develop- ment were not affected by the level of planting and suggest that the sediment conditions are adequate for the life of P. oceanica seedlings. Key words: fish-farm, planting level, Posidonia oceanica , seedlings, substratum type, survival, vegetative development. Introduction Seagrasses are key components of shallow coastal ecosystems for their contribution to biological productivity and the main- tenance of biodiversity, the control of water quality, and the protection of the shoreline (Hemminga & Duarte 2000). Sea- grass populations have decreased due to the impact caused by human activities such as coastal development, pollution, and trawling (Boudouresque et al. 2009). The increasing demand for marine products by human population has promoted the growth of marine aquaculture, which is the fastest growing animal food-producing sector (FAO 2009). Coastal fish aqua- culture has contributed to the decline of seagrass populations (Holmer et al. 2003a). For this reason, there is a growing con- cern about the environmental impact of marine aquaculture 1 IMEDEA (CSIC-UIB) Instituto Mediterr´ aneo de Estudios Avanzados, C/Miquel Marqu´ es 21, 07190 Esporles, Mallorca, Spain 2 Address correspondence to M. Domínguez, email mdominguez@imedea. uib-csic.es 3 Departamento de Ecología e Hidrología, Facultad de Biología, Universidad de Murcia, Campus Universitario de Espinardo, 30100 Murcia, Spain 4 Contesma & Comprotec SLP (C&C Medio Ambiente), C/Antonio Oliver 17, 30204 Cartagena, Spain © 2011 Society for Ecological Restoration International doi: 10.1111/j.1526-100X.2010.00762.x (Naylor et al. 2000) and as a result severe environmental impacts have been documented regarding net cage production (Hall et al. 1990, 1992; Holmer & Kristensen 1992; Karakassis et al. 2000; Holmer et al. 2002, 2003a). The loading of organic matter coming from fish feces and uneaten fish food is considered the main driver of habitat degradation (Pergent-Martini et al. 2006; Holmer et al. 2008). Fish-farm-derived organic matter inputs to the sediment increase sulfate reduction rates (Holmer & Frederiksen 2007) and promote the invasion of the rhizomes and roots by sulfide which is associated with reduced growth and increased mortality of seagrasses (Calleja et al. 2007; Frederiksen et al. 2007, 2008). The nutrients released by the mineralization of organic matter may also cause local nutrient enrichments and the increase of the epiphytes (P´ erez et al. 2008) and, likely, of their palatability to herbivores. Shading by epiphytic overgrowth has been considered another process involved in seagrass losses in fish-farm impacted areas (Pergent-Martini et al. 2006). Posidonia oceanica (L.) Delile forms extensive meadows in the Mediterranean Sea but its surface has declined by 5–20% during the last century. Coastal development, pol- lution, and trawling are considered the main causes of this loss (Boudouresque et al. 2009). Coastal fish aquaculture 180 Restoration Ecology Vol. 20, No. 2, pp. 180–187 MARCH 2012