Habitat use of fish in seagrass meadows of the Venice lagoon: implications for seagrass restoration and for conservation of the lagoon seascape

Abstract

Seagrass meadows play a primary role in supporting ecosystem services in coastal lagoons. Still, their importance as habitat for fish in transitional waters is poorly understood. Moreover, the persistent loss of seagrass beds during the last decades requires conservationists to provide scientifically sound plans to enhance their preservation. The objectives of this work are i) to investigate the influence of environmental factors, including habitat characteristics, on seagrass fish assemblages in the Venice lagoon (northern Adriatic Sea, Italy); ii) to evaluate the suitability of fish fauna as indicator of the effectiveness of seagrass restoration. Ultimately, this work aims at presenting approaches for planning seagrass conservation efforts and assessing their outcomes. This work features three main sections. Firstly, the role of different floristic composition and habitat structure of seagrass beds was linked to distribution of pipefishes and seahorses (Syngnathidae), highlighting the importance of enhancing conservation of Zostera marina meadows in shallow coastal lagoon waters. Secondly, the role of seagrass fish and other nekton fauna as indicator of the success of conservation actions was investigated. A seagrass restoration scheme that recently started in the Venice lagoon allowed to test a model-based method, to predict reference conditions for nekton fauna in Z. marina and Z. noltei transplantation sites, and provide an assessment of the progress of restoration towards designed goals. Thirdly, the potential role of habitat mosaic structure in influencing seagrass fish in the Venice lagoon was evaluated. The study highlighted the importance of conservation of seagrass habitat quality at multiple spatial scales for the preservation of the associated fish assemblages, and the need for including seascape ecology in seagrass restoration projects. On the whole, this thesis provides some new insights into the critical role of seagrass conservation for the maintenance of biodiversity, and suggestions for more successful management strategies in coastal lagoons.