The role of intertidal seagrass Zostera spp. in sediment deposition and coastal stability in the Tay Estuary, Scotland

The Tay estuary is situated on the east coast of Scotland. The estuary is dominated by sediment biotopes, including mudflats which support sparse beds of two nationally scarce seagrass species, Zostera marina var. angustfolia (Hornem.) and Z. noltii (Hornem.). Seagrasses have been described as ecosystem engineers, shaping their sediment environment, and this may increase sediment deposition and stability. In this thesis the ecosystem engineering characteristics of seagrass habitats are explored. In 2008, the distribution of Zostera spp. in the Tay estuary was surveyed and mapped for the first time. Sediments within beds of Z. marina and Z. noltii were compared to investigate the influence of seagrasses on sediment characteristics. To explore the role of seagrass in sediment deposition and erosion, and coastal stability, sediment depth measurements were made in patches of Z. noltii, Z. marina and bare sediment over one year. The role of the root/rhizome system on sediment retention over winter was also considered. Sediment deposition in Z. noltii beds, and the influence of the plants on near-bed flow dynamics was further explored in the laboratory, using an 8 m seawater flume. In the field the retention of particles over 2 and 14 tides was measured, and the results of this experiment led to a study of the influence of leaf and sediment biofilms on particle retention, using the novel method of magnetic particle induction (MagPI). The efficacy of artificial seagrass beds and Z. noltii transplantation as habitat restoration techniques were compared over one year. During the trial, sediment deposition and changes in sediment characteristics were determined, and the protection given to saltmarsh cliffs fringing the study plots was assessed. Mechanisms underlying the results are suggested and the findings discussed. This study provides an insight into the ecology of seagrass in the Tay estuary and its role as an ecosystem manager. It may offer valuable data which could be utilised for future conservation policies, habitat restoration schemes and management planning of the area.