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Scottish Seagrass Communities of the Genus Zostera

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Scottish Seagrass Communities of the Genus Zostera Introduction Seagrasses comprise < 0.02% of the angiosperm flora, representing a surprisingly small number of species, of which the principal genus is Zostera spp (Heeminga & Duarte 2000). Zostera occur widely in coastal zones throughout the world and therefore are integral to decisions about coastal management. Zostera can be biogeographically classified as temperate North Atlantic (Heeminga & Duarte 2000). All three species of the genus, Zostera marina L. (eelgrass), Zostera noltii (dwarf eelgrass), and Zostera angustifolia (narrow-leaved eelgrass) are found in Scottish coastal waters and are increasingly becoming threatened (Cleator 1993; UK BAP 2006). Zostera species are perennial angiosperms restricted to the intertidal and shallow subtidal fringe. The tolerable depth limit for Zostera species is set by light available for photosynthesis. The upslope limit to seagrass extension is imposed by sufficient immersion in seawater or tolerable disturbance by waves. Eelgrass communities will typically zonate in the following littoral regions: Z. marina in the sublittoral fringe; Z. angustifolia in the eu-littoral region; and Z. noltii in the upper littoral zone often adjacent to salt marshes. Seagrasses generally require salinity in excess of 5%o to develop, and a substratum ranging from sandy to muddy. Populations extend mainly by undersediment, vegetative, rhizomatol extension, and may form thick beds. Pollination and seed dispersal (most common in Z. marina) may occur via entrainment into water currents (Cleator 1993; Dawes 1981). It is recognised that seagrass communities bring many benefits to the coastal environment, that are imperative in the maintenance of biodiversity, the sustainability of industry, and the protection of the coastline. Seagrass communities are, however, also vulnerable and have declined substantially in many coastal areas due to natural and human pressures. During 1930s the Scottish west-coast Z. marina population catastrophically declined due the wasting disease epidemic (Cleator 1993). It is recognised that the role seagrass communities play in the sustainability of Scottish coastal marine ecosystems and the services they provide to coastal regions is of exceptional significance (UK BAP 2006). ...read more.


Estuaries and river plumes that are loaded with terrestrial borne sediment and in eutrophic waters that permit extensive phytoplankton productivity are examples of conditions which give rise to increased turbidity, and reduced light penetration (Hemminga & Duarte 2000). Around the British Isles, Z. marina typically occurs down to 4 m but may extend deeper in some locations (Rodwell 2000). In the very clear waters of Ventry Bay, south-west Ireland, Z. marina occurs in a continuous bed from 0.5 m to 10 m (Whelan & Cullinane 1985). Substratum type, water movement and stability of Zostera beds All three Zostera species require sandy to muddy substrata and sheltered environments, such as enclosed bays or coastal areas with a gentle longshore current and tidal flux (Cleator 1993). Dense swards of Zostera are typically found on muds and sands in sheltered inlets and bays, estuaries and saline lagoons. In more unstable, higher energy (wave or current exposed) sites, the beds tend to be smaller, patchier and more vulnerable to storm damage (Davis & Hughes 1998). This is because the physical action of waves can tear up plants from the substrate. Furthermore, increased erosion from strong waves and currents can expose the roots and rhizomes causing the plants to detach from the surface. In addition high rates of siltation and deposition can bury seagrasses (Portig et al. 1994). In addition, for rhizome elongation and firm attachment, a soft substrate is required (Heeminga & Duarte 2000). Carbon Bicarbonate is the most abundant form of inorganic in seawater (~pH 8) being around 150 times that of CO2 (at 15�C). It is known that bicarbonate use is a common feature in this plant group for photosynthesis. However, it has been observed that under normal conditions, inorganic carbon is limiting to photosynthetic rate, thus indicating an apparently inefficient acquisition system. In comparison to macroalgae, the photosynthesis system of seagrasses is evolutionary inferior. Hence, it has been suggested that seagrasses may profit from an increased atmospheric CO2 associated with increasing use of fossil fuels (Beer & Koch 1996). ...read more.


2004). Agricultural non-point source pollution may be remedied by the installation of vegetated buffer strips on agricultural land to barrier surface runoff into water courses (Hefting et al. 1998). Other objectives of conservation measures should entail the regulation of land use in catchment areas to reduce nutrient runoff and siltation due to soil erosion; regulation of land reclamation and coastal constructions; the regulation of fisheries and clam digging in the vicinity of seagrass beds (Duarte 2002; Borum et al. 2004). The monitoring of seagrass distribution and abundance is valuable in that they are instrumental vehicles to increase awareness of the important role of seagrasses in the ecosystem, and highlight the threats seagrass ecosystems are exposed to, and the importance to preserve the seagrass meadows to maintain the biological balance and the biodiversity of the coastal ecosystem (Duarte 2002; Borum et al. 2004). Effective monitoring can be achieved principally by the use of remote sensing data of Scottish coastal areas. From remotely sensed data, biological parameters such as biomass, leaf area index (LAI), and abundance can be directly extrapolated based on the reflectance values of a given location in the image feature space, and ground truthing. These indicators respond to environmental variables such as water quality, hence an additional value in seagrass monitoring. Given a high temporal frequency of data, effective monitoring can be installed (Borum et al. 2004). Effective protection can only be achieved by legislative acknowledgement of the importance of seagrass ecosystems. Currently, many concentrated seagrass populations are within Sites of Special Scientific Interest and it is an imperative of the Scottish Environmental Protection Agency that coastal management practices aim to conserve seagrass communities, actions be taken to mitigate potential impacts and that coastlines are used in a sustainable manor (UK BAP 2006). With the continual application of these conservation objectives, if coastal activities can be achieved with minimal impact, if a coherent monitoring system can be established, and if the awareness of the public on issues surrounding the sustainability of Scottish seagrass resources is increased, then effective conservation of these significant habitats may be achieved. ...read more.

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