The perilous state of seagrass in the British Isles

Abstract

Seagrass ecosystems face widespread threat from reduced water quality, coastal development and poor land use. In recent decades, their distribution has declined rapidly, and in the British Isles, this loss is thought to have been extensive. Given increasing knowledge of how these ecosystems support fisheries production, the understanding of their potential rapid loss, and the difficulty in restoring them, it is vital we develop an understanding of the risks they are under, so that management actions can be developed accordingly. Developing an understanding of their environmental status and condition is therefore critical to their long-term management. This study provided, to our knowledge, the first examination of the environmental health of seagrass meadows around the British Isles. This study used a bioindicator approach and involved collecting data on seagrass density and morphology alongside analysis of leaf biochemistry. Our study provides, to the best of our knowledge, the first strong quantitative evidence that seagrass meadows of the British Isles are mostly in poor condition in comparison with global averages, with tissue nitrogen levels 75% higher than global values. Such poor status places their long-term resilience in doubt. Elemental nutrient concentrations and morphological change suggest conditions of excess nitrogen and probable low light, placing many of the meadows sampled in a perilous state, although others, situated away from human populations were perceived to be healthy. Although some sites were of a high environmental health, all sites were considered at risk from anthropogenic impacts, particularly poor water quality and boating-based disturbances. The findings of this study provide a warning of the need to take action, with respect to water quality and disturbance, to prevent the further loss and degradation of these systems across the British Isles.

Light Stress Responses by the Eelgrass, Zostera marina (L)

“…is usually at its highest in summer months and lowest in winter months (Fourqurean et al, 1997) and sampling for the present study took place in late October (autumn in UK). It should also be noted that C:N has been identified as a robust bioindicator for Z. marina in a study that used an intensive field sampling strategy providing reliable evidence to this effect (Jones and Unsworth, 2016).…”

Variability of UK seagrass sediment carbon: Implications for blue carbon estimates and marine conservation management

“…Plant count at Drakes Island was reasonably high (10.42 ± 8.40 per 50cm 2 ) but standard deviation was also high, suggesting a less uniform cover of dense growth. Patchiness within sites was generally high, indicating potentially poor ecosystem health [ 11 ]. Fishcombe Cove (5.71 ± 7.64), Jennycliff Bay (2.84 ± 4.75), Firestone Bay (4.05 ± 5.88) and Yealm (6.70 ± 7.01) all displayed vast variations among surveyed quadrats but overall no relationship was noted between plant count, or patchiness, and C stock .…”

“…Following the outbreak of wasting disease, eelgrass was restricted to only the most sheltered sites, such as lagoons, and is now considered nationally scarce [ 10 ]. Meadows that do persist are reportedly in a ‘perilous state’, damaged and degraded, and healthy beds are now a rarity [ 11 ].…”

Role of Eelgrass in the Coastal Filter of Contrasting Baltic Sea Environments

“…The high C/N ratio observed in rhizomes is likely the result of plants storing starch and other non-structural forms of carbohydrates produced during photosynthesis (Touchette and Burkholder 2000). The stable isotope composition of seagrasses reflects their nutrient source (Jones and Unsworth 2016) and the anthropogenic impact of the aquatic environment (Jones et al 2018). The heavy influence of human activities around Roskilde Fjord is reflected by more 15 N-enriched eelgrass tissue (12‰) in Roskilde Fjord than in Tvärminne (7‰).…”