Distribution, structure and function of Nordic eelgrass (Zostera marina) ecosystems: implications for coastal management and conservation

Abstract

This paper focuses on the marine foundation eelgrass species, Zostera marina, along a gradient from the northern Baltic Sea to the north-east Atlantic. This vast region supports a minimum of 1480 km2 eelgrass (maximum >2100 km2), which corresponds to more than four times the previously quantified area of eelgrass in Western Europe.Eelgrass meadows in the low salinity Baltic Sea support the highest diversity (4–6 spp.) of angiosperms overall, but eelgrass productivity is low (<2 g dw m-2 d-1) and meadows are isolated and genetically impoverished. Higher salinity areas support monospecific meadows, with higher productivity (3–10 g dw m-2 d-1) and greater genetic connectivity. The salinity gradient further imposes functional differences in biodiversity and food webs, in particular a decline in number, but increase in biomass of mesograzers in the Baltic.Significant declines in eelgrass depth limits and areal cover are documented, particularly in regions experiencing high human pressure. The failure of eelgrass to re-establish itself in affected areas, despite nutrient reductions and improved water quality, signals complex recovery trajectories and calls for much greater conservation effort to protect existing meadows.The knowledge base for Nordic eelgrass meadows is broad and sufficient to establish monitoring objectives across nine national borders. Nevertheless, ensuring awareness of their vulnerability remains challenging. Given the areal extent of Nordic eelgrass systems and the ecosystem services they provide, it is crucial to further develop incentives for protecting them. © 2014 The Authors. Aquatic Conservation: Marine and Freshwater Ecosystems published by John Wiley & Sons, Ltd.

Export from Seagrass Meadows Contributes to Marine Carbon Sequestration

“…Widespread loss of eelgrass following the wasting disease in the 1930's and eutrophication in the 1970's and 1980's (Boström et al, 2014) may have reduced the contribution of seagrass to sediment carbon stocks in Danish waters relative to the large contribution reported by Boysen-Jensen (1914). Likewise, global losses of seagrass meadows (Orth et al, 2006;Waycott et al, 2009) may have impacted on their contribution to carbon sequestration in bare sediments elsewhere.…”

Blue carbon stocks in Baltic Sea eelgrass (&lt;i&gt;Zostera marina&lt;/i&gt;) meadows

“…The C org (obtained by depth integration of the carbon density (mg C cm −3 ) of the sampled region was multiplied by estimated seagrass area of the region based on the most recent areal estimates (in km 2 ) of seagrass distribution available in the literature and given as C org in g C m −2 . In Finland, the estimated areal extent was 30 km 2 , while in Denmark the extrapolations were based on the minimum and maximum estimates of the areal extent, respectively (673 and 1345 km 2 ; Boström et al, 2014). Results for carbon accumulation (applied by multiplying the depthintegrated C org stock by regional seagrass area and sediment accumulation rate estimate from the literature) in each area are given as C org accumulation (t yr −1 ).…”

“…The annual production rates were almost twice as high at Danish sites compared to the Finnish sites. Regional differences in seagrass productivity may be caused by differences in, for example, the inorganic carbon concentration in water column and light availability between the regions (with higher values in Denmark), which both affect the photosynthetic capacity of the plant (Hellblom and Björk, 1999;Boström et al, 2014). Eelgrass production tends to be higher in physically exposed areas compared to more sheltered areas, which can be due to improved sediment oxygen conditions and hydrodynamical effects (Hemminga and Duarte, 2000).…”

Effect of oyster aquaculture on seagrass Zostera marina at the estuarine landscape scale in Willapa Bay, Washington (USA)

“…Bivalve aquaculture has not been implicated in shifts to alternate states or reduced adaptive capacity of the larger ecological system. Typical thresholds that might be involved and have been linked to such catastrophic change and affect eelgrass at the landscape scale would likely be reached first with other human disturbances such as nutrients and eutrophication influencing the light environment or perhaps causing secondary shifts in macroalgal or herbivore abundance (Frederiksen et al 2004, Orth et al 2010b, Bostrom et al 2014, or large-scale habitat removal and sediment alteration . Location and scale remain important management considerations, however, and our results from Willapa Bay may not represent other systems such as small inlets with stratified water columns and less routine physical disturbance by storms that could exhibit lower thresholds to aquaculture operations.…”