I would like to thank all our committed volunteers who participated in one of our seed sowing, processing and monitoring events last year. The Restoration Forth team greatly appreciate the dedication shown by every one of you. Moreover, it was a rewarding experience providing training to the different community groups from across the Forth. We hope you enjoyed these sessions and that you left having learnt new techniques.
Seagrass Status Report
March 2023 marked the first milestone in our seagrass restoration journey, here in the Forth. In each restoration site (Burntisland Sands, Drum Sands, and Tyne Sands) ~6,500 seeds were injected into the substrate via caulking guns, a method known as Dispenser Injection Seeding (DIS). A moment we shared with local volunteers. This initial restoration effort was to serve as a trial, to compare different treatment types (injection density and injection depth), to determine the best procedure for future restoration activities. Since then, three monitoring sessions have been conducted to assess the success of our trials. Our monitoring programme is structured around the seasons; therefore, each location is surveyed four times a year.
Figure 1: Seagrass seed restoration on Burntisland Sands (Photo Credit: Maverick Photo Agency)
The first of these monitoring sessions occurred in June and was performed to ascertain the germination success of the seeds sown in spring. From this exercise we discovered that the germination success varied across the restoration sites. In Drum Sands, germination was recorded at 10.9%, which may seem low. However, seagrass germination rates typically hover around 10%, so our trial managed to reach this expected value. In Burntisland, germination was recorded at 0.6%, which was unexpectedly low. Our assumption regarding the low germination success was attributed to stronger tidal forces acting in this location and the substrate type, which would result in the transportation of seeds beyond the perimeter of our restoration plots. Finally, in Tyne Sands, we were presented with another issue. Our restoration trial site overlapped with an existing seagrass meadow, which produced inconclusive results, as we were unable to accurately discern which shoots were there as a direct result of our restoration efforts.
Figure 2: Newly germinated Zostera marina shoots (Photo Credit: Richard Lilley)
In light of these findings, we were able to modify our approach for the second phase of monitoring, which took place in August. For Burntisland, rather than continue to monitor only the area within the restoration plots, we expanded the observation distance to 1m around the plot to account for seed movement. Furthermore, based on our observations in the field we discovered newly germinated shoots within a 25-meter radius from the plot. These too were included in our final count. As these new shoots were expected to arise from our restoration trial, due to the lack of shoots in that area prior to our work. This alteration led to the germination success to rise from 0.6% up to 5.1% for Burntisland Sands. The germination success rose from 10.9% to 12.8% for Drum Sands, between the monitoring periods, as further shoots had emerged. Unfortunately, no compensatory measure could be taken for Tyne Sands, due to the inability to unpick what is natural opposed to what was introduced.
Figure 3: Drum Sands treatment (injection depth and number of seeds injected) results
Figure 4: Burntisland germinated shoots dispersal (Figure Credit: Esther Thomsen)
Our latest monitoring sessions were to assess seedling survival rather than germination success. The autumn monitoring session and the proceeding one in the New Year will better inform us on how successful the first restoration trial was. Our autumn monitoring sessions returned unexpected results, as there was a drastic decline in the number of shoots recorded. The seedling survival for Burntisland was 2.3%, down from 5.1%. Drum Sands observed the greatest decline, seedling survival for this site was recorded at 0.3%, down from 12.8%. Again, for Tyne Sands there is no conclusive way to differentiate between natural and introduced seagrass. However, there was a prodigious amount of seagrass shoots within the restoration plot, which was an encouraging sign.
Figure 5: Seagrass monitoring on Tyne Sands in November (Photo Credit: Richard Lilley)
Failure should not discourage scientists or communities from reporting their findings and it should be actively encouraged, as it is under reported in the scientific literature. Failure reporting leads to better practice within the scientific community and can help explain why certain procedures led to unfavourable outcomes.
Winter is typified by a reduction in the presence of seagrass, as colder darker months cause seagrass to enter a stage of senescence, whereby shoot density decreases as resources are reallocated towards maintaining the plants’ roots and the rhizome. The demands to maintain older leaves when resources are scarce is detrimental to the longevity of the individual plant, so leaves are sacrificed to ensure the survival of the plant. In addition to senescence there are other factors that lead to a loss of blades during the autumn and winter months. Herein I discuss two of the most probable pressures that led to a greater loss of seagrass blades during this period.
Throughout the autumn and winter the frequency and intensity of storms reaching the UK’s coasts increases. The wind and wave energy associated with storm systems has the ability to cause seagrass blades to snap and the strength to uproot whole plants (Portillo 2014). This autumn there were two named storms that reached the east of Scotland, the first storm Babet arrived on the 20th of October and brought with it 50 mph gales, which were sustained for several days. Easterly storms are more disruptive in the Forth in comparison to westerlies as they are able to inflict greater damage due to their direction of travel. These storms are able to build strength when travelling unperturbed across the North Sea before making landfall on the UK's eastern seaboard. The geography of the Forth and the wide estuary mouth enable storms to gain access and travel deep into its recesses.
Storm Babet caused wide spread damage to coastal infrastructure and private property throughout the outer Forth. There were several blow outs to the sea wall along Burntisland Sands and the force of the waves were able to punch a wide hole in North Berwick's harbour wall. The physical damage sustained to these hard engineering structures is indicative of the strength of this storm. It is therefore unsurprising that our restored seagrass shoots could be completely severed or for whole plants to be uprooted and transported away from the restoration plot. To conflate the disruption caused by Babet, Storm Ciaran arrived at the start of November.
Figure 6. Storm damage to the harbour wall in North Berwick (Photo Credit: Richard Lilley)
The second pressure takes the form of a biological one. The Forth is an important over wintering area and migration staging point for a range of migratory birds (Symond & Langslow 1987). The rich feeding grounds and roosting sites found within its boundary are fundamental to the survival for a range of visiting bird species (Scottish Natural Heritage 2016). During the winter, vast numbers of waders, ducks and geese return to the Forth's shores to over winter in Scotland's milder climate to build up their reserves. Amongst the overwintering species are Brent geese and wigeon both of which are herbivorous wildfowl that depend on seagrass as a component of their diet (Unsworth & Butterworth 2021). Previous studies investigating their feeding behaviour have shown that both species of bird graze on the above ground vegetation (blades and shoots) along with the below ground biomass (roots and rhizomes) (Nacken & Reise 1999). Moreover, these species are gregarious and feed in large groups (Kollars et al., 2017), the combination of their feeding behaviours can lead to the over grazing of seagrass, especially when the meadow or patch in question is small in size. This type of grazing has been known to completely outstrip seagrass from an area.
On the morning of our monitoring session on Drum Sands we disturbed a large aggregation of what was believed to be grazing wildfowl. Despite not having the precise species identification, number of birds and what behaviour they were expressing, it can be assumed returning Brent geese and wigeon could have devastating impacts on small seagrass patches. In order for seagrass recolonization to take place one of two things is required; for the roots and rhizomes to remain intact and or for a seed bank to exist.
Figure 7: Brent geese feeding on seagrass (Kollars et al., 2017)
This year we intend to run bird monitoring events to better understand the bird/seagrass relationship and what impact they have on seagrass in the Forth. By monitoring the species composition, behaviour, and spatiotemporal distribution of the assemblages in relation to existing seagrass patches and our restoration plots we hope to answer current gaps in our knowledge.
I hope this blog does not make you feel disheartened or discourage any of you from continuing to participate in the restoration of seagrass here in the Firth of Forth. This year was a scientific trial to test if seagrass could be restored in the Forth's intertidal area, which it initially showed to work well. However, working in nature presents certain challenges that are difficult to control for. Despite this somewhat sombre news, I am optimistic about the year ahead of us. We were able to collect many more seagrass seeds last summer for this year's seeding event. Hopefully with more seeds in the ground we can overcome some of nature's challenges.
Here is a video celebrating this year's hard work: End of Year Celebrations for Restoration Forth (youtube.com)
Thanks for reading and I hope to see you at one of our next events.
Lyle
Seagrass Officer
References
Kollars, K.M., Henry, A.K., Whalen, M.A., Boyer, K.E., Cusson, M., Ekolf, J.S., Hereu, C.M., Jorgensen, P., Kiriakopolos, S.L., & Reynolds. P.L. (2017) Meta-analysis of reciprocal linkages between temperate seagrasses and waterfowl with implications for conservation. Fronteers in Plant Science. 8(2119):1-17. doi: 10.3389/fpls.2017.02119
Nacken, M.; & Reise, K. (2000) Effects of herbivorous birds on intertidal seagrass beds. Helgoland Marine Research. 54: 87-94
Portillo, E. (2014) Relation between the type of wave exposure and seagrass losses (Cymodocea nodosa) in the south of Gran Canaria (Canary Islands - Spain). Oceanological and Hydrobiological Studies. 43: 29-40.
Symonds, F. L. & Langslow, D. R. (1984). Geographical origins and movements of shorebirds using the Firth of Forth. Ring. & Migr. 5: 145-152.
Unsworth, R.K.F.; Butterworth, E.G. (2021) Seagrass Meadows Provide a Significant Resource in Support of Avifauna. Diversity, 13, 363. https://doi.org/10.3390/d13080363