Seagrass reproductive survey results

This summer, Restoration Forth staff and volunteers conducted two reproductive assessments on the seagrass meadow at Burntisland, during the months of May and July. The two assessments were planned for the beginning and middle of the summer to investigate the timing of reproductive milestones for this meadow. In particular, the group sought to better understand the timing of reproductive shoot emergence and seed maturation, as these life cycle stages are important in the development of a meadow. Moreover, the data recorded during these assessments were used to provide an estimate of the number of seeds produced annually by this meadow. Recording the timing of these events over multiple years can inform how changes in the environment can influences the phenology of the meadow. Changes to the timing of these important life events can impact upon the survival of a meadow. It is therefore important to continuously monitor these habitats and the timings of such events.

Figure 1. Seagrass reproductive shoot and spathe

The figure above shows the reproductive shoot in yellow and ordinary shoots, which are the darker strap like blades. Visible on the reproductive shoot is a spathe, the portion of the plant which houses the reproductive organs. Reproductive shoots undergo a series of development stages during the summer months, starting with spathe formation and ending with seed dispersal. Volunteers identified the different development stage of each spathe present on one reproductive shoot. They did this by using the guide below. Each spathe was assigned a numerical value from 1 - 5, which was used to determine the reproductive state of the meadow.

Figure 2. Common eelgrass (Zostera marina) spathe development guide

The results below describe the number of spates, the stage of each spathe and the number of seeds, on one reproductive shoot. Volunteers selected one reproductive shoot from within their quadrat for assessment. During each assessment date, 30 quadrats were surveyed.

Figure 3. Reproductive assessment results from May and July 2025

The number of spathes counted between the two recording periods differed by 71, a greater number of spathes were observed in July, with 147 spathes in total. The average number of spathes per shoot was 2.5 in May and 4.9 in July. In May the most frequently observed reproductive stage was stage one, early development. While in July the most frequently observed reproductive stage was stage four, which indicates seed formation and maturation. There were 41 stage four spathes counted in July and five in May.

Figure 4. The percentage of each spathe stage recorded during the July assessment.

In July, the most commonly observed reproductive stage was stage 4, with 28% of all spathes recorded being of this stage. The least observed stage during the July assessment was stage 3, with 12% of all spathes recorded. Stages 1, 2, and 5 all had similar recorded percentages, with a 2% difference across the three stages.

Figure 5. Shoot and reproductive shoot numbers recorded at the two assessment periods

The figure above shows the average number of shoots and reproductive shoots in one metre square; this data has been extrapolated from the thirty 0.25m² quadrats take during both survey dates. There is a visible difference in the number of shoots and reproductive shoots between the two survey periods. The two variables were greater in July than in May. The greater abundance of shoots and reproductive shoots in July can be explained by either:

·       The development of the meadow during the summer months, when new shoots are recruited into the meadow, increasing the density of shoots and reproductive shoots, or,

·       The placement of the quadrat within the meadow, whether it landed in a patch of seagrass with greater densities of shoots and reproductive shoots.

Each quadrat was randomly thrown to minimise bias in its placement. Volunteers were encouraged to close their eyes when throwing their quadrat and to take measurements even when their quadrat landed in an area without seagrass. In addition to taking measurements of the number of shoots and reproductive shoots, volunteers were to record the percentage cover of both seagrass and algae, to determine whether this impacted the number of reproductive shoots present in each quadrat. Below is a figure illustrating the different seagrass and algae cover at each assessment date.

Figure 6. Seagrass and algal coverage at each assessment date

The average seagrass coverage decreased between May and July, with the average seagrass cover decreasing by 17% between the two assessment dates. Alternatively, algal cover increased between the two assessment dates, with algal coverage increasing from 1.9% to 2.6%, although this increase is minimal. Despite the decrease in seagrass coverage recorded in the quadrats in July, the average number of reproductive shoots per metre square rose by 139. The increase in the number of reproductive shoots from May to July is to be expected as more reproductive shoots should emerge as the summer progresses.

Using the spatial extent data of the meadow collected in 2024, it is possible to combine the data from the July reproductive assessment, to estimate the reproductive capacity of the meadow. This uses the average seed number per metre square to determine the total number of seeds present across the meadow. The average number of seeds/m² was 189, which when multiplied across the spatial extent of the meadow returned a total seed number of 876,878 for the meadow (Table 1).

	Burntisland Reproductive Assessment Results Table
Number of shoots collected	30
Average number of spathes per shoot (stage 4)	1.37
Average number of seeds per spathe (stage 4)	5.70
Average seeds per shoot	7.81
Average number of reproductive shoots (m2)	24.30
Number of reproductive shoots in meadow	112,290.79
Area of meadow (m2)	4,621.02
Seeds (m2)	189.76
Seeds in meadow	876,878

It was possible to estimate the number of seeds present in the meadow, through the use of the spatial data collected during the 2024 summer. Seagrass mapping sessions were held in 2024, which involved many Restoration Forth volunteers, to create a digital representation of the seagrass meadow and patches of seagrass present across Burntisland Sands. Volunteers recorded the perimeter of each patch of seagrass using a GPS unit, which was later uploaded into the mapping tool, QGIS. QGIS was employed to produce the map of the meadow but to also calculate the area occupied by the meadow. Through the combination of the two data sets, it is possible to determine the rough seed abundance present within the meadow.

Figure 7. Burntisland's seagrass meadow

Thanks for reading. If you have any questions related to this article and the data presented within it, please contact: lyle@theecologycentre.org