Macroalgae
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Increase macroalgae cover
No change observed
Gökova Bay to Cape Gelidonya
Türkiye
Problem: Macroalgae provides a key habitat for many native fish species. However, high abundances of invasive herbivorous fish, such as rabbitfish, are exerting an extreme grazing pressure on this habitat.
Action: Akdeniz Koruma Derneği (AKD) is playing a key role in the establishment and enforcement of No-Fishing Zones (NFZs). These are expected to lead to more complex trophic webs with more predatory fish, leading to more natural control of invasive herbivorous fish and reducing grazing pressure on native macroalgae.
Indicator: An increase in cover of macroalgae indicates reduced grazing pressure by invasive fish, allowing new macroalgae recruits to establish, and providing improved habitat for the native fish populations.
Methods
Macroalgae was monitored at sites both inside and outside No-Fishing Zones (NFZs) in order to understand the effect of NFZs on grazing pressure by invasive fish. Monitoring was carried out in three project areas: Gökova, Kaş and Göcek. In both Gökova and Kaş, monitoring took place from 2019 – 2023 at two sites within NFZs and one outside NFZs as a control site. In Göcek, two sites within NFZs were monitored from 2021 – 2023, while two control sites outside NFZs were monitored from 2019 – 2023. One further site outside NFZs was monitored in 2019 and 2020. Data was collected twice annually: once in spring and once in autumn.
To calculate coverage of macroalgae, a non-destructive method was used (Gerakaris & Tsiamis, 2014). After rapid assessments made by snorkelling to determine suitable and representative sites, transects were placed on representative habitats. Using SCUBA, at least 10 photos were taken of 20 x 20 cm quadrats placed randomly along the transect in the upper littoral zone (< 5 m). The number of replicates varied according to habitat type and homogeneity of benthic cover, and ranged from 7 to 10 across the three project areas. Relative surface coverage of each macroalgae taxon was measured using a digital grid using Adobe Photoshop software. Coverage of each taxon was calculated by summing each whole grid square covered by this taxon.
Diver completes macroalgae quadrat during macroalgae monitoring. Photo: AKD.
Example of macroalgae coverage measurement using the photo grid method. Photo: AKD.
Results
There was high inter-annual and intra-annual variability in coverage of all three types of macroalgae, but overall no evidence was found for an effect of NFZs on macroalgae recovery over time. There were no statistically significant differences in mean macroalgae coverage inside compared with outside NFZs in any of the three project areas. There were also no significant differences in thallus type composition inside or outside NFZs in any of the areas. In Kaş and Göcek, there were no significant changes in macroalgae coverage over the years. In Gökova there was a significant difference in macroalgae coverage among years, with the highest coverage in 2020. However, whether or not sites were inside an NFZ did not affect this relationship.
Figure 1: Macroalgae coverage (%) inside and outside No-Fishing Zones, across three project areas. Data were collected in two seasons, spring (top) and autumn (bottom). Error bars show standard deviation; some categories (e.g. outside-NFZ areas in Gökova) were represented by a single site, so no error bars could be calculated. Dashed lines show the period for which NFZs were enforced; Gökova NFZ was enforced for the full monitoring period.
Interpretation
There were distinct macroalgal communities within the project areas, which are dispersed along the coastline and separated by significant distances (>100 km) and complex coastlines. This was also seen within thallus types (i.e. turf algae was dominant in Gökova, while coralline and erect algae were dominant in Kaş and Göcek) highlighting the importance of tracking results for each of the project areas separately.
Although legal gazettement of the NFZ is in place in Kaş, this site had the lowest patrol and enforcement effort within the study period but consistently had the highest macroalgal coverage. In contrast, Gökova has had the longest NFZ protection and enforcement, but consistently had the lowest macroalgal coverage of the three sites. This could reflect levels of threat (i.e. higher fishing effort in Gökova leading to the greater enforcement focus), but is more likely due to other biotic and abiotic factors such as temperature change or variation in nutrient availability. Eutrophication due to nutrient inputs (which increases macroalgal coverage) was not measured, and the inhibition of photosynthesis caused by excessive sedimentation (which decreases macroalgal coverage) is also potentially important. Another factor may be natural interannual variation in populations of herbivorous grazing species. Whatever the drivers of macroalgal variation, it appears that NFZs have not yet had a sufficiently strong effect to balance increasing pressures from invasive herbivorous fish and allow for macroalgal recovery. This is likely to be a longer-term process, and long-term monitoring will be needed to track recovery.
Next steps
This indicator is helping to address a lack of knowledge about the extent and different types of macroalgal habitat in the region. Based on their results, data collection using the same methods will continue, in order to collect data spanning at least 10 years, to gain greater insight into the change taking place and potential drivers. If possible, nutrient levels and water turbidity will also be measured in future.
Publications
Kızılkaya, Z., Saydam, E., Walker, K. et al. Progress and challenges of multi-habitat marine restoration in the eastern Aegean Sea, Türkiye. npj Ocean Sustain 4, 12 (2025). https://doi.org/10.1038/s44183-025-00114-9
Citations
Gerakaris V & Tsiamis K (2014) Technical Assistance for Capacity Building on Water Quality Monitoring: Coastal & transitional BQES sampling and analysis procedures. Institute of Marine Biological Resources and Inland Waters, Greece
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