Laura Puk

Assessment of key fish species controlling macroalgae growth in a coral reef of Koh Panghan, Gulf of Thailand.

University of Bremen, Germany. February – July 2015

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Identifying important fish species possibly contributing to the prevention of a phase shift due to their role as macroalgae removers. Assessing whether local fisheries have an impact on these species.


Project Progress


Project Progress

Coral Algae interactions observed


Coral reefs are biodiversity hotspots which provide many goods and services to the communities depending on them. For many years they have been in serious decline with an estimated 30% being already severely damaged 1. This is due to a range of disturbances, such as over-fishing2, diseases3 and climate change4. Many of the reefs have undergone phase shifts from coral dominated systems to macroalgae dominance, which is often associated with overharvesting of herbivorous fishes5,6. The ability of a reef system to withstand these impacts and resist phase shifts, namely the resilience7, depends to a large amount on an intact herbivorous fish community8,9. More and more research highlights the importance of not just protecting general biodiversity but especially important functional groups, which can prevent or even reverse such a phase shift10,11. It is widely accepted that parrotfish and surgeonfish play an important role in the prevention of a phase shift5,6 but only current research highlights the importance of a “sleeping functional group” in the reversal of a phase shift11. There are major regional differences in species diversity, functional group composition and resilience6. It is to be expected that the important species for prevention and reversal of a phase shift vary on regional and temporal scales11.

Gaps of Knowledge:

Several studies documented the removal of macroalgae by fish, but the exact species remain largely unknown12. This is of great importance as the resilience of a system may be highly dependent on a small number of species to perform specific functions12. While some groups are generally accepted as being important herbivores, only some of the species within these groups actually seem to feed on macroalgae to a significant extent11. Since there are major regional differences and most research has been carried out in the Caribbean and on the Great Barrier Reef there is a lack of knowledge for other regions of the world, such as the Gulf of Thailand.


In order to keep the ecosystem as healthy as possible and to provide local communities with the resources needed, it is vital to figure out which species are especially important and, by doing so, enable the local fisheries to act on it. Many metrics for monitoring reef status still include coral cover and target species to a majority. In order to improve the monitoring it is essential to include important functional groups, functional redundancy and response diversity6. There is still a big gap of knowledge in this area6. Since there have been few studies carried out in the Gulf of Thailand, it is important to carry out research that can help to implement sustainable fishing practices.

Key questions

  1. Which herbivorous fish species are removing macroalgae in the coastal coral reefs of Mae Haad bay?
  2. Which herbivorous fish species are missing in the coastal coral reefs of Mae Haad bay?
  3. Are these fish species targeted by local fisheries?


Project Progress


Project Progress

Coral Algae interactions observed

Methods and Sampling Design

  1. To observe which fish species remove macroalgae in the bay “Mae Haad”, an area will be selected, where macroalgae are present but are kept in check by herbivores. This area will be caged for several weeks, until the algae will have grown to substantial size. Before presenting these macroalgae strands to the local fishes in replicates of three, wet weight will be measured. The species feeding on the macro algae will be recorded deploying cameras. This experiment will be set up in different locations in the bay, always at the same time of day to avoid bias by changing conditions. After the observation, wet weight of the algae will be measured again and the video footage will be analyzed for species feeding, their size and biomass, the time spent feeding and their bite rate. Possibly influencing factors, such as nutrients will be measured.
  2. Macroalgae which grow in Mae Haad bay, but are absent in the nearby marine-protected area “Ang Thong”, will be selected, sampled and their wet weight measured. They will be presented in the same set-up as explained for research question 1 (for Mae Haad) to the herbivorous fish species in Ang Thong and data will be analyzed as described above.
  3. Fishery landings information will be collected and analyzed to find out whether important herbivorous fish species are removed in Mae Haad bay. This will be done by visual observation and questioning of the local fishermen. Collected data will be compared with the findings of research questions 1 and 2.


  1. Moberg, F. & Folke, C. Ecological goods and services of coral reef ecosystems. Ecol. Econ. 29, 215–233 (1999).
  2. Jackson, J. B. et al. Historical overfishing and the recent collapse of coastal ecosystems. Science 293, 629–37 (2001).
  3. Harvell, C. D. et al. Climate warming and disease risks for terrestrial and marine biota. Science 296, 2158–62 (2002).
  4. Hughes, T. P. et al. Climate change, human impacts, and the resilience of coral reefs. Science 301, 929–33 (2003).
  5. Mumby, P. J. et al. Fishing, trophic cascades, and the process of grazing on coral reefs. Science 311, 98–101 (2006).
  6. Bellwood, D. R., Hughes, T. P., Folke, C. & Nyström, M. Confronting the coral reef crisis. Nature 429, 827–33 (2004).
  7. Nyström, M., Folke, C. & Moberg, F. Coral reef disturbance and resilience in a human-dominated environment. Trends Ecol. Evol. 15, 413–417 (2000).
  8. Hughes, T. P. et al. Phase shifts, herbivory, and the resilience of coral reefs to climate change. Curr. Biol. 17, 360–5 (2007).
  9. Burkepile, D. E. & Hay, M. E. Herbivore species richness and feeding complementarity affect community structure and function on a coral reef. Proc. Natl. Acad. Sci. U. S. A. 105, 16201–6 (2008).
  10. Bellwood, D. R., Hoey, A. S. & Choat, J. H. Limited functional redundancy in high diversity systems: resilience and ecosystem function on coral reefs. Ecol. Lett. 6, 281–285 (2003).
  11. Bellwood, D. R., Hughes, T. P. & Hoey, A. S. Sleeping functional group drives coral-reef recovery. Curr. Biol. 16, 2434–9 (2006).
  12. Fox, R. & Bellwood, D. Quantifying herbivory across a coral reef depth gradient. Mar. Ecol. Prog. Ser. 339, 49–59 (2007).


Ignorance is bliss, but knowledge is so much more attractive




Macroalgae can be defined as large, multicellular, photosynthetic organisms. The term macroalgae can also encompass three groups; red algae (rhodophyta), green algae (chlorophyta), and brown algae (phaeophyta). Macroalgaes structure consists of three main parts:

  • lamina/blade = leaflike structure where photosynthesis takes place.
  • stipe = stemlike structure that provides support, although may be absent in some.
  • holdfast = specialised structure that attaches the algae to substrate.

The most important abiotic factor that allow macroalgae to survive include sunlight availability. This limits how deep they can inhabit in seawater as they need to be shallow enough to obtain sufficient light for photosynthesis.

Macroalgae are environmentally important as they provide nutrients for the marine ecosystem being one of the main primary producers. Also, macroalgae can create a unique habitat for other organisms such as invertebrates and juvenile fish.






Kill all humans



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