Course:EOSC270/2023/Threats from the Shore: Analyzing the Impact of Coastal Construction Sediment Runoff on Coral Reef Health in Southeast Asia

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PHOTO OF CORAL REEFS

What is the problem?

Defining the problem

At the heart of the problem is the impact of sediment runoff into the marine environment on the health of coral reefs. Runoff from coastal construction activities increases water turbidity, which reduces the sunlight penetration needed for coral photosynthesis and does not provide enough nutrients for corals to survive. This runoff simultaneously smothers coral organisms, leading to coral bleaching[1], and some of these pollutants alter the composition of coral reef habitats.

Human Behavior is contributing to the Problem

Human behavior contributes directly to the problem. This includes the following points:

  • Construction activities: The construction of buildings near the coast disturbs the current land and produces a lot of sediments. Failure to implement or maintain adequate erosion and sedimentation controls during construction can result in more sediment being washed into the ocean[2].
  • Land clearing and deforestation: Land clearing and deforestation required for construction can result in the removal of vegetation that would otherwise help stabilize the soil, increasing the likelihood or volume of runoff.
  • Agricultural runoff: Agricultural activities in the vicinity, such as irrigation of land, can increase the amount of net sediment runoff.
  • Overfishing: Overfishing can affect corals by disrupting the ecosystem and food chain around them[3].

Where the problem mainly occurs

The problem occurs mainly in Southeast Asia because coral reefs are found in tropical marine ecosystems. Southeast Asia is close to the equator and has many coastal areas and tropical marine ecosystems[4] that have many coral reef systems, such as in Indonesia, the Philippines, Thailand, and Malaysia, which have rapid coastal development, booming tourism, and various infrastructural developments[4], which generate a lot of sediment runoff that affects the local coral reef systems[4].

Prevalence of the problem

Due to the rapid economic development in Southeast Asia, it prioritizes rapid infrastructure and urban development in the coastal areas and thus does not have enough measures to protect the environment. As a result, the problem is widespread in Southeast Asia and is getting worse as time goes by. The coral reefs in this region are among the most species-diverse reefs on the planet, and thus the heat loss induced by this problem can be extremely severe, and likewise, global threats to coral reefs such as climate change, pollution, and so on, compound this problem, so solving this sediment runoff becomes especially serious[5].

How does this problem impact marine ecosystems?

Fine carbonate sediment bound into a mucus sheet on a colony of Porites, Zanzibar, East Africa. This coral also exhibits the multilobate morphology believed to result from sediment stress.
Impacts of Sediment on Coral Reefs

How and why does it impact the coral reef ecosystems?

Increased Sedimentation and Pollution:

Coastal construction activities lead to increased sedimentation and pollution in marine environments. Sediment runoff can physically smother coral reefs, blocking sunlight essential for the photosynthetic activities of symbiotic algae (zooxanthellae) and significantly reducing the ability of corals to photosynthesize[6]. In addition to having an impact on coral growth, this also weakens the structure of the reefs, making them more vulnerable to disease and bleaching events. The runoff carrying chemicals and heavy metals further exacerbates the degradation of coral reef habitats by altering the chemical composition of surrounding waters, stressing coral communities, and disrupting the ecological balance of reef ecosystems[6].

Nutrient enrichment:

Runoff from coastal built-up areas is usually high in nutrients, mainly nitrogen and phosphorus, leading to nutrient enrichment in the marine environment[7]. This situation can exacerbate the growth of algae, which compete with corals for light and space. Under normal conditions, coral reefs have a competitive advantage over algal growth due to efficient nutrient cycling[7]. However, excess nutrients can tip the balance in favor of algae, leading to algal blooms that can overshadow corals, stunt their growth, and lead to reduced biodiversity[8]. This phenomenon can further affect species composition and reduce habitat for reef-associated species.

How does it impact coral polyps and symbiotic algae?

The main organisms affected by these environmental changes are the coral polyps themselves and the symbiotic algae in their tissues[6][7]. The coral polyps are directly affected by the sediment thus suffocating it and inhibiting its photosynthesis, feeding and growth. At the same time, nutrient enrichment from runoff can lead to algal blooms that compete with corals for sunlight and space[7]. When the symbiotic relationship between corals and zooxanthellae is disrupted, this affects the coral's ability to produce calcium carbonate, which is important for reef maintenance[6]. As corals weaken or die, the structure of the reef ecosystem is also disrupted, eventually leading to a decline in habitat complexity and biodiversity.

Do coral polyps and their symbiotic algae have unique characteristics that make them vulnerable?

The delicate balance of coral polyps and their symbiotic algae can be easily disrupted by environmental changes. They need clear, sunny waters, so they are particularly vulnerable to sedimentation. Their limited mobility and slow growth rate can also make them very slow to recover from damage[8]. In addition, the complexity of coral reef ecosystems means that any damage will have an impact on them. This has implications not only for the corals themselves, but also for the myriad of species that depend on them for their survival.

What is the extent of the problem?

Measurable change

Data of risk reefs

The data on coral reefs that changed includes information on the recovery from the 1998 mass bleaching event in Tubbataha, Philippines, where mean live coral cover decreased by 19% after bleaching but remained constant from 1999 to 2001, with no immediate decline in fisheries observed[9]. Additionally, in Vietnam, the 1998 bleaching event resulted in bleaching of 37% of coral colonies in the Con Dao islands, with surveys from 1998 to 2001 indicating a slow recovery in many places, exacerbated by anthropogenic stresses leading to continued reef decline since the El Niño event.[9]

Decline in coral cover

The coral reefs in Taytay Bay, Philippines, experienced a significant loss of coral cover following a mass coral bleaching event in 2010, with an average annual recovery rate of 2.8% over the subsequent nine years[10]. The recovery rates varied among reefs, influenced by factors such as macro-algal cover and coral composition. The massive growth of algae caused by Sediment runoff is one of the main reasons for the current situation. High macro-algal cover was found to increase post-bleaching coral mortality and hinder recovery by competing for space with corals. The dominant coral species, particularly Acropora, played a role in the recovery rates observed, with fast-growing corals contributing to faster recovery.

Coral bleaching and macroalgae cover of corals

Prediction

Sedimentation is expected to have significant impacts on coral reefs in the future due to its adverse effects on reef organisms and the overall ecosystem[11]. Excessive sedimentation can lead to fewer coral species, reduced coral growth rates, decreased calcification, and slower rates of reef accretion. Sediment particles can smother reef organisms, reduce light available for photosynthesis, and alter the physical and biological processes of coral reef ecosystems[11]. Additionally, sedimentation can disrupt the complex interactions between fish and their reef habitat, potentially leading to declines in fish populations . The structure and function of coral reef ecosystems can be adversely affected by sedimentation, impacting both physical and biological processes. Furthermore, sedimentation can alter coral distribution patterns and coral diversity, with varying sedimentation rates associated with different numbers of coral species and genera. In summary, sedimentation poses a significant threat to coral reefs in the future by impacting coral species diversity, growth rates, reef accretion, and overall ecosystem health.

Given the impact, what are the solutions?

Urbanization and business activity

The rapid urbanization, industrial development, and expansion of industries such as agriculture, forestry, mining, and tourism have led to substantial changes in the coastal structure of cities in the region[12]. The increase in artificial coastlines, including groins, jetties, harbors, aquaculture dikes, and urban coasts, reflects the development and adjustment of industries like aquaculture, which have grown rapidly over the years. Moreover, the level of urbanization in Southeast Asian countries has been on the rise, with Indonesia and East Timor experiencing more than a 10% increase in urbanization from 2000 to 2014, indicating the impact of human activities on land use changes in the region[12].

Mangrove

Mangroves in Southeast Asia are important due to their significant ecological and economic value, providing essential services and habitats for various species[12]. They play a crucial role in coastal protection, carbon sequestration, biodiversity conservation, and supporting local livelihoods.

Location map of Southeast Asia

Management policies

Local solutions to reduce the effects of human activities on land use in Southeast Asia include implementing sustainable coastal management practices, promoting mangrove conservation and restoration, regulating land reclamation activities, and enforcing stricter regulations on urban expansion and industrial development[12]. These measures can help mitigate the negative impacts of human activities on coastal ecosystems and land use, ultimately contributing to the preservation and sustainable management of land resources in the region.

Restoration of coral reefs

Ecosystem cycle after artificial intervention

To recover coral reefs on a global scale, it is recommended to address the causes of coral decline, align restoration efforts with protection measures, and adapt to climate change impacts by using temperature-resilient corals and implementing new techniques such as assisted evolution[13]. Additionally, Utilizing a combination of artificial reef designs with species-specific outplanting strategies can enhance coral cover and diversity, supporting the development of a more resilient coral community[13]. Monitoring at socio-ecological relevant scales is crucial to determine the effectiveness of reef restoration as a conservation tool.




References

  1. ↑ Baird, M. E., Mongin, M., Rizwi, F., Bay, L. K., Cantin, N. E., Morris, L. A., & Skerratt, J. (2021). The effect of natural and anthropogenic nutrient and sediment loads on coral oxidative stress on runoff-exposed reefs. Marine Pollution Bulletin, 168, 112409. https://doi.org/10.1016/j.marpolbul.2021.112409
  2. ↑ Dunning, K. H. (2018). Introduction. In Managing Coral Reefs: An Ecological and Institutional Analysis of Ecosystem Services in Southeast Asia (pp. 1–10). chapter, Anthem Press.
  3. ↑ Larsen, M. C., & Webb, R. M. T. (2009). Potential effects of runoff, fluvial sediment, and nutrient discharges on the coral reefs of puerto rico. Journal of Coastal Research, 25(1), 189-208. https://doi.org/10.2112/07-0920.1
  4. ↑ 4.0 4.1 4.2 Dunning, K. H. (2018). Introduction. In Managing Coral Reefs: An Ecological and Institutional Analysis of Ecosystem Services in Southeast Asia (pp. 1–10). chapter, Anthem Press.
  5. ↑ Dunning, K. H. (2018). Governing Natural Resources in Indonesia and Malaysia. In Managing Coral Reefs: An Ecological and Institutional Analysis of Ecosystem Services in Southeast Asia (pp. 25–34). chapter, Anthem Press.
  6. ↑ 6.0 6.1 6.2 6.3 Carlson, R. R., Foo, S. A., & Asner, G. P. (2019). Land Use Impacts on Coral Reef Health: A Ridge-to-Reef Perspective. Front. Mar. Sci. 6:562. https://doi.org/10.3389/fmars.2019.00562
  7. ↑ 7.0 7.1 7.2 7.3 Heery, E. C., Hoeksema, B. W., Browne, N. K., Reimer, J. D., Ang, P. O., Huang, D., Friess, D. A., Chou, L. M., Loke, L. H. L., Saksena-Taylor, P., Alsagoff, N., Yeemin, T., Sutthacheep, M., Vo, S. T., Bos, A. R., Gumanao, G. S., Syed Hussein, M. A., Waheed, Z., Lane, D. J. W., & Johan, O. (2018). Urban coral reefs: Degradation and resilience of hard coral assemblages in coastal cities of East and Southeast Asia. Marine Pollution Bulletin, 135, 654–681. https://doi.org/10.1016/j.marpolbul.2018.07.041
  8. ↑ 8.0 8.1 Risk, M. J., & Edinger, E. (2011). Impacts of Sediment on Coral Reefs. In D. Hopley (Ed.), Encyclopedia of Modern Coral Reefs: Structure, Form and Process (pp. 575–586). Springer Netherlands. https://doi.org/10.1007/9789048126392_25
  9. ↑ 9.0 9.1 Chou, L. M., Tuan, V. S., Philreefs, Y. T., Cabanban, A., & Suharsono, K. I. (2002). Status of Southeast Asia coral reefs. Status of coral reefs of the world. Australian Institute of Marine Science, Townsville, 123-153.
  10. ↑ Abesamis, M. R. R., Ang, J. L., Robles, R. C., & Licuanan, W. Y. (2023). Recovery of coral cover on inshore fringing reefs following mass coral bleaching in the philippines. Coral Reefs, 42(1), 99-104. https://doi.org/10.1007/s00338-022-02322-y
  11. ↑ 11.0 11.1 Rogers, C. S. (1990). Responses of coral reefs and reef organisms to sedimentation. Marine Ecology. Progress Series (Halstenbek), 62(1/2), 185-202. https://doi.org/10.3354/meps062185
  12. ↑ 12.0 12.1 12.2 12.3 Zhang, Y., & Hou, X. (2020). Characteristics of coastline changes on southeast Asia Islands from 2000 to 2015. Remote Sensing, 12(3), 519https://doi.org/10.3390/rs12030519
  13. ↑ 13.0 13.1 Knoester, E., Rienstra, J., Schürmann, Q., Wolma, A., Murk, A., & Osinga, R. (2023). Community-managed coral reef restoration in southern Kenya initiates reef recovery using various artificial reef designs. Frontiers in Marine Science, 10https://doi.org/10.3389/fmars.2023.1152106
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