Author: Summer Taylor
What is the health condition of coral reefs across Indonesia?
Indonesia sits almost perfectly in the middle of the Coral Triangle, which is famously home to the highest marine biodiversity on the planet. Naturally, this has led to Indonesia becoming a key hotspot for marine monitoring and research, especially of coral reefs. Corals, however, are slow-growing creatures so quantifying their health and growth at any given time can be difficult! Therefore, the key to successful coral reef monitoring is long-term datasets. These datasets, spanning upwards of 10 years, can show trends which answer some of the most important coral ecosystem health questions:
What is the health condition of coral reefs? Are they improving or degrading?
How have corals responded to specific changes in the environment on varying timescales (i.e. a short heat wave or prolonged mining activities)?
At what point (i.e. temperature, pollution level) can corals no longer recover?
Furthermore, trends in long-term datasets are essential for reef managers and policy makers to make educated decisions on how to best move forward. The Research Center for Oceanography (RCO) has been a leader in monitoring the condition of coral reefs across Indonesia for the past 26 years. Each year the RCO surveys 1,151 coral reefs across Indonesia and categorizes their health condition by its percentage of living hard coral coverage (HC). Each coral reef is then placed into 1 of 4 categories: Poor (when HC ≤ 25%), Fair (when 25% < HC ≤ 50%), Good (50% < HC ≤ 75%), and Excellent (when HC > 75%). This is the breakdown of the results from the 1,151 Indonesian reefs they surveyed in 2019:
- Poor: 390 reefs (33.8%)
- Fair: 431 reefs (37.4%)
- Good: 258 reefs (22.4%)
- Excellent: 74 reefs (6.4%)
In other words, only about 30% of reefs across Indonesia have more than 50% coral coverage (Good and Excellent), while the remaining 70% have less than 50% coral coverage (Poor and Fair). Even though the percentage of Poor corals has decreased from 46% to 34% in the past 26 years, researchers warn that Poor corals may have reached a “point of no return” and may be left to “perish” because of their exposure to intensive chronic stressors (RCO, 2020). Interestingly, the condition of a coral reef in Indonesia is largely dependent on its geographical location. Key differences in coral condition trends can be seen between reefs in western, central, and eastern Indonesia. The main reason behind these differences is that, due to Indonesia’s expansive area, each region is subjected to very different environmental conditions and anthropogenic factors (i.e. pollution), causing some regions to be exposed to more harmful conditions than others. So, let’s break down the condition of coral reefs by region.
In western Indonesia, reef conditions appear to be generally improving (Figure 1). Since 1993, the percentage of Excellent and Fair reefs have increased, while the percentage of Poor reefs have decreased by nearly 35%! Part of this success is attributed to western Indonesia’s great strides in increasing community engagement and awareness. For example, western Indonesia has developed a successful community-driven fisheries management approach to protect these natural resources from exploitation. As well, the practice of exploiting fish stocks that used to be common in western Indonesia, has moved eastwards, lowering the amount of stress coral ecosystems are subjected to in this region. Although this is positive, reefs in western Indonesia are still facing a surplus of major stressors including anthropogenic stressors (i.e. sewage runoff, mining activities), marine pollution, sedimentation, and low salinity.
In central Indonesia, coral reef conditions were improving until 2015 but have taken a turn for the worse in the last 4 years. Prior to the global bleaching event in 2015, the percentage of Fair and Good coral reef conditions were on a steady incline. Since 2015, however, the percentage of Poor reefs has nearly doubled, increasing from 21% to 36% of all central Indonesian reefs. Both central and western Indonesia are also impacted by the warming sea temperatures that flow in from the Indian Ocean every 3-7 years due to the natural activity of the El Nino Southern Oscillation (ENSO). Consequently, when paired with anthropogenic climate warming, this additional warming has accelerated the decline in coral reefs that we have witnessed in recent years in central and western Indonesia. (Whereas, Eastern Indonesia is influenced more by the western Pacific Ocean.)
Contrarily, coral conditions in eastern Indonesia are declining. Since 1993, the proportion of Excellent reefs has steadily declined from 10% to 4% and Good reefs have declined from 30% to 24%. Meanwhile, Fair reefs have climbed most significantly, from 23% to 39% and Poor reefs have fluctuated greatly but are currently slightly lower than their 1993 starting point, currently at 34%.
The stark difference between eastern Indonesia against western and central is likely correlated to the rise in resource exploitation that began in the early 2000s, when it moved over from western Indonesia. Other major stressors affecting eastern Indonesia include low community awareness and poor law enforcement and surveillance that is enabling destructive fishing practices and exploitation. Despite all three regions showing different trends, they shared one thing in common: the global 2015-2016 bleaching event negatively affected them all. Although there have been some promising signs of recovery, especially in western Indonesia after nearby mining activities declined, this is a good reminder showing just how fragile these ecosystems really are.
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References Johan, O., Budiyanto, A., Dzumalek, A. R., & Sulha, S. (2020). The Status of Indonesian Coral Reefs 2019. Research Center for Oceanography. https://www.researchgate.net/profile/Tri_Hadi4/publication/342663285_The_Status_of_Indonesian_Coral_Reefs_2019/links/5eff38aca6fdcc4ca4477d14/The-Status-of-Indonesian-Coral-Reefs-2019.pdf