*4.2. Threats to Blue Carbon Ecosystems*

Natural disturbances like typhoons resulting in strong waves and storm surges are perceived to be the most damaging threat to BCEs in Busuanga (see Table 4). The residents highly recognized natural calamities to destroy BCEs since they have personal experiences and observations. For example, when the super typhoon Haiyan devastated the Philippines in 2013, it caused significant damage to BCEs in the country [61,62]. During the conduct of household surveys, many residents recalled and shared their observations on how the super typhoon destroyed the mangroves and seagrasses. Similar findings were also documented from the residents in Eastern Samar where the super typhoon first hit the country [33].

Pollution from domestic wastes was also recognized to be one of the top concerning threats. Photo documents clearly showed solid wastes in coastal areas where communities live. The lack of discipline and effective solid waste management systems are common factors that propagate increasing pollution pressure to BCEs. Other concerning threats to mangroves include illegal harvesting for firewood and charcoal-making. This problem has been a consistent challenge to address since local communities have direct access to mangrove forests [1]; however, a recent survey in the locality has shown a decline in illegal activities due to the presence of local ordinances and national policies (i.e., [33]). Conversion to fishponds was identified as the least concerning threat since there are no converted aquaculture ponds in Busuanga. This is noteworthy since conversion to fishponds was one of the main causes of rapid mangrove degradation in the country in the early years [1]. Current programs and policies (i.e., Coastal Resource Management Programs, Revised Forestry Code of the Philippines (Presidential Decree No. 705)) at the local and national level have reduced these activities. Meanwhile, perceived threats specific to seagrasses include mangrove planting on seagrass beds, unregulated gleaning, and siltation. These pressures from human activities could result in a cascading effect in the whole coastal ecosystem. For instance, unregulated gleaning could result in biodiversity loss [63]. In the Philippines, cases of seagrass and associated organisms' decline were perceived and attributed to these human-induced stressors [55].

Conversely, the effect of natural disturbances on BCEs in Karimunjawa is perceived to be the least concerning threat as reflected in the results (see Table 4). Unlike the Philippines, the average number of tropical cyclones in Indonesia is seven (7) per year or about 9% of the average number of cyclones globally, because, in principle, tropical cyclones do not cross the country as they will always move away from the equator [64]. The lack of personal experiences and observations on the effect of natural disturbances on BCEs likely influenced residents' perceptions. In the perception study conducted by [59] in Karimunjawa, there are no questions about the effects of natural threats, as they are mostly human-derived. Their study showed that mangrove degradation in the island is correlated with human-derived disturbances; mangrove logging has the strongest correlation (*p <* 0.01) while the development of offshore inns (guesthouses) has the weakest correlation (*p <* 0.05). Conformingly, the results of this study also identified anthropogenic threats (i.e., mangrove cutting, pollution) as the top perceived causes of mangrove degradation. The recognition of human-induced threats to mangroves has been long supported by quantitative researches (i.e., [65,66]) and has been observed not just in Karimunjawa but also in other areas in Indonesia. For instance, mangrove losses due to conversion into oil palm plantation and other land uses were observed in the islands of Mentawau (West Sumatra), Lankat (North Sumatra), Bawal (West Kalimantan), Seram (Maluku), Bangka Belitung, and Enggano

Bengkulu [67]. The results of this study and previous researches (i.e., [59,68]) indicate that mangroves in Indonesia are still threatened by manmade activities despite an increase in management strategies (i.e., [66,69,70]).

Seagrasses in Karimunjawa are also perceived to be most threatened by anthropogenic disturbances (i.e., pollution, unregulated gleaning). There are not many published studies on seagrass ecosystems in Karimunjawa, however, seagrasses in small islands in Indonesia are generally highly vulnerable to human-induced activities [58]. Destructive fishing methods (push nets and trawls), coastal constructions, and sedimentation from coastal development are also among the top activities in Indonesia that damage the seagrasses [16]. Household wastes also affect the seagrasses; for example, in Spermonde Archipelago in South Sulawesi, seagrasses' health is influenced by the nutrient loading, turbidity, and total suspended solids coming from domestic solid and liquid wastes [71]. The results of this study conform with the survey conducted by [72] with seagrass experts in Indonesia such that current and future threats are mostly human-derived activities such as coastal development, sedimentation, poor water quality, seaweed farming, overexploitation of herbivores, and coastal erosion.
