Dinamika Spasio-Temporal dan Ketahanan Komunitas Karang Pada Rezim Lingkungan Yang Kontras Di Perairan Sumatera

Abstract

Terumbu karang menghadapi tekanan akibat pemanasan laut, gelombang panas, dan pemutihan massal. Namun, respons komunitas karang terhadap gangguan termal dapat berbeda antarwilayah karena dipengaruhi oleh rezim lingkungan, komposisi taksonomi, bentuk pertumbuhan, dan riwayat paparan. Penelitian ini menganalisis dinamika spasio-temporal, resistance, dan recovery komunitas karang pada wilayah barat dan timur perairan Sumatera sebelum, selama, dan setelah pemutihan tahun 2016. Penelitian dilakukan pada 93 stasiun transek permanen di delapan lokasi, yaitu Nias Utara, Tapanuli Tengah, Mentawai, dan Pulau Pieh di wilayah barat, serta Belitung, Bintan, Natuna, dan Batam di wilayah timur. Pengamatan dilakukan pada 2015, 2016, dan 2018. Data komunitas diperoleh melalui Underwater Photo Transect sebanyak 13.950 foto, sedangkan data suhu permukaan laut, Degree Heating Weeks (DHW), salinitas, dan turbiditas berasal dari NOAA Coral Reef Watch, Copernicus Marine Service, dan MODIS-Aqua. Analisis meliputi perubahan temporal, keanekaragaman, nMDS, PERMANOVA, CCA, environmental fitting, serta perubahan taksa dan bentuk pertumbuhan. Hasil menunjukkan respons yang sangat kontras. Di wilayah barat, tutupan karang hidup menurun dari sekitar 37,33% pada 2015 menjadi 19,38% pada 2016 dan hanya meningkat menjadi 21,99% pada 2018. Di wilayah timur, tutupan relatif stabil, yaitu 34,27% pada 2015, 32,80% pada 2016, dan 32,57% pada 2018. Seluruh lokasi barat mengalami penurunan nyata, sedangkan Batam, Bintan, dan Natuna relatif stabil. Belitung mengalami penurunan yang diikuti pemulihan parsial. Reorganisasi struktur genera dan bentuk pertumbuhan juga lebih kuat di wilayah barat. Wilayah barat umumnya lebih hangat, lebih asin, dan lebih jernih, sedangkan wilayah timur lebih dingin, bersalinitas lebih rendah, dan pada beberapa lokasi lebih keruh. Puncak suhu dan tekanan termal terjadi pada 2016, tetapi DHW berbeda antarlokasi dan tidak sepenuhnya mengikuti suhu absolut. Acropora, terutama bentuk branching dan tabulate, mengalami penurunan terbesar di wilayah barat, sedangkan Porites dan bentuk masif menunjukkan resistance lebih tinggi. Namun, Acropora relatif mampu bertahan di beberapa lokasi timur, menunjukkan bahwa sensitivitas taksa bergantung pada konteks lingkungan. Turbiditas yang lebih tinggi di wilayah timur diduga mengurangi irradiance dan tekanan foto termal, meskipun hubungan ini bersifat asosiatif. Penelitian ini menunjukkan bahwa ketahanan komunitas karang ditentukan oleh interaksi antara paparan termal, rezim lingkungan lokal, dan sensitivitas biologis taksa serta bentuk pertumbuhan. Kebaruan penelitian terletak pada perbandingan geografis barat–timur, penggunaan transek permanen lintas periode gangguan, analisis multilevel komunitas, dan pembuktian context-dependent vulnerability. Hasil penelitian mendukung pengelolaan berbasiskerentanan spasial, perlindungan lokasi dengan resistance tinggi, serta pemantauan yang mencakup tutupan, komposisi taksonomi, dan sifat fungsional komunitas.

Coral reefs are increasingly threatened by ocean warming, marine heatwaves, and mass bleaching events. However, coral community responses to thermal disturbances may vary among regions due to differences in environmental regimes, taxonomic composition, growth forms, and exposure history. This study examined the spatio-temporal dynamics, resistance, and recovery of coral communities in the western and eastern waters of Sumatra before, during, and after the 2016 bleaching event. The study was conducted at 93 permanent transect stations across eight locations: North Nias, Central Tapanuli, Mentawai, and Pieh Island in the western region, and Belitung, Bintan, Natuna, and Batam in the eastern region. Surveys were conducted in 2015, 2016, and 2018. Coral community data were collected using the Underwater Photo Transect method, generating 13,950 photographs. Sea surface temperature, Degree Heating Weeks (DHW), salinity, and turbidity data were obtained from NOAA Coral Reef Watch, the Copernicus Marine Service, and MODIS-Aqua. Analyses included temporal change assessment, diversity analysis, nMDS, PERMANOVA, CCA, environmental fitting, and evaluation of changes in coral taxa and growth forms. The results revealed strongly contrasting responses between the two regions. In the western region, aggregate live coral cover declined from approximately 37.33% in 2015 to 19.38% in 2016 and recovered only slightly to 21.99% in 2018. In contrast, coral cover in the eastern region remained relatively stable, decreasing from approximately 34.27% in 2015 to 32.80% in 2016 and 32.57% in 2018. All western locations experienced substantial declines, whereas Batam, Bintan, and Natuna remained relatively stable. Belitung showed an initial decline followed by partial recovery. Reorganization of genera and growth-form composition was also more pronounced in the western region. The western region was generally warmer, more saline, and clearer, whereas the eastern region was cooler, less saline, and more turbid at several locations. Peak temperatures and thermal stress occurred in 2016, although DHW varied among locations and did not fully correspond to absolute temperature gradients. Acropora, particularly branching and tabulate forms, experienced the greatest decline in the western region, whereas Porites and massive growth forms showed greater resistance. Nevertheless, Acropora persisted at several eastern locations, indicating that taxon sensitivity is context dependent. Higher turbidity in the eastern region may have reduced irradiance and moderated photo-thermal stress, although this relationship remains associative. These findings demonstrate that coral community resilience is shaped by interactions among thermal exposure, local environmental regimes, and the biological sensitivity of coral taxa and growth forms. The novelty of this study lies in its west–east geographical comparison, use of permanent transects across disturbance periods, multilevel community analysis, and demonstration of context-dependent vulnerability within the same taxa. The results support spatial vulnerability-based management, protection of highly resistant sites as climate adaptation priorities, and monitoring approaches that incorporate coral cover, taxonomic composition, and functional community traits.