Seabird-Derived Nutrients Supply Modulates the Trophic Strategies of Mixotrophic Corals

The ability of corals to modulate their nutrition strategy in response to variable nutrient supply remains poorly understood, limiting our understanding of energy flow in coral reef ecosystems and thus our comprehension of their resilience to global changes. We used a naturally occurring nutrient gradient along the reef flat of two seabird-inhabited islets in the SW Pacific to characterize spatiotemporal fluctuations in coastal nutrient availability, and how it modulates the trophic response of the mixotrophic coral Pocillopora damicornis. The clear gradients in dissolved [NOx] and δ15N values of macroalgae and both P. damicornis tissues and symbionts observed along the reef flat during the dry and the rainy season revealed that seabird-derived-N is supplied year-round to the reef flat. Yet, nitrogen isotope values of macroalgae show that the seabirds’ effect on coral reefs varies with sites and seasons. Metrics derived from the SIBER framework revealed that coral nutrition seasonally favored autotrophy when exposed to higher seabird guano concentrations and at inshore stations, while heterotrophy dominated in corals less exposed to seabird-derived nutrient supply. P. Damicornis is therefore able to cope with large changes in nitrogen supply induced by seabird island communities by switching between autotrophy and heterotrophy. These results shed light on the flexibility of resource sharing within the coral-algae symbiosis and highlight the importance of seabird populations to the functioning of coral reef ecosystems.

IDENTIFIKASI SPONS BERDASARKAN TUTUPAN KARANG DI PERAIRAN SOMBU TAMAN NASIONAL WAKATOBI

Spons merupakan hewan multiseluler paling primitif yang hidup diberbagai tipe perairan mulai dari tawar, payau, dan laut. Biota ini hidup di dasar perairan dan biasanya menempel pada substrat keras seperti batu atau karang dan berkompetisi dengan organisme penempel lainnya untuk memperoleh ruang dan makanan. Penelitian ini bertujuan untuk mengetahui keanekaragaman dan kepadatan spons berdasarkan tutupan karang. Penelitian ini dilaksanakan pada bulan Desember 2020 – Juli 2021, di Perairan Sombu Taman Nasional Wakatobi. Pengambilan data spons dilakukan dengan menggunakan metode belt transect dengan panjang line transect 50 m dengan lebar 4 m pada kedalaman 3 m (reef flat) dan 7 m (reef slope) pada masing-masing stasiun. Data diambil bersama dengan tutupan karang menggunakan metode line intercept transect (LIT) dengan panjang line transect 50 m pada kedalaman yang sama dengan data spons. Hasil penelitian didapatkan bahwa keanekagaraman hayati spons yang ditemukan dilokasi penelitian yaitu sebanyak 2 kelas, 19 famili dan 23 genus. Yakni keanekaragaman jenis spons tertinggi yaitu pada stasiun I sebesar 20 genus, serta kepadatan spons tertinggi sebesar 0,18 individu/m2 terdapat pada genus Spheciospongia sp., kepadatan spons tertinggi berdasarkan stasiun terdapat pada stasiun I zona reef slope yaitu dengan nilai 0,32 individu/m². Persentase tutupan karang pada stasiun I dan II masuk dalam kondisi baik, sedangkan pada stasiun III masuk dalam kondisi sedang. Keanekaragaman dan kepadatan spons dipengaruhi adanya keberadaan terumbu karang, sehingga keberadaan tutupan karang yang tinggi menyebabkan melimpahnya pertumbuhan spons.Kata Kunci : Keanekaragaman, Kepadatan, Spons, Terumbu Karang

DOMINASI GENERA KARANG KERAS (HARD CORAL) DI PERAIRAN DESA TANJUNG TIRAM, KAB. KONAWE SELATAN

Ekosistem terumbu karang di Desa Tanjung Tiram memiliki sumberdaya yang beranekaragam dan berlimpah. Namun dalam beberapa dekade terakhir, keberadaannya terancam oleh kegiatan penangkapan ikan yang tidak ramah lingkungan. Penelitian ini bertujuan untuk mengetahui dominasi genera karang keras dan persentase tutupan karang hidup serta hubungan faktor lingkungan dengan sebaran kondisi terumbu karang di perairan Desa Tanjung Tiram. Penelitian ini dilaksanakan pada bulan September 2020. Hasil penelitian ini ditemukan 3 genera dominasi yaitu Porites, Fungia dan Favites dimana Porites merupakan genus karang yang paling dominan ditemukan di area reef slope dan reef flat. Secara keseluruhan persentase tutupan karang hidup Perairan Tanjung Tiram berada di bawah 60%. Semakin dalam perairan presentase tutupan karang hidup makin rendah dan patahan mendominasi.Kata kunci: Dominasi, Karang Keras, Tanjung Tiram.

Seagrass Condition at Some Small Islands in The Taka Bonerate National Marine Park, South Sulawesi Indonesia

The assessment of seagrass bed condition in Indonesia still refers to the Decree of the State Minister for the Environment (KMNLH) no. 200 of 2004, which considers only one variable, namely the percentage of seagrass cover. To assess the seagrass beds condition to be more in-depth and meaningful, it is necessary to consider the addition of several variables, such as the biotic variables (seagrass species diversity including macroalgae and macro-benthos components) as well as the abiotic variables (reef flat areas and the substrate components). The purpose of this study is to determine the seagrass beds condition in several small islands in the Taka Bonerate National Marine Park by considering the additional analysis using both biotic and abiotic variables as mentioned above. The methodology used in this study is a combination of the use of the standard seagrass transect method, interpretation of satellite imagery related to the seagrass bottom habitat area, and its components on the reef flat of a particular island, as well as weighting and scoring based on those considered additional variables. By applying the criteria in the method, the seagrass bed conditions were then classified into three categories, namely seagrass in good, moderate, and unfavorable conditions, respectively. The results of the total score assessment on several small islands in Taka Bonerate Islands show that the seagrass bed in Latondu Besar Island is in good conditions with the highest score of (316) compared to Tarupa Besar, Jinato, Rajuni Kecil, and Tinabo Besar Islands with an average score of (173). The results of this study indicate that the assessment of seagrass conditions is more meaningful in terms of seagrass ecology than based on seagrass cover alone. However, this study requires a lot of validation for its application in assessing the condition of seagrass beds in other islands in Indonesia.

Signatures of Adaptation and Acclimatization to Reef Flat and Slope Habitats in the Coral Pocillopora damicornis

Strong population-by-habitat interactions across environmental gradients arise from genetic adaptation or acclimatization and represents phenotypic variation required for populations to respond to changing environmental conditions. As such, patterns of adaptation and acclimatization of reef-building corals are integral to predictions of the future of coral reefs under climate warming. The common brooding coral, Pocillopora damicornis, exhibits extensive differences in host genetic and microbial symbiont community composition between depth habitats at Heron Island in the southern Great Barrier Reef, Australia. An 18-month reciprocal field transplant experiment was undertaken to examine the environmental and genetic drivers behind variation in survival, weight gain, heat tolerance and algal symbiont community between the reef flat and slope habitats. We observed population-by-habitat interactions for in situ partial mortality and weight gain, where trait-related fitness of natives was greater than transplants in most cases, consistent with local adaptation. On average, flat colonies transplanted to the slope had a relatively low partial mortality but minimal weight gain, whereas slope colonies transplanted to the flat had relatively high partial mortality and average weight gain. Experimental heat tolerance was always higher in colonies sourced from the flat, but increased when slope colonies were transplanted to the flat, providing evidence of acclimatization in these colonies. The performance of certain slope to flat transplants may have been driven by each colony’s algal symbiont (Symbiodiniaceae) community, and flat variants were observed in a small number of slope colonies that either had a fixed flat composition before transplantation or shuffled after transplantation. Host genotypes of previously identified genetic outlier loci could not predict survival following transplantation, possibly because of low sample size and/or polygenic basis to the traits examined. Local environmental conditions and Symbiodiniaceae composition may provide insight into the adaptive potential to changing environmental conditions.

HARD CORAL (SCLERACTINIA) RECRUITMENT BASED ON THE GEOMORPHOLOGY ZONE IN BINTAN ISLAND WATERS, RIAU ISLANDS

The health of coral reef ecosystems can be seen through the emergence of coral recruitment. Aim of this research was to compared the scleractinia coral recruitment list based on genus, life form, and variations in size of the scleractinia coral recuit in the waters of Kampung Baru Lagoi and Teluk Bakau Village, Bintan Regency by geomorfology zone. The research was conducted using a Purposive sampling method in consideration of the presence of scleractinia coral in reef flat and reef slope areas using a 1x1 m square frame mounted along a 70 m transverse line parallel to the shoreline. Research has found 164 colonies of 24 genus dominated by Favia and Favites. Based on the most extensive life form of Coral encrusting and Coral massive variations in size 4.5-6 cm or medium category. The results of t test showed that the geomorphological differences in the research locations did not have a significant impact on the abundance of corals recruitment

Three-Dimensional Seismic Response Analysis of Zhubi Reef in the South China Sea

Reef islands are valuable terrestrial resources for ocean exploitation and utilization but face the serious threat of earthquake disasters. This study takes Zhubi Reef in the South China Sea as the research object and establishes a three-dimensional (3D) reef-seawater model to investigate the seismic response of Zhubi Reef. The 3D local topography and the effect of fluid-solid interaction are comprehensively considered. The artificial boundaries of fluid and solid domains are adopted to simulate the wave radiation and absorption of the semi-infinite seabed and the infinite seawater layer. The boundary substructure method is used to input the seismic waves into the numerical reef models. The results indicate that the seismic responses, including the peak values of the ground motions and the acceleration response spectra, are significantly amplified over Zhubi Reef. The acceleration response spectra on the reef flat shift closer towards the low-period direction compared with those of the seismic waves input from the subsea bedrock. In addition, the 3D topographic effect on the seismic response of Zhubi Reef is studied through a comparative analysis between two-dimensional (2D) and 3D reef models. The distribution laws of the peak response in the middle region of the reef flat calculated by the 2D and 3D models agree well with each other, and the differences are obvious in the edge areas where the local 3D topographies change drastically.

IDENTIFIKASI ANEMON DI DAERAH TERUMBU KARANG PERAIRAN KASWARI, TAMAN NASIONAL WAKATOBI

Anemon merupakan salah satu hewan laut dari filum Cnidaria atau Coelenterata yang sering dimanfaatkan sebagai penghias akuarium dan sumber makanan bagi masyarakat pesisir Wakatobi. Berdasarkan literature, anemon telah berhasil di identifikasi sebanyak 12 jenis tersebar di seluruh dunia, 10 jenis diantaranya terdapat di Indonesia. Penelitian ini bertujuan mengetahui keanekaragaman dan kelimpahan anemon pada daerah terumbu karang di perairan Desa Kasuari, Wakatobi. Pengumpulan data dilaksanakan selama 2 bulan yaitu Februari – Maret 2020. Metode pengumpulan data menggunakan metode belt transect yaitu dengan luas 200m² dengan 3 kali ulangan untuk mewakili area reef flat dan reef slope. Jenis anemon yang ditemukan di perairan Desa Kaswari yaitu Heteractis crispa dan Heteractis malu. Kelimpahan anemon di perairan Desa Kaswari pada stasiun Reef Flat adalah 0,045 individu/m² sedangkan pada stasiun Reef Slope adalah 0,065 individu/m². Hasil Uji-T diperoleh nilai t-hitung (-2.000) ≤ t-tabel (2.776). Artinya bahwa tidak terdapat perbedaan yang nyata antara nilai rata-rata individu anemon pada daerah reef flat dan reef slope meskipun berada pada zona terumbu karang yang berbeda.Kata Kunci: Kelimpahan anemon, Terumbu karang, Kaswari.