Batimetri adalah pengukuran dasar laut. Data batimetri yang rinci di perairan dangkal pulau kecil belum memadai sehingga tidak bisa memberikan informasi bagi aktivitas di sekitar perairan dangkal tersebut seperti aktivitas pelayaran oleh kapal-kapal rakyat. Nilai kedalaman dapat ditentukan dengan menggunakan teknologi penginderaan jauh yang menggunakan teknologi akustik dengan sistem propagasi suara. Tujuan penelitian adalah mendapatkan nilai batimetri secara rinci, menampilkan dalam bentuk 3D serta mendapatkan nilai slope dan melihat perbedaan terhadap koreksi pasang surut. Pemetaan batimetri dilakukan di perairan dangkal pulau Tunda, Serang, Banten pada 21 sampai 24 Agustus 2014. Data Akustik dikumpulkan menggunakan GPS map echosounder 585 Singlebeam. Data pasang surut diterapkan untuk koreksi. Data itu pasca diproses menggunakan Surfer software 11, Global Mapper v8 dan ArcGIS 10.1. Berdasarkan penelitian ini, kedalaman maksimal yang didapat adalah 52 m dan bentuk dasar laut yang termasuk landai dengan kondisi tubir yang mengelilingi pulau.

Jenis angur laut Caulerpa sp saat ini menjadi komoditas ekspor sebagai produk makanan, obat-obatan, dan kosmetik. Caulerpa sp memiliki sebaran yang cukup luas terutama pada kawasan beriklim tropis. Jenis Caulerpa sp juga dijumpai hingga perairan Natuna. Kepulauan Natuna merupakan suatu wilayah di utara dari Provinsi Kepulauan Riau dengan potensi lautnya menyimpan sumberdaya yang beragam, termasuk komunitas anggur laut Caulerpa sp. Culerva sp  merupakan salah satu jenis tumbuhan laut yang memiliki nilai nutrien yang baik tertutama untuk kesehatan dan kosmetik, sehingga penelitian terkait dengan sebaran jenis dan komposisinya sebagai upaya awal untuk pengembangan budidaya perlu dilakukan. Penelitian dilaksanakan selama periode bulan Juli-September 2019. Sampling dilakukan pada 8 lokasi yang berbeda mulai dari kawasan Ranai Kota hingga Klarik. Pengambilan data jenis Caulerpa sp mengunakan metode transek garis sepanjang 100 meter kearah laut dengan kuadran ukuran 10 x 10 m, sebanyak 3 kali sampling per stasiun. Hasil penelitian ditemukan 3 spesies dari anggur laut Caulerpa sp yakni C. taxifolia, C. lentilifera, dan C. recemosa. komposisi tertinggi pada jenis C.taxifolia mencapai 53,7%. Hasil penelitian menunjukkan tingkat keanekaragaman yang rendah, keseragaman tergolong tinggi, dan dominansi yang rendah. Hanya ada beberapa stasiun dengan tingkat dominansi yang tinggi yakni stasiun 2 dan stasiun 6 masing-masing di dominasi oleh jenis C. taxifolia dan jenis C. lentilifera.

The increasing use of plastic in various aspects of life impacts the increase in plastic waste in the environment. The plastics are degraded into the smallest fragments to a size of <5 mm called microplastics. Further, microplastics will accumulate in the water, marine biota, and sediment. Sea cucumbers are deposited feeder and found in the seagrass ecosystem. This study aims to examine the abundance of microplastics in sea cucumbers, which are scattered in seagrass ecosystems in the waters of Bintan Island and the surrounding area. The method used is a purposive random sampling in a seagrass ecosystem area of 100 × 20 meters. The sea cucumbers obtained will then be dissected and observed for their microplastic content. The results showed that the sea cucumber found in the seagrass ecosystem on the Bintan island are Holothuria atra, H. scabra, and Sticopus variegatus. The highest density of sea cucumbers was found in Pengujan waters, with a value of 90 ind/ha. The highest microplastic content in sea cucumbers was found in Pengudang water, with a total of 52 ± 7.68 particles/ind. The dominant type of microplastics is fiber, with a total of 84 particles/ind.

Teluk Sebong is one of the areas around Bintan Island, Indonesia, that has potential coral reef resources. Bintan borders directly with neighbouring countries and with a major shipping lane (ALKI I) traversing the Indonesian Archipelago. This makes the coral reef ecosystems in this region particularly vulnerable to disruption from changes in the aquatic environment. There is a need for primary data on the coral reef ecosystem condition as a basis for understanding changes in this ecosystem. One commonly used method is the Coral Reef Health Index (CRHI), which can describe the current status in terms of live coral cover, the level of resilience (potential for recovery) during times of stress, the condition of economically important reef fish biomass, and ecologically related functions. The CRHI can be used in monitoring coral reef status and can provide a basis for the management of coral reef ecosystems. This study examined five sampling sites located in Teluk Sebong, Bintan Island. The in-situ data collection included the condition of coral reefs using the Underwater Photo Transect (UPT) method and reef fish condition using the Underwater Visual Census (UVC) method. The coral data collected were analyzed using the CPCe (Coral Point Calculate with Excel extension) software version 4.0 to determine the percentage benthic cover. The coral reef fish data were analyzed to provide target fish density and biomass values (carnivores and herbivores). The live coral cover in Teluk Sebong ranged from 30.87 - 45.40%. Out of the five research sites, Berakit, Pengudang, and Lagoi Bay had coral cover in the high category while coral cover at Banyan Tree and Rawa Island was in the medium category. Reef fish biomass in Teluk Sebong ranged from 9.26 - 108.07 kg/ha, and at all research sites fish biomass was in a low category. The coral reef ecosystem resilience in Teluk Sebong was high at the Berakit and Banyan tree sites; in contrast, Pengudang, Lagoi Bay, and Rawa Island were in the low resilience category. The coral reef index (CRHI) value was highest in Berakit (CRHI = 6), followed by Banyan Tree (CRHI = 5), Pengudang (CRHI = 4), Lagoi Bay (CRHI = 4), and Rawa Island (CRHI = 2).

Three groups of marine biotas in the coral reef ecosystem were analyzed to determine the overall condition coral reef ecosystem in Natuna Island (coral, reef fish, and megabenthos). Nineteen sampling sites are distributed completely in Natuna Island, including Natuna Besar Island, Tiga Island, and Sedanau Island. The coral reef monitoring refers to the Underwater Photo Transect (UPT), and data processing used the Coral Point Count for excel (CPCe). The reef fish observation using the Underwater Visual Census (UVC) and megabenthos observations using the Benthos Belt Transect (BBT). The percentage of the benthic cover was analyzed for several benthic categories. The analysis for reef fish consisted of diversity and abundance for the three fish groups, including the corallivore, herbivore, and carnivore. The megabenthos community’s analysis consisted of diversity and density from eight groups, including giant clams, lobster, Drupella sp., Linckia laevigata, sea urchin, sea cucumber, trochus, and Acanthaster planci. The Coral Reef Health Index (CRHI) analysis was used to determines the coral reef condition in Natuna. Nine sites were categorized as the fair condition of live coral cover with 26.53–36.87%. The largest composition of coral reef fish groups from herbivorous groups and the highest density megabenthos was sea urchins.

Caulerva racemosa seaweed is a superior commodity with both ecological and socio-economical benefits. It is technologically developed into different products which include antioxidants, antibiotics, medicinal ingredients, cosmetics as well as other organic products and also used conventionally as food ingredients for human’s consumption. Meanwhile, the presence of C. racemosa is observed to decrease as the exploitation rate is one of the factors affecting its stock in the nature. Changes in environmental conditions contribute majorly to its availability in aquatic ecosystems. Furthermore, natural factors in the form of seasonal changes that cause fluctuations in water dynamics are the main focus affecting its lifespan. The results showed that C. racemosa growth parameters, which include percentage cover, productivity, together with morphometrics, failed to be significantly affected by seasonal changes. Meanwhile, the highest percentage cover was found during the northern monsoon, which has an average value of 37.99 ± 7.67 (Average±STDEV), while the lowest was during the eastern monsoons with 28.03 ± 9.09 respectively. The best morphometric size was during the northern monsoon with a tallus dimension of 0.25 with an average of 0.201 ± 0.03 and length of 0.825 ± 0.16, a stolon length of 2.09 with an average of 1.95 ± 0.08, 9 stolon grains with an average of 8 ± 0.2. However, the grain diameter, as well as the biomass, was 0.85 gr and 0.054 gr with an average of 0.825 ± 0.22 gr and the grain biomass was with an average of 0.040 ± 0.01 and 0.041 gr with the best average stolon was 0.031 ± 0.01 g in the western season. The results showed that C. racemosa, which grows up in different seasons, having its highest productivity during the northern season and the lowest one was during the eastern season with an average value of 0.439 ± 0.36 kg/m2 as well as 0.326 ± 0.37 Kg/m2, respectively

This study aims to provide reliable information to mapping the potential of coral reef ecosystems for development of sustainable marine ecotourism in Benan Island and surrounding areas. The mapping was done by considering the carrying capacity of the environment which includes the limits of the island’s ability to receive several tourists with the intensity of optimum use of natural resources. Approach to the assessment of the potential and status of coral reef ecosystems was carried out to evaluate reef fish and benthic conditions using the LIT transect method and presented spatially using ArGis 10.3. The results showed the status of the coral reefs ecosystem in Benan Island waters and the surrounding areas were categorized as moderate conditions with average live coral coverage were 37.76%. The highest live coral cover reached was 55% in Katang Island. The carrying capacity of the utilization of diving tourism in Benan Island was reached 444 people/day, 69 people/day at Selada Island, 66 people/day at Segenting Island, 234 people/day at Sunda Air Island and 76 people/day at Nopong Island. The carrying capacity of small islands was different from one region to another. Hopefully, this will be able to minimize the vulnerability of small islands to ecosystem degradation.

Graphical abstract