Model Distribusi Larva dan Konektivitas Habitat Rekrutmen Ikan Kerapu (Famili Serranidae) Berdasarkan Dinamika Oseanografi Kepulauan Misool, Kabupaten Raja Ampat

Abstract

Kepulauan Misool membentang di selatan Kepulauan Raja Ampat dan menempati ruang pada pusat segitiga karang dunia dengan keanekaragaman hayati laut tropis terkaya di dunia. Perairan Raja Ampat memiliki keanekaragaman tinggi disebabkan habitat yang kompleks dan perairan mengalami pencampuran massa air Pasifik Utara dan Selatan. Aspek sirkulasi, topografi kepulauan dan kondisi dasar perairan berterumbu karang menciptakan turbulensi. Kondisi demikian menyebabkan sirkulasi dan karakteristik massa air menjadi kompleks. Aspek biologi sangat penting di lingkungan perairan. Kesatuan proses biologi dan fisika tidak bisa dipisahkan sebagai kesatuan sebab akibat dalam menjamin keberlangsungan sumber daya. Sumber daya ikan kerapu (famili Serranidae) memiliki lima stadia kehidupan yaitu stadia telur, larva, yuwana, dewasa dan stadia tua membentuk siklus kehidupan. Rentang masa pelagis (larva) dan settlement (stadia postflexion atau awal yuwana) merupakan periode yang kritis. Diketahui bahwa dari total telur yang berhasil dibuahi menjadi larva, kurang dari satu persennya menjadi populasi ikan dewasa karena stadia awal hidup ikan rentan terhadap kematian. Ikan kerapu pada saat memijah secara bergerombol (spawning aggregation) akan melepaskan telur dan sperma ke kolom perairan dan pembuahan terjadi di kolom air. Sirkulasi air dan kualitas perairan menjadi fungsi kontrol keberhasilan pembuahan. Larva bersifat pasif dan dikontrol oleh aliran arus. Jika aliran arus membawanya ke daerah lingkungan perairan yang sesuai, maka peluang hidup dan berkembang menjadi dewasa relatif besar. Jika sebaliknya maka peluang kematian massal besar terjadi. Tujuan utama penelitian ini adalah (i) mengkaji pola arus, proses hidrodinamika dan karakteristik massa air di perairan Misool; (ii) mengintegrasikan proses sirkulasi dan biologi dengan memodelkan aliran larva ikan kerapu; (iii) menemukan lintasan penyebaran larva ikan kerapu dalam bentuk konektivitas. Pertukaran larva ikan antara populasi sangat sentral dalam ekologi laut dan menjadi penjamin kestabilan struktur komunitas ikan dan menambah keanekaragaman spesies. Penelitian ini diharapkan sebagai rujukan sistem pengelolaan dan pembaharuan kawasan konservasi Misool. Penentuan kawasan konservasi Misool yang eksisting masih bersifat tradisional yakni sistem Sasi yang mengadopsi perspektif nondinamis dan spesies tunggal. Jaringan konservasi laut selayaknya menggabungkan komponen lingkungan terkait ke dalam algoritma pemilihan lokasi sehingga tujuan konservasi dapat tercapai. dst ...

The Misool Islands stretch south of the Raja Ampat Islands and occupy space at the center of the world's coral triangle, with the richest tropical marine biodiversity in the world. Raja Ampat waters have high diversity due to complex habitats and waters experiencing the mixing of North and South Pacific water masses. Aspects of circulation, the topography of the islands, and the bottom of coral reefs create turbulence. Such conditions cause the circulation and characteristics of the water mass to become complex. Biological aspects are fundamental in the aquatic environment. The unity of biological and physical processes cannot be separated as a cause-and-effect unit in ensuring the sustainability of resources. The early life history of Grouper has five life stages: egg, larva, juvenile, adult, and old. Pelagic (larval) and settlement (postflexion or early juvenile stages) are critical periods. It is known that of the total eggs successfully fertilized into larvae, less than one percent become adult fish populations because the early stages of fish life are vulnerable to death. When spawning, grouper fish will release eggs and sperm into the water column, and fertilization occurs in the water column. Circulation and water quality are the controlling of the success of fertilization. The larvae are passive and controlled by current flow. If the currents bring it to a suitable aquatic environment area, then the chances of it living and developing into an adult are potential. If it is the other way around, there is a big chance of mass death. The main objectives of this research are (i) to examine current patterns, hydrodynamic processes, and characteristics of water masses in Misool; (ii) to integrate circulation and biological processes by modeling grouper larval flow; (iii) to find the distribution trajectory of grouper larvae in the form of connectivity. The exchange of fish larvae between populations is essential to marine ecology, guarantees the stability of fish community structures, and increases species diversity. This research will serve as a reference for managing and renewing the Misool conservation area. Determination of the existing Misool conservation area is still traditional, namely the Sasi system, which adopts a non-dynamic perspective and a single species. Marine conservation networks should incorporate related environmental components into site selection algorithms to achieve conservation goals. The current recording was carried out with Mooring ADCP at coordinates 130°24'9.50"E and 2°3'18.40"S. The recording interval is every 15 minutes and divides the water column into ten layers. Investigation of water characteristics using CTD recording. Hydrodynamic 3D modeling using DHI MIKE3. The power of exchange of larvae of two or more populations is carried out by running the Langevin Lagrangian model. Biological aspects of the simulation use the characteristics of grouper fish larvae from the Serranidae family. A simulation of larvae dispersal was released on 12 grid coordinates of spawning aggregation sites. Geographic distribution is controlled by the pelagic larval duration, hydrodynamics and water topography. Connectivity predicted by larval dispersal model, spatial biogeography. The location group is declared to have a connectivity value if the partial potential connectivity index value is ≥ 0,20. The current circulation of Misool waters is known to be dominated by tidal forces. The amplitudes of the tidal constituents M2, K1, O1 and S2 are strong in the channel system. The maximum current velocity of the M2 component is 67 cm/s, then the K1, O1 and S2 components are 50 cm/s, 28 cm/s, 20 cm/s, respectively. The Misool Seabed has coral reefs triggering mixing. The characteristics of the water mass show similar conditions of salinity, temperature and relatively homogeneous density in strong currents on the northeast and southeast sides. Salinity values range from 33,5 – 34,3 psu, temperature 27,5 – 30,0◦C, and density 24,5 kg/m3. The interaction of the topography of the Misool Islands and the pattern of tidal propagation causes the rectification of tidal currents. Current rectification is seen in the mainland channel system and islands on the east, northeast and southwest. The water column is relatively stable, the surface layer up to 200 m, and the salinity increases with depth reaching 34,3 psu. The characteristics of the water mass in Misool waters do not show similarities with the Pacific water mass but rather with the local water mass in Misool waters. The larval dispersal model obtained the farthest dispersal range of ≥30 km. Recruitment of post larvae is dominant around the Misool islands because the source of larvae is limited by the islands' topography and coral reefs as a barrier. The hydrodynamic characteristics of the dominant tidal currents so that the dominant larvae's distribution directly to the north, south, southwest and southeast follows the flow pattern of the tidal currents. The average larvae retention is 35-45%, and the rest spread and recruit in other habitats but are still in the Misool archipelago. We emphasize the importance of incorporating early life history of species, larval trajectories and recruitment habitats when designing conservation networks. This stage is important for the success of conservation goals, with larvae as the forerunners of adult fish. The conservation network must accommodate 1.5 times the distribution area of fish larvae in all directions so that the stock and survival of the species are guaranteed. Core protection distance must be ≥ 15 km from the source spawning aggregation site. The larval exchange dynamics and population connectivity patterns in Misool waters form at least five main routes of larval exchange. The optimal conservation network for each varied route is a minimum protection distance of 10 km in all directions from the spawning source and the farthest 30 km. Based on the biogeography of larval dispersal from spawning sources, the conservation network design in the Misool Islands was carried out partially, covering five main routes of habitat connectivity in all directions for the designated locations.