Telah dilakukan penelitian ekologi Pinna muricata yang mencakup kepadatan, morfometri cangkang, sudut posisi kedudukannya lerhadap garis pantai, serta hubungannya dengan kepadalan dan biomassa lamun Cymodocea rotundata di Pulau Semak Daun, Kepulauan Seribu, Teluk Jakarta. Hasil penelitian menunjukkan Pinna muricata hanya ditemukan di antara lamun Cymodocea rotundata di 6 transek dari 16 transek yang digunakan, 4 transek (transek 7- 10) di bagian Selatan dan 2 transek (transek 12 dan lj) di bagian Utara. Kepadatan terbanyak terdapat di bagian Selatan pulau (0,6 individu per m3}, sedangkan di bagian Utara puiau kepadalannya hanya mencapai 0,03 individu per m2. Pinna muricata mempunyai panjang cangkang yang berkisar antara 12,5 - 17 cm dengan rata-rata 14,25 cm, sedangkan lebar cangkang berkisar antara 7 - 11,4 cm dengan rata-rata 8,43 cm. Sudut kedudukan Pinna muricata terbanyak (17%) antara 130" - 139° terhadap garis pantai. Kepadalan dan biomassa akar lamun Cymodocea roiundata tidak berkorelasi atau tidak ada hubungannya dengan jumlah Pinna muricata, sedangkan bkimassa daun menunjukkan korelasi negative (R= -0,36).

---

We examined fan mussel Pinna muricata (Mollusca, Bivalvia) such as the density, shell morphomeiry, angel of shell position against the shoreline, as well as his correlations with the density and the biomass of seagrass Cymodocea rotundata in the Semak Daun Island, Jakarta Bay. Results of Ihe research pointed out Pinna muricata were found only in seagrass meadows Cymodocea rotundata in 6 transects from 16 transects lhat was used, 4 transects (transect 7 - 10) on the South and 2 transects (transect 12 and 13) at the North of Island. The Pinna density was recorded 0.6 individuals per m2 at the southern of the island, whereas at the northern of the island only reached 0.03 individuals per m2. The length and wide of shells were measured between 12,5 - 17 cm (average 14,25 cm) and between 7 ? 11,4 cm (average 8,43 cm) respectively. The most angle of shell positions were measured between 120° - 139" against the shoreline. The density and the leave biomass seagrass Cymodocea rotundata did not correlate with the density of Pinna, whereas the root biomass have negative correlation (R= - 0,36).