Research on the effect of nitrate and phosphate concentration on the abundance of chlorophyll-a at Gapang beach, Sabang, Aceh Province was conducted in March 2017. This study aims to determine the effect of nitrate and phosphate concentration and its association with the abundance of chlorophyll-a in coastal waters of Gapang, Sabang, Aceh Province. Determination of 4 location based on purposive sampling method and analysis of chlorophyll-a concentration and nitrate and phosphate nutrients using UV-Vis spectroscopy. The results of the study at 4 location showed that the content of chlorophyll-a at Gapang beach ranged from 25 to 16 mg/L while the concentration of nitrate and phosphate at Gapang beach ranged from 840 to 630 mg/L and 64 to 51 mg/L. The abundance of chlorophyll-a is closely related to the availability of nitrate and phosphate elements so as to know the trophic status of the coastal of Gapang waters. Based on the relationship between chlorophyll-a abundance, nitrate and phosphate concentration indicates that the coastal waters of Gapang, Sabang are included in the category of eutrophic waters. Penelitian tentang pengaruh konsentrasi nitrat dan fosfat terhadap kelimpahan klorofil-a di pantai Gapang, Sabang, Provinsi Aceh telah dilakukan pada bulan Maret 2017. Kajian ini bertujuan untuk mengetahui pengaruh konsentrasi nitrat dan fosfat serta keterkaitannya dengan kelimpahan klorofil-a di perairan pantai Gapang, Sabang, Provinsi Aceh. Penentuan 4 lokasi penelitian berdasarkan metode purposive sampling dan analisis Kelimpahan klorofil-a serta unsur hara nitrat dan fosfat menggunaakan spektroskopi UV-Vis. Hasil penelitian pada 4 lokasi menunjukkan bahwa kandungan klorofil-a di pantai Gapang berkisar antara 25 – 16 mg/L sedangkan konsentrasi nitrat dan fosfat di pantai Gapang berkisar 840 - 630 mg/L dan 64 - 51 mg/L. Kelimpahan klorofil-a erat kaitannya dengan ketersediaan unsur nitrat dan fosfat sehingga dapat mengetahui status trofik perairan pantai Gapang. Berdasarkan hubungan antara kelimpahan ...