CONCENTRATIONS OF HEAVY METALS (Cr, Cuand Zn) IN DIFFERENT SIZE OF BLOOD COCKLE Anadara granosa FROM GEMURUH VILLAGE COASTAL WATER OF KUNDUR ISLAND KARIMUN REGENCY, RIAU ISLANDS PROVINCE - Barus, Agnesia Jaiyani br (Jurnal Online Mahasiswa (JOM) Bidang Perikanan dan Ilmu Kelautan, 2017)