Catalyzes the addition of sialic acid in alpha 2,8-linkage to the sialic acid moiety of the ganglioside GM3 to form ganglioside GD3; gangliosides are a subfamily of complex glycosphingolipds that contain one or more residues of sialic acid (PubMed:18348864, PubMed:22885356, PubMed:7937974, PubMed:8058740, PubMed:8195250, PubMed:8631981, PubMed:8706663). Can catalyze the addition of a second alpha-2,8-sialic acid to GD3 to form GT3 (PubMed:8631981). Can use GM1b, GD1a and GT1b as acceptor substrates to synthesize GD1c, GT1a and GQ1b respectively (PubMed:8706663). Can synthesize unusual tetra- and pentasialylated lactosylceramide derivatives identified as GQ3 (II3Neu5Ac4-Gg2Cer) and GP3 (II3Neu5Ac5-Gg2Cer) in breast cancer cells (PubMed:22885356). {ECO:0000269|PubMed:18348864, ECO:0000269|PubMed:22885356, ECO:0000269|PubMed:7937974, ECO:0000269|PubMed:8058740, ECO:0000269|PubMed:8195250, ECO:0000269|PubMed:8631981, ECO:0000269|PubMed:8706663}. This is the function of ST8SIA1 (ST8 alpha-N-acetyl-neuraminide alpha-2,8-sialyltransferase 1, Ensembl gene identifier ENSG00000111728).