This dataset provides clam species abundance and size data from intertidal and subtidal mixed sediment habitats in Glacier Bay National Park and Preserve (GBNPP). Data are provided for all observed clams, horse mussels, or urchins 14 mm or larger. Sampling involved excavating 25 cm of substrate from quadrats (approximately 0.25 sq meter) along transects at random and selected sites, 10 quadrats at the 0 Mean Lower Low Water (MLLW) tide level for intertidal sampling and 20 quadrats at approximately 9 m depth for subtidal sampling. Site and taxonomic information are provided. Abundance and size data are provided in two tables with different data configurations: (1) a compact version with data for those species observed (and indicators of completely empty quadrats) and (2) a 'zero-populated' version that includes indicators of abundance (including zeros) for all possible year, site, quadrat, species, and size class combinations.