ABSTRACT: The variability of the marine intertidal environment poses unique challenges for sessile species. Diurnal, tidal, and seasonal cycles introduce drastic variations in temperature, salinity, availability of nutrients and water. The California ribbed mussel Mytilus californianus is a filter feeder that dominates a middle range of the intertidal of many wave-swept rocky shores. The bivalve attaches to the substrate by several byssal threads. This sessile lifestyle allows us to accurately document the thermal history of an individual. We have profiled gene expression in M. californianus during a natural tidal cycle using a cDNA microarray composed of genes from mussels exposed to various stressors. Over three days, mussels were sampled from two sites differing in emersion exposure and average temperature. At each time point, three mussels were cut open in the field and frozen immediately on dry ice and stored at -80 degrees C until the gill, hepatopancreas, and adductor muscle were excised and processed for RNA extraction, reverse transcription, and hybridization to our microarrays. The resulting expression profile showed that genes involved in the cell cycle were diurnally regulated, heat shock proteins increased with temperature, and expression of several hundred other genes varied across the tidal cycle. Tide series (times and tide height): 26th July, low tide 0052, 0.8 ft; high tide 0705, 3.1 ft; low tide 1113, 2.4 ft; high tide 1810, 5.9ft. 27th July, low tide 0154, 0.1 ft; high tide 0837, 3.3 ft; low tide 1216, 2.7ft; high tide 1903, 6.2 ft. 28th July, low tide 0249, -0.6ft; high tide 0943, 3.5 ft; low tide 1323, 2.8ft; high tide 1903, 6.2ft. 15th Aug, low tide 0530, 0.26 ft; high tide 1200, 4.08 ft, low tide 0432, 2.65 ft; high tide 1036, 5.84 ft.
