Variations of Gene Expression in the Formation of Macroalgal Blooms in Ulva rigida and Ulva compressa in Narraganset Bay, RI

Two species of the macroalgal genus Ulva, Ulva compressa and Ulva rigida, are the most abundant species in harmful macroalgal blooms in Narragansett Bay, RI.  These dense aggregations of algal biomass can have significant ecological and economic impact on coastal communities and have increased in both size and duration over the past several decades. This study seeks to identify a link between temporal changes and gene expression potentially causing bloom behavior. This was carried out by sampling U. compressa and U. rigida in subtidal and intertidal regions at three sites in the Narragansett Bay, RI at relevant seasonal stages of the bloom cycle.  After collection, samples were identified and RNA was extracted and sequenced using HiSeq 2000 NGS technology.  The resulting sequence was assembled using the Geneious software, and was annotated using Blast2Go. Gene candidates were identified through computational screens that showed differential gene expression in samples obtained at different time points and locations. To validate these findings, gene candidates were tested using qPCR with the collection sample cDNA. One such candidate is the lhcSR gene, which is a stress-related light harvesting complex specific to algae, plays an important role in non-photochemical quenching, a key regulatory function for photosynthetic species. Through qPCR experiments, lhcSR was shown to have differential expression correlated with seasonal changes. These data combined indicated large gene expression changes through the year that are indicative of the formation of harmful macroalgal blooms.