Genomic resources and transcriptomic evidence of thermal stress in the southern saucer scallop (Ylistrum balloti)

Marine heatwaves can lead to mass mortality events, affecting bivalves. The saucer scallop (Ylistrum balloti) is an important commercial species found in Western Australia (WA) and central Queensland. The largest fishery for this species in WA is at Shark Bay, on the central WA coastline. The fishery has been impacted by heatwaves in the recent past and has yet to fully recover. Whether thermal pressures are influencing the fishery's recovery is uncertain, as other factors, including larval advection, could also influence recovery. A functional genomics approach was used to address this uncertainty. Scallops were collected from multiple locations in Shark Bay with different water temperatures and from a small, more southerly fishery adjacent to Perth. A full genome was assembled. The genome contains comparatively few gene copies of heat shock protein 70, an important indicator of thermal stress, particularly from class 12, which has been highly duplicated in other heat tolerant bivalves. Transcriptomic profiles in scallops collected from the different locations were compared, with the greatest differences observed in scallops collected from an area of Shark Bay with the warmest water temperatures. Some transcripts with altered abundance encoded heat shock proteins, proteins involved in macromolecule repair, and those with a primary metabolism role. Although this study is a snapshot of a few individuals at a single time point, it adds to the weight of evidence that extreme heatwave events and climate change impacts the recruitment of this commercially important species.