French oyster aquaculturist Jean-Christophe Cabrol swims in a shellfish farm in the pond of Thau near Marseille. /VCG Photo

He examines the oysters for growth and checks if tunicates, commonly known as sea quirts, covering the molluscs, are causing any harm. /VCG Photo

These invertebrate marine animals grow on oysters, scallops and mussels and can at times smother them. /VCG Photo

Scientists are concerned that the rise of water temperature will cause the species to reproduce faster, spelling danger for shellfish farming. /VCG Photo