Complex sentence: It was claimed in 1998 that caulerpa had grown to cover 7400 acres (Bright 1998) and was believed to be preventing other plants from growing, leading to the nickname "Killer Algae".
Split into simpler sentences: It was claimed that caulerpa had grown to cover 7400 acres (Bright 1998). A belief arose that it was preventing other plants from growing, leading to the nickname "Killer Algae".