请根据文本的主题，从下面给出的单词中找出最合适的5个单词。
Text: "The Great Barrier Reef is the world's largest coral reef system composed of over 2,900 individual reefs and 900 islands stretching for over 2,600 kilometers."
选项：ocean, island, marine life, ecosystem, coral
island, marine life, ecosystem, coral, reef