They can be kilometers long, they can be meters deep, and arguably, they're the most dominant influence on how healthy any coastal marine ecosystem is going to be, because what they do is they're filtering the water constantly, they're holding sand and dirt in place.
de quilômetros de comprimento e metros de profundidade; possivelmente são a maior influência sobre a saúde de um ecossistema  marinho costeiro, porque elas filtram a água constantemente, e mantêm areia e sujeira num lugar só.