When Paul Kabai was growing up on Saibai he was taught how, when and where to plant food, such as the root vegetable cassava, by his Aunties and Uncles.
"Now it's all gone, the ground is too soft, too salty," he said.
"That knowledge has been passed from our ancestors, from them to us, and then from us to our kids."
Mr Kabai has been giving evidence in the Australian climate case, where he and fellow Torres Strait Islander elder Pabai Pabai are challenging the Australian government's inaction on climate change.
The federal court has been holding on-country hearings on Boigu, Badu and Saibai islands in the Torres Strait.
The people of the Torres Strait fear if sea levels continue to rise, their ancestral homes will become uninhabitable and they will be rendered climate refugees.
"If we leave the island and leave our ancestors behind under water we lose everything, our culture, our identity, our livelihood - it will be all gone," Mr Kabai said.
"If we don't have our ceremonies here on Saibai, if we had to go to mainland, we don't have our culture."
He told the court how his ancestors used constellations to navigate and as a seasonal calendar, which told them when to plant certain vegetables and when to hunt different species.
"It is now all changed because of climate change - these patterns are all mixed up," he said.
"This is meant to be dry season, your Honour, the patterns have all changed."
Uncle Herbet Warusan has lived his entire life on Saibai and has worked as a ranger since 2012.
He is worried changes in the ocean are affecting sea grass meadows, which are vital for dugongs and turtles.
"The sand has changed and the high tides are changing, the meadows are being pulled up around the eastern part - the main habitat for the dugongs, but it's all around the island - the turtles are everywhere," Mr Warusan said.
The hearings will continue on Saibai on Wednesday.
