But he said the university had had shown courage by changing its protocols, which had put the safety of its people ahead of research tradition.
Ms Gui was within weeks of finishing her thesis on aquaculture when she went missing at Goat Island Marine Reserve on June 5, 2011.
She was awarded her doctorate posthumously.
Coroner Shortland found she most likely drowned after being washed off the rock platform where water samples were gathered.
The university had clear protocols in place to prevent such accidents, including abandoning sample collection in bad weather, but Ms Gui had not followed those protocols.
"In my view Alice's decision to collect samples that day was clearly an error of judgment on her part. She didn't observe the protocol.
"The sea conditions were such that it would have been totally unsafe for her to be in that vicinity during those particular conditions.''
Coroner Shortland said the tragedy had had an impact among Ms Gui's friends and colleagues within the close-knit community of the Leigh Marine Laboratory
He said he was satisfied with the steps the university had taken, and made no recommendations.