Several hundred toheroa on Orepuki beach were lost in a mass die-back, the first of its type since the early 1990s.
"In scientific terms, we call this an ecological catastrophe - a short, sharp event that comes out of the blue," Associate Prof Henrik Moller, of the Centre for the Study of Agriculture, Food and the Environment, said.
Prof Moller, who is studying traditional Maori wildfoods with the support of the Ministry of Fisheries, said it was too early to know what killed the toheroa.
Starvation, a biotoxin or an algal bloom were all possible causes.
An estimated 58,000 toheroa lived on the beach and it was a concern some of the mature shellfish, which can live up to 20 years, appeared to have died.
Toheroa were located at Oreti, Orepuki and Bluecliffs in Southland.
Kapiti and Northland were other strongholds of the shellfish.
Staff from the university, Environment Southland and the iwi resource management agency Te Ao Marama Inc spent Saturday collecting samples, which had been sent for analysis to the Cawthron Institute in Nelson.
"The birds beat us to most of the samples," he said.
Environment Southland would continue to monitor the beach this week.
