UP to 300 people turned up at Exploris yesterday to show their solidarity with the under-threat facility.
Ards Borough Council will vote tonight on whether Northern Ireland's only aquarium will be closed or kept open.
SDLP councillor Joe Boyle claimed that closing it will rip the heart out of Portaferry and endanger businesses who rely on passing trade from the 100,000 annual visitors.
More than 2,500 people had signed an online petition urging the council to keep the aquarium open.
Chairman of Portaferry Regeneration and Friends of Exploris spokesperson, Doug Edmondson, said local people are "extremely disappointed".
"We accept that this is a national asset and therefore we have a measure of sympathy for the predicament that Ards Council finds itself in, nonetheless, that is not a reason to close it," he said. "What has come as a great big nasty surprise is that we are 36 hours from closure."
Renowned businessman Bill Wolsey has also appealed to councillors to keep Exploris open.
"I think it's a shame to close it, as they were close to getting another operator in who could have reinvigorated the whole project," he said. Meanwhile, in response to a call by Alliance MLA Kieran McCarthy to intervene, Environment Minister Mark H Durkan admitted that he is concerned for jobs.
Mr Durkan revealed he has written to the council asking for an urgent report on the procedures undertaken.
Exploris supporters are planning a protest outside Ards Borough Council this evening.