Around 300 people signed a petition on Saturday calling on the Welsh Government to protect Cardigan Bay from scallop dredging.
Aberystwyth University Nature Society hosted a Save Our Sea event at Aberystwyth bandstand.
The Welsh Government approved plans to reopen areas of Cardigan Bay to scallop dredging in October.
But opponents argue it is a "highly destructive fishing method".
The Welsh government said a two-year study found limited fishing was possible in specific areas.
Revised legislation was introduced in 2010 which imposed restrictions on scallop dredging in Cardigan Bay.
Naomi Davis from the university's Nature Society said there was a great turn out at Saturday's event which included Aberystwyth Sustainability Society.
"I spoke to a lot of people and the general feeling seemed to be that few people in Ceredigion actually want this to go ahead."
She said Cardigan Bay was vital in supporting the UK's largest breeding population of bottlenose dolphins, the Atlantic seal, as well as a large variety of fish, molluscs and crustaceans.
Ms Davis added the Welsh Government had a "responsibility to protect all conservation areas from dangerous commercial practices" and to listen to local people.