A zoo will not reopen when lockdown measures ease because the trust that owns it has had to "make efficiencies" during the Covid-19 pandemic.
Living Coasts in Torquay, Devon, has been owned and run by Wild Planet Trust since 2003.
The owner said closing other zoos in the same network for lockdown meant they cannot afford to keep Living Coasts open.
Living Coasts employs 44 people, who are now "at risk of redundancy".
"This will be considered within the context of the wider restructuring of the trust's zoos, and potential redundancies at their other sites", added Wild Planet Trust, which also owns Paignton and Newquay Zoo.
Living Coasts said it has hosted 6,500 school visitors a year since opening and has focused on the conservation and protection of many of the marine species it looks after, including penguins, otters and seals.
"The next stage is to find homes for the animals," it added.
The owners are confident that "good new homes" for the animals will be found, although the "difficult decision to euthanise" has not been ruled out.
"As things stand, we do not anticipate that this is a likely scenario," it added.