Having the experience of owning and running a coral reef aquarium (and frequenting this particular shop about once a week) - I was sad to hear it closed it's doors. Their reef display tank was always amazing. These pictures were taken from PetCo at Union Square (I also used to go there for my saltwater needs).
Beach approachable by public transportation and can be connected with a visit of MOMA PS1 Art Installation (Katharina Grosse House) Also less crowed than other beaches in NYC.