主语和be动词是省略了吗

Now known as "New York's shared space for art and play," the island, which lies between Manhattan and Brooklyn in Upper New York Bay, is closed to cars but open to summer tourists who flock for festivals, picnics, adventures, as well as these "legal graffiti" sessions.

后面理解，主要就是第一个逗号之前这部分

1.我想这应该是从句吧，但是是什么从句呢？

2.还有主语和be动词是省略了吗？为什么可以省略呢？

求问各位老师！