Yes, It's the Q100 LTD, run by the MTA Bus Co. Here's a link to the MTA's pdf schedule: https://new.mta.info/document/6661

Here's a link to the GTFS schedule:
https://rrgtfsfeeds.s3.amazonaws.com/gtfs_busco.zip

Here's a link to the MTA's Queens Bus Map that shows the Q100 last stop within Rikers Island
https://new.mta.info/map/5371

Here's an OSM link to the way within Rikers with tags: highway:service and bus:yes

https://www.openstreetmap.org/way/185158098

Here's the OSM link to the bridge leading to Rikers
https://www.openstreetmap.org/way/11836206

with tags highway:tertiary, access:no

and no qualifier for public bus access.

Thanks for your quick reply.