Interesting topic, these sea caves. Most are not karstic and of little interest, except Fingals, for inspiration !
In warm interglacial periods, sea levels rose by as much as 100 metres, so some limestones were invaded by a brackish water-table. In Plymouth, the reef limestones are up to 800 feet deep, and work is being done via boreholes to establish the extent and nature of the halocline. There is evidence of some Devon caves having been formed along haloclines.
Linking cave's hydraulic profiles to haloclines is a growing field of research. Just think of the Chunnel construction !