A ceasg is a mermaid in Scottish mythology, a supernatural half-woman and half-grilse (salmon). It is also known in Scottish Gaelic as maighdean na tuinne ("maid of the wave") or maighdean mhara ("maid of the sea"). The ceasg is said to be able to grant three wishes to anyone that captures her.Now mhara means sea, and I'm guessing is the equivalent mer and also Mary. Now if you switch maighdean mhara (maid of the sea) round you get mhara maighdean (sea maid), which looks, or rather sounds, like Mary Magdalene. Tenuous I know, but still worthy of mention I think. So does Mary Magdalene mean sea-maid/mermaid?
Something else which springs to mind is the fact that in Tudor times mermaid was used as a euphemism for prostitute. In fact Mary Queen of Scots (another Mary) was branded with the slur. And Mary Magdalene was of course portrayed as a prostitute.
Another tenuous link I came across was with Madeleine cakes - cakes cooked in the shape of a shell. Shells, particularly cockle shells, are associated with female sexuality. They're likewise associated with the goddess Venus and various other watery, womany, fertility-type goddess figures. The name Madeleine is a variant of the name Magdalene. Magdalena sponge cakes also come to mind.
Also the name Mädelein in German means "little girl" - similar to the term maid or maiden. Again going back to maighdean mhara - maid of the sea.
Actually, come to think of it, Maid Marian might also be some kind of variant or relation. And in French legends Mary Magdalene often arrives in France from across the sea. Mary Maiden. Sea Maid.