Funghi in my bathroom

Having moved the shampoo bottle in the shower – i noticed something plasticky and rubbery lurking behind it! I had to double take as I had absolutely no idea what it was. I initially thought it was a slug – but how on earth did it get there? So to describe what it was actually like – I’d say it was like a mini seaweed thing mixed with some funghi. It almost looks like some piece of fake set from Lost In Space or Doctor Who from the 1970’s. I then checked the other corner of the shower and there was another one. Looking at the overall state of the shower I couldnt believe how minging it was with mold also apparent on one of the walls too. I can’t believe i’ve let it get into this state without taking any action!

This bit of mold has always been there in some fashion – i can wash it, remove it, repaint it but within weeks it always returns! Does anyone know how to totally eradicate this mold from ever returning?
Outside the shower was an even bigger ‘growth’ which makes me think there is some other underlying issue here.
For the last few weeks whenever taking a shower a small amount of water has leaked from under the shower base but I’ve always mopped it up and forgot about it!.
I wonder whether small pools of water and moisture under the shower base have spurned some bacteria resulting in this mold and growths?

Can anyone suggest some sort of treatment or cleaning – or is it going to be a plumber job and let them treat it all and also repair the small leak?