Stigmidium marinum as lichen not LF?

Just recently holidaying in Morar, Scotland, where I believe I observed Stigmidium marinum on Wahlenbergiella (Verrucaria) mucosa. But it’s not a taxon with which I’m at all familiar, so I’d appreciate confirmation if possible.

Sadly, I didn’t realise what I might have been looking at, so I didn’t attempt to take a sample. My intention was just to photograph W. mucosa underwater to show the change in appearance. But later examination, and comparison with photos on the AFL and Lichens Marins websites, put me in mind of S. marinum.

Underwater photos below — with apologies that, as the tide was coming in, the water was a bit turbid and some sand was stirred up. So the photos aren’t as sharp and clear as they might otherwise have been in calmer conditions.

The other question I have is much more speculative — though I think Alain Gerault has views on it, and if so I’d be keen to hear them. Andre Aptroot has suggested for some time that S. marinum is a lichen in its own right, and not (or perhaps not only) an LF parasitising W. mucosa. He describes the S. marinum thallus as thin and filmy, and occuring directly on rock substrate.

For his part, Alain suggests on his website that S. marinum causes a ‘colour change’ in the W. mucosa thallus, but no further description is given there.

So I wonder — are the greyer patches on the close-up photo perhaps the thin and filmy thallus of S. marinum overlaying the greener thallus of (hydrated) W mucosa? They seem to correspond to the potential perithecia of S. marinum, though that’s a first impression. If so, could this mean that S. marinum is growing epiphytically on (or at least not merely parasitising) W. mucosa?

And even more speculative still — if the above is plausible, could the black dots on the nearby orange encrusting sponge (possibly Hymeniacidon perlevis) potentially be S. marium perithecia, produced from a marginally visible (if I’m not imagining it) thin, filmy and epiphytic thallus? I know nothing of encrusting sponges, but perhaps Alain who understands rocky coasts very well might have seen something similar before.

(Again, I was after a photo of the sponge, and didn’t realise what I might have been looking at.)

I certainly understand if there may be nothing further to be said here in the absence of samples to analyse — but I thought it intriguing enough to share even if just for interest. Many thanks in advance for any views!

Best regards,

Anthony

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