Unfortunately the capsules of the freely fruiting species shown below had all disintegrated, leaving just patches of very long, thin setae. The habitat it was growing in was the steeply cut edges of the scraped slack in the north of the reserve with the rather unwieldy name 'Slack south of Jeff's Mistake Slack', which in the photograph is the sharp transition between the green dry-dune vegetation in the foreground and the yellowy flooded slack vegetation (SS78438286). My first thought when I saw it, was that it looked a bit like Pohlia melanodon, but the setae were far too long. Closer inspection at home made me think that in might in fact be Amblyodon. Direct associates included Pellia endiviifola, Didymodon tophaceus, Bryum pseudotriquetrum, Calliergonella cuspidata, Aneura pinguis and Riccardia chamedryfolia. I've packaged my specimen, but any comments based on the images would be welcome. Hopefully in time I'll find some plants with intact capsules to make a more confident id.
A couple more reference images below that show the extremely broad-based costa and lax cell structure.