From the high tide mark upward for about 0.5 m is the barnacle belt. The barnacles are so successful in the competition for space that only their shells are available as a substrate for lichens. The lichen Arthopyrenia halodytes is found here in pits dissolved into the barnacle shells.
Arthopyrenia halodytes (Nyl.) Arn. Ber. Bayer. Bot. Ges. 1:122. 1891. Verrucaria halodytes Nyl. Mem. Soc. Sci. Nat. Cherbourg 5:212. 1857.
DESCRIPTION: Thallus epilithic (siliceous rock), endolithic (calcareous rock and shells), yellowish if epilithic, greyish or blackish-brown if endolithic. Perithecium almost wholly immersed in substrate or sessile with black hemispherical to broadly conical involucrellum, 0.15 to 0.5 mm diameter, excipulum colorless to pale brown. Spores eight per ascus, ovoid, two-celled, one cell usu- ally broader than the other, 9-20 x 4-7.5µm.
Swinscow (1965) considered this to be the only littoral species of the genus and treated A. sublitoralis (Leight.) Arn. , A. foveolata A. L. Sm. and A. gyalectoidea Knowles as synonyms and reported a range of 10-20 x 5-10µm in spore size. Richard C. Harris (1975) treats this species as co.,a Pyrenocollema.
Arthopyrenia halodytes is often associated with shells or calcareous rocks but may also be found on siliceous rock.
Pyrenocollema halodytes occurs on limestone rocks as well as on barnacles (both rich in calcium carbonate).
