The Ecology of Saltmarsh Acarina

Abstract

Llanrhidian saltmarsh is situated on the north coast of the Gower Peninsula in South Wales at the southern edge of the Burry River estuary. It is an ancient marsh composed of post-glacial alluvial deposits with boulder clay. The hills behind are composed of red sandstone conglomerate, carboniferous limestone and millstone grit. Very little reclamation has taken place since 1750 (Plummer 1960), although the marsh turf is now designated as common land and is grazed closely by sheep, cattle and horses. The immediate effect of this is to cause the saltmarsh plants to assume dwarf proportions producing a compact turf. Primary and creek-type pans are numerous in all phases of the marsh and the larger creeks are susceptible to erosion owing to the rather sandy subsoil. Soil profile studies show that the surface layers of soil are composed of organic gleys which overlie sand at all levels. The marsh gleys become thinner towards the sea and eventually disappear on the sand flats. As on most saltmarshes the vegetation exhibits a marked zonation. The lowest zone, established in 1957 in the sampling area, consists of Spartina townsendii H. & S. Groves growing in sand. These Spartina clumps have caused the deposition of a small amount of silt which provides a substrate for Salicornia europaea L. The next zone, submerged by tides every day, is mainly composed of S. europaea, together with some Puccinellia maritima (Huds.) Parl., Suaeda maritima (L.) Dum., and strands of the alga Enteromorpha. Next to this is a Puccinellio-Salicornietum (or Puccinellio-Suaedetum near the creeks) containing a high proportion of Aster tripolium L. From here the Puccinellietum proper extends as far as the High Water Spring Tide mark and has an abundant associated vegetation of typical saltmarsh plants. Above this is a sward of Festuca rubra L. (the Festucetum) which is the most heavily grazed area. Plants such as Armeria maritima (Mill.) Willd., Plantago maritima L., Aster tripolium and Cochlearia officinalis L., which are found in large numbers here, are always very low-growing and dwarfed. The climax vegetation is Juncus maritimus Lam. with Festuca rubra and Puccinellia maritima as