Distribution and abundance of the intertidal saltmarsh beetle, Bledius spectabilis

ABSTRACT.

• 1 The burrowing intertidal beetle Bledius spectabilis Kraatz (Coleoptera: Staphylinidae) occurs on all but the very youngest marshes on Scolt Head Island, Norfolk, U.K., and may reach densities of up to 4000 m^?2 (combined adult and larval densities).
• 2 The beetles are restricted to a narrow band about 1m wide along the edges of creeks draining the low marsh areas of the island, and the vertical range is restricted to a zone between 0.8 and 1.55m above Ordnance Datum. The majority of the aggregations and the highest densities are between 1.2 and 1.3m O.D., that is between about 24 and 40cm below MHWN (mean high water at neap tides).
• 3 Poor drainage, in particular the presence of long-standing pools of water over the soil surface, is important in restricting the beetles to well-drained edge regions.
• 4 Transplant experiments suggest that displacement by saltmarsh vegetation, in particular Halimione portulacoides (L.) Aell., sets the upper limit of the beetles’distribution.
• 5 The zonation of B.spectablis fits well into the general scheme that has been proposed for the zonation of marine animals from rocky shores.
• 6 The beetles produce large (3–6 mm diameter), rapidly draining, abundant (up to 9% of soil volume) and persistent burrows. We suggest that these beetle aggregations may play an important role in the development of the saltmarsh.