THE ROLE OF CALLIANASSA-SUBTERRANEA (MONTAGU) (THALASSINIDEA) IN SEDIMENT RESUSPENSION IN THE NORTH-SEA

The mud shrimp Callianassa subterranea (Montagu) is a common member of the macrobenthic community at the site in the North Sea selected to s tudy the dynamics of suspended sediment behaviour. The extensive burro wing habit of this deposit-feeding species makes it an important contr ibutor to the degree of bioturbation experienced at the site. Individu als recovered from the site were returned to the laboratory to investi gate the influence of body size and temperature upon the amount of sed iment expelled. A clear relationship between these variables and the q uantity of expelled sediment was identified, and a well-defined tempor al pattern of expulsion activity and inactivity was demonstrated. Thes e experimental data, together with field information on seawater tempe ratures and aspects of mud shrimp population dynamics, allow the const ruction of an estimated annual sediment turnover budget of 11 kg(dry w eight)m(-2) yr(-1). Field observations at the North Sea site show that the sediment expelled by the mud shrimp forms unconsolidated volcano- like mounds, which significantly modify seabed surface topography. The dimensions of these surface features were measured from bottom photog raphs of the site and used to determine values of boundary roughness l ength(Zo). In January Zo was 0.0007 cm, whilst in September Zo equaled 0.79 cm. Callianassa subterranea's maximum contribution to resuspensi on was assessed by calculating a derived lateral sediment transport ra te of 7 kg m(-1) month(-1) (from values of near-bed current velocity, modified boundary roughness length and sediment turnover rate). (C) 19 98 Elsevier Science Ltd. All rights reserved.