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Simultaneous measurements of the velocity profile and turbulence were made at 4 heights within 2 m of the sea bed in the Eastern Irish Sea. A photographic unit was also deployed to observe sediment motion. The design, construction and performance of the instruments are described and the results from 36 trials, for a variety of bedforms and water depths of 8 to 50 m, are discussed. The velocity profile was recorded by means of Aanderaa rotors and the velocity fluctuations with e.m. heads. Their measurements, according to flume calibrations, were accurate to ±l%. Angular corrections were necessary to compensate for the loss in response when the turbulence rig was poorly orientated with respect to the mean flow direction. The minimum in situ velocity was 20 cm s-l, at which speed inertial 'pumping' of the rotors by turbulent fluctuations was estimated to produce overreading by - 1 cm s-l. At speeds above 30 cm s-l this effect was negligible. The resolution of the e.m. heads was at least 5.0 mm s-l, as determined by the noise level, and d.c. drift less than 1.0 mm s-l over periods of up to 17 hours. Data were recorded on 9 track tape aboard ship for later analysis onshore. The measurements were made in a bottom boundary layer which could be decribed as accelerating, non-rotational, hydrodynamically rough, neutrally stratified and comprised a layer of constant Reynolds stress. The stress, as determined from the log-profiles, either uncorrected or corrected for acceleration, was observed to be significantly greater (- 26%) than that determined by eddy correlation techniques. This could not be attributed to uncertainties introduced by misalignment of the e .m. heads, or inadequate correction for cospectral losses. Doubt was cast on the validity of von Karmann's constant (KO) = 0.4, with a more appropriate value apparently being closer to 0.35. KO and u*2/-U7""WTexhibited no dependence on bedform or sediment type, except in one case, where high ratios corresponded to high zo's. Evidence of a tidal hysteresis of stress was observed at one station only. Apparent Zo minima at peak tidal velocities were, for the most part, attributed to the non-removal of accelerating effects when applying the log-law. Initially high values of zo' when present, were supposed to be due to streamlining of bedforms with ;ncrnasing velocity. Zo and C100 varied from 0.02 - 0.25 and (2 - 3) x 10-3 respectively for mud, unrippled sand and various sand combinations. For gravel and rippled sand values they were 0.10 - 0.20 and (3 - 8) x 10-3. A comparison of events comprising 90% of the stress with movement of bed material, observed by the photographic unit, failed to reveal a Correlation. During periods of sediment motion events in which u' > 0 were dominant. For events comprising 90% of the stress, those in which u' < 0 and u' > 0 occurred in groups of 5 - 20. In addition, a number of coherent events, occuring between 5 - 12 times per minute independently of velocity, were observed between 100.0 and 172.5 cm above the bed.

This study investigated the biology and predatory behaviour of Asterias rubens (L ), as a potential predator ofcommmeroial scallopst Pecten maximus (L. ý and quejen scallops Chlamys opercularis (L. ). A population of A. rubens was monitored in a sub-littoral area by divers. The density of A. rubens varied little, annually, but lower densities were associated with an increase in sub-sea swell or with darkness. Parallel studies on activity were carried out in the field and in the laboratory. A high recovery rate but little net movement of tagged starfish was found within the area. This contrasted strongly with estimates of daily distance travelled and led to the suggestion of a "home range" in A. rubens. Different sized starfish spent equal time foraging and feeding, while "substrate" feeding was the most common form of feeding. Smallstarfish fed on sedentary items such as barnacles, while larger starfish fed on a greater variety of larger and more mobile prey e. g. prosobranchs* The importance in the diet of calorifically rich9rare food items, such as bivalves and carrion was noted, Five other asteroid species were commonly found and details of their biology noted. In particular# Stichastrella rosea fed, exclusivelyt on sedentary prey, while Marthas , terias glaciatis-and Henricia oculata showed broadly similar diets to large A. rubens. Sampling of two separate populations of A. rubens led to the development of reliable techniques for weighing and measuring starfisho The (armlength/armwidth) ratio (LW) was proposed as a condition factor for starfish. The trophic conditions of the two populations were indirectly assessed from bionomic factors. Mean weight for size, LW ratios and organ indices were combined with results from feeding experiments to demonstrate differences in trophic condition between the two populations. The differences were also reflected in bodywall, pyloric caecum and gonad indices, Improved trophic conditions, however, did not necessarily lead to a great Increase In reproductive output, The benthic populations of two sampling sites were examined to assess the relationship between scallop and starfish speciesq their relations to substrate type and the effect of fishing pressure. Little correlation between density of scallop species and A. rubens was found. An aggregated pattern of dispersion was found for (P. scallop species maximust C. -opercularis and C. tigerina)9 while A. rubens displayed a more random dispersion* The aggregated nature of scallop stocks was discussed in terms of spat settlement and active movement. The shell orientation and the numbers of recessed or byssally attached scallops was studied in relation to patterns of tidal flow and substrate type. The importance of physical availability of prey9 compared with density estimates was revealed In field and laboratory work. Observations on starfish behaviour and evidence of predation led to the suggestion that infaunal bivalves and Chlamys tigerina, were of greater significance in the diet of A. rubens than commercial scallop species.