Effects of barite on aspects of the ecology of the polychaete Mediomastus ambiseta

Bante (BaSO,), a major component of drilling muds, can change the texture and erosion properties of surface sediments near offshore d r i h g sites. The effects of barite on the ecology of the marine polychaete Mediomastus arnbiseta (Hartman) were examined in laboratory experiments: a migration experiment, 2 feeding experiments and a growth experiment. In the migration experiment, 18 of 19 worms left 100 % barite withn 2 d. This was significantly more worm movement than from natural mud to 100 % barite; only 3 of 15 worms moved into 100 % barite. Worms did not move into 10 % barite sediments, but neither did they show high movement out of 10 % barite. There was no difference in worm movement into and out of 1.0 % barite sediment or natural mud with a 1 mm barite cover. In 2 separate feeding experiments, lasting 6 d and 18 d, the mean number of fecal pellets produced per worm per day did not differ between treatments with barite concentrations ranging from 0 % barite (natural mud) to 50 % barite, by weight, and a treatment with a 1 mm barite layer over mud. In the second feeding experiment, growth (number of setigers added) differed between males and females. Females grew more than males, but growth did not differ between treatments. In the fourth experiment, growth of worms in natural mud did not differ from worms in 10 % barite sediments after 8 wk. Worm tube production (number of tube openings per worm) did not differ between natural mud and barite treatments in the 2 feeding experiments and the growth experiment. These experiments show essentially no deleterious effect on fecal pellet production, growth and tube production of adult M. ambiseta living in realistic concentrations of barite found in marine sediments subjected to drilling activity, although worms may migrate out of 100 % barite patches.