Increased drag reduces growth of snails:comparison of flume and in situ experiments

Snails Littorina littorea with and without artificial epibionts were exposed in situ for nearly l mo.Measurement of individual shell length increase over this period revealed that clean snails grew 3 times faster than fouled snalls These results compare well with previously conducted flume experlments (Wahl 1996).T h ~s epibiosis effect IS thought to be due to increased drag-the only feature dist~ngulshlng the 2 treatment groups-caused by the presence of ep~bionts on the shell.lncreased drag probably entails higher energy expenditure for pedal activities (attachment and locomotion) and a reduced allocation of resources towards growth and, possibly, reproduction.