SPECIFIC DYNAMIC ACTION DEMONSTRATED IN THE HERBIVOROUS MARINE PERIWINKLES, LITTORINA-LITTOREA L AND LITTORINA-OBTUSATA L (MOLLUSCA, GASTROPODA)

1. Respiration rates of starved periwinkles, Littorina littorea and Li ttorina obtusata, increased by 40-60% when fed their preferred algal f ood for 1 hr, or after having been exposed for the same period to an a queous extract of the alga. 2. The stimulus causing the rise in metabo lic rate by algal extracts is therefore thought to be chemosensory in nature, and possibly composed primarily of dissolved free amino acids. 3. The respiration rates of L. littorea responded only to the green a lga Enteromorpha intestinalis while L. obtusata demonstrated an increa se in respiration rates when fed the ubiquitous brown alga, Ascophyllu m nodosum, and to a lesser degree to Enteromorpha. 4. These results co mpare very well to postprandial increases in oxygen consumption demons trated in vertebrates and marine bivalves where the components of spec ific dynamic action (SDA) are thought to be chiefly biosynthetic costs of digestion and assimilation.