The benefits and costs of deposit feeding in the polychaete Abarenicola pacifica

A mass‐balance approach was used to assess the relative importance of benefit and cost terms in a model of the energy budget of Abarenicola pacifica, a subsurface deposit‐feeding polychaete. Some model terms (sediment consumption rate, organic matter consumption rate, growth rate, standard metabolic rate) were measured directly. Other terms (absorption efficiency, mechanical cost of feeding, specific dynamic action) were obtained by simultaneous solution of model equations. Despite high rates of sediment processing (up to 280 times ash‐free dry body weight per day), the mechanical cost of deposit feeding was insignificantly low. Growth rate increased linearly over a 50‐fold range in organic matter consumption rate; this relationship was unaffected by sediment consumption rate. The model that provided the best fit to the experimental data contained a nearly constant absorption efficiency, a term for specific dynamic action (”cost of growth”) that increased linearly with intake rate of organic matter, and no mechanical cost of feeding. Models based on optimal foraging theory thus require modifications in order to describe more realistically the feeding behavior of microphagous animals.