ABSTRACT: Callyspongia vaginalis, a common reef sponge in the Florida Keys, USA, exhibits depth-specific differences in bioenergetics and growth that are a function of food availability. We measured several physiological parameters in situ to construct the bioenergetic budgets of sponges living in deep and shallow waters. Respiration rates were measured in a recirculating flow respirometer and pumping rates were measured by filming dye ejected from sponge oscula. In addition, inhalent and exhalent water sampled from around sponge colonies at both depths was analyzed using flow cytometry to quantify the concentration and clearance rates of picoplankton. These parameters were used to construct an energetic budget for sponges from each depth and revealed that the scope for growth was substantially greater for deep sponges compared to shallow sponges. The greater scope for growth of deep sponges is likely due to the greater abundance of picoplankton in the deep versus shallow habitat. Both naturally occurring sponges and those used in a reciprocal transplant experiment between 12 and 25 m exhibited significantly greater growth in the deep than the shallow habitat. Hence, bottom-up forcing in the form of increased food availability may be of principal importance to the growth and physiological ecology of suspension-feeding sponges.