ABSTRACT: Pomatoschistus microps (Pisces: Gobiidae), a predatory, benthic feeder, occurs in high densities in variable, shallow, muddy coastal waters where prey availability can be unpredictable. Here, we investigate the effect and consequences ofprey depletion on the body condition and nest building of adult male fish using manipulative mesocosm experiments in which the comparative value of meiofaunal and macrofaunal prey was investigated. Fish maintained in mesocosms from which macrofauna hadbeen removed from the sediment had a significantly reduced hepatosomatic index (HSI), and were less likely to build nests than fish in mesocosms containing macrofauna and meiofauna, suggesting an indirect link between prey availability and nest quality.Reduced resource availability, in the form of scarcity of macrofauna, appears to have profound implications for the fitness of natural field populations.