Quantitative surveys of the Colorado Lagoon and Marine Stadium (Long Beach, California, USA) indicated that the bivalve communities in the Lagoon and in the Stadium were dramatically different, even though water exchanged freely between the two systems for most of the year. In the Lagoon the mean total bivalve density was 143 · m−2 with a density of the introduced clam, Mercenaria mercenaria, of 78 · m−2. In the Stadium the mean total clam density was 57 · m−2 and M. mercenaria was absent. In the Lagoon, bivalve populations were dominated by suspension-feeders, while in the Stadium deposit-feeders were most abundant. Quantitative surveys of ghost shrimp, Callianassa californiensis, burrows suggested this shrimp was more abundant in the Stadium than in the Lagoon. This research supports the trophic group hypothesis, which states that deposit-feeding and suspension-feeding species have a positive influence on species of the same feeding type and a negative impact on species of the opposite feeding type, primarily through their effects on sediment stability. This paper shows how a deposit-feeding shrimp controls the distribution of a suspension-feeding bivalve through turbidity. Field studies and controlled experiments suggest that sediment characteristics and predation on juvenile M. mercenaria could not explain this bivalve's distribution. This work demonstrated a strong negative correlation between both growth and survival of M. mercenaria and suspended particulate matter. Laboratory experiments showed that Callianassa can create levels of turbidity and sediment destabilization sufficient to reduce the growth and survival of M. mercenaria.It was hypothesized that the absence of C. californiensis in the Lagoon resulted from stressful conditions such as elevated summer temperatures, low winter salinity, periods of anoxia, and possibly pollutants. The hardiness of M. mercenaria and its need for elevated temperatures for spawning probably contribute to its success in the Lagoon.