The environmental variables are central to the population dynamics of all organisms in this model. For example, temperature alters metabolism and growth rates, salinity and DO play important roles in spatially structuring the crab population while hypoxia causes clam and background prey mortality. The environment variables were assessed without crabs present in the estuary. Most of the assessment criteria used are highly qualitative in nature because data sets which would enable more quantitative criteria to be used were not available. Relevant MPG movies are provided in the online appendices.