We know that some halophiles are heterotrophic, but in those highly saline environment what do these organisms eat as there might be very little chance of survival of any other organism?
When we look at the definition, Halophiles are just archaebacteria that require salt in their environment to live. Wikipedia states that they live in salt concentrations of 0.3 to 0.8 M (1.7 to 4.8% — seawater is 0.6 M or 3.5%).
According to The Saltwater Wetland bacteria in estuaries will get their food from dissolved organic mater in the water. An estuary can have a salt concentration of 0.5 to 35 ppt (according to google). This would be 0.05 - 3.5% salinity depending on the estuary, so obviously there are some estuaries would not be able to host Halophiles, but the concept is still the same. They would get their food from dissolved organic matter in the water.