Estuaries are considered stressed environments because of the high variability in their physico-chemical properties; however, estuarine biota are able to thrive in this perceived stressful environment. The environmental homeostasis hypothesis states that this natural stress provides estuarine communities with the ability to reach stability by compensating for changes in the environment. Species diversity is one of the most important mechanisms contributing to community stability, although its influence is less evident in environments exposed to high environmental forcing. This study aimed to determine the variability and temporal stability of communitylevel properties such as phytoplankton biomass and zooplankton and macrobenthos density and biomass over a dry/wet cycle in the Mlalazi and Mpenjati estuaries. Despite the significant seasonal changes recorded for the density and biomass of the planktonic and benthic communities of both estuaries throughout the study, the variability of these community-level properties did not differ significantly among seasons. Of the community properties analyzed, phytoplankton and macrobenthos biomass exhibited the lowest and highest variability, respectively, in both systems. The temporal stability was similar among community-level properties and systems, and species synchrony was the main driver of community stability in both estuaries, probably because of the prevalence of environmental forcing in estuaries. Our study suggests that stable variability and an asynchronous response by species could be the mechanisms used by the estuarine biota of these 2 systems to compensate for environmental changes and reach environmental homeostasis. © Inter-Research 2014.