MEPS 492:111-123 (2013)  -  DOI: https://doi.org/10.3354/meps10474

ABSTRACT: Mouth state is a key determinant of estuarine processes in arid and semi-arid regions. While this factor is well researched for periodically open systems, it is much less researched for estuarine lakes. Here we used a 4-year data set to determine spatio-temporal patterns in responses of benthic macrofauna to changes in mouth state in a subtropical estuarine lake system during a drought cycle, with a focus on understanding the ecological mechanisms driving community change. We also assessed the effects of changes in mean levels of environmental factors relative to their statistical variability (measured as standard deviation, SD) in driving changes in species richness and abundance of dominant macrofauna. Results showed that greatest variability in physico-chemical factors and macrofaunal assemblages occurred in the upper lake sections, especially under closed mouth conditions. At the community level, changes in salinity under different mouth states played an important structuring role, but were less important at the level of individual species, being important for only 1 of the 6 dominant species. Low oxygen levels under closed mouth conditions, particularly in the lake complex, were also an important determinant of macrofaunal community structure and species richness. A major finding was that variability (SD) in environmental factors was more important in determining species richness and abundance of dominant macrofauna than changes in mean levels. This suggests that, while dominant species in the systems can tolerate significant environmental changes, the rate and magnitude of change exert an important control over species abundance. 

KEY WORDS: St Lucia Estuary · Benthos · Drought · Mouth dynamics · Environmental variability