Community dynamics of meiofauna during a wet phase in the St Lucia estuarine system, South Africa.

Abstract

Meiofauna are an important component within the benthic environment of any aquatic habitat. Despite their significance and ubiquitous nature, these organisms are relatively poorly studied in Africa. Following a decade long drought period, the St Lucia Estuary experienced higher than average amounts of rainfall at the end of 2010. These heavy rainfall events replenished the freshwater capacity of the system, raising the water level and subsequently reducing salinity throughout the estuarine lake, thus marking the start of a two year long wet phase. Meiofauna community dynamics were assessed to determine their response to a wet phase and to the disturbance brought on by intense rainfall. Diversity indices and a host of multivariate analyses were used to gain an understanding of the meiofaunal communities of the system during this wet phase. Meiofaunal density and richness tended to be higher during the first year of the wet phase. Meiofauna communities within each site became more homogenous in the second year of the wet phase, indicating a more established community adjusted to wet conditions. Following a flood disturbance in early January 2011, meiofaunal communities at each site differed in terms of primary and secondary colonisers. Over time, communities increased in dissimilarity, suggesting succession at some level. A successional pattern was observed as the taxonomic composition of the communities shifted over time. The lack of a climax community in St Lucia in the medium term was likely due to the uneven impact that the lake experienced with the onset of the disturbance, with the northern reaches experiencing a greater degree of impact than the southern reaches. The continuity in disturbance occurrences also caused the system to move back to a previous successional state. The meiofauna of St Lucia are therefore able to recover after disturbances related to a wet phase and maintain some form of resilience. In the long term, meiofaunal communities may require a longer time period, than the one considered in this study, to reach the levels of abundance previously recorded.