State Changes in Tropical Intertidal Systems: A Palaeo-Ecological Approach

The aim was to review ecosystem state changes and the role of palaeo-ecological tools with application to intertidal subtropical and tropical intertidal wetlands. These systems are especially vulnerable to stress from sea-level change, climate change, and development activities. Responses to stress can lead to significant state changes with the system passing thresholds, potentially beyond recovery. Indicators of state changes and approaching tipping points include a critical slowing down following perturbation signalled by, for example, slowing recovery rates, increased attribute variance, and changed skewness. To identify such changes, data are needed for the relevant variables such as vegetation, sea level, and sediment processes so as to observe the indicative changes and their timing. Because changes may be relatively slow in ecological terms, very long-term data are needed to inform management about future likely states or thresholds so that mitigation or adaptation can be planned. One approach is to use palaeo-ecological data. These data are relatively scarce in tropical intertidal systems. This paper reviews a range of palaeo-indicators. These include state indicators (pollen, foraminifera, and diatoms), stable isotope analysis, and stratigraphy and temporal indicators involving sediment dating. Each is potentially useful, although there are uncertainties related to, for example, the redistribution organic matter in sediment cores. In conclusion, it is recommended that integrating or combining several indicators can assist in triangulating results, thereby increasing confidence in their interpretation. It is also suggested that data, if available, can be retrofitted to assess at least some of the state change indicators, such as data variance and skewness.