Living on the edge : saltmarsh spiders and beetles

Saltmarshes are an intriguing ecotone representing the transition between the marine and terrestrial environments. Much is understood in terms of zonation and vegetation communities in saltmarshes, however considerably less is understood about their edaphic factors. In Australian saltmarshes, terrestrial arthropod fauna and factors that determine invertebrate assemblages are largely unknown. The aim of this study was to understand the factors that influence the presence of epigeal spiders and beetles in a coastal saltmarsh. The chosen site at Long Point, a saltmarsh on Tasmania's east coast, included adjacent woodland which enabled expansion of the study to incorporate a full environmental gradient. Moisture, salinity and pH gradients were analysed alongside vegetation community structure. During the 12 month study period 5 606 spiders (37 taxa) and 1 165 beetles (84 taxa) were caught in 141 pitfall traps. Indicator species (spider and beetle) were identified for each vegetation community within the saltmarsh zone and adjacent woodland zone. Spiders and beetles reacted in a similar fashion to edaphic factors and vegetation species. However, the sequential order of importance for spiders was moisture, salinity and vegetation, whereas, the response order for beetles was moisture, vegetation and salinity. Further investigation into the interaction between saltmarsh vegetation species and spider and beetle species will assist in our endeavours to understand the loss or gain of arthropod species due to climate change and sea-level rise.