Invertebrates in rock pools

Abstract

Rock pools are eroded depressions that occur in a matrix of bedrock (Fig. 2.1 ). In intertidal zones these habitats contain seawater and house communities of marine organisms; however, further up the rock platform, rainfall input becomes a more important source of water than saltwater spray resulting fi rst in brackish and, further inland, in freshwater supralittoral habitats (Ganning 1971 ; Egan and Ferrington 2015 ). Rock pools are found in different types of bedrock but most often in granite, sandstone, and limestone. Granite is an intrusive igneous rock which forms at high temperatures and under great pressure below the surface. Subsurface weathering can fragment the granite, and only the sturdiest fragments, rich in the more resistant potassium feldspars and quartz, typically remain when they become exposed after erosion of the covering sediments (Campbell 1997 ). This type of granite outcrop is common in the inland areas of Western Australia. Pools may already be present in these rock slabs (Fig. 2.1a ) upon exposure as a result of weathering below the surface (Twidale and Bourne 1975 ). Once exposed, corrosion by acidic water along near-surface horizontal cracks formed by cycles of hot days and cold nights and rare frosts results in a pool basin, with detritus blown away by wind (Timms and Rankin 2014 ).