John Huisman

Intertidal platform reefs are a distinctive feature of the Perth coastline. Occurring adjacent to shoreline beaches and also as isolated offshore reefs, these limestone platforms have been formed by wave action over many centuries. Rising and falling tides exert a major influence on the structure of intertidal reef communities, and this influence typically results in a distinctive distribution of organisms based on their tolerance to being exposed to the air when the tide is low. Those inhabiting the highest part of the rocky shore, and therefore exposed more often and for longer periods, are typically hardy, desiccation-resistant species. Those living further seaward are more frequently submerged, although even these organisms may be exposed to the drying sun during particularly low tides, or can be periodically buried by the deposition of shifting beach sand. During winter storms, large waves may crash onto these reefs, stripping away algae and dislodging animals. Yet despite such harsh conditions, intertidal reefs can support a diverse assemblage of algae and invertebrates. Intertidal reefs are recognised as key ecological values of the Marmion and Shoalwater Islands marine parks that are located adjacent to the Perth metropolitan area. Between 2009 and 2012, marine scientists from DEC’s Marine Science Program and the WA Herbarium worked with local marine park staff to survey some of the numerous intertidal reefs in these marine parks to improve our understanding of the communities they support.

The Walpole and Nornalup Inlets Marine Park located on WA’s south coast is a discrete estuarine system comprising two connected inlets and the tidal reaches of three rivers. This estuary is relatively unusual in this region because its mouth is permanently open to the sea instead of being periodically closed by a wave-generated sand-bar. This means that marine-like conditions prevail within the inlets for most of the year, except during periods of high rainfall when freshwater flows from the rivers into the inlet basins. This inlet system has not experienced the significant environmental degradation present in many other estuaries in south-western WA, and its remarkable scenery and surrounding forests has made the inlets a focus for recreational activities for many decades. These very high ecological and social values led to the Walpole and Nornalup inlets being made a marine park in 2009. Since formation of the marine park, scientists from DEC’s Marine Science Program and the WA Herbarium have been working with the local management staff to undertake research that will improve our capacity to manage this remarkable area and preserve its ecological and social values. During 2010, this included making the first dedicated survey of benthic algae and seagrasses in the marine park, which turned up some surprising results.

Located on WA’s arid mid-west coast, the Shark Bay Marine Park was created to preserve the outstanding, World Heritage listed, marine biodiversity of this remarkable region. While Shark Bay is very well known for its dramatic coastal landscapes, rare marine stromatolites and iconic marine fauna, fewer people realise that the area also supports the southern-most substantial areas of mangrove in Western Australia. This is despite the fact that Shark Bay is an unusual marine environment with a naturally-occurring salinity gradient within the semi-enclosed gulfs that ranges from normal seawater to nearly double that concentration in the inner reaches of L’Haridon Bight and Hamelin Pool.