Intertidal Habitats

The intertidal zone is divided into separate zones based on the influence of the tide, presenting a wide range of intertidal habitats.

The highest, most exposed section


These areas are generally wetted only by extreme high tides or by spray. The zone is known as the ‘littoral fringe. In South Australia, this zone is dominated by:
  • littorinid snails (Nodilittorina unifasciata)
  • dark patches of cyanobacteria (Calothorix fasciculate, Entophysalis)
  • lichens (Lichina confinis) in the lower reaches.

The high tide limit


The zone at the limit of the high tides is known as the ‘upper eulittoral’ zone and is dominated by small barnacles.

Below high tide limit


In the ‘mid eulittoral’ zone where surf conditions are strong larger barnacles dominate along with limpets. Below the limpets a band of mussels or tubeworm generally dominate.

Submerged regions


In regions that are submerged for most of the tidal cycle, known as the ‘lower eulittoral’ zone, and under strong wave action the rock surface is generally covered by turf or mat forming algae, particularly coralline algae and red algae (Gelidium pusillum). The mat of algae is able to retain water when exposed by the ebb of the waves.

In many places, under conditions of very strong wave action, large barnacles, limpets and chitons are also abundant and may form distinctive bands.

On sheltered coasts and horizontal platform reefs, such as Aldinga reef, the brown algae known as Neptune’s Necklace is common.

The lowest region


This region of the shore, the ‘sublittoral fringe’ or ‘surf zone’ is dominated by algae and is only exposed during spring low tides or as waves retreat. A few conspicuous species of brown algae occur only in this zone, namely Cystophora intermedia, west of Robe, and the giant Bull Kelp, or Durvillaea potatorum, east of Robe. In the more pristine areas of South Australia, species of abalone may also be found in the lower reaches of the intertidal zone.

Intertidal width


While the width of the intertidal shoreline is determined primarily by the tidal range, the degree of wave exposure and air temperature is also important. Sheltered habitats generally have fewer species of barnacles and more grazing gastropods (such as abalone and octopi) than wave exposed habitats, and a reduced cover of algae.

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Soft bottoms – tidal mudflat and beaches


In contrast to rocky intertidal shores, our knowledge of ‘soft bottom’ habitats is poor. Unvegetated soft bottoms, such as sandy shores and mudflats, remain the least studied marine habitats in Australia.

In contrast to rocky shores, sandy beaches and tidal mudflats are essentially three-dimensional environments - with the type and range of fauna and flora primarily determined by the interactions between the sediment and water. As such, sediment depth, grain size, and chemistry are all-important factors in determining the types of organisms living on, and within, a tidal mudflat or beach.

On soft bottoms, animals either ingest sediment or live on or within it. In contrast to rocky shores, plants are usually inconspicuous and microscopic. While these unvegetated habitats may appear barren and lifeless on the surface, beneath the surface this three dimensional world is dominated by an abundance of worms, molluscs and crustaceans. For this reason, these intertidal environments are not only a haven for wading birdlife, but also for humans looking for fish bait or food.