Biological Environment of the West Coast Coastal Marine Area: an outline of Marine and Coastal Ecosystems and Habitats

3.4 The Intertidal (Open Coast) Domain

The intertidal (open coast) domain includes both rocky shores and sediment beaches, two very different habitats for marine plants and animals. Their distribution is mapped in Figure 3.2. In these habitats, certain types of species attach to the rocks (e.g. seaweeds and mussels) or burrow into the sediment (e.g. sandhoppers and worms). In addition, some mobile animals tend to congregate in specific locations within or near the intertidal zone, sometimes in predictable distributions related to their breeding, feeding, roosting or social behaviour. For example, Fiordland crested penguins, blue penguins and fur seals swim ashore on certain beaches adjacent to their breeding and resting areas.

3.4.1 Biodiversity associated with different Substrates

Intertidal Rocky Shores, Rock Stacks and Islands
Where mountain ranges and hill country reach down to the coastline, rock formations extend out into the sea to form intertidal rocky shores and shallow subtidal rocky reefs, as well as rock stacks and islands (see Chapter 2).
Intertidal rocky shores
Intertidal rocky habitats in the West Coast region have been studied for:

seaweeds (Neale & Nelson 1996);
intertidal communities (University of Canterbury Marine Ecology Research Group (MERG) and
coastal reef fish (Roberts et al 2005).

The intertidal rocky shores of the central West Coast between Greymouth and Heretaniwha Point are less extensive and are considered to be less diverse than the northern and southern areas. They lack rock stacks and islands and are mostly dominated by species that prefer bouldery habitats and can withstand the heavy scouring effects of waves and sand. The rocky shores of the northern West Coast provide a stronghold for about six species that prefer shallow turbid pools and reefs (such as the giant triplefin, orange clingfish and olive rockfish), while South Westland is more suited to some intertidal species that prefer holes, overhangs, and open turf/seaweed reefs (such as several species of triplefin). The form, geology and substrate of the rocky shores can help to determine the plants and animals that live there: for example, some invertebrates such as half crabs and green chitons prefer the shelter provided beneath boulders, to the more exposed nature of bedrock shores.


Intertidal rocky shore zonation often includes separate bands of scoured rock, mussles, and barnacles. Photos: D Neale, DOC.

Figure 3.2
Intertidal (open coast) substrate typpes.
Sources: Neale 2006f, Neale unpublished DOC data.

The West Coast intertidal reefs include a range of distinctive biota that are uncommon or absent in other parts of New Zealand. Together, these features produce ecological patterns which make the West Coast intertidal environment different to other parts of New Zealand. These biodiversity features include:

a genetically distinctive wild population of greenlip mussels throughout the West Coast – Fiordland area40;
the mottled clingfish, a rockpool fish that is presently known from only two sites on the West Coast (at Mikonui and 14 Mile), despite extensive surveys around New Zealand41;
‘Gigartina’ sp. ‘terete’, a little-known type of agar-rich seaweed that appears to have a stronghold on the West Coast among dense intertidal seaweed turfs between at least Cape Foulwind and Okarito. It is generally uncommon or absent from other parts of New Zealand42;
Karengo (Porphyra spp.), a genus of ‘splash zone’ seaweeds that, along with the closely related Bangia genus, have a high diversity at some sites on the West Coast43;
New Zealand fur seal colonies that support an estimated 20% of New Zealand’s breeding population of this species44, as well as large winter haulout colonies;
Littoral spiders (such as Amaurobioides maritimus), a little known group of intertidal spiders with ancient origins, that has been found in high densities at Tauranga Bay, Seventeen Mile and Jackson Bay/Okahu45. New Zealand is the centre of diversity with seven of the twelve known species. The long beaches and large rivers of central Westland appear to act as a barrier between the northern and southern species in the group.

NZ Fur seals (kekeno) gather in colonies on some of the West Coast's rocky shores: Arnott Point colony.
Photo: L.F. Molloy

Rock Stacks and Islands
Many of the plants and animals around rock stacks and islands are discussed to some extent in the section above on rocky shores. However, intertidal shores around islands tend to be less affected by sand scour and turbidity, and provide sheltered sites on their leeward sides. Consequently, a greater diversity of species tends to occur at such sites.

In all, about 70 islands and vegetated rock stacks have been identified on the West Coast (Neale 2006e) and the distribution of these is mapped in Figure 3.3). Of this number, 24 have been visited and adequately surveyed to describe their natural features. The distribution of the West Coast’s islands and rock stacks, and their significance as breeding habitats for many seabirds and marine mammals, is discussed in more detail in section 3.7.1.

Sediment Beaches
Sediment beaches occur along most of the West Coast, often interrupted by rocky shores, and varying in length from tens of metres to tens of kilometres (see Figure 3.2). There are three main types:

sand beaches,
sand and gravel (including pebble) beaches, and
cobble ridge beaches.

Sand beach at Kohaihai

Sand and gravel beach at Bruce Bay

Cobble ridge beach at Coben

Photos: T Hume, NIWA

Figure 3.3
Islands and vegetated rock stacks
Source: Neale 2006e

Their physical composition depends not only on the types of sediment that is supplied to the coast by the nearby rivers, but also on the degree of wave exposure and the sediment transport dynamics of the beaches themselves. Consequently, the beach type tends to remain consistent along stretches of coastline up to several tens of kilometres in length.

Sediment beaches have mostly been studied in relation to their physical dynamics, sedimentation patterns and coastal hazards46. Biological studies and collections that have been done47 indicate that West Coast intertidal beaches generally have a very low biological diversity. However, shallow water shellfish species can be found in the lower intertidal zone, especially on gently sloping sand beaches; they include the triangle shell, tuatua and the venus shell. Larger marine species, such as fish, seabirds and marine mammals, occupy the intertidal beaches depending on the state of the tide and are generally similar to those in the shallow subtidal zone

3.4.2 Existing Protection in the Intertidal (Open Coast) Domain
The intertidal (open coast) domain is administered mostly under the Resource Management Act. Coastal erosion can affect the position of the foreshore in a variety of ways, and can sometimes cause Crown conservation land to become part of the intertidal zone. There are no substantial parts of the West Coast intertidal (open coast) domain that are clearly within Crown conservation lands. The Whakapoai and Jackson Bay Okahu Wildlife Refuges are an overlying Wildlife Act management regime that extends to 20 metres below mean high water spring (MHWS) (see sections 11 and 13 of Chapter 5).

The West Coast Regional Coastal Plan recognises several types of protection and management areas that include intertidal areas of beach and rocky shores such as: Coastal Protection Areas, Culturally Sensitive Areas, Coastal Recreation Areas, Coastal Hazard Areas, Marine Mammal and Bird Sites and Outstanding Natural Features and Landscapes.

Blue penguin (korora).
Photo: P Ryan, DOC collection

3.4.3 Uses associated with the Intertidal (Open Coast) Domain
Intertidal rocky shores are used for fishing, shellfish gathering, fossicking/exploring, tramping, sightseeing, tourism and education. Some sites are used for scientific (e.g. biological and geological) studies. West Coast beaches are used by local communities and visitors and others for a wide range of activities including:

recreation (e.g. swimming, surfing, beachwalking, fossicking, firewood gathering, quad biking, fishing);
commercial operations (gravel extraction and mining, stone picking, firewood gathering, fishing, tourism); and
cultural and social uses (e.g. access)

Some sites are used for scientific (e.g. biological and geological) studies including:

Physical monitoring sites such as the NIWA sea level recorder at Constant Bay
Geopreservation Inventory sites such as the internationally important Perpendicular Point fossil site; and
Biological monitoring sites (e.g. by University of Canterbury and Oregon State University) such as at Gentle Annie Point, Twelve Mile and Ocean Beach.


Recreation is a common use of the intertidal (open coast) domain. Photos: S Nimmo

0 Star et al 2003
41 Roberts et al 2005
42 W. Nelson, pers comm 1998
43 W. Nelson pers comm 2003
44 H Best pers comm 2001
45 B. Opell, pers comm 2005
46 e.g. Benn & Neale 1992
47 e.g. Neale 2007, Davidson et al 2003, Grange et al 2001, Knox 1991