Shingle beaches

Shingle beach at Cobden Beach, West Coast (Susan Wiser)

Shingle beaches are comprised primarily of a mixture of sand, water-smoothed gravel (>50%, particles 2-64 mm), and cobbles. Low vegetation occurs inland from the foreshore on the berm and backdune. Shingle beaches occur where rivers deliver large quantities of shingle to the coast or where it is being eroded from nearby coastal cliffs. Shingle beaches usually rise to a ridge beyond the high tide mark that is rarely disturbed by the sea. A lagoon or wetland may be impounded behind. Shingle beaches are subject to intermittent disturbance during storms. Nationally, plant composition varies with climate and the nature of the adjacent vegetation. The native vine shore bindweed (Calystegia soldanella) increases in importance on warmer beaches, and the exotic grasses ripgut brome (Bromus diandrus), hares-tail (Lagurus ovatus) and perennial rye grass (Lolium perenne) increase in importance on drier beaches. Beaches adjacent to native woody ecosystems are characterised by the presence of small native herbaceous species representative of forest understories and margins such as Hydrocotyle novae-zeelandiae var. montana, and native woody species such as broadleaf (Griselinia littoralis). On beaches distant from native woody ecosystems, exotic species such as the grass Yorkshire fog (Holcus lanatus), the herbs catsear (Hypochaeris radicata) and hawkbit (Leontodon taraxacoides), and the shrub gorse (Ulex europaeus), species that are widespread in pasture and wasteland, increase in importance. Within an individual beach, compositional variation among microsites reflects substrate stability and texture.

Synonyms

Storm beaches; gravel beaches, gravel banks

Where do they occur?

Vegetated shingle beaches occur in many coastal areas, and are particularly abundant on the North Island and South Island east and south coasts.

Notable flora and fauna

Threatened plants include nationally critical grey saltbush (Atriplex cinerea), nationally endangered Myosotis brevis, declining coastal eryngo (Eryngium vesiculosum), thick-leaved mahoe (Melicytus crassifolius), and leafless pohuehue (Muehlenbeckia ephedroides), relict saltbush (Atriplex australasica), and pingao (Ficinia spiralis), naturally uncommon prostrate broom (Carmichaelia appressa), trailing fuchsia (Fuchsia procumbens), Banks Peninsula button daisy (Leptinella minor), small vegetable sheep (Raoulia beauverdii), Senecio carnosulus, and New Zealand spinach (Tetragonia tetragonioides), and the taxonomically indeterminate/declining shingle beach endemic Raoulia aff. hookeri [AK 239529].

Rare invertebrates include an egg-laying velvet worm (Ooperipaltellus viridimaculatus), an ant-like flower beetle (Floydwernerius gushi), the Cloudy Bay mat daisy jumper moth (Kiwaia sp. cf. jeanae), and a minute flightless parasitic wasp (Maaminga marrisi) that, along with its sister species, forms a new family of wasp unique to New Zealand. The exotic crypt ant (Hypoponera confinis) new to New Zealand, is known only from one shingle beach locality near Wellington. Rare vertebrates include the relict spotted skink (Oligosoma lineoocellatum). The nationally endangered black-billed gull (Larus bulleri), the nationally vulnerable banded dotterel (Charadrius bicinctus) and the coloniser black-fronted dotterel (Charadrius melanops) can have breeding populations on these beaches. Nationally vulnerable Caspian terns (Hydroprogne caspia) roost on Hawke's Bay beaches and in winter the nationally endangered black-fronted tern (Chlidonias albostriatus) migrates there from South Island braided riverbeds.

Threat status

Endangered (Holdaway et al. 2012)

Threats

Shingle beaches are prone to invasion by numerous exotic herbs, grasses, and shrubs, especially when adjacent to urban or agricultural areas. When adjacent to agriculture, landward areas are particularly vulnerable to fertilising and grazing. Many have been planted with exotic trees. Rabbits and hares may be locally abundant. Where accessible, roads and tracks are often built along them and 4WD vehicles can be especially damaging to the low, scattered vegetation.

Shingle beaches are particularly susceptible to long- term damage from marine oil spills because they capture and hold oil for longer than sandy beaches.