4. Sand Dunes and Sandy Shores Coastal Ecology 4. Sand Dunes and Sandy Shores

Druridge Bay, Northumberland

Cape Coast, Ghana

Development of sand dunes Sand dunes are an example of succession: if one progresses inland from the beach one is, essentially, seeing all the stages through which a community develops. Really, the only way to appreciate the extent to which the habitat changes on a small scale with time is to make regular visits at different times of the year. Ultimately dependent upon one grass species: Ammophila arenaria (Marram grass).

Marram grass Tolerates – and, indeed, thrives – on being buried by sand. Sand accumulates in the wind shadow behind plants. Because plants take a long time to decay the old parts of plants add a fibrous mass to the sand. Xerophytic: fibrous rolled leaves with stomata on inside.

Marram grass (continued)

Leaf of marram grass

Leaf of marram grass (SEM)

Leymus arenarius: Sea Lyme grass Larger, broad blue-green leaves.

Early stages of sand dune system (mobile dunes) Soil essentially just pure sand: well drained, mobile, lacking in nutrients. Very few plant species present: at first, just Marram Grass and then a few tap-rooted species start to appear. For example, Dandelion, Coltsfoot. (Tap roots supposedly seek for the water table, which may be many feet below).

Taraxacum officinale: Dandelion

Tussilago farfara: Coltsfoot

Further development of first dunes Arrival of leguminous plants such as Bird’s foot trefoil (Lotus corniculatus) and Rest harrow (Ononis repens). These have root nodules which contain bacteria responsible for fixing atmospheric nitrogen (useless) into nitrates (usable by plants). Thus, the ‘soil’ is starting to become enriched.

Lotus corniculatus: Bird’s foot trefoil

Bird’s foot trefoil (in fruit)

Ononis repens (Rest harrow)

Continuing development Further plant growth stabilises the soil. Break down of dead plants (and the occasional buried dead seagull) adds to the nutrients in the soil and improves its water holding capacity. Mosses growing across the surface of the sand further stabilise the surface. Many new plant species appear causing the vegetation community to become more complex and diverse.

Sand dune mosses Tortula ruralis

Sand dune mosses Hypnum cupressiforme

Geranium sanguineum: Bloody Cranesbill

Calystegia soldanella: Sea bindweed

Tropical species of bindweed: Ipomoea pes-caprae

Rosa pimpinellifolia: Burnet Rose

Galium verum: Lady’s bedstraw

Dune slacks Behind the dune ridges, and representing a later stage in development, the dune slacks are produced when there is a stable cover of vegetation and the soil has water holding capacity (partially as a result of humus and decaying plant remains) and nutrients (from the decay of generations of plants. Number of plant species continues to increase.

Salix repens: Creeping willow

Epipactis palustris: Marsh Helleborine

Epipactis dunensis: Dune Helleborine

Corallorhiza trifida: Coralroot Orchid

Dactylorhiza incarnata: Early Marsh Orchid

Dactylorhiza fuchsii: Common Spotted Orchid

Dactylorhiza purpurella: Northern Marsh Orchid

Later stages in development The continuing development of the succession depends on soil types (and inland land usage to a certain extent – farmers often encroach onto dunes). Acidic soils may develop into dune heath. Shrub/tree species cause the development of dune scrub.

Problems with sand dunes Very fragile habitat. Fore-dunes susceptible to winter storms. Dune system in its entirety is a thin skin of vegetation – as a result, any damage to the surface exposes the sand underneath and wind very rapidly scours this out so that large areas of uncolonised sand exposed. Problems range from rabbits to mountain bikers.

Management techniques Variety of strategies are used in the management of sand dunes: Manually replant with marram grass. Cover exposed areas with chicken wire. Bury old Christmas trees (or, in some instances, e.g. in Jutland, plant pine trees). Discourage damaging behaviour – includes fires, camping, bicycles, etc.

Blyth Beach

Common Jellyfish: Aurelia aurita

Common Jellyfish: Aurelia aurita

Common Jellyfish: Aurelia aurita

Compass Jellyfish: Chrysaora hyoscella

Compass Jellyfish: Chrysaora hyoscella

Blue Jellyfish: Cyanea lamarkii

Blue Jellyfish: Cyanea lamarkii

Sea Potato: Echinocardium cordatum

Ensis minor: Razor Shell

Ensis siliqua: Razor Shell

Ensis siliqua: Razor Shell

Scallop

Scallop for the artistically minded

Sea Mouse: Aphrodite aculeata

Sea Mouse: Aphrodite aculeata

Lugworm: Arenicola marina

Lugworm: Arenicola marina

What you cannot see: Diatoms

…and a couple of things to look out for on tropical beaches